.

WSRC-MS-93-446

NEUTRONICS AND SAFETY CHARACTERISTICS OF A 1~ MOX FUELED PWR USINGWEAPONS G~E PLUTONIUM (U)

by

Debdas Biswas 1, Roy W. Rathbunl , Si Young Lee1, and Phil Rosentha12

1 Westinghouse Savannah River CompanySavannah River SiteAiken, SC 29808

2 Westinghouse Electric CorporationP. O. Box 355Pittsburgh, PA 15230

A paper proposed for presentation at theAmerican Nuclear Society 1994 TopicalMeeting on Advances in Reactor PhysicsKnoxville, TNApril 11-15, 1994

and for publication in the proceedings

The information contained in this article was developed during the course of work under ContractNo. DE-AC03-93SF19683 with the U. S. Department of Energy. By acmptance of this paper, thepublisher and/or recipient acknowledges the U. S. Government’s right to retain a nonexclusive,royalty-free license in and to any copyright covering this paper along with the right b reproduce, andto authorize others to reproduce all or part of the mpyrighted paper.

~;i:”{:~

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of theUnited States Government. Neither the United States Government nor anyagency thereof, nor any of their employees, makes any warranty, express orimplied, or assumes any legal liability or responsibility for the accuracy,completeness, or usefulness of any information, apparatus, product, or processdisclosed, or represents that its use would not infringe privately owned rights.Reference herein to any specific commercial product, process, or service bytrade name, trademark, manufacturer, or otherwise does not necessarilyconstitute or imply its endorsement, recommendation, or favoring by theUnited States Government or any agency thereof. The views and opinions ofauthors expressed herein do not necessarily state or reflect those of the UnitedStates Government or any agency thereof.

This report has been reproduced directly from the best available copy.

Available to DOE and DOE contractors from the Office of Scientific andTechnical Information, P. O. Box 62, Oak Ridge, TN 37831; prices available from(615) 576-8401.

Available to the public from the National Technical Information Service, U. S.Department of Commerce, 5285 Port Royal Rd., Springfield, VA 22161

.

Neutronics and Safety Characteristics of a 100% MOX FueledPWR Using Weapons Grade Plutonium

Debdas BiswasaRoy RathbunaSi Young LeesPhil Rosenthal

aWestinghouse Savannah River Company, Savannah River Site, Aiken, SC 29803, USA,(803) 725-3406

bWestinghouse Electric Corporation, P.O. Box 355, Pittsburgh, PA 15230, USA(412) 374-4713

KEYWORDS: Plutonium, Reactor, Dmign

ABSTRACT

Preliminary neutronics and safety studi~, pertaining to the feasibility of using 100% weapons grademixed-xide (MOX) fuel in an advanced PWR of Westinghouse design are prmented in this paper.The preliminary raults include information on boron concentration, power distribution, reactivitycoefficients and xenon and control rod worth for the initial and the equilibrium cycle. Important safetyissues related to rod ejection and steam line break accidents and shutdown margin requirements arealso discussed. No significant change from the commercial design is needed to denature weapons-grade plutonium under the current safety and licensing criteria.

INTRODUCTION

Westinghouse performed an extensive study where three plutonium disposal reactor (PDR) optionswere developed for the disposal of excess weapons grade plutonium horn returned and dismandednuclear weapons. This is a part of DOE’s Plutonium Disposition Study 1 launched at the behwt ofCongr~s, where denaturing the excws quantitiw of weapons grade plutonium to a form similar tocommercial reactor spent fuel was investigated. The Westinghouse advanced passive PWR of 600MWe capacity is the state-of-the-art reactor and its plant designs are selected as the basis for the PDRreactor concept, called the PDR600. The following sections d~cribe the core design philosophy andcore characteristics of the PDR600.

.

