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FOREWORD

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,a

JPRSI 16&703

DOSI12TRIC CONTROL O ATOMIC4SHIP4

-USSR-

£ Following Is the translation of the Jussian-languwebock by D. V. Lyash and B. IN IkolMoay entitled,P80 42u 'a- I t&M .(&W~lish Ter-

a)ouse of theas.ipbduilig Industry, 1962, pp 1-132.1

TABLE OF CONTTENTS liUPoI~5vord,..,.o ~.o GO.....GO.oo. o e. e~o°e..e...e.G...* I

Chapter I. The Notion of Ionizing Radiation......... 31 . Radioactivity... "''''".. "''''" "'''' "". "''s.''." 32. The Concept of the Radiation Dome. Maximum

Permissible Doses and Concentrations .e.. a.. .*3. Nuclear Binding Energy and Nuolear Reaotions... 12

Chapter I1. Reactors -- Sources of Ionizing

4. Fission Rkactors.....0......... .............. 1 65. The Chain Reaction and the Nuclear Reactor...:. 226. Zonizing Rad1 ation from Nuclear Reactors...*..e 31

Chapter III. Principles of Ship Nuolear Power Plant(11p?) hedn,.......•....437. Protection from NPP Radintion..o............... 438. Shielding Check@ and Construction of Isodosal

Ohapter IV. Some Information on Dosimetric Apparatus 589. General R mrke ............................. 58

10. Ionizing Radiation Deteotore................... 60it. Control-Recording and Measuring Devices of

Dosimetrio Apparatus..°..s..................... 6412. Measurements of Radioactive Gas and Aerosol

Concentration............*. ..... 64. o. 613. Portable Douiuetere...................... 6814. Individual-Use Douineter.... ..•.... . 69Chapter V, Possibilities of the Spread of Radio-

activity of a Ship With a EPP and Me'thodsof Combatting It............... ..... 70

a

15. General. ae70,............16& AcLtual Sources *f P~tt~i aito

and Haticaotirt S'abst~nce and Their WayspfSreadlng Over Us Shipao 7217. Proolem, of Radioactivity Localliuation on

a ship With a PI..,,...**....* 8118, ?ovva~aition of the Pxoblea of Removing Nuclear

Ntel Vieseion fogmeittm fro* N~ao~ear-Povere I

Obpe V~,OEmxaii fro.btry Service oni

20e A fsmJ4e Organixatloxal Scheme for a Doosiatry219 Sk*U f~tcabhou tar Mosiaotwy Control. and

SI~~i~ti~~..s a*Ss a** 04*,e**e S@S00500 s*& 9122. Pimoment of Mosunatry~pseu....... 97230 Me 7.4eistmetwatch aw Its hnot2taMw9**...... 103

0btte"*r V11 Ftnd&aatsa Solutiozsm to Problems ofRadiation Befety end the Systemu of vT Doximetr7Coatra'l on the Isoulalooebroeker OTwLaeaizew...*Sao*. 10824~. 7oeznl1ation of the Problem of Radiation

3afety art the 1082!5. Contro2 of Perutratftlag dlaiou Lvmsean....... 11026, Badlonetry of Udloaetive Subs towe Bos )e the

Mimito Of the PriMaryOotu..,......1127, Radionetry of Sewage Water ftem thA ftosor

28a fladlmatz7 of the lon-4edn~.oa I ~uvt)

29. RidiomewU of the Sarface of fte Udy* OUUtIJONftoVvear wO 2ndiIidlal D5ti..... 117

30, Portable 'festro,999 ***save* ........ 118OhepteizVIMi some laromationOa UaG16tion Sinfey31 c ftA fnssenprofaro Ship 12032. Ur~ liolearaftowrad amsne......,.6 12

Oo~out~oa.. 0 *,e........e~*e~* . h.. 125505@@**,***** t~b**00**.** @@S **1 29

b

The present work deals with the problems of radia-tion safety and dosinetrio control methods on vessels withnuolear power plants. It Includes the necemsary informationfronm the fields of physims and nuclear teohnology., Aloincluded in a brief description of the system of radiationsafety and dosimetrio control on the atomic Icebreaker"Lent1n", along with some Information on radiation safety onforeign nuclear vessels.

Th3 book Is designed for engineers and techniciansIn the shipbuilding Indust il and the Navy, and will likewisebe useful to students of shipbuilding institutes.

FOUWORD

The wide application of atomic technology In generaland nuclear power In particular has also been extended tomodern shi.pbuilding. Soviet shipbullding slienoe Is In thevanguard of world thinking in this branch of technology.

The atomli Icebreaker lninaf" is the worldes firstmerchant vessel with a nuclear power plant (NIPP), This Is thecrowning achievement of s.otentists, designers, sad workersIn the shipbuilding Industry and other Industries of the USSR.Following in the footsteps of the Soviet Union, fte US designedand built a nuclear passenger-oargo vessel, Sveden began con-st-ructisn of a large tanker, etol !"c can be stated oonfidentlythat nuclear shipbuilding will develop even more with theaccumulation f experience in the use of economical and effi-cient ship reactors.

However, a major portion of the engineering foreeAnthe shipbuilding industry and the Navy has little knowledge ofthe basic pro',ýlems of nuclear technology, and moreover, lacksa clear conception of the specifics of exploiting nuclearpower plants. Frequently, they harbor an exazggrated fear ofthe danger of operating such plants. This feeling has been'Postered by the appearance of accounts in the press dealingwith difficulties and tieups in the testing of nuclear sub-marines in the US.

The literature on the problems of nuclear safety on'assele with NPP consists of just several papers presentedOy Soviet scientists before the 8econd International Conferenceon the Peaoeful Uses of Atomic Energy (Geneva, 1958).

1

Ou~r book repreeente the first att~e~pt "0e~r~ithi.. >-,!,ObleMS of dosimetrio control and radlt iaton saety OU.nI'r vausels. It ccontal.r± a systemnatic~ presentatiot of naterF.al5 Publisihed In Soviet and foreign periodicalo, with an aeoou~ntof -'ani latest achievements in the field of Ionizi~ng radiation

The author's have striven to present the material ina pop'ilar fashion., without overloading the test vith ziat~bemttes, while preserving the rigor of the forwilatioiis.

The oont(nt of the book miust weorstrate that with acoarzetly planned 1NP installa~tion &ad the realiza-tion, ofproper' oontrol, Ite ezpleitatiozi under ship conditions doesnot p~rsseat Wm funda~mental Wifiocilties or danpre,

The first ahapter eoutfti a barief preseetatlen of theba3ie notiolis of nuclear, physics &W~ technology to an *rt~ntne~eesyary for the rnaderst~anding of the physical essewo of theki]-ev~t pt~non- irnd pr~ocesses,

Use subsequent othaptero contatin Irfrmat2.o onk thetfoxnss of~ radiAtion dozger &An means of combatting thsm aswell as on biollogical proteatioki and domIzetria controlmethods on nuclear *hips.

The last two chaptersm eonaitan a brief description ofthe eystem of dosilmwtric control aboard the atomic icebreaker

"Uni~n"d some information on radi~tion safety on fer'eign

Th* seet, orkdoes not deal with tUe pfblew ofradocem anlyisand tecivto arising in Ifa. exloit..

ation of nuo ear reactorse, sizce those are Independent aspectsof the rattlation oafety problem.

Th authors consider iy. their p:-asaaxt duty to extendAislicere tba*ks to V.I. Zadeatiev and XU V. SIvIntmv far theirconaiderable assistanas "n advice.

The authors would also appreela-.a all rnritima r~mrksoni the vost; these rcould 'be addressed~ -%oi Lan4Zgd D-45,0Dzerzhinskly Ostreet (Ulitea Daershluskoi:?o) 100 8 ttrowgIs(State Union Publishing House of t*.'ic 9b:pbuilding - dustry),

2b

Ohapter X

TN! NOTIONJ OP IONfIZING RADIATION

All naturl bodies are -ade up of atoms an~d mOle-cules which are inl a state of @ontintUOUs mOtion.

The atoms in elements, oombining In various ratios,form an enormous variety of eompounds. The smallest particleof a eompound which retains the specific chemical propertiesof the compound io called a foleocie. The atom is the smallestparticle in ordinary matter ibSeh remains unchgd inl chemi-cal reactions. It constitutes a complez electrically-neutraleystem made up of a pouitively-charged hucleus and negatively-c harged electrons in motion about the nucleus in closed orbitsvhich constitut~e the elect~ron shell,.

The nucleus of an atom consitst of a deflete numberof positively-charged ptarticles -- protons, end unchargedneutral particles -- neutrons.

The proton is the nueleus of the lightest element(hydrogen) and has a mass apprezimately equal to the mass ofthe neutron. The positive charge of the proton is equal inmagnitude to the negative eharge of the electron.

In nuclear physics, protons and neutrons azte frequentlyreferred to as nucleons.

Since the atom is electrically neutral, the number ofelectrons orbiting the nucleus is equal to the number of pro-tons making up the nuoleus of the atom of a given elemnet andis the main characteritict of the given element. The changinof the number of protons in the nucleus sinifeites a transitionfrom one substance to another. icr example, the hydrogen nuc-leus consists of one proton (3.1), the boron nucleus con taisefive protons ('-5), cadmium -0 48( (s48), uranium -- 92 (s=92).It has been established that the nuclear charge s correspondsto the number of the element in the Periodio Table, while thepeculiarities of electron shell structure determine the perio-dici.ty of repetition of their chemical proper'ties.

Another important propertyeof atomic nuclei is theirmass, which by anale• with the charge is expressed in opeosalunits called atomic mass unitse, approximately equal to the mass

of the Preete or noutres. mhe eae suaber A of & weweroegate ther "a of Pr, toe am OW utr.=I i6tab~ims

As dietimot from the Os"aP It who" iat~ereasfeterave I* alwms Ncoompa-ift by a e;6Wg I& UO bCau"properties ofs a vbetsanoe, the vartlatiss of atesole Asuw Acan also bU ifete 0ObBAPe I JA inbeal of mewtreas is thenucleus. 5iCs msno ehAMees leave the, =*bet of PrmtN= 1 e.the nuclear shsr" x aowetsaxt the now mamete due &t a W

aboaesa tis teir valber" 1L. the 261400 As the Neameohesta oinIfterat ubroU v ara &Vnuclevs obsaftsetriehle a 4itfMM elsee or inls widiffr I. eir phsea.. prepertleelave aeke Mobc TOv0b Sa Charge mauter. or em 0"10e010lem) 'butfoer In mawe (amber of Deetvouc) awe *suied liteeapeaq Le.,teoempylag tte" pomittlaIs thejoreuiedl TOM* (froul the

Atemle mactel are wuimiy denoted by %th gymbel

wheres, a t the ateulo *uMber of tme avolcuelX In the nam to the eleamst;A to the mass zau*r,

PST 0l ,the _%Mtens ameslus Is wrIttem ows%be sodium amiu to Il13 o

"wh smbter of proloe usalis UP a WWI~e detetuinesthe sen of the positive asoleer ha M ad .1bserete Vhenumber of eleetroea In the olerei:6o the wfte. xtalso deteiwwles the atomic auewo? of e *elmat s, Writingthis subeewipt IR spoecIfytag eleusats helps 12 veeerdag=&cleer roeastei.

