Seminar Ib - 1st year, Nuclear engineering

Reactor Monitoring with AntineutrinoDetectors

Author: Klara Rupnik

Mentor: doc. dr. Luka Snoj

Ljubljana, November 2015

AbstractCurrent safeguard inspections of civil nuclear facilities are performed only on-site. They are

based on tracking fuel items with counting assemblies and video checking their serialnumbers. Fissile inventory is estimated at the end of a cycle by gamma measurements.

Existing safeguards methods relies on operators' declarations of power throughout the fuelcycle. Antineutrino detector is a promising safeguard tool. It measures unavoidable and

unique signal from operating reactor and enables tracking operational status, thermal powerchanges and �ssile content in real time. Method and current results from applied

experiments are presented in this seminar.

Contents

1 Introduction 1

2 Nuclear material 2

3 The antineutrino 3

3.1 Production and features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33.2 Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

3.2.1 Detection method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43.2.2 Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43.2.3 Antineutrino signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53.2.4 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

4 Experiments 8

4.1 Safeguard applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84.1.1 Rovno . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84.1.2 SONGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84.1.3 Nucifer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

4.2 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

5 Conclusion 10

6 References 11

1 Introduction

Nuclear reactors use �ssile material (e.g. 235U and 239Pu) as fuel. Nuclear reactors arecommonly used for production of electricity, as a source of neutrons for research purposes,for production of isotopes or for education and training. However �ssile material can be usedalso for other, non-peaceful, purposes, such as nuclear weapons [1]. Safeguards agencies, likethe International Atomic Energy Agency (IAEA), have used and developed an ensemble ofprocedures and technologies in order to check and control nuclear activities in states whichsigned the Non-Proliferation Treaty (NPT), that entered into force in 1970[2]. Safeguardingmethods provide measuring the scope of defect and their early detection. For safeguardpurposes the IAEA de�nes a signi�cant quantity (SQ) of nuclear material as the approximateminimum quantity of nuclear material, that in the case of any conversion process involved,the possibility of manufacturing a nuclear explosive device cannot be excluded. The direct use(without further chemical separation or enrichment) values are 8 kg of elemental Plutonium,25 kg of 235U contained in Highly Enriched Uranium (HEU) or 75 kg of 235U in Low Enricheduranium (LEU)[3]. The frequency of inspections depends on the quantity and structure ofnuclear material, facility type and extension, the type of the safeguards agreement, etc. Thesafeguard activities take place once a month in case the facility possesses unirradiated directuse material (HEU, separated plutonium, Mixed Oxide (MOX)), once in three months incase of irradiated direct use material (plutonium in spent or core fuel) and once in a yearin case of indirect use material (LEU)[4]. Current reactor safeguard practice is based ontracking fuel assemblies with item counting and video checking their serial numbers, and doesnot include direct measurements of �ssile inventory. The latter is estimated at the end ofa cycle by gamma measurements and relies on the reactor operators' formal declarations ofpower throughout the fuel cycle[4]. A vast majority of safeguard surveillance methods involvevisiting the nuclear facility. Hence e�orts are put into development of methods that would

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allow remote surveillance. One of such methods is detecting antineutrons from an operatingnuclear reactor. The purpose of this seminar is to describe and evaluate this method.

Throughout the reactor cycle the core structure is changing due to nuclear reactions, i.e.,radioactive decays and nuclear transformations by interactions of neutrons with the nuclei.One of the reactions is also the beta decay, which represent the origin of the antineutrino,one of the beta designation products that is the subject of discussion in this seminar. Theantineutrino signal is an unavoidable and unique indicator of the presence of an operatingreactor, and can not be masked or imitated by any source other than reactors. Therefore theantineutrino measurements could be invaluable for detecting undeclared nuclear activities,monitoring an reactor operational status (ON/OFF), and non-intrusive, continuous, indepen-dent and real-time tracking of the reactor power and consequently the fuel inventory. As amatter of fact, the early shutdowns in the fuel cycle could reveal the diversion of nuclear mate-rial for the proliferation of nuclear weapons. The antineutrino monitoring was �rst proposedmore than 30 years ago and is based on the fact that the number of antineutrinos producedand their energy spectrum depends on the reactor power and on the �ssile isotopes that com-pile the antineutrino source[5]. The antineutrino detectors have already been deployed andhave successfully demonstrated stable tracking of the operational status, thermal power and�ssile content in real time. The complementary, non-intrusive nature of the antineutrino-based methods, as well as the robustness and ease of use of the fundamental detectors, pointto its strong potential as a new safeguard tool[4].

