denaturing generated pu in fast breeder reactor blanket

Denaturing Generated Pu in Fast Breeder Reactor Blanket

Yoshitalia MEILIZA, Masaki SAITO� and Hiroshi SAGARA

Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8550

(Received April 22, 2009 and accepted in revised form March 19, 2010)

Protected Pu production (P3) is a recently developed concept to enhance the proliferation resistanceproperties of Pu by increasing the fraction of even-mass-number Pu isotopes thus leading to the denaturingof Pu. The present paper deals with the possibility of denaturing Pu by consideration of Pu and minoractinides (MAs) multicycling in medium-size fast breeder reactors (FBRs). It was found that multicyclingof Pu and MAs in FBRs enhances the proliferation resistance of Pu by increasing the fraction of even-mass-number Pu isotopes. The proliferation resistance of Pu in P3 recycling options satisfied criteria basedon Kessler’s proposal, i.e., 6% 238Pu content, and Pellaud’s proposal, i.e., 30% 240Pu content. Thenormalized attractiveness of Pu in P3 recycling options satisfied both criteria in the core as well as inthe blanket with the combination of even-mass-number Pu isotopes. At the initial introduction, two P3

FBRs (714MWth class) with the addition of 5wt% MA into the blanket can be operated using the annualdischarged spent fuel in Japan.

KEYWORDS: protected Pu production, denaturing Pu, proliferation resistance, FBR, fuel cycle,minor actinides, multicycle

I. Introduction

Pu recycling is important from the viewpoint of energyresources; however, one of the most sensitive issues is non-proliferation in the future fuel cycle based on fast breederreactors (FBRs). Pu produced in the FBR blanket includes alarge amount of the 239Pu isotope and only a small amount ofeven-mass-number Pu isotopes, which leads to severe pro-liferation concerns. Given the proliferation risks associatedwith the global expansion of nuclear energy, proliferationresistance should be a constraint on the design and develop-ment of new systems.

There are several proposals to burn Pu and minor actinides(MAs), thus minimizing the quantity of fissile materials andwaste in reactors. However, it is misleading to considernonproliferation concerns solely in terms of minimizingfissile materials; an inherent isotopic barrier against fis-sion-explosive production is also an important factor. Inreference to the nuclide transition chain, MAs could affectplutonium composition properties and buildup of the amountof plutonium once it is incorporated into the nuclear fuel.

Recently, Saito1) has proposed the Protected Pu Produc-tion (P3) concept. It conceives intrinsic denaturing of Pu byMA transmutation, which makes Pu in spent fuel unusable asweapons material. The P3 concept utilizes the transmutationof MAs, such as Np, Am, and Cm, as a source for even-mass-number Pu isotopes to enhance the proliferation-resist-ant Pu fuel since the dominant 237Np, 241Am, and 243Am are

well transmuted to 238Pu in thermal reactors1,2) and the FBRblanket.3) In this concept, increase in the 238Pu isotopicfraction causes a high rate of internal heat generation by �decay and is also a large spontaneous fission neutron gen-eration in Pu; these are disadvantageous conditions thatwould be encountered during the manufacturing and main-tenance of nuclear explosive devices (NEDs).4,5)

The properties of Pu isotopes have been studied as indica-tors to specify proliferation-resistant Pu and they are shown inTable 1.6) Thus far, several criteria for Pu categorizationconcerning proliferation risk have been proposed. The cate-gorization of Pu protection based on the 238Pu isotopic ratiowas studied by Kessler7) who reported that Pu with the 238Pufraction of about 12% is effectively protected against prolif-eration. Kessler8) later improved his model with detailed ther-mal analysis calculations for implosion-type NEDs and hedetermined that Pu containing 6–8% 238Pu isotopic fractionwas necessary to consider a material as proliferation-resistant.