The radiu rn o f an satoic nuenleuc San be evolvated.aprezlmately with the aid of kbo tusatisa

r a 51 1

wbere A Is the swce amber of the nusleus equal to te ams ofpretons aad aeutrnoa It Oesatlue.

ef Roeam we cam Galoulate that the radius, of the MCleusof te liu eat*Ioat - hyrogea - I g e~a" tI em a

(a~ Proimaely), wtlt the =clear nd s of the heavi.eleve" swt asuranium Is PW#* I COanZ& the Sesurs of studs" o uet aleer Pw.~rtles # It was

established that Neow avoleS, spem-AtaMuealy, - i hout say ester-3.1 Inlaflueoes, disintegrate sa" euit eles168 f erminnuclei of other types as a i-evult. Thi phemossemws mesailedradioactivity.

4

As earl7 as in 1896 the physicist Becquerel foundthat uranium uoupounds emit Invisible rays which blacken aPhotosensitive plate. Two years later It was disoovered thatthe msw elements (radius and polonium) discovered by Pierreand Marie Ourie likewise exhibited radioactivity analogous tothat of uranium compounds, but stronger in Intensity.

Studies with the aid of a magnetic field have shownthat three types of radiation are In evidence In the disin-tegration of heavy elementst positively-charged alpha partic-les negatively-charged beta particles, and electromagneticradiation of very short wavelength -- pm rays. The commonproperty of all three forms of radlateen Is its ability toIonize atons In passing through matter, i.e., to remove oneor more eleotr•ns from th shells of neutral atons, Becauseof this, all three types of radiation are referred to asIonizing radiation.

Lot us oonsider ese of the other properties ofradiation which aeoompanies the deasy of radioactive stons.

Alpha particles have a positive eleotrical chargeequal In absolute value to two electron charges, and a massequal to that of the hellum nucleus. The penetrating powerof alpha particles *I determined by their Interaction withnuclei and atoms of matter and in measured according totheir range in a given substance. Usually, the range ismeasured in centimetere. Per alpha particles of naturallyradioactiv materials the range in air does not exceed 10 o,while In solids ad liquids It im extremely small and doesnot exceed tons of microns, For example, several sheets ofpaper are sufficient to fully absorb most of the alpha par-ticles emitted by radioactive oleosents.* As distinct from alpha partiols, beta partioles of

comparable energies, which are essentlally faet eleotrons,are characterised by much greater ranges in ir. Severalsheets of paper are no longer adequate to blook theou some-thing like a sheet of alumnum several millimeters thick isrequired. The thickness of material required for total ab-sorption will be strongly dependent on the initial energl ofthe beta particle and the density of the absorber mater 1.

Gamma rays constitute a stream of photons which areno different than X-ray. * Pr the same wavelength, the proper-ties of these two types of radiation are the same; the onlydifference is in the souroet photons emitted by a nucleusare called gmma rays (gamms quanta) while photons producedby the slowN of electrons in a field of atomic nuelei arecalled X-rays,

As distinct from alpha and beta particles, game,particles have a high penetrating power. High-ener~l a11rays, with energies on the order of millions of ev (ecotronvolts) (see note) can pass even through several tens of oenti-meters of lead, despite the fact that lead, just as other

5

elements with a bhla atoai nmbor, is a mere offeotive ab-soroer of rma ia tio than • l•t elogao set Note# Anolectron volt is the unit of emWer aoquirod by an eletr•in being aeooleratod throso a- potential differtoneo of enmvolt].

j firf • ['IT

Figre . Rlatvepentrab owrus of alpha a&M beta partia-:Los and g ns1ys. A •lPaper a 1uainual 0 a lead.

Let 1n01ao1s a ndoasetlve MN Owlh4ish miltsalphat beutam MYs (PiM "0 )O ver the sou"s wplaoee a absemier emmeatlagef several sohooto of or•lnarypaper (Pig ft). he alpha partioles ae absrbe Y thepapor but the beta pmW pse throg wAth.~t m1ysigaiheoat I*" of Onrgy. g lb shOws the efot of anasoolrber eammistiat of several DIiteor of shbmt alumium.In this ease the i1safim filters out or abecr t aluhlphaeand betas, wLle th; pamem are Suet somewhat weshoesd. FPialsly,Pi Igo shows that ma aborbiag layer of several ofatimaters ofled oomlderabl redmoess thW intensity of - am s Mp buttill does not stop theon OO•l0etaeyo As distlat from alphas

Wad botaus pm:.rSays ae frequeat y .alnlo pnetaotstigradiation.

There ;snoe atothor form of Wmtlatie -- neutronsproduoed durlng s operation of nuclear reators. IMe propertiesof %ese partloles v1 be oessidered later.

In tIe earliest soeas of resesrh on the propertiesof radieaotive atoms it wme disoeverod that their acitivitydrops off with time.

d The euoose of the radlieotive £ooay prooess for a•ymaterial Consisting of IL give umbero f stmilar ato"" sanbe J"eoibed with the. aid of a oertaia senstant called thebalf-life. It at a given Instant we have a eert"ai nmber. ofstole nueiGo o*f type A. then after the hUlf-life period Uo

elapsed, one half will have been transformed Into atomicnuclei of a now type B. After a period of two half-lives,one-fourth of the original type A nuclei will remain, afterthree half-lives, one-eighth type A nuclei are left etca

A new substance can also turn out to be radioactiveand in turn be transformed to a third substance 0e Zn suchoases we say that materials A, B, and 0 constitute a radio-active family.

Zf T is the half-life, then after a time t, theremaining nnmber.of the original number of atoms N% will be

N = %1eN t/T°

Along with the half-life T, we frequently wake use ofanother quantity X, which Is called the decay constant and Isgiven by

0 = 1o" t (1)

(which In called the radioactive decay law).Hence

N = (1/)l.n2 = 0.693/T.

The radioactive constant is 9 Laasure of the Instability ofatoms and Is defined as the fraction of nuclei decaying perunlt time for the given radioactive substance, The minus eignin (I) means that the number of decaying nuclei decreapes withtime; the dimensions of the decay constant are AtLMe]-1

Using as an example the decay of radioactive carbon.we will show how It results in the production of a nitrogenisotope accompanied by the emission of an electrons

14 14

6 -1 7 N

14i.e., carbon 60 decays with the emission of a single betaparticle, an electron, to become nitrogen 7 N 1.

Similarly to chemical reactions, the radioactivedecay prcese Is recorded in the form of symbolic equations.On the left-hand side we write the symbol for the Isotope orinitial nucleus; to the right of the arrow are written thesymbols for the final decay products. The following notationIs useds -- electron, n -- neutron, p -- proton, g -- + gamquantum.

The concept of activity Is introduced to comparevarious radioactive materials,

7

Let us denote by I the hMber of nu0lei Ot a rSdio-active a tortsal In meo mia q; t thea th4 eaber of neeleideoaitng pew meocad wilpN1 * Where tio he t•sulatdecay constants te pre not IN represents the aotivity ot

tk.given samPleIf we denote by Go the Initial aotiVtit, and by 0

the aotivity at laastat t, tbhon aecording to the doeay lawwe osall hesv the relation

a a "aIn 4otoe•2mn the quantity of radloactiveematerial

(aotivity) th onet v do*17used slt Is the 'ourle', in honorof Pierre and Xerle Our•e. the opiqio ts the quantity of radio-so&tav material In which 3.7 001v dsliatoerations ecur persecond, Approximately the @ase number of dIsintoegrtiona occur,for examples In a rsan of radius each second. Thus, t:e activityof one gram of radium is practically equal to one eurie•

mslonose from rsdioactive elemente and the products ofnuclear reaotions, suoh an gammas rays, neutrons, protons, alphaand beta particles, all produot lonisation In pasting throughmatters

Charged particles produce lonisation along their pathdirectly through the action of the electric field on the orbi-tl electrons of the aret matertale uamma rays aed nutronsdo ant produee lonisation direotly. However$, so-oslied secondaryelectrons &rising In the absorption of passe rays by matter,do result In losistlaton.

The Irradiation of live tissues with lonising radiation;-over specific, so-called maximuz permissible levels thloh Villbe indicated below, oan be dangerous to human life and health.This Is due to damage to celle which is the result Of theInteraction of radiation with the atome In the bUo01oloaltissue.

the danger from which the oPeratla• personnel ofnuclear power installations must be p 4 oto c man be twofold:in the first place external radlation, and seoondly the moreconcealed and pernicious danger of internal irradiatlc as anresult of the oontamination of sir water, and food.

The penetrating power of alpha sad bets particles tonot great, go that in operating a uelear reactor there io toneed for special measures to protect personnel frou externalIrradiation by thee rays, In these oases, as will be shownbelow, it Is necessary to deal merely with protection fromneutrons and g•,am rays.

8

However, alpha and beta rays assume ma3or Importancein the presence of the second type of danger, i.eo, with thepossibility of radioactive substances entering the organism.

For a quantitative evaluation of the effeots of ion-Ising radiation on the irradiated medium we use the notion ofthe absorbed radiation dose.

The absorbed dose is defined as the radiation energyabsorbed by a unit mass of irradiated medium:

D a I/me

where D Is the absorbed radiation doseII is the energy absorbed by the .rradiate• matter;M In the mass of the irradiated material.

The amount of energy absorbed by a unit mass of ir-radiated material per unit time Is accordingly called thedose rate:

P = D/t9

where P is the dose rate;D Is the radiation dose;t Is the duration of irradiation.An the praotioal unit for measuring the radiation

dose ve use the roentgen (r) -- the dose of X-rays or gammarays in the air with which the concomitant corpuscular emis-sion per 0.001293 gram of air will produce ions In the aircarrying a charge of one electrostatic unit of electricity ofeach sign.. The number 0.001293 Is the mass in grams of onecubic centimeter of air at 00C and 760 am Rg.

The thousandth and millionth fractions of a roentgenare written ar and mcr and are called the milliroentgen andmlcroroentgen.