2 Nuclear material

Nuclear material stands for any source material (natural uranium (NU), depleted uranium(DU) and thorium, excluding uranium ore) or special �ssionable material (239Pu, 233U, ura-nium enriched (UE) isotopes 235 or 233) in either metal, alloy, chemical compound or concen-trate. The IAEA considers uranium enriched to 20 % or above a 'direct use' weapon-materialand de�nes it as highly enriched uranium (HEU). The key ingredients for nuclear weapon areweapon grade uranium, which contains at least 90 % of 235U, and plutonium[6]. Uraniumis the only naturally occurring material which can sustain a �ssion chain reaction. Naturaluranium contains 0.72046 mol% 235U, 99.274210 mol% 238U and 0.00533 mol% of 234U [7].It is used as a fuel in heavy water reactors (as CANDU, graphite reactor), where majorityof the �ssions include 238U , which reacts with fast neutrons with energies over 1 MeV. Forother purposes, such as nuclear weapons and light water reactors (LWRs), uranium has to beenriched to di�erent stages, since the �ssions are mostly caused by thermal neutrons (energiesbelow 0.025 eV) that react with 235U . As was already mentioned in the introduction, IAEAestimated SQ of �ssile material based on previous experiences. Similar to uranium, thoriumcan be used as a nuclear fuel. It exists in nature as single isotope. Although not �ssile itself,232Th, when loaded into a nuclear reactor, absorbs thermal neutrons to produce 233U, whichis �ssile (and long-lived):

10n+ 232

90 Th→ 23390 Th

β−−−→ 233

91 Paβ−−−→ 233

92 U.

It is possible to use 233U in nuclear weapon. The production of 233U inevitably also yields 232Uwhich is a strong gamma-emitter. Some 232U decay products (such as 208Tl), thus making thematerial extremely di�cult to handle and also easy to detect[5]. Plutonium does not occurin nature. It is manufactured in nuclear reactors when 238U captures a fast neutron. Aftertwo β decays, 239U is converted to 239Pu:

10n+ 238

92 U → 23992 U

β−−−→ 239

93 Npβ−−−→ 239

94 Pu.

If the 23994 Pu absorbs an additional neutron, 24094 Pu is produced and so on.

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3 The antineutrino

Neutrinos are electrically neutral and nearly massless elementary particles. There are threedi�erent �avours of these particles: electron, muon and tau. The antineutrino is neutrino'santiparticle. Depending on the origin, the arti�cial and natural antineutrinos are known.The �rst are produced by beta decay in nuclear reactors (electron antineutrinos) or by piondecay in proton accelerators (muon antineutrinos). Additional feature about antineutrinosand neutrinos was discovered by observing natural neutrinos. These are produced in the Sunor they arise from core collapse of supernova, cosmic-rays interactions with air molecules orfrom radioactive decays throughout the Earth[8]. The natural neutrinos prove the neutrinooscillation theory which assume that neutrinos are not massless. This result was awardedwith Nobel prize for physics in 2015. The three antineutrino �avours (electron, muon, tau)are in a superposition of three di�erent mass states:

|νl >=3∑i=1

Uli|νi >, (1)

where l stands for e, τ, µ, and i stands for three di�erent mass states and U is the mixingmatrix. Antineutrinos can change their �avour. Probability P , which express as the con-servation of �avour, depends on the antineutrino energy and on detector distance from theantineutrino source. The derivation of P exceed the frame of this seminar.