CORE DESIGN PHI~WPHY

The basic daign objwtive is to meet the program requirement of denaturing 100 MT of weapons gradeplutonium in a reactor as economically as possible using conservative d=ign and proven hardware andsoftware. This objective is, therefore, quite different from a commercial reactor, where fuel cycle costbenefit is a main criterion. The PDR600 requirements nw=sitate as high a plutonium enrichment asfeasible in the core, and consequently a heavy loading of burnable absorbers to hold down the excasreactivity. The end of cycle may contain a higher boron level than -10 ppm, because the cycle lengthis limited by the discharge bumup consistent with the objective of denaturing and not limited by themaximum amount of energy that can be extracted from the fuel. In other words, due to higherenrichment, the cycle bumup goal may be reached before the end of reactive life. The dischargebumup is selected such that the Pu-240 content of the discharge fuel will be at least 20%, thedenaturing goal.

The basic core characteristics of one-third core MOX fueled PWRS are well-studied and understood.2Principally due to higher capture and fission cross sections of Pu-239, the thermal absorption in aMOX fueled reactor is nearly twice that of an equivalent, uranium fueled reactor. This phenomenon,coupled with considerable spectrum hardening, leads to a substantial diminution in boron, xenon, andcontrol rod worth. 3 These effects will accentuate with higher enrichment and till MOX core inPDR600. Therefore, the challenge is to daign a core with negative moderator temperature coeti]cientat ail operating conditions, and to increase the number of control rods to compensate for the loss ofcontrol rod worth. Efforts are also made to design the PDR600 core under the existing core dwignand safety envelope of the advanced Westinghouse PWRS so that the 1icensing effort can be minimtied.In addition, the PDR600 has been designed using the standard and proven fuel rod, assembly, burnableabsorbers, and control rod system, thereby minimizing tinting and deployment time.

CORE DESIGN

The reactor core consists of 145 fuel assemblies arranged in a modified checker board pattern in cycle1 and employs the out-in shuffling for subsequent cycles. The standard 17x17 Vantage 5-H fuelassembly daign is chosen for PDR600. Zircaloy+ cladding is replaced by 304 stairdws steel tomaximize plutonium enrichment. The first core loading us~ enrichments of 4.5, 5.0, and 5.5 w/o intotal plutonium content for regions 1, 2, and 3 rwpwtively. Weapons grade plutonium with anisotopic composition of 93.6%, 5.9%, 0.4%, and 0.1 % is used for Pu-239, Pu-240, Pu-241, and Pu-242, rwpmively. A heavy loading of pyrex burnable absorbers is used to reduce peaking and solubleboron in cycle 1. To further reduce the soluble boron concentration, zirconium diboride coating in theform of integral fuel burnable absorbers (IFBA) with a loading of 1.57 mg/inch is used in all fuel rods.The cycle burnup is kept at 13,300 MWD/MTU consistent with the discharge burnup being 40,000MWD/MTM. One-third core is discharged every cycle. There are 69 rod control cluster assemblies(RCCA) made of Silver-Indium-Cadmium in PDR600 as shown in Figure 1.

The equilibrium cycle model is developed by using 5.5 w/o (total Pu) enriched once burnt, twice burntand feed assembiiw. Although the 1.57 mg/inch IFBA loading is retained, no discrete glass burnableabsorbers are required in the equilibrium cycle for flux flattening or for reducing soluble boron level toprovide negative moderator temperature coefficient (MTC).

The core design limits such as peaking factor, shutdown margin, etc., of the Westinghouse advancedPWR are chosen as the initial goal. me moderator temperature coetilcient should be negative at alloperative conditions. All calculations are performed with the standard W~tinghouse design codw

2

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which were also validated against the operating PWR plant (Beznau Plant in Switzerland) using one-third core MOX fuel, providing additional confidence in critical core physics and safety parameters.All reactor calculations are done with three dimensional core models.

CORECHARACTERISTICS.