The X-ray or gamma-ray dose is a measure of radiationbased on its ionizing ability. By the absorbed radiation dosewe mean the energy of the ioniting radiation absorbed by aunit mass of material. The unit of absorbed radiation, thered, Is equal to 100 ergs per gram of irradiated material.

Let us cite some data In order to indicate the mag-nitude of the one-roentgen dose.

Natural. conditions -- cosmic rays -- 0.018 mr/day.Natural conditions -- naturally radioactive substances

inside and outside the human body -- 0.001 r/day.Maximum permissible dose of total occupational ir-

radiation for the human body ;- 0.3 r/week.Maximum single dose permissible in total irradiation

of human body -- 3 r,Radiation sickness with overall irradiation of the

human body m- 100 r and up.Minimal absolutely fatal dose with overall irradiation

of the hiuman body -- 600 r.

9

Therapeutic doses (local irradiation) -- up to15,,000 r.

At the present time, In connection with the practicalnecessity of determining the intensity of beta rays and neu-tron beams, the concept of the ,byelial eouivalent of theroentgen, the rep (roentgen equivalent, physioal),has beenintroduced. A 1-rep dose corresponds to the lonisation forwhich, reprdless 6f the nature of the ionizing particles,about 2.10Y ion pairs are formed In one cubic centimeter ofair at t = 000 and 760 ma 11g; this ix equal to one electro-static unit of charge.

The situation, however, is complicated by the factthat, as was shown by studies on experimental animals, variousbiological effects are produced by the same degree of loni-zation of air produced by different types of radiation. Itwas necessary to introduce the notion of relative biologicaleffectiveness (RBE) of various types of ionizing radiationand the unit called the rob (roentgen equivalen%, biological).

The rob Is the amount of energy In a type of radiationwhose biological effect is equivalent to that of I r of X-raysor gamma-rays. The reb is different for various types of radi-ation.

The relative biological effectiveness of various typesof radiation Is a quantity equivalent to the effect on theorganism of a single maximum permissible daily dome of occu-pational radiation.

Let us alte some data on the relative biologicaleffectiveness of various types of radiation; our unit Isthe biological effectiveness of X-rays with a boundaryenergy of 200 key (Table I).

Table IRelastve Blo1o.ical 3ffectivenes8 (RDE land %.IunMPerm~w-ibie _D022 o1 Aadlat;A Frogy ou8~ea,.onyn• I

SNc, u4eAYMe 1•,3 0.0Z7.9.rw.N* a yT~e •,• 0,017ersm-.m e ._0a017

10 0 0e017 0,017Teuasu~~*ft10r 0.0017BWtpue t 1o 0.0017

A = Isotope; B = RBE; C Maximum perumiesible daily domes;D = rob; E = rep or r; P : X-ray.; G a Gamma rays; H = Betarays; I = Alpha partioles, protons; J = Thermal neutrons;K = Fast neutrons.

10

As was pointed out above, radioactive isotopes enter-lng an organism are a particularly great danger. This Isbecause of the difficulty and slowness of their removal fromthe organism and the direct action of their radiation on thevital organs of the system.

In examining the questions having to do with the con-tent of radioactive materials in the organism, we introducethe concept of the so-oalled critical organ, I.se, an organon which the offset of a given concentration of a radioactiveelement determines the basic portion of the biological effect.It is Introduced because of the fact that various elementstend to concentrate in some particular organ or tissue, asa result of which their action on this organ or tissue hasdecisive importance.

The maximum permissible concentration of radioactiveisotopes in a critical organ is calculated assuming a maximumpermissible dose of 0.3 reb/week, taking into account theenergy of radioactive decay, the average weight of the criticalorgan, the half-life, and the natural biological eliuinationof the isotope from the organism in waste matter.

Maximul Permissible Ogncentrat Ions of SoaqMe RMiactiag~Laua a.je th f kn

f~lAPeauoaoymMICWs KO ne@NT.

CTPO"uuA'90 t) 3.10-11 3. lO'--1Ao.-13, 1,1- I 9-10"11Kceo.- 133 -finowssi 3210 ,. 2.0-011 I. 0-11paJ1111-M ý_. 6.10-11 3. 10-14

nlayToH 1-M2 ' 5.10-11 "-1

A = Isotope; B Maximum permissible concentration, curies/liter; C = in water; D = in air; R = Strontium-90; P = Iodine-131 ; G = Xenon-133 ; H = Polonium-2101 I -=adium -226; J =Plutonium-239.

The maximum permissible concentration in air andwater is determined under the assumption that the amount ofwater consumed by a human b*ing Is about 2200 cc/day, whilethe excreted amount is 2.10' co/day. Table 2 shows the maxi-mum permissible concentrations of cortal radioactive Iso-topes in air and water.

11

3. bjuolar Biatig, DnerZ and bangar 10tAnss

S.nm c ;,3sball sleetrorxare bha4 inithe &teoo y •ee relet eoatt3'atcti of tuer seti*veeharse to the positive charge on the auogauu, The bladingenergy of thes eleotreoA and the au4e6us SA 2.menezabGsnmeltr than the bindiAg emerop between h aUolea'r p artloe,Whiek Ls one the order of several m1011L0n electro vol.to(mv). The high binding energy of neutrons and proton$ insteoeP nuacls enlgins their ezmosus stability.

At first glace it night seen that atomic nucleioenWot be stable ainoe the protons contained In them NAotrepel each other mines they earMr the awne charge* 1he energyof this repulsion is given by Ooulenb's law. Rovever, thestability of most atomiao MialO I0sL evido se of the fact thatvhon protons approaoh, attractive forces are supetUopoed onthe repulsive force Ahich Uef&Asae rapidly the oloser theapproacb. At distance* of 10"4 on they eignificantly ezoeedCoulomb repulsion. The same forces ariae when protons appreaehneutronse These attractive force* between nucleons are ea~lednuolear forces.

"Mrese Is as yet o eeple"tely aduate theory ofnuclear farce", nor is everything known about their #rope0ies.However, there is no need to dewtermne the binding eoe1orfor a nucleus -- her we •end merely make use of Vhe energyconservation law. if we were able to pull apart all of thenueleon emne by one without endowing then with au6itienalkinetic energy, then this would require an amuomt of workequal to the nuclear binding energy. In aoordance with theenergy onservation law# the ean amount of enery m•ust bereleased upon the formation of a nucleus from tbeae meleen.regardloes of how it occurs. This energy Is made Up by thecbangs in mass of the coalescing nmleon. Tho la* of inter-action of mses and energy, theeretieally JuSstified by istesinand subsequently eefirmsed by experiments on nuclear re~etions,Is esbodied in the formula

where I is the energy;a is msesna is she velocity of light.

lom this relatian It fellows that one atomin smasunit (0 am a 1/16 of the Mass of the basic xy8eA isotope

8016 sad constitutes I .657,10 -4 g) is equivalent to

I = 1 ,657.10h24 (2.99790-100), De .1 9.Q10"3 erg a 931 vey.

12

it the energy 3 released upon the Creatien of an

atonle nucleus In large, then the mass defeat

As a]/02

has a noticeable value. This defeat to called the me$ defeot.In other words, the mass defeat to the difference between thetheoretical sun of the assets of electrons end nucleus maskingup the given ato& or nucleus an the ssn determined eperl-mentally.

Lot z protons snd A-t neutrons form an aton of anucleus with a mass a. Let us denote the rsso of the protonby up and the sase of the neutron by a.

Then the smas defeatAn a * + - a.

If the mases* are expressed In sou, then the nuclearbinding energy (In iev)

I a 931i,& a 9 3 1 n (A-)3,1 - )].In praotisev the binding energy in tev is more easily

calculated from the formulaI a 931 [i 4 (A-s)% - K],

In which m 1 .00814 anu Is the mass of the hydrogen atomla 1.00895 anu Is the mass of a neutron; N is the sase of

the isotope in ann.As an example, let us determine the ms defeat and

the nuclear binding energy for the Isotope of uxaima435whose nms n a13 is equal to 235.21

Anm 92*1.00814 + (235-92)1.00895 - 235.2 a 1.90 amsI = 931.1,90 n 1770 mev.

Renoe the binding energy per nucleon is 1770/235o7.5

haljat al . Under certain Conditiens, certainatonic nucle•ican react Vith other nuclei. As distinct fromchemical reactions when there io a rearrnoment of theouter electron shells of the at*o, the nauoei themselvesundergo restructuring in nuclear reaction., In ma oasesthis leads to the transmutation of certain ohemlial elementsInto others.

linilarl to Chemical remotions, nuclear reaction.are written in the form of symbolic equations, For example,the reaotion of neutron Capture by hydrogen which leads to theformation of heavy hydrogen (deuteriu), is written as

n 13

or.RI (a# y)W2

It Is easy to see that twoacm an the total number,of Moucaeos (protons and neutroas) io conserved In Macleermo.tiou, fth smo of the wee, mambers of the isitla1 solous

and iateftestiag arttleo is equal .to' theaeta ~it the Uweu Rum-ber oftheflul racion prohots. &8hi&rly tina seoreraao

with the vellkaowu law of stmswp oeaservation, the sum ofthe vsubsripts In the systbols Weore and after the reactionrenals tUS NNW,

holeer reactions can arise In the Irradiation ofsubtasoes wIth neuatrens, protomm &lphs, partioleles *tooft prebability of the .oourenoe of nuclear r~ellz toeInolsractsriued wi1th th~e aid of a certain quantity called theWttotIve reaction corss-seeto tes Au Swtpre~sed In uaits of

area; i.e.,, the bombarded misloe le asaif d an effectivetarget area which It Is =*smesary to bit Corder for thereaction to occur.

lot us explan tWe In greater dttail 41.voa the Pao-se ef W~ particlos, suchb asomutronsa O tres& matter,various typen of Interactiosn pay take plase between Itse andthe nuclei of the su'bastane * wevy.r, *oms of the neutrons willpass thrugh the substanoe without any lateractiors witb itsatow. If the svdUbstae Is hoempnseeuc whle* tb# 3mttons areof equal eseorui an direction, the prebab~l~ty of portioipa-tica Ina the ancolar reaction must to the sass for all. outwon~swsaG 1 atomset tfhe subs tasoo Irradiated with the SmUtroaboam. knee IS felows that the law ftich tusm~a~tivelydetsreimes the iatermaoton of Mutrous "A- -3-le 4 havea purely static ebaratete. The naUmbr of noetrovm, ='vesetingwith stone must be preportional to the musber N, of aftiroesin the be"9 the number a of aMons per usite velves of Ikesubstance and the free path of Ute nestronin la t00 substaxice.