3.1 Production and features

Antineutrino emission in nuclear reactors arises from the β-decay of a nuclei with more neu-trons than protons:

AZX → A

Z+1Y + β + νe, (2)

where A and Z stands for mass and proton number, respectively. The net change in thebinding energy of the elements X and Y determines the kinetic energy Emax that β particle(electron) and antineutrino share. The di�erential distribution of the antineutrino kineticenergy depends on the isotope. On average, �ssion daughter nuclei require six beta decayto reach stability, which corresponds to six antineutrinos per �ssion[10]. Distribution of thetotal antineutrino energy for 235U and 139Pu per �ssion is shown in Figure 4. The totalantineutrino emission number rate in reactor core is:

nν = Pth(t)∑i

fi(t)

Ei

∫dEνΦi(Eν), (3)

where Pth is the thermal power of the reactor, fi the power fraction contributed by theisotope i, Ei the average energy released per �ssion for the disintegration of the i-th isotopeand Φi(Eν) is the number density per MeV per �ssion for isotope i. The Φi(Eν) are measuredand tabulated [11]. The antineutrino energy distribution contains spectral contributions fromall of the beta-decaying �ssion daughters and depends on the �ssile nuclei. Precise estimatesof the distribution have been derived from beta spectrometry measurements. The emittedantineutrino spectra for two most important nuclei in nuclear safeguards, 235U and 239Pu,are in Figure 4. Shape of the antineutrino spectra is similar for both discussed isotopes, butthe amplitude is di�erent. The di�erence in the antineutrino rate increases with increasingenergy. There are also others isotopes in the fuel core, namely 239U , 239Np, 237U , 240Pu,242Pu. Contribution of 240Pu and 242Pu disintegration to the total number of antineutrinosis less than 0.1%, while 239U , 239Np, 237U decays are relevant for part of antineutrino spectrawith energy lower than 2 MeV [12].

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3.2 Detection

Antineutrinos interact with protons (free or bounded) or are scattered on electrons (exchang-ing a Z0 boson). While antineutrinos can not be detected directly, knowledge about itsinteraction with matter and its consequences are very important.

3.2.1 Detection method

The inverse beta decay (IBD) represents the interaction between an antineutrino and a freeproton:

νe + p→ e+ + n. (4)

Schematic representation of IBD is on Figure 1. The minimum energy carried by antineutrinois 1.8 MeV. The cross section for this reaction is of the order of 10−43 cm2. It depends onenergy and is practice in measured with an accuracy about 0.5 % [4].

Figure 1: Schematics of inverse beta decay [14].

3.2.2 Detectors

For safeguard purposes it is possible to use many di�erent detectors like non-hazardous liquidscintillators or blocks of solid plastic scintillator coated with neutron capture agents, dopedwater Cherenkov detectors. The choice of the detector depends on di�erent design criteria,as robustness of the detector, deployment location (distance from reactor core, depth), thedetector target mass, the temporal stability of the detector response, the background rejectionsystem and also on cost, minimization of the operator impact on the results and detector'sdisruption of plant's activities. Combination of chosen properties must provide an appropriateratio of antineutrino signal to background. Demanded ratio depends on the detector goal(monitoring power, detection of SQ or undeclared reactor). In Figure 2 is the plot of therequired detector mass for a given distance between reactor core and detector and di�erentoperating mode for water Cherenkov detector and liquid scintillator. Since the antineutrinorate decreases with increasing distance L from the reactor as 1/L2, the required detectionvolume must increase. So far, organic liquid scintillator has been the most common choicebecause it can be obtained in large quantities at low costs, has a high density of free protontargets and it can be doped with di�erent neutron capture elements to enhance sensitivity tothe neutron interactions. The liquid scintillator medium is convenient for detecting neutrinoswith lower energy (from roughly 4-5 MeV in water Cherenkov detectors down to the inversebeta decay kinematic limit of 1.8 MeV). Its advantage is also roughly ten-fold better energyresolution compared to the Cherenkov detector. Beyond distances of a few tens of kilometers(for detecting undeclared reactors) and above detector masses of the order of 100 kilotons,the detection technology must almost certainly change from liquid scintillator to using waterbased detectors, mostly because of detector costs.

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Figure 2: A plot of required detector mass (in kilotons) for a given distance between thedetector and reactor core (in km), assuming zero background and using the most commonly

employed antineutrino detector interaction (inverse beta decay). [4]

Water Cherenkov detectors are �lled with pure water and surrounded by photomultipliertubes. Such detectors are used for detecting charged particles moving faster than the speedof light in the medium:

v >c

n, (5)

where n is the refractive index and c the speed of light in vacuum[11]. So far, deployed waterCherenkov detectors are sensitive only to neutrions. To be relevant for reactor monitoring,they must be sensitive to the antineutrinos. The dominant interaction is once again the inversebeta decay.