The following sections d~cribe important core characteristics of the initial and the equilibrium cycle ofthe PDR600. The core dwcription and associated core dmign limits are given in Table 1. A summaryof the core physics characteristics is given in Table 2. -

A. CRITICAL BORON LEVEL

The boron level in cycle 1 is 2144 ppm at begiming of life (BOL),condition. Equilibrium cycle and cycle 1 have almost identical

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hot full power (HFP), no xenonboron levels at BOL, but the

equilibrium cycle boron at end of life (EOL) is only 249 ppm as compared to 838 ppm for cycle 1 asshown in Figure 3. The boron letdown with depletion behavw similar to a typicaI uranium fueledcore. The boron concentration reduction with fuel burnup is 108 ppm/GWD/MTM for the equilibriumcycle, which is similar to a uranium fueled core without any discrete burnable absorbers. During thefirst cycle, the glass burnable absorbers are prwent, which significantly reduca the boron depletionrate compared to equilibrium cycle. The boron depletion rate is comparable between uranium and100% MOX fueled cores. This is because the boron worth in PDR600 is very low, but the reactivityloss for the MOX core has a much slower rate due to the formation of fissile Pu-241 isotope. It maybe noted that the soluble boron level can be kept within the range of a typical uranium fueled core(-2000 ppm) by the addition of sutilcient discrete as well as integral burnable absorbers in order tomeet negative MTC criterion.

B. POWER DISTRIBUTION AND PEAKING FACTORS

Assemblywise power distribution for the unrodded core consistent with the boron letdown curve iswell behaved. Figure 2 identifies the assemblywise average and peak power. Core average axial powerdistribution is shown in Figures 4 and 5. The maximum peak hot channel peaking factor (FAH) is

1.358 and remains under the dwign limit of 1.53 excluding the uncertaintim. The Hot channelpeaking factors are comparable between cycle 1 and equilibrium cycle. The equilibrium cycle totalpeaking factor (FQ) is 1.72 at HFP, all rod out (ARO), BOL, and 1.57 at HFP, ARO, EOL, while thedesign limit for FQ is 2.4 excluding the uncertaintiw. Axial peaking factors (Fz) for cycle 1 are 1.39and 1.21 at BOL and EOL respective y. The axial peaking factors are decreased by about 10% in theequilibrium cycle. Thwe PDR600 peaking factors are, therefore. well within the peaking factor limixof the advanced PWR d=ign.

Since the core is fully loaded with MOX assembliw, there is no spectrum transition at the interfacebetween assemblim, and no intra-assembl y zoning is needed. Intra-assembly zoning with differentenrichments is, one the other hand, essential in one-third MOX cores.

C. MODERATOR TEMPERATURE COEFFICIENT

The MTC at different ppm and moderator temperatures is shown in Figures 6 and 7. The MTC versuscycle burnup plot is shown in Figure 8. The most negative MTC is found to be -28.3 pcm /°F at theEOL, HFP, equilibrium cycle, The least negative MTC is 4.3 pcm /°F at the cycle 1 BOL, HZP

3

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critical boron conditions. The MTC in the equilibrium model is more negative than in cycle 1. ~usthe PDR600 MTC valu~ lie within the d~ign basis limit of the advanced PWR (O pcm /°F to -40pcm /“F).

A very important fact of the PDR600 design is that there is enough flexibility to tailor MTC values tosuit reactor operation and safety rids. Calculations indicate that MTC valuw similar to uraniumfueled cor~ can be easily achieved by balancing burnable absorbers and soluble boron, even though ata particular boron and moderator temperature level, the MTC for the PDR600 tends to be morenegative than the uranium fueled mre. Consequently, the effect of MTC on cooldown accidents is notexpmted to be more severe than that in a uranium fueled mre.