Deno"i b I the number of soutroms falling at,right an4es on a flat layer of material of Whoae ft &adbyN the aember of neutts emerging from the Ivor, tiopossible to show that

13r~ or% s rx

wbo 4ris ame propertiematity seeffi lent.Sinoo 3 has d~mossions of W-7 and x ts &A em the

coefficient of pz'eportiommUty W mot be Uin o2 It o ainedthe offtctive =uclear ersesmseotion and represents a ucestre ofthe probability of the gives reaction.

In the case of a nualser reacotr, the most Importantreaotions are those Involving the interaction of neutronswith matter.

1d4

The collision of neutrons with the nuclei of bom-barded atoms can be classified as numerous types of nuclearreactions, among which the most important are the following.

I, Nuclear fission (n,p) in which the nucleus of aheavy element following neutron capture splits up into twofragments (approximately equal In mass) with the emission oftwo or three neutrons.

2. Radiation capture (n, f ) -- the most probable pro-cess for thermal and slow neutrons.

3. Elastic scattering (n,n) -- scattering withoutalteration of the structure of the bombarded nucleus, inwhich the kinetic eaergy of the neutron-nucleus system re-mains constant.

4. Inelastic scattering (n,n') -- scattering Ir whichthere occurs a nuclear Interaction between the bombardednucleus with a neutron, and a subsequent release of the neutronwith an altered kinetic energy.

A special case of interaction between a neutron andan atomic nucleus is the scat tering of neutrons by atomicnuclei. Ae we shall see below, this phenomenon is importantin reactor operation.

lo conclude this section, let us cite several examplesof nuclear reactLons.

Nuclear fission:

slum + an' -S aIra + "Ba2 + 3i';%Pumw + on1 * .Zr" + 4Xe"4o + on1

Padiation capture:

1H1 + on' -+ .H% + +;

(n,p) reaction:

,N"M + gn1 _. ,C,, + IH,;,$Ni's + t" -•.Co" + ,

Chapter II

REACTORS -- SOURCES O IONIZING RADIATION

The nuclear reactor Is the heart of a nuclear powerplant; It produces the energy which puts machines In notion:turbines, generators, etc. The operation of a nuclear reactoris accompanied by the foreation of powerful streams of Ioniz-ing radiation.

It Is necessary to have a clear Idea of the processinvolved In the appearance of ionizing radiation in a reactorand other elements of a nuolear power installation in orderto be able to assure reliable radiation safety to the operat-ing personnel.

4. The Fiesion Reaction

The fission process Is most easily explained byappealing to the so-called drop model of the nucleus. It Isknown that due to the mutual attraction of molecules in thesurface layer of a drop of water, the drop assumes a sphericalform stable to deforming forees.

It is supposed that an analogous phenomenon occurs inthe atomic nucleus. Quite naturally, if a drop or nucleus issupplied with enough energy, It is likely that it will splitup Into two smaller parts. In this process, a significantrole is played by the nuclear binding energy in the form ofCoulomb repulsive forces and surface tension forces. Thedeformation of the nucleus under the action of a bombardingparticle first Increases the binding energy to a maximum dueto the enlargement of the surface and the surface forces.Then the binding energy diminishes rapidly due to Coulombforces (charged particles drawn apart to great distance*), andthis is no longer oompensated by an increase in the surfacebinding forces. There Is a fission process (Fig 2).

In each of the fragments formed In the splitting ofan unstable nucleus, the attractive forces already outweighthe repulsion, and the energy of the new system Is lowerthan that of the original one. For this reason it can beassumed that some amount of energy must be released in theformation of two fragments.

16

The fisesen of uranlt an elL. Is acomoaie bw thefromation of fIlsion Mgmente with a mass veatezr then tutof hydrogen by 72-4 59 times. They are the nuelaL of olnsextlocated In the middle portion of the Periodic ftble.

Figure 2. Schematic representation of the proue -of tM d*i-vision of a nucle into two wt~p" (fragmeat).

BeeD** or the. fe•t ohat the nuolei Of bheav elmawtcontain a largm namber ef nuttere Ixa eoeparien with Uh*nuclei of axeo in..the middle portion *ad beg ,naLs pe:tt otthe Periodic Tble, their fragmnto likew.is have at e0."66*of neutronlst which aoouitsk •n peartoular for their beta-activity, Such beta-actiVe nvolei give rise to an Oeao'ouev•riety of 4444m. desay reaotieon [nnate the 1ormrefers to a series of iatopes foftsd $:s a ful Ift.successive dtozy of each of the deogy afgfhhta Ust.il t.heformation ot a stable Isotope], POf. exeple ths . mt

36 Kr 9 2 formed In uraulut dey7 hast the tollowlhA defay eh"tin

in S) M? I

Tbhe final yield of say filsson pviduot, oo,'w its.percentage istio to the other poduota, to defined to therelative nuibe• of fission ee"AtS laeing to the formatineof a given tnagmzt. Pig 3 shows the y;9] of various ftl.soafragments of uramtUm-235 (as pe.senutage) upn a netlr% Vi,.radiation.

Tho *set L'Sporlat eosi•t of fission ts ohe usleaseof •targi. It to known, t tor fissien fragm•e•nit with menumbess 70- 60 the bldI4g energy amounts to an aeerago of8.35 me,, and tor the u iWdux 610149, X. weas shown above to7.5 wov per nuoeoon. The dtffore•ce between the total winigonergy of the uranium nualesm contalaing 235 aucloons and thetotal binding of the two frqgenit nuclei is about (8,35-7,5)235Z

S200 mov.

17

Thus, the fission of a uranium nucleus liberatesenormous energy -- on the order of 200 million electronvolts. More precisely, the total fission energy Is distri-buted as follows:

Kinetic energy of fission framents.............167 mevEnergy of fission gamma rays and fissionfrements .. .. .... ... .e.,..e............*.., 1 1 mev

The remaining portion is spread over a number ofprocesses taking place in fission

In the process of nuclear fission, in place of theabsorbed first neutron which produced the process, severalsecondary neutrons are formed. This can be explained asfollows. fun

1"-

E I'N -go W W

Figure 3. Yield of various fission fragments of uranium-235upon its irradiation with thermal neutrons, A = Fragmentyield, 1; B = Mass number.

All of the fission fragments possess a higher ratioof neutrons to protons than is the case for stable, non-radioactive nuclei. The great majority of fragments are forthis reason beta-active, however, in some of them the excesscf neutrons is diminished by their emission. Neutrons emittedby nuclei are classed either as prompt neutrons or as delayedneutrons. Prompt neutrons are those which are emitted direclyin the fission process lasting 10-12 see. An average of 2 or 3prompt neutrons are emitted during a single fission event foruranium-235.

The relative number of such neutrons in certain energyintervals is given below:

18

OverEnergy interval, moe 0-I 1-2 2-3 3-4 4-5 5-10 10Relative number ofneutrons (per fis-sion neutron)ingiven energy inter-

0,'3 0.134 0,186 0.103 0.056 0.082 0.00211.0000W

In addition to the prompt neutrons Immediatily-eoooa-panying the act of fission, In a smail number of oases (lessthan 1%) we also observe a phenomenon of neutron emission overa considerable time interval following fission. The sourcesof such neutrons, whiob have been called delay d noutr ne,are certain of the fission fragments: e.g., Br" or V7.It is interesting to note that these isotopes emit neutronswith the same half-life that is characteristic of theirbeta activity (Pig 4),

o8r

•Se

M/r V•

3r1u Ica

Pigure 4. Decay scheme of 3 5 Br87 nucleus with emission ofdelayed neutron.

In Table 3 we present sove data on delayed neutrons.To conclude this section, let us briefly oonsider

the problem of uranium nuoleus splitting by neutrons ofvarious energies. Pirst of all we note that the secondaryneutrons formed in fission can have the most diverse energies,up to and Including 10-20 mov.

Neutorns with an energy of 0,025 ev are called thermal,while those over 0.5 mey are fast neutrons. Quite naturallp,

19

the fission process requires some excitation energy Efie

(Fig 5) to overcome the so-called potential barrier [note:the potential barrier is a region of states of a materialsystem with increased potential energy, separating regionsof lower energies]. Thus, it will occur only under the con-dition that in amount of energy at least equal to Efig is

added to the system. In one case, it turns out that suffici-ent energy is provided by the binding energy which is re-leased upon the addition of a thermal neutron to the nucleus;in the second case, a faster particle must be added. From thestandpoint of industrial exploitation, the most feasibleapproach at the present time is thermal-neutron fission.Actually, uranium found In nature contains about C,79 ofU-215, traces of U-234, and over 999 U-238. Of the twouranium isotopes, only U-235 undergoes fissior under bombard-ment by both fast and thermal neutrons.

Table'I'elayed N~eutrons UTpon-rission-of U•-235-U-nder Bombardment b

Thersal Neutrons

no I 33F3S 5 OiUWNcJNaUuI $UXOAoO nxoro q$[W uIepouoe

56.6 0.02520.0 570 0.IP4,51 412 0,2131,52 670 0,2410.43 400 0,086

rlOaAnul I x( : 0.730

A = Half-life, seconds; B = Energy, kev; 0 = Relative yield(percentage of total number of fission neutrons); D = Totalyield: 0.730.

U-238 uLdergoes fission only when bombarded by fastneutrons with an energy greater than I mev; with energiesbelow I mev, the fission probability sharply falls off tozero, Fast neutrons are formed directly in the fission pro-cess, but already after several collisions with nuclei ofsurrounding matter or uranium itself they lose velocity andcan no longer effect the fission of U-238. As a result, theybecome thermal and remain In this state until the moment of

20

capture now by U-45 nuclei in large meaure. WoNreve atthe present time great str1des a"e belng made in the dvelop-meant of reaotore using medium-energy and fat neutrons, inwhieh the fission proeeso Udaee place largely due to neutronswhose energies rasne from 0.1 toe 0.5 mey and from 0.5 My up.

Ita

Figure 5, Qualitative representation of Potential barrier

which must be overcome in fission. A a NfIal 3 a Elongationof splitting nuoleusl C 0a Piseon reaetion ener'p.

The advastage of sueb reactors lies neafy in theirsubeta•tially smil•er size, whioh Is of spoeeal isportenoein marine engineering.

21

5.Me Cha .. Raction_ and the Nuclear Reactor

As was pointed out Above, nuclear fission is a&Com-pinled by the emission of secondary neutrons, whose numberin greater than one. Let us assume for the sake of concrete-ness that two new neutrons are formed in fission (Fig 6) andeach of them produces new fission events, i.e., the newnucleus has split to form two new neutrons whiloh producefour neutrons eto. This idealized oase constitutes anIdealized chain, reaction. The name "chain reaction" is bor-rowed from chemistry where the term refers to a reactionwhose products enter into combinations with the initialproducts, as a result of which the reaction develops con-tinuously.