3.2.3 Antineutrino signal

The details of antineutrinos can be obtained by positron and neutron measurements. Boththe positron and the neutron are detected. The positron slows down in media and annihi-lates in the detector. The annihilation results in two γ rays that cause signals within a fewnanoseconds of the antineutrino interaction. The so called prompt signal is proportional tokinetic energy of the positron. The neutron is absorbed by a nuclei and they form a heavierand usually unstable nucleus. The new nucleus is in an excited state and it quickly decays tothe ground state by the emission of gamma rays which cause the second, delayed signal:

n+ AZX → A+1

Z X∗ → A+1Z X +

∑i

γi. (6)

The neutron capture time and the energy released by the decay depend on the detector media.The summed gamma energy is detected by the Photo-Multiplier Tubes (PMTs) and the timeof each deposition is recorded. The positron and neutron are detected in close time coincidencethat allows a strong background rejection.[4].

The detection rate of the antineutrinos from ith isotope Nνe depends on the core structure,detector's features and its distance from a given source. It is expressed as:

Ni = Pνe→νenpT

4πL2Pth∑i

fiEi

∫dEνσ(Eν)Φi(Eν)Ri(Eν), (7)

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where np is the number of protons in the detector, T is the measuring time interval, L isthe distance between the detector and the center of the reactor core, Ei the energy releasedfrom �ssion for ith isotope, fi the number of �ssions per second from the ith isotope, σ thecross section for IBD, Φi the number density per MeV and �ssion for the ith isotope theand the Ri(Eν) is the detector response function that includes detector's e�ciency[10]. Thelast parameter is the Pνe→νe that express the probability of �avour conservation. The resultsfrom di�erent experiment are presented in Figure 3. Its shows that the neutrino oscillationphenomena does not in�uence the total antineutrino rate for distances of 500 m or less.Results also include measurements from some experiments that were not necessarily designedfor safeguard purposes.

Figure 3: The ratio of observed to expected antineutrinos as a function of the distance fromreactor[4].

Since the rate depends on the thermal power and �ssile isotopic content of the reactor, themeasurements of the antineutrino number rate allows monitoring of the thermal power inreal time and determination of the reactor's operational status (on/o�). If thermal poweris known, the measurements of antineutrino rate can be used for determination of the coreisotopic content. The degree of neutron irradiation is known as burn-up, de�ned as energyreleased per mass of initial fuel. The fuel burn-up is directly connected with the amount ofplutonium in spent fuel.

In addition to the antineutrino number �ux, the antineutrino energy is accessible throughthe measured positron energy. The quantities are related by the formula:

Eν = Ee −Mp +Mn +me +O

(me

Mp

), (8)

where Eν is the antineutrino energy, Ee is the positron kinetic energy,Mp,Mn and me are

the proton, neutron and electron masses, respectively, and O(meMp

)are terms of order me

Mpthat

mainly account for the nuclear recoil[4]. The schematic representations of the energy spectrafor the two basic isotopes are shown in Figure 4. Event to event, it is impossible to identifywhich �ssile isotope produced an antineutrino of a given energy. Because the probability of theprocess depends quadratically on the incident antineutrino energy, the inverse beta interactione�ectively selects and enhances the higher energy part of the antineutrino spectrum, which isthe most sensitive to changes in the �ssile isotopic content of the core.

Like the antineutrino rate, the antineutrino energy spectrum depends on the reactor powerand �ssile isotopic content. Both can be derived from spectral measurements without the needfor independent measurement of the reactor thermal power.

The antineutrino direction can in principle be used to determine the location of a reactor.For reconstriction the inverse beta decay has been used. The determination of the directionrelies on the energy and position reconstruction of individual events.