Table 1 Properties of Pu isotopes6)

Isotope DH (W/kg) SFN (n/g/s)

238Pu 567 2,660

239Pu 1.93 0.02

240Pu 7.06 1,030

241Pu 3.4 0.05

242Pu 0.12 1,720

�Atomic Energy Society of Japan

�Corresponding author, E-mail: [email protected]

Journal of NUCLEAR SCIENCE and TECHNOLOGY, Vol. 47, No. 10, p. 853–866 (2010)

853

ARTICLE

Pellaud9) also proposed a Pu classification scheme basedon spontaneous fission neutron generation and determinedthe suitability of a Pu mixture for NEDs according to the240Pu isotopic content as shown in Table 2. Although 240Puhas a large spontaneous fission neutron rate (Table 1), it hasa relatively low decay heat rate. The neutron source enhan-ces the probability of preignition, thus leading to ‘‘fizzleyield,’’ a minimum possible yield of explosion for implo-sion-type NEDs. Pellaud further determined that MOX-grade Pu is practically unusable for NEDs since its handlingbecomes extremely difficult in terms of radiation and heatlevels. Information Circular 153 issued by the IAEA10) men-tioned that Pu containing more than 80% 238Pu is exemptedfrom proliferation concerns due to the high decay heat.

Denaturing of Pu can be characterized by high decay heatdominated by 238Pu as well as large spontaneous fissionneutrons governed by even-mass-number Pu isotopes(238Pu, 240Pu, and 242Pu). There are two pathways for pro-ducing 238Pu by MA transmutation. One is through �� decayfrom 238Np (T1=2 ¼ 2:36 d), which is produced from 237Npneutron capture reactions, and the other is through � decayfrom 242Cm (T1=2 ¼ 162:79 d), which is the �� decay daugh-ter of 242Am produced from 241Am neutron capture reac-tions. Plutonium-242 is produced through electron capturefrom 242Am (T1=2 ¼ 16 h), which is produced from 241Amneutron capture reactions, and 240Pu is produced through �decay from 244Cm (T1=2 ¼ 18:1 y), which is the �� decaydaughter of 244Am produced from 243Am neutron capturereactions.

The possibility of protected Pu production in the FBRblanket was previously studied from the viewpoint of 238Puaccumulation control in the Pu production by MA transmu-tation thus leading to protected plutonium breeding.3) Theobjective of the present paper is to investigate the possibilityof denaturing Pu by MA transmutation in a medium-sizeFBR nuclear fuel cycle from the viewpoint of accumulatingeven-mass-number Pu isotopes by multicycling of Pu andMAs. The proliferation resistance property of Pu is alsoevaluated based on the specific decay heat, spontaneousfission neutron generation, and an evaluation function, at-tractiveness, and it is compared with several criteria appear-ing in the literature. If the Pu isotopic fraction is satisfied forthe criterion based on Kessler’s proposal, 6% 238Pu content,or the criterion based on Pellaud’s proposal, 30% 240Pucontent, there is a possibility that Pu is practically unusablefor NEDs.

II. Concept

The present paper describes a concept for multicycling ofPu and MAs in FBRs for denaturing of Pu. Multicycle modesof Pu and/or MAs are implemented by recovering the ele-ments during reprocessing and retaining them in the recycledFBR fuel itself.

Depending on the fuel cycle options used in the presentpaper, calculations are done with the assumption that cool-ing, reprocessing, and refabrication occur during five yearsfollowing discharge for each cycle. The overall recovery andrefabrication ratio of 99.5% is assumed for all transuranicelements in the recycle calculations. There is no reprocess-ing and recycling of uranium, and the core and the blanketalways use depleted uranium (DU). The addition of MAsinto the core is not considered in the present paper. All caseoptions are irradiated under the same power.

The present paper deals with two types of Pu and MAmulticycle schemes in FBRs; the first is designated as theconventional recycling scheme and it is based on multicy-cling of Pu only and the second is designated as the P3

recycling scheme and it is based on multicycling of Pu andMAs. At the beginning, hence, the 0th cycle, Pu and MAscome from LWR discharged spent fuel. Figures 1(a) and1(b) show the 0th cycle of the schemes. For further discus-sion, the 0th cycle of the conventional recycling can bedefined as the reference (REF) case. The isotopic composi-tions of Pu and MAs from LWR spent fuel are listed inTable 3.