8)

Figure 6. Comparison of chain reaction involved in uraniumnucleus splitting with atsorption (b) of some of the neutronsand without It (a). A = Primary neutron; B = Fission neutrons;C = •eutron remaining after fission; D = Absorption of nucleus.

The idealized case differs greatly from the actualone, however, Inasmuch as there are several Sactore hinderingthe development of a chain reaction. Among these are:

1) the absorption of thermal neutrons by the fissionablematerial itself (e.g., radiation capture of neutrons by U-238)not aoccpanied by fission;

2) the presence of admixture, which absorb thermalneutrons in the uranium;

3) the leakage of neutrons from the reaction zonethrough the surface of the nuclear fuel. This process ofneutron escape through the uranium surface without furtherfission has been termed neutron leakagel

4) fission occurs most effectively when realized bymeans of thermal neutrons; at the same time the majorityof secondary neutrons have an energy of about 1-2 mev, sothat it becomes necessary to slow them down by special means.

22

The letter fact ts of deeieive impertanoe In the deigsn ofkloeiar reactors.

in order to crteate favoable ooedtlzu tow naeutemroladttlesa it Is seoesNsry to mix the uatam with sub-ataneos eoaan ol emoeatv of low ato•le witt Vhlb ancapable f slowing down neutreos t thermal **Orel*s we•eattheir Its sive absorptles. The eomposition of the ofxt"0(psOeeat~e onteat of modesster materal aMd tmwasM) Itcarefully ee2.oet. U the preptioe Is property dotunedo,the number of seeooadw7 sutzesso fosed il suh * mUsersupon the 0ooqietiam of Gae fission l0 Gas eoeed4 thenumbr of primay aetroam by seveu eroent, so that tosuch a system is possible to tavea esolf-maantatalmu -oaccelerating chain re"ation.

The devU* in whiclh a eel-nmintaiiniag nuele• Obanareaction takes plaoe has Uees ealled a nuoer resetor. Torealize the ehaln reaction I it necessary that the neaetosobtaied In fisasion produce new fiseio eventa. When thevolums of tShe mixtur of the fissionable matorW aMr w##er-tor Is , it is possible that a outreoa wll not *6111t4with a 1-,- -2. 15 nuoleus a44 will net prodGee a 81MOeflexion Iseat i paos sig thrugh the volume Nowever, as themodoeratlbo, a*Sm itute is Ierased the nauber of scooadaryneutrons, preolrtioaal to the tso~ter volume, rlie*s ira ?pid-ly than their l•akagp, ek ts proportional to tUe reactersurfal.. lt ths uhasoa, starting with a certaian ve.nu, thenumber of seoopdaly noutrons begsu to balance out thee atvaorof those absenbte, and a self-. latalagng nuclear oelA reactionbecomes poesible In the reeota,. Ife smun at uole)"*ewaoorrespondia to this volume 'I* bees called the eritioal mass.

To reduce tse nwtron lakago froM the eowd•o, theauclear reactor is surrounded with a speial, nestM rie~otior[noter th e reelootor is a material whiob wten hit by awatrowproduces the elastic soattotreN of the Utter bek Into theactive sons. The most sultable materials for this urpoft 46dense substances of low atomle weight, e.g., beorlltum,graphite water, etc.]

ite critical reacteo *in depends In the first pUseon the surfaee-velan ratio. *Por eza.le, a sphere has tUemnlurns ratio so t1ht a sphaeioal reator we roe the leastamount of auoiear fuel. Pigs 7 ad 8 are curves boving the"relatlon of critical dSiensions to mase.

To quaatitatlvely evaluatt te do semaina of the activesone of a reactor 6ad detoxeimo the ratio of reaetor power &adfuel charge weight (mixture of U-238 and U•35) let us makeuse of the folloavin formulae.

The eritiootl rcetor dimenuions ns found$ as we havealready established, as a funotioe of its f•r• aewoedig tothe expressions:

23

r = 3.14/P for a spherical shape;r = 2.945/? for a oylindrioal shape, (H = 5.4i4/1);a w 5.34/P for a cubical shape.

.

Pigure 7. Dependence of criti- Pigure 8. Dependence ofoal mass of cylindrical reac- critical mass of sphericaltors on the amounts of fuel and reactor on its diameter.moderator. A = Critical height A a Critical mass or radius;or mass; B a Diameter; C = Mass; B = Critical mass; 0 = Cri-D = Height. tical radius; D = Ratio of

moderator mass to fuel mass.

Here r is the radius of the sphere,or cylinder, R isthe height of the cylinder, a Is the side of a cubs, and P isthe so-called material Laplacian which depends on the breedingcoefficient and neutron diffusion length fAote: thisis the distance in which the density of the neutron beamfalls off by a factor of e].

For a reactor with a power on the order of 50,000 kwtand 144 heating units, researchers at Oak Ridge determinedexperimentally that P a 8.1-93 om"1.

Using the formula for a cubical reactor (its activezone), we obtain a cube size of a a 5.84/S.10- = 670 am.

The reactor charge is one the order of 800-1000 kgof U 238 in combination with U-235, provihed there is a 5-7%enrichment of the indicated mixture with U-235 (i,9., theweight of pure uranium-235 will be about 40-70 kg).

A diagram of a nuclear reactor is shown in Fig 9.The basic reactor elements are as followesthe active zone ;- the space in which the uranium

24

blacks and moder'ator' are locatel; 0.# *'rosai- fission tea@-tions aoccur haro

'tht 000,11SK Osytafi 0,160 Which tht PrimawY heattrsawtor agent (water or other' materials) circulates to renet.heat from teostive tons; this It called tUe prisary heat

transpecalv control elements.Lot us introduce the concept of the MoUtron bOreedinp

coofftelent which will fac224tat*.tbo explanation or rosotoroperation* Yb. neu'tron bwe61A$ ovefflicent I 2.5 4effm.d so

theraleof the number of uovzroas tormed. In fission ts -thenumber of neutrons disappearin~g duo to absorption or le~ts,,t

K =f neatritn fiao BU S N A A19%=20misator or neutroxt dist& oren~es *o*naft

Un eases" where the chalis maotion begin* with breedingcoefficients somewhat is etae** of unity (1> I )* the ioasityof neutron streams (and therefore the rne tor power) beiagbto Increase gra-dually. ftex the reactor power has been . wougutup to the necessary Lvolt the nratisn breedlag ose.ftioentsust be made to equal one, In Mtin case the number of wastroasand the &no=% of energy released per unit tive will reswi*constant,

Reac tor power lit varied by seans of control over thesize of the thermal neutron stresaa ftr this purposes tUsreactor In equipped with control rods whose waiting - ~Is%COntaIUing isotopes Is ous rged in the aotive sone Cr'e. Itabsorbs thermal neutrema le"-g., *datum I beton) * Mps M~s* Ion of the *63strol rods into the active sou of espeft~tigreactor, the 'breeding coefficient ralse off and osa b* Made toequal one or less due to ad44tlonal absorption of thermalneutrons Nr those rods, As a rult, rator Vviewe toeftconstant a I1) or drops oftf ,

When It "eaches the required iewell, tbe cona~l rodsare once again returned to a position. eorweepondlag toI * 11,and the reactor continues to operate at redmoed power, Taoameass* In reator pmwer are realized analogously -m treughthe removal o." the control rois from the active son**

In addition to theo control rods, each relater iS"quIppod with rods which Goapessate tue reacto IsoalooXIaffect* This consists In the accumulation of fission frag-mants which absor'b neutrons Is tbe beat release lslenetoOHn). These rods'quench oxo*&eiVe reactor reactivity, Uhi@oiis unnecessary ix the Initial stage of operation and to groda.,ally reintrodu@*d as reactor' poisoning preiresses. With res-peat to design and Seans of costrOl, shim (cospensatiag) rodsueed not differ from the onttrol rods. For this reason, shimrods and control rods are referred to by the gqneral term"coontrol rods". [note: the quantity X.1 is the excess neutron

25

040

43 Of'

40 0

q4

4D

vij

ii026

breeding coefficient, while the ratio (K-i)/K is the reactorreactivity. ]

Generally speaking, the control rods can be brokendown into three groups in accordance with their functions:emergency shut-down rods, shim rods and control rods as such.

The control rod, as was indicated above, Is intendedto maintain the specified power level constant. The rod Isusually shifted automatically, but manual control can alsobe provided for.

Shim rods are used to compensate for "poisoning"ofthe reactor, for sharper and more significant variation ofactivity (than that of which the control rods are capable).

ftergency shutdown rods are intended for normal oremergency reactor shutdown and must move very quickly in theactive zone. "'he*e rods are actuated automatically in theevent of an emergency by means of various emergency signals.All of these types of rods are designated by the abbreviationCPR (control and protection rods),

However, there is a factor which facilitates therealization of a controlled chain reaction in uranium. As wealready know, all neutrons are emitted simultaneously withthe splitting of the uranium nucleus: about 11 of the neutronsare emitted by fission fragments with a considerable delay,which is sometimes as high as 50 see. These delayed neutronsgreatly retard the development of the chain reaction processfor values of the breeding coefficient I close to unity.

Lot us assu=e that we have brought K to tmity. Thisimplies that the loss of neutrons is totally compensatedby the neutrons newly formed in fission. In this case thecahin process takes place due to the delayed neutrons, sincewithout them the value of K Is about 0.99. if we now increaseI to 1.01, this will not occur Imdiately. )ue to the promptneutrons, the value of K will rapidly rise to unity. Thedelayed neutrons will be able to increase the value of thebreeding coefficient no sooner than 50 see, so that therewill be a gradual development of the chain process, Ananalogous situation exists when K is reduced to values belowunity.

Thus, varying K in the neighborhood of 1, we caneffect the gradual acceleration or retardation pf the fissionprocess, and consequently regulate energy release in thereactor.

Nuclear reactors are classed somewhat arbitrarilyaccording to the following criteria:

1) the neutron energy -- the fission process canbe brought about by thermal, fast, and medium-energy neutrons;

27

2) desiaerL ot" act~ve Zone -- -.o-cal"ed homornccreaueand hterogentzeous reactors;

A r-eacsor in whicn. the fuel anti oderatcr constitutea single~ mixture in the fox-n of s solution, alloy, achemicalcom~pound, or suspension is called a homogeneous reactor.