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Figure 4: The schematic representation of (a) antineutrino energy spectrum, (b) the crosssection of the inverse beta decay and (c) detected antineutrino energy spectrum for 235U and

239Pu.[4]

3.2.4 Background

Antineutrino signal could be also constituting a other e�ects known as background. Com-prehension of each e�ect and its contribution to the measurement signal is fundamental.Antineutrino signal is composite from prompt and delayed part detected in close time co-incidence, which allows strong background rejection. Background is usually separated into'correlated' and 'uncorrelated' type. Correlated are those for which a single physical processis responsible for both, the apparent positron and neutron signals, while uncorrelated back-grounds arise from two independent physical processes (combination with real antineutrinosignal is also possible). Regards to the type, it could be subdivided to fast neutrons, stoppingmuons, nuclear reaction after an α-decay, cosmic produced isotopes and gamma rays.

Fast neutrons originate from hadronic interactions in the atmosphere or from operationalreactors. They induce proton recoils in the homogeneous organic scintillator detectors. Theprotons are thermalized and captured with practically the same statistical behaviour in timeas the neutron produced in (4). They usually do not lose all or most of its energy in asingle scattering event, so that most neutrons thermalize over a length scale larger thanneutrons produced in (4). Consequently, segmented detector could e�ectively separate trueIBD antineutrino interactions from fast neutron interactions. Contribution of fast neutrons,that arise from hadronic interaction in the atmosphere, to the total signal is important fordetectors deployed above Earth's surface.

Muons naturally arise from interactions between cosmic rays and molecules in the atmo-sphere. Because of their high mass and speed they can reach Earth surface, (where theyrepresent about 63 % of the total cosmic �ux) and penetrate even further. They decay viathe weak interaction as:

µ− → e+ νe + νµ. (9)

The cosmic ray muon �ux, which is responsible for much of the correlated background mea-sured above surface, falls o� exponentially with increasing depth of the detector location. Thesecond approach to decrease muon in�uence on results in so called active muon veto system.It is normally used to time stamp the passing of muons through or near the main detector,allowing further rejection of muon-related background. Muons that pass through the detector

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and nearby materials can also induce secondary fast neutrons or produce light isotopes as 9Liand 8He, that decay further and produce delayed neutron emissions.

The source of α particles is the decay of 210Po, a daughter of the 222Rn decay chainintroduced during the scintillator �lling. The α particles undergo 13C(α, n)16O reaction.

Gamma rays backgrounds in combination with neutron background could present acci-dental coincidences between these independent event classes. Gamma rays arise from naturalor induced radioactivity or from operational reactors. Their contribution to background isreduced by external shielding layers, where rays are attenuated [4].

4 Experiments

Most of the existing experiments were deployed to study the detection and to research theneutrino/antineutrino behaviour. Some of them, Rovno, SONGS and Double Chooz (Nucifer)were built especially for safeguard purpose. The safeguard applications and the results willbe presented below.

4.1 Safeguard applications

4.1.1 Rovno

Through operational years, beginning in 1982, many basic and applied experiments wereperformed at the Rovno Atomic Energy Station in Kuznetsovsk, Ukraine. The experimentsdemonstrated the possibility of monitoring reactors and proved correlation between the reactorantineutrino �ux, thermal power, and fuel burnup. The antineutrino source was PWR with anominal thermal power of 440 MW and loaded with light enriched uranium fuel. The detectorwas organic liquid scintillator doped with Gadolinium (Gd). Dopants improve the signal byreducing the neutron capture time and increasing the energy released. Some other detectorfeatures are shown in Table 1.

Table 1: Detector's features.ROVNO SONGS1 NUCIFER

TYPE liquid scintillator liquid scintillator liquid scintilatordoped by Gd doped by Gd doped by Gd

LOCATION 18 m below 24,5 m from and 10 m 7,2 m from and 11 mreactor core below core center below core center

PHYSICAL target volume:510 l target volume ∼1 000 l target volume: 850 lFEATURES shield volume: 540 l total footprint: 3×3×2.5 m

mass:640 kg mass: 1000 kg

EFFICIENCY 30% 10% 30%

MEAN ON: 909±6/day ON: 564±13/day ON: 281±7/dayRATE OFF: 149±4/day OFF: 105±9/day