D. DOPPLER AND POWER COE~CIENT

Doppler~nly contribution to the power coefficient (DPC) is shown in Figure 9 as a function of corepower. Doppler temperature coetilcient OTC) is shown in Figure 10 as a function of the effectivetiel temperature. The effective fuel temperature is lower than the volume-averaged fiel temperature,since the neutron tlux distribution is non uniform through the pellet and gives preferential weight tothe surface temperature. In general, the Doppler coetilcient is more negative which is expected in a100% MOX fueled core than in the advanced PWR dmign. The range of Doppler temperaturecoetilcient in the PDR600 vari= from -1.9 pcm/°F to -3.5 pcm/°F. The higher negative valu~ of theDPC/DTC are benetlcial for accident mitigation and rmuit from spectrum hardening of the PDR600core.

The combined effwt of moderator temperature and fuel temperature change as the core power levelchangfi is called the total power coetilcient. The total power coefficient as a function of core powerlevel and at HFP boron concentrations is shown in Figures 11 and 12. These coefficients arecalculated using a threedimensional model; therefore, spatial reactivity effects due to changes in theaxial moderator density distribution with power level are implicitly included. The power coetilcientsare strongly negative under all conditions.

E. BORON COEFFICIENT

The boron worth is noticeably smaller in the 100% MOX fueled core. It varim slightly from -2.8 to-3.8 pcm/ppm at different power and burnup conditions, whereas the boron worth is around -10pcm/ppm in a uranium fueled core. The inverse boron worth in units of pprn/%Ap as a function ofburnup is shown in Figure 13. The low boron worth is beneticiai for boron dilution accidents, andearly indications do not reveal any impact of low boron worth on the steamline break accident.

F. XENON WORTH

Like all other reactivity worths, the xenon worth has b~n decreased by about a factor of two in thePDR600. The xenon worth at HFP BOL and EOL is 1230 pcm and 1500 pcm, rapectively, for theequilibrium cycle. Typically, in uranium fueled cor~, the xenon worth is around 2500 to 3000 pcm.The low worth of xenon has an important advantage for stability against xenon induced oscillations.making axial xenon transients less severe in the PDR600.

4

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G. CO~OLROD WORTH

The control rod worth is expected to go down in a 100% MOX core. The control rod worth is also, ingeneral, dwreased in the equilibrium cycle, the normal trend. The preliminary control rod patterndeveloped for the PDR600 is different from that for the advanced PWR, as this core is not d~igned forload-follow operation. The loss of worth is rwovered by replacing 16 gray rods with 16 Ag-In-Cdfull-strength rods and also by adding 8 rods on the periphery. The cycle 1 total control rod worth for69 rods is about 9.5% Ap at BOL and 10.7% Ap at EOL and the vaiua gow down by about 0.3% Apin the equilibrium cycle. The cycle 1 “5 rod, D Bank” worth is around 600 pcm which is reduced byabout 10% in the equilibrium cycle. This D bank worth is similar to an existing PWR having a lightD bank.

H. SHUTDOWN MARGIN

The calculated shutdown margin (SDM) varies from 4.9% Ap in cycle 1 to 4.4% Ap in equilibriumcycle at BOL and from 5.5% Ap to 4.7 % Ap at EOL. This represents a relative reduction of SDM ofabout 10% to 20% at BOL and EOL from cycle 1 to the equilibrium cycle, respectively. Butconsidering the dwign basis minimum shutdown requirement of 1.6% Ap for the PDR600 (assumed tobe the same as in advanced PWR), a substantial 3% Ap margin exists in the design.

1. ACCIDENT ANALYSES FOR PDR600

Analysis has been performed for selected transients thought to be most sensitive to certain nucleardmign characteristics of PDR600. The reduced delayed neutron fraction led to selecting the controlrod ejection event for analysis, while reduced boron worth brought consideration of the main steamline rupture event. The general methods applied to both these accidents are consistent with those longused for standard Westinghouse PWR dmigns, though the specific analysis models used reflect both thepassive plant and plutonium core related features of the PDR600 design.

The rod ejection analysis for the PDR600 considers two representative sets of initial conditions: BOL,HFP and EOL, HZP. Typically, HFP cases are limiting with respect to the peak fuel pellet enthalpyand fuel pellet melt criteria, while HZP casa are generally limiting with rmpect to peak cladtemperature.