If the f~uel is aistributed in the torm. of spatiallysevarateo. blocks surrounded by the moderator, then such are~orscIled hcterogeneous;

3the type o"'iuon.l materlh2. extployad. Re-acoci.s rnay use eit-her nottural uranl.nn' or vrs?,riium en-63cbed

.41t' tlhý- V-231:x Lso toe~4+ t*,- ir ature of the mode-rator -~grophitep heavy

water, ordinaryr watler, etc;5) the ,.ype of heat transfer agent -- water, gas,

or;7,anic, or Th2cA4-7rn~Tal cooling;6purrcocs *- r~ezerch, e~ptsinmen-al. test, or

pcwer-prodaceictraactar',lj

In rietigning reactors witbtin a given~ nari~v- inad64-tion 4tc the. ordin~ary requirehie r. tz witfý* respect to th;ýmaterials used -- anticorroel.venes.e, hlgh etre~ngtth, plas-ticity and good heas-, c3nductizr., special atlterttlozi Mustbe paid to nuclear properties, depending on. th~e acotiualpurpose and design.

It 4-9 recessar;. to 6seti.ny'uiih the folloving bizruor of n at ar Ia I s

2) retarding materia.).A. -moder9.tor3;31) coolants or he-at transfe:.* agents;4 ) 3 t-r-,Aorx7al i t er la Is Ifor pipe 9, cc-;rerings , and

other elementE, 1r. the active- zonr-;5,) rsedlatloz. ::hioldlng; mater i s ". s6) neutrorn ahtorbers (-for cotrols):Barj.sc ±~ort.~on t-he mos-t -iXpo*.Lt-:', malterials

employed in incdern nucl~ear tachnolo~y w!2.1 bp found irn7ahlt- 4.

Tabl e 4~ .. teria.2s Us'rc-d in "'Aile~ar Tregbnoloy

-2.!. ur.v'-2L

He~ t ex; o*t'P1izn9FreZv t ordinary waze~r,a ..e:.t...Is, a d b sma.b .. * sa itm

P_ 1e.: or~ s oay or ordinary water,, qxaphite.t~i berva17!.ura.'aeer almn.i ai'O.

Sb(1ýdlrq atpriptle Waeter,~ conorezeteel Read,''o

245

Among the fissionable materials used at the presenttime are U-235, plutonium-239, and certain other materials.

Moderators are usually materials of low atomic weight.One of the most important properties of moderators, of decis-ive importance in their selection Is the ability to retard andabsorb neutrons. It is desirable to have a moderator whichabsorbs fission neutrons minimally, but effeutively lowerstheir energy down to a thermal level. For this purpose, forexample, it is possible to use ordinary or heavy water.Ordinary water absorbs neutrons somewhat more intensivelythat heavy water and can be used as a moderator ttt onlyin reactors with an enriched fuel.

Heat transfer agents are materials having a highheat-transfer coefficient, low fission neutron absorptivity,low chemical aggressiveness, stability of physical propertiesupon heating and ionizinr irradiation, absence of toxicityand flammability.

Practically no real substance fully satisfies all ofthese requirements. For this reason, a heat transfer agentis chosen with proper regard for concrete reactor operatLsgconditions.

in low-power reactors, where the released heat isactually not used, air is a widely-empl.oyed coolant.

Natural and heavy water are widely used as heat-transfer agents. At the same time, they play the role ofmoderators in high-power reactors (ship power plants), due totheir high heat transfer coefficients (100 times greater thanof gases;.

Other heat transfer agents are liquid metals -- lead,bismuth, sodium, and their alloys and oxides. As a rule, theseare employed where very hgih temperatures and heat transfercoefficients are needed.

Among the most important structural materials are lead,beryllium, aluminum, stainless steel, zirconium, and a numberof others. Such a choice is explained by their sufficientlyhigh chemical stability and physical strength under hightemperatures. The most important among them are certainlyaluminum, zirconium, and stainless steel. Aluminum is employedin reactors with low heating temperatures; zirconium andstainless steel are used widely in high-temperature reactors.

The Nuclear Power Plagt

In nuclear power plants the source of energy is thenuclear reactor 1. The energy it releases due to the fissionprocess is converted into heat, which is then transformedinto mechanical work or electricity (Fig 10).

The loop along which the heat transfer agent cir-culates is called the "primary technological loop". Theheat transfer agent give3 up its heat to a special working

29

fluid in heat exchanger 3; this fluid ciroulates in theso-called secondary technological loop,

The secondary loop operates a steam turbine orsome other device (4). Poth the first and second loopscontain special circulation pumps 2 and 6 which continuouslydirve the fluid or steam ever the closed loop.

Part of the heat transfer agent passes into thespecial heat exchanger 5 where it is cooled by sea waterand enters the system which cools the bearings of the cir-culating pumps, special filters, etc. The heat exchangerbetween the first and second loops is called the steamgenerator (3): as distinct from the heat exchangers performingthe cooling functions.

The following basic types of nuclear power plants(NIPP) are used to power nuclear vessels.

Water-cooled steam turb~pe plant. Such a plantrequires high water pressure, which In turn makes it neces-sary that extra-high-strength materials be used. Installa-tions of this type usually require enriched nuclear fuel.

HeliuM-cooled gas turblge plant. Its advantage con-sists in the fact that helium Is on-reactive, and thismakes it possible to reduce the total weight of shielding.High pressures in the heat exchange system are not a neces-sity. Its disadvantage is the low heat capacity of helium,which requires an increase in the size of the active zoneand compressor power.

Figure 10. Diagram of nuclear power plant, A = Loop I;B = Loop I1; C = Steam; D = Water.

jijuId-M8tal dsole t and steam jurbine 2a.The metallic heat tranfer aen possessees very high heat

30

capacity, and does not require relatively high temperaturesand pressures. Its disadvanta.e is the high radioactivity ofthe primary loop (when sodium-potassium alloys are used).

gp This isPlant with oCSanl• heat transfer agent.Thssconceivab e In principlei There Is Inufficient Informationon this type of NPP available at the present time.

Plant of the so-called ,boiling reactor" type. Insuch plants the nuclear fuel -s used analogously to reactorswith water under pressure, with the sole differerce that thesteam turbine receives steam formed directly in the activezone. This makes it possible to construct a very economicalpower reactor, which however requires the inclusion of theentire secondary loop in the zone Cf possible radioactivecontamination.

At the present time, nuclear vessels are makingwide use of water-cooled reactors. These have already beenInstailed on nuclear submarines built by the US and Britainand the atomic icebreaker "Lenin"; the installation ofreactors of this type is planned for planned ships of theUS, Britain, Japan, Sweden, and other countries.

In connection with the fact that only reactors withwater as the heat transfer agent are used in world shipdesign at present, this work will examine the problems ofradiation safety only with reference to reactors of thistype. However, it should be noted that there is greatpromise in the use in UPP of liquid-metal and organicheat transfer agents, which will make possible a considerablereduction in the dimensions and weight of power installations.

6. Ionizini Radlatog tfrom Nuclear Reactors

The sources of ionizing radiation in NYPP are dis-tinguished according to the type of reactor and the typesof nuclear fuel employed, the heat transfer agent, and themoderator.

The peculiarity of the danger of ionizing radiationis related to the fact that humans lack sense organs whichsould react to this type of radiation, so that the leastamount of carelessness can lead to irreparable damage tothe organism. Radioactivity formed in reactors is indeedenormous. wi' 1 the amount reouired to Inflict damage tohealth is very small, it is qu4te natural that measuresto prevent the spread of contaminationi and radioactivematerials must be observed very strictly.

As is known, nuolear fission in uranium blocks isaccompanied by the formation of radioactive fragments andintensive gamma and neutron radiation. The fission fragmentsthen decay, emitting beta particles and gamma quanta; theyare therefore a great source of radioactive danger. For thisreason, uranium blocks are enclosed in hermetic containers

31

which prevent the escape of fragments and their spreadbeyond the active reactor zone. It should be rememberedthat in. the event of some violation of the wholeness ofuranium block shells, the fission fragments (both solid andgaseous) will certainly enter the heat transfer agent. Thiswill produce intensive contamination of the plumbing of themain circulation pumps and other primary-loop elements.There arises the dAnger of eeepage from various joints,gaskets, packing, etc., which may lead to a contaminationof enclosures and equipment.

All of this requires stringent control over thestate of the radiation plant on the ship,

Neutron and ,qMM Radiaton Ln-the Active Zone

Amcng all of the elements of an IMP, the active zoneis the most powerful souse of ionizing radiation,

Reactor radiation consists of gamma quanta and"neutrons. This inoludes prompt and delayed neutrons, spon-taneo'us fission gamma. rays, gawmn rays from fission fragments,capture gamma rays of the nuclear fuel or heat transfer agentwlzh the moderator, and a number of other forms of radiationwhich are of no great significance.

Figure t1. Energy spectrum of fission neutrons. A = Neutron/mev per fission neutron; B = 2, mev.

Neutrn ragadiagn,. Prompt neutrons are neutronsemitted Wt the moment of nuclear fission lasting 10-12 secand making up over 99% of the total number of emitted neu-trons. Delayed neutrons make up a negligible portion (e.ag.,0.7% for uranium) of the total number of fission neutrons,

32

There are f~.ve uliqttnct grouips of delayed rneitrons,olanisd ex.,ordl~ng; to the rate of decresse of tiheir Intensity(se,: 1able 3)

F~ro trie vtandpoirnt cf shielaingi iwo histmaj.J prouortion In the cverall stream, the delayed neutroziscan. . e negl*~eted in ccnptarlison witn *trie. promipt ones, 'However,

intecs o aae to tP active zone structure, it IsDosible for the f~ssiou. products -to enter the heat" -transferagent in the primary loop, ar, a result of whicii the latter

becoms 9 30uroe of delayed neutrors. Neutronas emitteed direct-l1y durlnF fission f(prompt neutrons) have a significantltygreater er~erqzy and Intensity, and~ for this reason have theFreateat effect on the 9tructurs of shieldin;- froyr neuitronradlation, The average enertzy of such neutrons is4 extremely

n P - a b o, ,,-- " ~ev ( FtpirIIAS an. e~a~rle Wblcý! clearly shews Thre great ane

101 neu'trion streams In the event of Insufftcient -shielding,let us con-sder a reactor with a therma power o.,; ;.00 thou-.. ?4 kwT. 41th such a polofer, the total size or .hp neutron.3tream In. about 6.1!019 neutrons, This Is eAsily seen. If wetake into acoo)unt the f'act that q e,;trcr.9 are emittedIn the production. of 1wt of energy per second. Hooe-ver,se.Lf-,.bsorptlon o1' radia~tion within the reactor Is greaitL--e rnoteli as a resu1'r. of which only about 1-2'A of theneutrcns will resch the shielding maiterial, i1,e., about2

-11n17 neutrons. Wiith an active zonip surface of about c.1we obtain a. value of about 101 3 nputrons/cmr2 sen for theneutron flow tý!rouq.h the s-urfac--.