4.1.2 SONGS

The second safeguard application is at the San Onofre Nuclear Generating Station (SONGS)in Southern California and was deployed explicitly to demonstrate the feasibility of monitor-ing with relatively small antineutrino detectors. The SONGS1 detector has been operatingsince 2002 with the full detector volume being operational continuously from 2006 throughsummer 2008. The antineutrino source is the light-water reactor with a nominal power of 3.64GW. Detector was deployed in tendon gallery, a room which is located in many commercialreactor. Target is contained in four stainless steel cells, which are connected to two PMTs.It is shielded by water and polyethylene layer which serves as passive shield of neutrons and

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gamma rays. It is surrounded by muon detectors from �ve sides which present an activeshielding. A total of twenty-four PMTs were used to read out both the muon veto and maindetector signals. Schematic presentation is shown in Figure 5 on left and detector featuresin Table 1. SONGS1 demonstrated sensitivity to the three antineutrino-based safeguard met-rics: operational status, power and �ssile content. An important drawback of the detectoris its low �ashpoint, high �ammability and relatively high toxicity. A more recent e�ort atSONGS has demonstrated antineutrino sensitivity with a non-toxic plastic scintillator baseddetector, SONGS2, with two identical modules. Each module consists of plastic scintillatorslabs interleaved with thin Mylar sheets painted with Gd-doped paint. Each module is readby a total of four PMTs and is placed in an aluminium framework for portability. The totalactive volume of this detector was 0.4 m3. A cutaway view is shown in Figure 5 in the middle.So far, the results are similar to SONGS1 and further analysis is needed to demonstrate longterm sensitivity to burn-up. The most important advantage over the previous version is thatthe �ammable, toxic and carcinogenic liquid organic scintillator is eliminated. Secondly, thedetector can be fully assembled o�site making the transport easier and cheaper. The dis-advantages are some reduction in overall detection e�ciency due to the detector design andlower in the proton density plastic scintillator[4].

Figure 5: Schematic presentation of SONG1 detector (left) and a cutaway of SONG2detector (middle) and Nucifer detector scheme with basic elements[4,15].

4.1.3 Nucifer

The last detector, Nucifer, designed and deployed especially for safeguard purposes was de-ployed in 2012 at the research center in France. Antineutrino source is the Osiris researchlight-water reactor with the nominal power of 70 MW. The scintillation light is detected by16 PMTs located on the top side of the detector. Between PMTs and the target liquid is a25 cm thick acrylic disk. It optically couples the PMTs with the liquid surface while shield-ing the intrinsic PMT radioactivity from the scintillator. The detector is protected from thebackground by a 15 cm of polyethylene and 10 cm of lead. The scheme of the detector isshown in Figure 5 on the right and some other features are in Table 1.

4.2 Results

It is now possible to monitor the operational status, power levels, and �ssile content of nuclearreactors in real time with known technology at distances of tens of meters from the source.The rate-based measurements require additional information about the reactor power andinitial fuel loading. The detected antineutrino spectra from an actual reactor consists ofa sum over the individual spectra from each isotope, weighted by the �ssion rates. Thepredicted �ssion rate for four main isotopes in fuel is in Figure 6 (a). The major �ssileelements are 235U and 239Pu. At the beginning of the cycle, 235U contributes the biggestpart to the �ssions rate. It decreases through the circle. On the contrary, the rate of 239Pu�ssions increase. The measured antineutrino energy spectrum and the average number of

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detectable antineutrinos produced per �ssion di�er signi�cantly between the two dominant�ssile elements. Their relative mass fractions and �ssion rates change during the cycle. Thetotal measured energy spectrum and the number of antineutrinos would change due to thosechanges. Typical example of measured antineutrino rate throughout the commercial PWRreactor cycle is shown in Figure 6 (b). The antineutrino rate changes for around 12% overentire cycle.

In San Onofre, the measurements, relative to a known initial value, has been made. Thepower has been determined with 3% accuracy in one week, which corresponds to consumptionof 500 kg of 235U and production about 80 kg of Pu in around 4 months (10-fold SQ). A 20%change in power measurements has been seen in 15-12 hours, shut down or start up at the 99%con�dence level within 5 hours (Figure 6 right). The newest results from the last deployeddetector Nucifer shows big improvements. By considering the same Nucifer detector installedon SONGS1 position, the same sensitivity of 10 % of the mass of �ssioning elements could bereached in less than 3 days.