The conventional recycling scheme is divided into twooptions, XA and XC, as shown in Figs. 2(a) and 2(b). TheXA option uses Pu from the blanket only that contains Puwith high 239Pu content in the next cycle. In the XC option,all the Pu produced in the blanket is mixed with the remain-ing Pu in the core as MOX fuel for the next cycle; hence,its name is the closed-Pu cycle.

Table 2 Grades of Pu9)

Grade Composition Usability

Super grade (SG) 240Pu < 3% Best quality

Weapon grade (WG) 3 � 240Pu < 7% Standard material

Fuel grade (FG) 7 � 240Pu < 18% Practically usable

Reactor grade (RG) 18 � 240Pu < 30% Conceivably usable

MOX grade 240Pu > 30% Practically unusable (a)

(b)

core

blanket

DU

DU

PuLWR

core

blanket

DU

DU

PuLWR

MA

Fig. 1 FBR recycling schemes (a) conventional and (b) P3

854 Y. MEILIZA et al.

JOURNAL OF NUCLEAR SCIENCE AND TECHNOLOGY

The P3 recycling scheme, based on multicycling of bothPu and MAs, is divided into four options, as shown inFigs. 3(a) to 3(d). The DA option uses Pu produced in theblanket and MAs produced in the core for the next cycle toinvestigate the behavior of denaturing Pu itself as nuclearfuel and to investigate the possibility of using MAs producedfrom MOX fuel to enhance the proliferation resistance of Pu.In the DB option, Pu produced from the blanket is used forMOX fuel and MAs produced in the core are mixed togetherwith the remaining MAs in the blanket for the next cycle(hence, the name closed-MA cycle). The DC option uses amixture of all the Pu produced in the blanket and the re-maining Pu in the core and a mixture of MAs produced inthe core and the remaining MAs in the blanket for the nextcycle. This option can be described as a closed cycle for Pu

Table 3 Isotopic composition from LWR spent fuel�

Pu isotope wt% MA isotope wt%

238Pu 1.46 237Np 56.93

239Pu 54.73 241Am 26.26

240Pu 26.22 242mAm 0.007

241Pu 11.51 243Am 13.56

242Pu 6.08 244Cm 3.02

�33GWd/tHM irradiated fuel of presently operating PWRs with 3.3%235U fuel, followed by a 3-year cooling time. (a)

(b)

core

blanket

DU

DU Pu

Option XA

core

blanket

DU

DU Pu

Option XC

Fig. 2 Conventional recycling scheme options: (a) XA option and(b) XC option

(a) (b)

(c) (d)

core

blanket

DU

DU Pu

MA

Option DA

core

blanket

DU

DU Pu

MA

Option DB

core

blanket

DU

DU Pu

MA

Option DC

core

blanket

DU

DU Pu

MA

LWRMA

Option DD

Fig. 3 P3 recycling scheme options: (a) DA option, (b) DB option, (c) DC option and (d) DD option

Denaturing Generated Pu in Fast Breeder Reactor Blanket 855

VOL. 47, NO. 10, OCTOBER 2010

and MAs in an FBR (hence, the name closed-cycle FBR).The DD option uses a mixture of all the Pu produced in theblanket and the remaining Pu in the core and a mixture of allMAs from an FBR and LWRs for the next cycle; hence, itsname is the hybrid LWR-FBR. The analyses are conductedto show the behavior of denaturing Pu during multicyclesfrom the viewpoint of even-mass-number Pu isotopes.

Previously reported calculations revealed that the FBRblanket with the addition of 5wt% MAs from LWR spentfuel was enough to enhance the proliferation resistance of Puand gave 17–19wt% 238Pu isotopic fraction from the earlytime of irradiation.3) Based on these calculations, the casewith MOX fuel containing Pu from LWR spent fuel in thecore and 5wt% MAs from LWR spent fuel doped into theblanket is described as the 0th cycle of P3 recycling.

An important assumption imposed on the FBR systemdiscussed during multicycles is no change in irradiation timewith the same power. In order to achieve this assumption,fresh fuel fissile quantity in each cycle is complementedby adjusting the enrichment of Pu to keep the followingcondition.