F-om a Comparison of this value with the maximumpermis~~ible rate. having the following values for a dailyýý -rou'r IrraFdiation perlod: for fast neutrons 17 neutrons/cm~sec,and for thermasl -neutrons 15~0C neutrons/crn2 sec. we see thefir-ecssity for special protection for lbe oper~iti.ng, personnel.

1'-P gawma rdiation from a nuclear rea'-!tor isc "assea as pron.,'t gamma radiation, gamma radiation from theradioactive fission fr3.gmente, and gamma r~idtatton from theInduced. Retivi-ty in th~e roderator, heat transf'er age nt,reflector, and structural. materials in the active tonie,

e1-olw w;: Present some da.ta or. the energy spectrum ofprompt. gamaa em~ission In uran'4.mm fission:

Energy 0,25- -0,75-.~1,26-- 1,75-.- 2,25- 3,25- 4.25-- 5,75--interval, 0,75 1,25 1,75 2,25 3.95 4,25 5.75 6,75

meltNumber of 3,1 1.9 o.84 0,555 0,2 0,062 0,02 0; M?

per fissionevent

Total. of 7.0j q,;iant~a,,even-t, 11 mev/event

The relative proportion of high-energy gamma radiation(so-called hard radiation, over 1-2 mev) is quite negligible,

In Table 5 we list somne of the isotopes having hardgamma radiation.

The basic group of gamma quanta is the group withan energy of 0.75 mev, although we know that some gammaquanta are released with an energy of up to 7 wev.

It Is necessary to deal briefly with so-called cap-ture emission. It is formed at the moment of absorption ofthermal neutrons by nuclei of the material in the active zone.This process in turn can lead to the appearance of radioactivenuclei and the subsequent emission of quanta through theirdecay.

Some data on gamma quanta emitted by means of captureradiation are presented in Table 6.

Uranium Fission Fragmente Egitting Hard Gamma Radiation

u rlepaoA I3eprug ra"Ka, 4ncjio rauua.Kias-Hoo0 OAYPSCRSAS (OsNTOB. MM K 104 pacnaAOD

Rh'" 30 ceufsee 2,9 1Prim 17.8 = aom n mi 2,18; 2.6 11; II

Us," 154 amsu&. 2.0 1LaM' 4001. a•e,, 250J'im 2.4 qaca -k.I 2,0 12Tell 25 U"H. - , 2.21 10JU6 6,7 qaca. k..t 2.4; 1.8 11; 22Rb" 17,8 mH..m;A 2,8. 1.86 46; 56

A = Isotope; B = Half-life; Gamma quantum energy, mev = C;D = Nmber of gamma quanta per 104 decay events.

Along with the aformentioned forms of radiation,there are also sources of emission whose sources are locatedoutside the active zone.

We are referring to gamma radiation accompanyingeither the capture of thermal neutrons or the diffusion offast neutrons in materials outside the reactor zone. In thefirst instance the basic contributing factor is gamma radia-tion accompanying the capture of neutrons in structuralmaterials of the reactor body. The intensity of these sourcesdepends on reactor power and the distribution of the thermalneutron stream. In the second instance gamma radiation isproduced by induced activity in the reactor body and shielding.It is considerably less dangerous than direct radiation from

34

the .aotive zorie. 1jewev-a-l, this forv of rMdlatlon shc-cld betakeni in-to atcccount, Partic*Osrly follwn h htono

luelrear powe platnt.ofTable 6ý;ajna~ Lagiatiuiuon tO 12 012rre by '4'ne M~at~erapUe

Keatpzgoamtrugtipzi

X" 13uprus 7;"T 9seco1 Up!raOd~yuaeua ~ i-E.- y'iavaewl OadM 3fus~pu I J1 38- , j MP8 ast001130- "a

IAammootO 't 1.5 4,9 i Ko06Bsb? Q 0.9 5,3T~p~~4~ 1,3 f5.4 .11 Me*b 0,9 6,2BK~f jý 1,0 4.2 1 L 6,41

Sop Q;110 I0.6 J ~1.0 2,2KOAMHI 2,3 2,2 Camu 1.0 7,3KaiblaNA U 2.1 4,5 2,1 1,Yriepox Z 1,3 '3,6 mara j 0IO8 5.7

I~(~ 1.6 6.2 Ka2RA(IV .-. 1.2 44111 4.6 il Kjemptst 3.9OHW~n ~ 1.12 I7.0 HatpP4 i Ut 2:4 2,3

Aw. 1,7 j6.1 i!EwroN 10 6:0

A =Irradiated rAterial; B .Number of ganuas quanta percapzr~recd neatrr.,n; 0 zi Gamma quantum energy, mev; D Al~uminum;E = Beryllium; F = Piamuth; G = Boron; H* = admium; ICs.-aoiiu; J Oarbori; K = mChromium; 1"; M olybdenum; IMý91.ckel; f Nitrogen; 0 = Cobalt; 1.11 CopTer-- 1 = Iron;

R = ydrogen; S = Lead; 'T = Yagnesiuim; U = I~atganeset- Vpote.ssl~i; # Silicon; X = Sodiumn; Y = ?Ooncrete.

~e~sly ~air~n adiaX~ o this type 4 Sh euLof t:'ý3t1J.ic of atalnlesE steel widely vt-!ed liý reactorvonstructior, Som data on activa-tioni are ;iver- -4%.- "ab~le 7.

In or ;,r to" obtain A. clear picture of' the Intensityor amma. rad"..tion of a niialrar re~ator, let ur. turn to the

alove exap1a of the operati'cn. of &"ýreactor with ai thermalpowar o '4 about RO thousaý-d [sic: example on. p 33 (,, 34 ofSCoItrýOeý reads SOC) thousarndl kwt. Over a. period of several

mintsoff operat.t.on at fuli pc~wer, it. produoee several~iriion ouriles of Pgamr.;ia activity. 1-owever, the percentangeof' the total ga~mma ray streait reachir thne s~hleldizng willdepend o,-L the physleal dimeneions and Astruoture of' the reac-tor. The order of mnagnitude of thie gariims ray stream at theedge of, the act~ive zone Is Lbour, lOV3 quant(a/otrnsea (taking

into account self-absorption ini the Active zone), rtsoomftparlson with the m.~.iium perxisatblt f tream for an 8-hourIrradiation period, equal to 0.7.10:1 quanta/crn2ssc with amean quantumi energy of 1,.5 nov (which corresponds to 0.017roentgen), gives a clear Indication of tixe necessity ofusing particularly powerful protection against gemma radiationwith compulsory control of the dosage beyond ehIelding limits.

Znduoe Aoti ity of Bar Ic Co pnento of Stal toSjg

Iflep"OAI IaKTHRNOCT6 )ehl_______i poACOS pnnaa.cu cew H KMarbm/N' Cxamce

%_ I -'ý-_-cn

3. 4. 0- " ,17

Coft (tin, C.61 /c~ao 5,2 QuaASm 5nr, 6 1 1v. 3

F'romn the above consicierationis we see that In~ theoperation (if the' nuclear r.-actor, thý- miost Important rolein played by *;4 prompt neu~trons of nuclear fuel combustionas well as the rarmnm radiatftn, both accompanying fissionani arising as a result of thermal. neutron capture.

The baeic sources of radiation following reactorshutdown aire gamma. rariition of fission products,, and gaumaradlatica due to activity induoid in materiale. For purposesof clarity, we have aompiled summary Table 8 containing d.ataon radiation fr~om a hypcthetleal uuclear reactor duringoperation ,,r shutdown periods, when a given type of radia-tion predomiucten. The rable doers nut require additionalexplanation.

36

~ * t . it -M

0"1 -W4,g

I Net

-b -tw

Imwtaa v &4- f-4

8 .

'ita I~ xz)C' " P 1 o

4 -Z

0 -

coA

A A7

Table 8, 1 -egndA = 7y-pe of radistion; P = Source of' radiation; C = Energy,mov; D = Source Intensity; E Rema~rks; V = Neutrons; G =V -quanta; HI = Ditto; I = Neutrons/om~sec; J = Quanta/cm3sec;K = Fission; L = hotoneuitrons; M = Prompt Y-emission withfission; N = D)elayed t-emission of fission fragments; 0 ='(-emission in neutron capture by ziroorium; P =-emissionfrom Inelastic neut~ron ecattaring In zirconium; I 1- emis-sion frox neutron captare by urarium, xenon, cadmium, and sil-ver nuclei; R = -emission from neutron capture by waterhydrogen nuclei; S =Basic source of neutrons in reactoroperation; 11 = Basic source of neutrcne severa). minutesfollowing reactor shutdown~; U = Basic source of -quantaemitted from active zone during reactor operation; V = Basicsource In aczive zone of banked reactor.

loiiC Radiation Frcon Techn~olopgioal Loops in a NP?

it Wag pointed out above that it i.s possible to usewater, certair. low-melting metbal:i and their alloys,, gaset,and a number of organic compounds in NPP as heat transferagents. Under cfertain condItions all of these IVYP heattransfer agents do or are able to become radioactive. Trnecauses of their induced radioacti'vity can be the following:

absorption of fissicn neutrons by the agent itself;activation of isubs-tances arlsing In corrosion of

astructural materials used in the loops and which enter 'theheat transfer' &gernt;

entry Into the agent of fission fragments as a resul~to!" the disruption of the hermetic seal of the heating elements hells.

A4t.vlttv In loop oontairing ~ter ly.ider pressiure.The hest transfer agent MU9_ti The frat place possess theproperties which assure the removal of heat from the activezone. Water In part-Icular happens to have satisfactory heat-trannqfer properties and~ a relatively low activation cross-sec tion.

In des~igning it Is taken into account that the heattrannfer agent munst be under a preassure such am would preventany excess over the temperature corresponding to the boilingof water at fthe given pressure. In the contrary case, steam.wdill form around the beatinp element due to the h gh temperatureof the active zonie siarfaco; thil: can lead to a sharp decreaseIn. heat transfer, overbeating, of* tLho element, dicruption oftrio hermeticA sea.ls of -teie heating el.emen~t sne'lls, and even.the me).ting of' ttie ruuulear fu'.l.,

To attain. the nacezisary tem~peratures on. the orderof 30090, It In necezsary to provide high presaures (munytense Of atmospheres). VThis impones rigid requirements onloop design.

38

A water-cooled ship reactor Is aboul 1-2 m in dia-meter, with a water pressure ever 100 kg/ev and a temperatureof about 3000 (about 80 megawatts in power).