To provide bounding rwuls that allow for future cycles, standard W=tinghouse rod ejection analys~have typically used conservatively low delayed neutron fraction values of 0.55 and 0.44 percent atBOL and EOL, rmpectively. For the PDR600 casw, a delayed neutron fraction of 0.30 percent hasbeen assumed for all times in life.

Despite this, the RCCA ejection analysis for the PDR600 core has produced far less limiting rmultsthan those for a typical standard plant design. The primary reason is the reduced worth of individualcontrol rods in the PDR600 core, which is offset by an increased total number of RCCAS. The neteffect is the reduction of maximum ejected rod worth and associated power peaking, thereby mitigatingthe overall transient. All applicable licensing requirements for this event are met by the PDR600analysis, with significant margin to the safety limits still available.

The main steam line rupture analysis for the PDR600 examin~ a single repr~entativeintended to ass=s the impact of the reduced boron worth. Specifically, the analysis

5

limiting case,considers the

.

complete severance of a main steam line with the plant initially at no-load EOL condition, with fullreactor coolant flow, and offsite power available. The PDR600 passive protection system includa anautomatic safety-related signal that initiates reactor cuolant pump coastdown in parallel with wremakeup tank actuation, which occurs wsentially at the outset of the event. Therefore, most of thesteam line break trartsient takes place under natural circulation renditions.

The PDR600 analysis assuma a conservative boron worth of -3.0 pcm/ppm, which is otdy about one-third of the typical value for a standard PWR. To partially offset the reduced boron worth, theanalysis assumes increased core makeup tank and accumulator boron concentrations of 5000 and 3500ppm, rwpectively. The specific nuclear model used for the PDR600 employs approximate inputs tomodel MOX fuel characteristics and the nuclear feedback associated with natural circulation. APDR600 specific DNB evaluation has not been performed as part of the current steam line breakanalysis. Instead, the intent of the current analysis is to provide a comparison of the general passiveplant dmign raponse to a MOX core rather than a standard uranium based core.

The rwul~ of this steam line break analysis demonstrate that, with somewhat increased protectionsystem boron concentration, the response of the PDR600 is msentially consistent with that of auranium fueled passive plant. Based on this analysis, it is expected that a detailed, PDR600 specificsteam line break analysis would produce acceptable results that meet all the licensing requirements.

CONCLUSION

A feasible design has been demonstrated that employs a 100% weapons grade MOX core and satisfi~ail core limit criteria of an advanced uranium fueled PWR. The expected changes in corecharacteristics with MOX loadings are observed, yet the control rod worths, moderator and Dopplerreactivity coefficients and peaking factors are found to be within the realm of normal experience. melower delayed neutron fraction and boron worth do not impact the safety of PDR600. Thus, a MOXfueled Westinghouse advanced passive PWR is an ideal machine to denature weapons grade plutonium.

REFERENCES

1. Debdas Biswas, Roy W. Rathbun, and Hans D. Garkisch, “Characteristics of a 100% MOX FueledPWR Dmign for Weapons Plutonium Disposition, ” Trans. Am. Nucl. Sot., (1993) (To be published).

2. Gerhard J. Schlosser, Wolf-Dieter Krebs, and Peter Urban, “Experience in PWR and BWR Mixed-Oxide Fuel Management, ” Nucl. Tech, 102, 54 (1993).

3. G.A. Sofar and D. A. Nauman, “Swords to Plowshares: Recycling Weapons-Origin Uranium andPlutonium in Light Water Reactors, ” Proc. Future Nuclear Systems: Emerging Fuel Cycles and WasteDisposal Options, Global 93, Seattle, 807 (1993).

ACKNOWLEDGEMENT

The informationcontained in this article was developed during the murse of work under contract No. DE-AC03-

93SF 19683 with the U. S. Department of Energy. By acceptance of this paper, the publisher and/or rwipient

acknowledgesthe U. S. Government’sright to retain a nonexclusive, royalty-free license in and to any copyright

covering this paper along with the right to reproduce, and to authorize others to reprodum all or part of the

copyrighted paper.