�f

�a

� �ðiÞ¼�

�f

�a

� �ðiþ1Þ

; i ¼ cycle ð1Þ

�f = effective fission macroscopic cross section in fuel�a = effective absorption macroscopic cross section in

fuel

III. Attractiveness

A new evaluation function, attractiveness, defined as theratio of the potential fission yield to the technological diffi-culties in manufacturing NEDs, is generally proposed for Pucategorization.

The attractiveness function used here is expressed inEq. (2),11)

ATTR ¼

�1

�2391

DH

DH238þ

SFN

SFN238

; ð2Þ

where �1 is the alpha-Rossi of infinite system Pu metal.Alpha-Rossi, the meaningful feature of the explosive yield,is defined as the ratio of supercriticality to prompt neutronlifetime, as shown in Eq. (3). DH and SFN are the specificdecay heat and the spontaneous fission neutron generationrate of Pu metal, respectively, representing technologicaldifficulties. The terms of DH and SFN are normalized totheir maximum values, which are the characteristics of 238Puisotope. The attractiveness function shows that not only238Pu but also other even-mass-number Pu isotopes havean important role for denaturing Pu due to the noticeablylarge spontaneous fission neutron generation. Alpha-Rossiis estimated using the MCNP4C12) code coupled withJENDL3.313) nuclear data libraries.

� ¼k � 1

�ð3Þ

k = criticality� = prompt neutron lifetime

IV. Calculation Method

As a reference core, a medium-size FBR with the samesize as the Japanese prototype FBR, MONJU (714MWth), ischosen with MOX fuel in the core and DU in the blanket.The core and the blanket comprise one-batch refueling. Themaximum linear heat rate during multicycling is less than360W/cm. Other major specifications are summarized inTable 4. The core layouts and calculation model adopted inthe present calculations are shown in Figs. 4(a) and 4(b),respectively.

Table 4 Plant design specifications

Item Unit Specification

a. Plant Parameters1. Reactor thermal power MWth 7142. Coolant temperature (inlet/outlet) �C 380/5303. Fuel/coolant/structure vt% 44.8/18.3/36.94. Subassembly pitch mm 115.6

b. Core Fuel Parameter1. Fuel material PuO2.UO2

2. Pu enrichment (inner/outer) wt% 21.96/31.65� PuO2/(PuO2+UO2)3. 238Pu/239Pu/240Pu/241Pu/242Pu wt% 1.46/54.73/26.22/11.51/6.08�

4. U isotope ratio (235U/238U) wt% 0.3/99.75. Refueling pattern one-batch6. Core diameter/core height m 1.80/0.93

c. Blanket Parameter1. Blanket composition UO2

2. U isotope ratio (235U/238U) wt% 0.3/99.73. Refueling pattern one-batch4. Thickness of axial blanket (upper/lower) m 0.30/0.35

�Pu enrichment and isotopic fraction used in REF case



Computer codes, SLAROM,14) JOINT, and CITATION,15)

and the 70-group cross sections library, JFS-3-J-3.2R,16)

which is based on the Japanese Evaluated Nuclear DataLibrary JENDL 3.2,17) are used in the present calculations.The nuclear characteristics are investigated using a calcula-tion of two-dimensional RZ diffusion theory with a depletionchain by CITATION. In this calculation, the right-half coremodel with 96 zones was divided into 48� 50 mesh inter-vals, and each zone has uniform nuclide number densitiesand the same set of microscopic cross sections. The detailedheavy metal transmutation chains shown in Fig. 5 are usedin the present analysis.

V. Denaturing of Pu in the Cycle Options

Figure 6(a) shows the burnup-dependent Pu isotopiccomposition in the blanket of the REF case and the 238Puisotopic fraction. Without the addition of MAs, Pu producedin the blanket consists of a high 239Pu isotope content at alltimes in the irradiation (> 96wt%) and low content of even-mass-number Pu isotopes. Plutonium-238 appears after morethan 200 days of irradiation. Since the blanket consists ofonly DU, the major MA isotopes produced are 239Np and237Np isotopes as shown in Fig. 6(b).