Under the action of neutron streams there Is an acti-vation of the water and the admixtures in It which are presenteven if the water in ub3oeted to double distillation. TMewater becomes radioactive even In the absence of admixturesas a result of (.z,p) reaotions of the oxygen isotopes

016(np)N1 6 and 0 1 7 (n,p)NI T .

The decay of isotope V16 which occur& with a smallhalf-life (7,35 see) Is accompanied by the emission of ex-trenely rigid gamma quanta (7.5 and 6.1 nov). The half-lifeof another radioactive nitrogen isotope (N1 7 ) ie equal to4.04 eec; this is accompanied by the emission of beta particleswith a maximum energy of 3.7 mey and neutrons with an energyof I mov. Despite their short half-life, these emissionsgreatly complicate the servicing of the primary heat tranaferloop. Loes Important sources of radiation are the reaotions

01 (Nat V)019 H HI(n V )H2.

"* The probability of such reactions in small, and theyare usually disregarded in caloulating biological shieldingfor MP.

Some information on the activation of various heattransfer agents is given in Table 9,

...... .. .j~ aK N R.~I Pr . ........ _

Sl" t Arma, )Ar" :g11s qa l

jfAi(n, I) A0N 2.4 s.8 "4 .,--MnN(n, P) Mn" 2,6 sac., 645(.); 1,81 (.);FH M(n, 7) PN 4, uns 1,1(v);

A = Beat transfer agent; B a Rgaotion; 0 = Half-life; D mRadiation energy, sev; E = Air; P a Ordinary and heavy water;G = Sodium; H w Water with admixtures.

39

Along with the Induced activity of the heat transferagent, the qotlvated admIxtures prevent in the water consti-tute an additional source of radiation which can be neglected.Actually, for water for example, the ratio of Its own Inducedactivity to that of the irradiated admixtures In about 300.

The wqter employed for reactor cooling containsabout 0.5.10"44 admixtures (by weight), which Is the prac-tical limit of modern purification methods. Only a bidls-tillate can satisfy such conditions. For the sake of com-parison we light point out that ordinary drinking water containsup to 1 .10-% impurities, while water in ordinary boiler sys-tems -- from 2.5.10-3 to 2.5.10-2%.

Radiolative Isotoiern &Ad Water geat Transfer Atunt A SIM~iS

h15ne!5L Was ax"AusocM H4ciomKaC

N" 7.3 ceosm e 0. O Mpu/ IV 0o H.ONit 4.1 cex.s,•c 8O)ehrMp/txaccx ,Ot1 H90Ku 7,7 uns.,-,m . t-10- l fopu/JAr"1 1,8 %eca. & 4.10- xoplAtEC) j,,Bo3Ayx a HtOF" 1.9 ,aca 4.10-' coopult ,

MnW 2.6 qaca " 0.5.tO-- .pu/A.) bCfaalbNa" 14.6 W I0-6 K"p/IA OP (lajaP3 a 3oeGow 5.2 roa -, 2 5. I-O inopu/.#j) WCrarnbFew 46 ui.. I-1.1O-8ou/,aC44Tat" It? O,6.6-10- *MoP.UI- _

A = Isotope; B = Decay time; C =_Specific activity; D = Source;E = curie/liter; P = neutronu/on3 sec; G = in; H = Air in H2 0;I = Steel; J = Sodium in water.

The corrosion products formed as a result of chemicalreactions of the heat transfer agent with the material of thetechnological loops are activated upon their irradiation witha powerful stream of neutrons during the passage of the heattransfer agent over the active zone. For sturctures usuallymade of stainless steel, the basic portion of the totalactivity is contributed by the activity of manganese-56 witha short half-life (2.6 hours) The proportion of long-livingisotopes, such as oobalt-60 (5.2 years) and iron-56 (46 days)is not large. As was shown by a preliminary estimate carriedout for the atomic Icebreaker "Lenin", the activity of cor-

40

roslon products in the primary heat transter agent -- thebidistillate -- makes up no more than 10"4 curie/litero804 of the activity is due to the decay of manganese-59nuclei, while the remaining 204 i3 due to the decay ofiron-59, cobalt-60, ohromium.-51, and niokel-65 nuclei.In this estimate it was assumed that the structural materialsare corroded homogeneously and evenly, while the chemicalelements In the corrosion products are in the same ratio asin the structural material. Some data on the isotope compo-sition of heat transfer agent admixtures are given in Table10.

The basic gai activity of the primary heat transferagent (water) provided the heating elements are hermeticallysealed will be due to the argon in the air found not onlyIn the water itself, but also in the cooling system afterit in filled with water, as well as the gases of fragmentorigin -- due to the surface coritamination of the heatingelements with uranium.

Radioactive gases can oreate a danger with gasseepage both from the primary and secondary technologicalloops of a NIP.

The activity of the heat transfer agent at thereactor oulet according to calculations carried out for theNPP of the "Lenin" in O. 8 curie/liter due to gamma radia-tion, io3i0- o-4 curie/liter due to gas activity, and about500 neutrons/cm2sec due to neutron streams.

Eadioactivy eases and "992811. Even under normalconditions of NPP operation, insignificant amounts of radio-aotivA gases and aerosols are still formed In the immediateneighborhood of the reactor. The gas and aerosol activityarise both as a result of heat transfer agent evaporationin the presence of and uncontrollable minute seepage and ofair activation,

For example, the design of the graphite reactor atOak Ridge (US) features 30-03 spaces in the upper portionbetween the graphite neutron reflector and the concreteshielding in order to prevent thermal damage to the shielding.In these spaces there was intensive activation of argon inthe air with the appearance of gas activity of about 0.5curie of argon-41 per hour,

An analogous picture holds true with the reactorfor physical and thermal experimentation of the Academy ofSciences USSR, in which about 4 curies of activity appear bet-ween the hermetic steel shell and the concrete shieldingeach hour.

Radioactive aerosols are formed largely due to theseepage from the primary technological loop of both theprimary heat transfer agent itself and the volatile fissionfragments (krypton, xenon, bromine, etc.) contained in itwhich then decay with the formation of radioactive aerosols.

For this reason, in designing teohnologioal loop elements --piping, fittings, and mechanisms -- it is necessary to reduceall Soints, including welded ones, to a minimum. At the sametime, a small unavoidable leakage with a normal NPP operatingregime does not as usual~oonstttute a serious danger (seeChapters V and VII), Other forms of leakage capable of arisingas a result of the disruption of the hermetic seal of theloops or steam generators are best classed as characteristicsof a hazardous operating regime. They are considered in theapp•'opriate section.

o ° aIn conclusion Itnecessary to cons NPP explosion.

It is known that the present heterogeneous reactors run onnuclear fuel which is also used in modern nuclear weapons.

However, one should not draw parallels between auranium power reactor and the atomic bomb. In order for thebom' to explode, it must incorporate a large excess criticality(K 4 1 1?)-,

In order to accelerate the chain process It is neces-ear;r for It to be capable of developing in a time so shortthat the fuel (uranium) molecules have no time to come apart,this reducing the critical ases. Thus, an enormous amountof snergy in released in a very short time and an explosion

Sou11rs ,In contrast to this, the supercriticality of a reactor

is small (K 4 1.075, i.e., no higher than the amount of delayedneutrons -- 0.75% of the total stream), In addition, shipreactors have a special emergency protection system whichis actuated in case the reactor power begins to increase toorapidly as a result of certain faults In the regulation andco:atrol apparatus.

But even if the reactor should go out of control, andan uncontrolled nuclear reaction does begin, as a result ofthe slow rate of increase of the energy released in uraniumfission, the fuel molecules will have time to dissociate(lowering the critical mass) and the energy required for anexplosion is not accumulated. At the same time, a water-cooled heterogeneous reactor experiences a water boiloutwhich shifts the neutron balance, and the chain reaction isquenched.

The above factors reduce the possibility of a reactorexplosion practically down to zero.

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Chapter III

PRINCIPLES OF SHIP MCLEAR POWER PLANT (NPP)SHIELDING

7. Protoction From ? Radiaion

The problems of protection against radiation froma nuclear-power plant are complex and varied in general, andpartiolularly so under shlp conditions. On the one hand, itis necessary to afford reliable protection to the personoelfrom ionizing radiation, and on the other, the constructionof shielding smut leave at least partial access to indi-vidual VPP comnunioations, mechanisms, and apparatus. Thebasic task with which we deal in calculating shielding fora ship IPP is the assurance of its reliability with minimalsize and weight,

The design of shielding is determined basically bythe ;roperties and nature of the radiation and the necessarydegree of its weakening. The latter can be determined on thebasis of the initial Intensity and the maximum permissibleradiation level at variou points beyond the shielding

The following factors must be taken Into account Inselecting and calculating the proper shWelding:

Sthe energies of penetrating radiation;2) distribution of radiation in the direction of

ship living and service quarters;3) geometry of NPP radiation sources.From the standpoint of protection from gamma rays,

the zost effective shielding is afforded by heavy elementswith a high *ýomie number; such materials are not very effec-tive In weakening fast neutrons, however. In view of the factthat the neutron capture crose-section increases rapidly withtheir reduction down to a thermal energy level improvedneutron shielding requires that It be made of light elementsfulfilling the role of mocorators, along with heavy ones.The shielding can be made up of successive layers of heavyand light elements or In the form of a homogeneous mixture ofthese elements.

Neutron capture Is accompanied by gamma radiation.This complicates the problem of neutron shielding, since for

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Isotopes the gamma radiation due to capture is characterizedby fairly high energy ranging approximately from 7 to 10 mew.

The requirements imposed on NIPP shieldtni are to aconsiderable degree determined not only by the active zone ofthe reactor itself, but also by other portions of the primarytechnological loop -- the pumps, heat exchangers, pipes, etc.

There are two types of NPP radiation shielding --primary and secondary,

Primary shielding not only weakens the neutron streamto a point at which gaem radiation accompanying neutroncapture in the shielding Is down to a minimum together withthe activation of the secondary heat transfer agent andstructural elements of the UPP beyond the primary shielding,but also affords protection from thermal effects of theactive zone on the radiation shielding structures.

Shielding lowers the intensity of penetratingradiation down to maximum permissible levels and serves asa barrier to the penetration of radioactive gases and aerosolsinto ship enclosures.

Let us consider some of the problems of shieldingcalculation.

In calculating gamma-ray shielding, we make use ofthe exponential attenuation law

l--1 0 Ax (2)

where 0 is the intensity of primary radiation;

is the attenuation coefficient for the shieldingmaterial;

x is the thickness of the shielding layer.H.owever, this formula takes into account- only the

chnange in the intensity of the direct (primary) radiationin a narrow beam. It is assumed that any Interaction of agamma. quantum with the medium remove