In Rovno, the absolute thermal power has been observed at 2% accuracy. Nowadays, themost accurate methods precision ranging from 0.5-1.5%. From the rate-based measurementsthe net consumption of 521 kg of 235U and 239Pu over the cycle was determined. Fromindependent reactor`s thermal power records the value 525± 14 kg was derived[4].

Figure 6: The predicted (a) �ssion rates for 235U , 238U , 239Pu and 241Pu (b) antineutrinodetection rate in SONGS1 throughout one fuel cycle (left) and the SONGS1 output example

(right)[10].

5 Conclusion

The antineutrino detector is a promising safeguard tool. Since the particle footprint is practi-cally impossible to mask, with the exception of additional reactor presence, the measurementswould provide an undeniable information. Also the ease of use, robustness and the comple-mentary, non-intrusive nature of detector are features, which expose the antineutrino methodsas potential safeguards too. Deployed applications have demonstrated the antineutrino de-tection and the possibility for a real time power and reactor's �ssile content monitoring forthe �rst time. So far, the results do not achieve the safeguard requirements. The absolutemeasurements are not precise enough but in conjunction with other safeguards measurementscould approach the SQ level. Some studies based on fault-tree analysis of one diversion sce-nario, has shown that an usage of the current knowledge of antineutrino-based measurementcan provide a three-fold improvement in ability to detect diversion of fuel in comparison tomomentary approach. Further improvements in each step of detection are possible: size, ef-fectiveness, material of detector, his deployment location, better knowledge of antineutrino

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physics.

6 References

[1] https://www.iaea.org/safeguards/basics-of-iaea-safeguards, accessed 18th November 2015.

[2] IAEA, IAEA safeguards glossary: 2001 Edition, International nuclear veri�cation seriesNo.3, IAEA, 2002.

[3] IPFM, Global Fissile Material Report 2013 Increasing Transparency of Nuclear Warheadand Fissile Material Stocks as a Step toward Disarmament, Seventh annual report of theInternational Panel on Fissile Materials, IPFM, 2013.

[4] A. Bernstein, G. Baldwin, B. Boyer, M. Goodman, J. Learned, J. Lund, D. Reyna, R.Svoboda,Nuclear Security Applications of Antineutrino Detectors: Current Capabilities andFuture Prospects, Science & Global Security, 18:127�192,1547-7800 online, Taylor & FrancisGroup, LLC, USA, September 2010.

[5] E. Christensen, P. Huber, P. Ja�ke, Antineutrino Monitoring for Heavy Water Reactors,Physical review letters, Vienna, Austria, July 2014.

[6] T. B. Cochran, H. A. Feiveson, W. Patterson, G. Pshakin, M.V. Ramana, M. Schneider,T. Suzuki, Frank von Hippel, Fast Breeder Reactor Programs: History and Status, ResearchReport 8 International Panel on Fissile Materials, February 2010.

[7] https://www-nds.iaea.org/relnsd/vcharthtml/VChartHTML.html, accessed 18th Novem-ber 2015.

[8] http://t2k-experiment.org/,accessed 18th November 2015.

[9] N. R. Tolich, Experemental study of terrestrial electron antineutrinos with KamLAND,Dissertation, Stanford University, department of Physics, 2005.

[10] N. S. Bowden, A. Bernstein, S. Dazeley, R. Svoboda, A. Misner, T. Palmer, Observationof the Isotopic Evolution of Pressurized Water Reactor Fuel Using an Antineutrino Detector,arXiv:0808.0698v2 [nucl-ex], October 2008.

[11] F.H. Attix, Intorduction to Radiological Physic and Radiation Dosimetry , 2nd Edition,WILEY-VCH Verlag GmbH & Co. KGaA, 2004.

[12 ]P. Huber, T. Schwetz,Precision spectroscopy with reactor anti-neutrinos, Technical Uni-versity of Munich, Physics department,Germany, October 2004.

[13] J. A. Formaggio, G. P. Zellery, From eV to EeV: Neutrino Cross-Sections Across EnergyScales,arXiv:1305.7513v1, 2013.

[14] R.G. Arns, Detecting the Neutrino, Birkhauser Verlag, Basel, 2001.

[15] http://www-dsm.cea.fr, accessed 18th November 2015.

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