Figures 6(c) and 6(d) show Pu and MA isotopic compo-sitions during burnup in the core of the REF case. The even-mass-number Pu isotope fraction increases by more than12.5 wt% compared with Pu feeding from LWR spent fuel,except for the 238Pu isotope that decreases by 24wt% at theend of radiation. Due to Pu transmutation, 241Am and 243Amare the major MA isotopes produced (48 and 32wt%,respectively) in the core, while the 237Np content is only3wt%. A comparison of Pu and MA isotopic compositionsin the conventional and P3 recycling schemes after irradia-tion in the 0th cycle is presented in Table 5.

The net production of plutonium isotopes for a certainpoint in the irradiation time and independent of space for1-group neutron energies is driven by their generation andincineration rates, which can be formulated as follows.

Neutron Source

Inner CoreOuter CoreRadial Blanket

Control RodNeutron Shielding

(b)

(a)

AXIALSHIELD

AXIALSHIELD

0.45

m

AXIALSHIELD

AXIALSHIELD

0.45

m

AXIALBLANKET

0.35

m

AXIALSHIELD

AXIAL SHIELD

0.70 m 0.20 m 0.3 m 0.45 m

0.30

m

CR-ADP

INNERCORE

CR-ADP

INNERCORE

CR-ADP

INNERCORE

CR-ADP

OUTERCORE

0.93

mRADIALSHIELD

AXIALBLAN-KET

AXIALBLAN-KET

AXIALBLAN-KET

AXIALBLANKET

NS

RADIALBLAN-KET

AXIALBLAN-KET

AXIALBLAN-KET

AXIALBLAN-KET

CR

CR

AXIALSHIELD C

RCR

AXIAL SHIELD

CR = Control RodCR-ADP = Control Rod Adapter

Fig. 4 (a) Core layout and (b) calculation model

Cm245 Cm246XA Cm243 Cm244

Pu238 Pu239 Pu240

Np240

Am243 Am244

Pu241 Pu242 Pu243

Am241

U238 U239

Np237 Np238 Np239

U234 U235 U236 U237

162.795 d

82.7%

87.78 y

20%

14.36 y

2.36 d

29.12 y

17.3%

18.12 y

(n , γ)

(n , γ) simplifiedβα

(n , 2n)

(n , 2n) simplified

( n,f )

Fissile Material

Burnable Poison

Source of Pu238

Intensive Spontaneous Fission Neutron

2.1 d

Am242

Cm242

Am242m

Fig. 5 Nuclides chain



Generation rate ¼Xi

NPi �

Pi �þ

Xj

NPj �

Pj ð4Þ

Incineration rate ¼ N�R�þ N� ð5Þ

Generation rate is defined as the sum of any possible reac-tions ([n, �],[n, 2n], etc.) of any precursor nuclide, whichlead to the generation of the nuclide of interest and the sum

of the decay reaction of any parent nuclide of interest, whileN, �, and � represent nuclide density, microscopic crosssection of a particular reaction, and decay constant, respec-tively. Incineration rate of the nuclide of interest refers toany possible neutron reaction (with �R representing anyremoval cross section such as fission, neutron capture,[n,2n], etc.) and radioactive decay.

Figure 7 features the major contributor nuclides in thegeneration of even-mass-number Pu isotopes for the conven-tional recycling cases. In the core of the REF case, � decayof 242Cm dominates the accumulation of 238Pu with someportion coming from �� decay of 238Np. Net production of238Pu remains negative up to the end of irradiation. For 240Pugeneration, the major contributor is 239Pu for all burnupintervals and net production of 240Pu remains positive atthe end of irradiation. Production of 242Pu is mainly due to241Pu rather than electron capture of 242Am and � decay of246Cm.

In the blanket of the REF case, �� decay of 238Np dom-inates the accumulation of 238Pu with some portion comingfrom the (n,2n) reaction of 239Pu. For 240Pu generation, themajor contributor is 239Pu for all burnup intervals. Produc-tion of 242Pu is mainly due to 241Pu rather than electroncapture of 242Am. The net production of even-mass-numberPu isotopes is still positive up to the end of irradiation.