6

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TABLE 1

CORE DESCRIPTION (All Dimensions Cold)

Discr*e Burnable Absorber Material Borosilicate Glass (cycle 1 ordy)Integral Fuel Burnable Absorber (IFBA) Loading, B10 1.57 mg/inchPower, MWth 1933Number of Fuel Assemblim 145Lattice Configuration 17 x 17Clad, Thimble, Grid, Sleeve MateriaJ SS-304Fuel Rod Diameter, Inches 0.374Enrichments, w/o Pu TotaI, cycle 1 4.5, 5.0, 5.5Enrichments, w/o Pu Total, eq. cycle 5.5Fuel Loading, MTM 66.8Control Rod Material Ag-In-CdNumber of RCCA Clusters 69Average Coolant Temperature, 0F

Hot Zero Power 545.0Hot Full Power 566.7

Hot Channel Factor Limits:Total Heat Flux, FQT 2.60Nuclear Enthalpy Rise, FNAH 1.65

Average Linew Power Density, kW/fi Fuel 4.1Cycle Length, MWD/MTM 13,300Discharge Burnup, MWD/MTM 40,000

TABLE 2

SUMMARY OF CORE PHYSICS

Parameter

PPM, HFP, ARO, BOL/EOLPPM, HZP, ARO, BOL/EOLF~, HFP, ARO, BOL/EOL

MTC, HFP, BOL/EOL (pcm/°F)MTC, HZP, BOL/EOL (pcm/°F)Doppler ordy Power Coef., HFP, BOL/EOL (pcm/%P)Doppler only Temp. Coef., HFP, BOL/EOL (pcm/°F)Power Coef., HFP, BOL/EOL @cm/%P)Boron Worth, HFP, BOL/EOL (pcm/ppm)Total Rod Worth, HFP, BOL/EOL (%Ap)Available Shutdown Margin, BOL/EOL (%Ap)Required Shutdown Margin (%Ap)

CHARACTERISTICS

Cycle 1

21W / 8382789 / 13311.38 / 1.32

-14.4 I -22.04.3 I -12.4-12.9 I -9.2-2.4 I -1.9-17.3 / -16.5-2.8 I -3.49.5 / 10.74.9 I 5.51.6

Eq. Cycle

2168 I 2492710 i 7521.38 / 1.35

-15,5 / -28.3-5.3 I -17.5-12.3 I -8.7-2.3 I -1.8-17.1 / -18,5-3.2 / -3.89.3 / 10.54.4 / 4.71.6

7

.

go.

A so ‘A

SD so SD so

c B D B c

SD SD so SD

A ‘O1s ‘o c ‘o I‘oB A

so SD so so so SD

so ID c D c D SD 270-

So so so so so so

A B so c so B A

sol 1s0 SD sD so SD

Ii B D .91 c

/ 1’0 ‘o ‘o 1s0I4 so Al I

1.

Number of Mumbu ofRGd Clustam ~ ad Clustam

FIGURE 1. PDR600 - CONTROL AND S~TDOWY ROD LOCATIONS

0.688BOL, EQCILIBRIL.M CYCLE

0.717 (150 WDN~)

0.802 0,8310.893 (),929

0.848 0.991 0,9810.939 1.120 1,075

1.078 1.028 1.142 1.0601.205 1.147 1,274 1.143

1.088 1,189 1.088 1171 1.1241.185 1,322 1.186 1,294 1.339

1.127 1.061 1.201 1.036 0.7711.244 1.179 1.358 1.231 1.115

0.900 0,897 0,868 0.6751.159 1.156 1.162 1.016

%

0.720EOL, EQUILIBRIUM CYCLE

0.744 (13300 wD~lW)