1. Conventional Recycling Scheme Options(1) XA Option

This option uses MOX fuel that contains Pu produced inthe blanket for the subsequent operation cycle as shown inFig. 3(a). Since this option uses Pu with high 239Pu isotope

0

4

8

12

16

20

0.001

0.01

0.1

1

10

100

0 200 400 600 800

238 P

u f

ract

ion

(w

t%)

Pu

Acc

um

ula

tio

n (k

g/t

HM

)

Irradiation Time (days)

238Pu

239Pu

241Pu

240Pu

(a) REF, blanket

0

4

8

12

16

20

0.001

0.01

0.1

1

10

100

1000

0 500

238P

u f

ract

ion

(w

t%)

Pu

Acc

um

ula

tio

n (k

g/t

HM

)


238Pu

239Pu

241Pu240Pu

242Pu

(c) REF, core

0.001

0.01

0.1

1

10

100

0 200 400 600 800

MA

Acc

. (kg

/tH

M)


237Np

Total MA239Np

(b) REF, blanket

0.001

0.01

0.1

1

10

100

0

MA

Acc

. (kg

/tH

M)


237Np

241Am243Am

242Cm

Total MA

242mAm

239Np244Cm

(d) REF, core

0 200 400 600 800

Fig. 6 HM composition of REF case: (a) Pu produced in the blanket, (b) MAs produced in the blanket, (c) Pu burned inthe core and (d) MAs produced in the core

Table 5 Isotopic composition at the end of irradiation for the 0th

cycle

Conventional FBR P3 FBR

Core Blanket Core Blanket

Pu isotopic composition (wt%)

238Pu 1.17 0.01 1.18 18.23

239Pu 52.98 96.33 53.00 77.65

240Pu 30.24 3.54 30.20 3.02

241Pu 8.63 0.11 8.65 0.07

242Pu 6.97 0.00 6.97 1.03

MA isotopic composition (wt%)

237Np 3.99 97.81 3.98 56.42

241Am 52.51 2.13 53.14 25.36

242mAm 1.89 0.02 1.87 0.65

243Am 34.97 0.02 34.53 13.30

244Cm 6.64 0.00 6.47 4.26



content, the Pu accumulation in the core has a differentbehavior compared with the REF case. Even though theamounts of even-mass-number Pu isotopes increase duringburnup, the 239Pu isotopic fraction is still more than 80wt%of the total Pu at the end of irradiation. Plutonium-240 isdominant compared with other even-mass-number Pu iso-topes.

Since fuel in the core for this option contains only a smallamount of the 241Pu and 242Pu isotopes (� 1wt%), the majorMAs produced are 237Np and 241Am isotopes. The 237Npisotope fraction in MAs produced is twice that of the 241Amisotope at the end of irradiation. Plutonium and MA behaviorin the blanket for the XA option is similar to that in the REFcase. A comparison of Pu and MA isotopic compositionsfor conventional and P3 recycling schemes after irradiationin the 1st cycle is presented in Table 6.

As shown in Fig. 7, in the core of the XA option, at thebeginning of the cycle, the (n,2n) reaction of 239Pu domi-nates the accumulation of 238Pu with some portion comingfrom the �� decay of 238Np and at the end of the cycle, themajor contributor is the �� decay of 238Np. In the case of240Pu generation, the major contributor is 239Pu for all burn-up intervals. Production of 242Pu is mainly due to 241Purather than electron capture of 242Am and � decay of246Cm. The net production of even-mass-number Pu isotopesremains positive up to the end of irradiation.

In the blanket, as shown in Fig. 8, the major contributornuclides in the generation of even-mass-number Pu isotopesof the XA option have the same tendency as in the REF case.(2) XC Option (Closed-Pu Cycle)

All the Pu produced in the blanket was mixed with theremaining Pu in the core as MOX fuel for the next cycle. ThePu and MA isotopic compositions after irradiation in the 1st

cycle are summarized in Table 6. The 238Pu and 242Pu iso-topic fractions in the core decrease with cycle number, and

(a)

(b)

(c)

0%

20%

40%

60%

80%

100%

BOC EOC BOC EOC BOC EOC BOC EOC BOC EOCRea

ctio

n C

on

trib

uti

on

to

Net

Pro

du

ctio

n o

f 23

8 Pu

(%

)

Np-238 --> Pu-238Cm-242 --> Pu-238Pu-239 --> Pu-238Pu-238 --> U-234Pu-238 removal

REF1st cycle 5th cycle 10th cycle

conventional (core)

XAXC XC XC

0%

20%

40%

60%

80%

100%


ctio

n C

on

trib

uti

on

to

Net

Pro

du

ctio

n o

f 24

0 Pu

(%

)

Pu-239 --> Pu-240Cm-244 --> Pu-240Pu-241 --> Pu-240Am-241 --> Pu-240Pu-240 --> U-236Pu-240 removal


conventional (core)

XAXC XC XC

0%

20%

40%

60%

80%

100%


ctio

n C

on

trib

uti

on

to

Net

Pro

du

ctio

n o

f 24

2 Pu

(%

)

Pu-241 --> Pu-242Cm-246 --> Pu-242Am-242 --> Pu-242Pu-242 --> U-238Pu-242 removal


conventional (core)

XAXC XC XC

Fig. 7 Core diagrams of the conventional recycling scheme op-tions: (a) contributors to 238Pu production, (b) contributors to240Pu production and (c) contributors to 242Pu production

Table 6 Isotopic composition at the end of irradiation of the 1st cycle

Option XA XC DA DB DC DD

Core Blanket Core Blanket Core Blanket Core Blanket Core Blanket Core Blanket

Pu isotopic composition (wt%)

238Pu 0.04 0.01 0.73 0.01 12.99 8.79 13.00 17.80 3.30 17.80 3.34 17.83

239Pu 85.13 96.28 57.83 96.32 73.66 84.67 73.65 77.91 55.48 77.93 55.55 77.92

240Pu 13.73 3.59 29.93 3.55 11.47 4.17 11.46 3.17 29.51 3.15 29.45 3.14

241Pu 1.04 0.11 5.50 0.11 0.85 0.10 0.85 0.08 5.48 0.07 5.46 0.07

242Pu 0.06 0.00 5.13 0.00 1.03 2.26 1.03 1.04 6.22 1.04 6.20 1.04

MA isotopic composition (wt%)

237Np 64.52 97.76 5.60 97.80 36.31 4.07 36.29 54.57 5.40 54.58 5.43 54.69

241Am 32.43 2.18 40.94 2.15 15.77 50.00 15.77 25.47 40.83 25.47 40.79 25.47

242mAm 0.86 0.02 1.42 0.02 0.41 2.79 0.41 1.17 1.39 1.17 1.39 1.14

243Am 1.94 0.03 43.61 0.03 39.75 34.19 39.75 13.94 44.01 13.94 44.02 13.90

244Cm 0.24 0.00 8.41 0.00 7.76 8.94 7.78 4.85 8.36 4.84 8.37 4.80



the 240Pu fraction is almost the same during multicycling. Bycontrast, the 239Pu fraction increases due to the Pu having ahigh content of 239Pu. During multicycling, the major MAisotopes produced in the core are 241Am and 243Am. Re-duced 242Pu accumulation during multicycling results indecreased 243Am accumulation. Plutonium and MA behav-iors in the blanket are similar to that in the REF case.

In the core of the XC option, the (n,2n) reaction of 239Pudominates the accumulation of 238Pu at the beginning of thecycle and � decay of 242Cm dominates it with only a smallportion coming from the (n,2n) reaction of 239Pu at the endof the cycle. In the 1st cycle, the net production of 238Pu and242Pu remains negative, and at the equilibrium cycle, itbecomes positive due to 242Cm and 241Pu production. Thenet production of 240Pu remains positive during multicy-cling.

2. Protected Pu Production (P3) Recycling Scheme Op-tionsMOX fuel in the core with the addition of 5wt% MAs in

the blanket is assumed as the 0th cycle case. In the 0th cycle,all the Pu and MA isotopes in the core behave in the sameway as normally encountered in the REF case. As shown in

Fig. 9, the blanket with the addition of 5wt% MAs gives notonly increased 238Pu accumulation from the early time ofirradiation, but also increased 242Pu isotope content at thesame time. The contents of remaining MAs in the blankethave a similar tendency to the one at the beginning ofirradiation (from LWR spent fuel).