0.818 08330.886 0.905 R

1.025 0.975 1.085 1.)091.118 1.064 1.189 1o78

1.032 1,142 1.046 1.149 1.1571.106 1,261 1.132 1.246 1.332

*

1:193 1:145 1:346 1:219 1:160

FIGURE 2. POWER DISTRIBUTION AT ARO, HFP, EQXE

8

o 2000 4000 6W 8~ 10000 12~ 14000

CYCLE BURNUP ( \5W0/MTM)

FIGURE 3. CRmCAL BORON COSC~TRATION VERSUSBLmNUP(HFP, ARO, EQXE)

1.4

12

10

0.8

06

0,4

02

l..................{Qu<cyc&. . . ..+ ......~.,.

o 20 40 m 80 IOiIPEUCE.V OF CORE KIIGHT

HCURE 5. RELATIVE AXIAL POWER DImRIBUTION ATHFP, ARO, EQXE

z

g — BOL

$--- EOL

* ,,:1~:~

-15 1000PPM .. . . . . . .. . ...+. . . . ... .. ....{... .-l-. .+. s, . . . . . . .~~

5 .20 -OPW7x

.25 -:& ?z: -mx

.. .. . . . . . . .s ! ; . . ..l .. . . ..+. . . . ..) .. . ..l . . . .. . .. . . .. . .. . ../....... . . . . . .

: -35 .: ) ,,

j[[j;”~:;~=: .@ : :’:1 : ,,,1

.

14

12

1.0

0.8

0.6

0.4

0.20 20 40 60 80 100

PER~~ OF CORE iiEIG~

FTGURE 4. RELATTVE AXIAL POWER D1~RIBL~ONAT HFP, ARO, EQXE

--w 545 550 555 %0 565 570

MODERATOR mMmRATLW (°F)

~GbWE 6. MODERATOR TEMPERATURE COEFFICIE~ ATDIFFEREV PPM AND MODERATOR TE}iPERATL~E

k -26IG

I

~1. -30

540 545 5W 555 560 565 570 Zo 2000 4000 m 8000 1~ 120CH3 14~

MODERATOR T22M?ERATLW (%) CYCLE BURNUP (MW/m W

FIGURE 7. >1ODERATOR TEMPERATLXE COEFFTC2E~ AT FIGURE 8. hlODERATOR TEMPERATURE COEFFICIENTDWFERE~ PPM A.ND %1ODERATOR TEMPERATURE VERSUS CYCLE BL!RNUP AT ARO, HFP, EQXE,

CRITICAL BORON CONCENTRATION

9

.

.8

-10

.12

w

-16 IBOL, ,

l~r~ : l:;!!;:

-18l:! I

.20

i'; . . ..'\ . . . ...l . . . . . . ..j .. . . . ..J. . . . ..j .. . . . . ..i . . .. . . ..! . .. . . . ..~. .. . .. . .

o 20 40 60 80 lCO

~RCENT OF ~TL POWR

FIGL~E 9. DOPPLER ONLY POWER COEFFICIEhTS AT BOL

AND EOL

o 20 40 60 80 100 120

PERCENTOF ~LL PO~R

FIGLRE 11. POWER COEFFICIE.W VERSUS POWER LEVELAT CYCLE 1

-260 ,,,,,; ;:

::: :....... ...... ...... ............. .............~, .?...,.+..,........ .....

.3mo 2000 4W 6000 80CMI 10000 12000 14000

CYCLE BL~.WP (W~TU)

-1,0

-1.5

.2.0

-2.5

.3.0

.3.5

FIGURE 10.DOPPLER T~PERATLXE COEFFICIENTS AT

BOL .4YD EOL

Gz~

Y+~ ... ... .. . ....,3s

o 20 40 60 80 Im 120

PERCENT OF ~lL POWER

FTGLWE 12, POWER COEFFICIENT VERSUS POWER LEVELAT EQUILIBRIA, CYCLE

FIGLRE 13. LNWERSEBORON WORTH VERSUS BUKNUPAT HFP, ARO, EQLTLIBRILW XEYON

10