In the core of the 0th cycle of P3 recycling, the incinerationrate dominates the net production of 238Pu at the beginningof irradiation. Since the production of 241Am isotope fromMOX fuel is higher than that of 237Np isotope, � decay of242Cm dominates the accumulation of 238Pu with some por-tion coming from �� decay of 238Np at the end of irradiation.The net production of 238Pu and 242Pu remains negative up tothe equilibrium cycle and the net production of 240Pu re-mains positive due to the 239Pu neutron capture reaction. Inthe blanket, �� decay of 238Np dominates the accumulationof 238Pu with some portion coming from � decay of 242Cm.The net production of 238Pu remains positive up to the end ofirradiation. In the case of 240Pu generation, the major con-tributor is � decay of 244Cm at the beginning of irradiation,and 239Pu dominates the accumulation of 238Pu at the endof irradiation with some portion coming from � decay of244Cm. The production of 242Pu at all burnup intervals ismainly due to electron capture of 242Am. Generally, amongMA nuclides, 237Np plays the largest role in building up Puisotopes in the blanket since higher Pu isotopes are producedmainly from the successive capture of 238Pu. Nevertheless,242Cm and 241Am also give noticeable contributions.(1) DA Option

For the next cycle, MOX containing Pu produced from theblanket is used as fuel, and a mixture of MAs from the coreand DU is loaded into the blanket. The fraction of MA dopedinto the blanket is kept constant at 5wt%. The denaturingbehavior of Pu by itself as nuclear fuel and the possibility ofusing MAs produced from recycled fuel to enhance prolif-eration resistance of Pu are investigated.

Since 241Am isotope is the dominant MA isotope pro-duced from MOX fuel at the 0th cycle, Pu produced in theblanket of the 1st cycle has a different behavior from the oneat the 0th cycle. As shown in Fig. 10(a), the 238Pu accumu-lation decreases by one order of magnitude at the early timeof irradiation compared with the accumulation at the 0th

cycle. It can be understood because the half-life of 242Cm,a daughter nuclide from 241Am neutron capture reaction, is

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Pu-241 --> Pu-242Cm-246 --> Pu-242Am-242 --> Pu-242Pu-242 --> U-238Pu-2 42 removal

Fig. 8 Blanket diagrams of the conventional recycling schemeoptions: (a) contributors to 238Pu production, (b) contributors to240Pu production and (c) contributors to 242Pu production

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Fig. 9 Pu composition in the blanket of the 0th cycle P3 recycling



163 d. The 240Pu and 242Pu accumulations have the sametendency as the one at the 0th cycle. Even though the 238Puisotopic fraction in the blanket is improved to as high as 8to 9wt% at the end of irradiation, as shown in Table 6, it isstill less than the criterion based on Kessler’s proposal, 6%238Pu content at the early time of irradiation until �250 daysof irradiation.

In the 2nd cycle and after, the amount of 241Pu isotope isthe least among all Pu isotopes in the core, so that 241Amproduction through �� decay from 241Pu (T1=2 ¼ 14:4 y) isless than 243Am and 237Np production. With this MA com-position, Pu produced in the blanket in the next cycle has asimilar behavior to the one at the 0th cycle. Even though theaccumulation of even-mass-number Pu isotopes fluctuatesduring multicycling, the 238Pu isotopic fraction is alwaysmore than 6wt% for all burnup intervals except in the earlytime of irradiation of the 1st cycle. For instance, in the 10th

cycle, it decreases to � 13wt% as shown in Fig. 10(b)owing to reduced fractions of 237Np and 241Am isotopes.In general, the 238Pu and 239Pu isotopes are the major Puisotopes produced in the blanket with only small amounts of240Pu, 241Pu, and 242Pu isotopes.

The 238Pu and 239Pu isotopes in the core are burned, whilethe amounts of other Pu isotopes are increased during burn-up, as shown in Fig. 11. The 238Pu isotopic fraction de-creases to � 8wt% at the end of irradiation of the 10th cyclecompared with 11wt% at the 1st cycle.

Figures 12 and 13 show the major contributor nuclides inthe generation of even-mass-number Pu isotopes of the DAoption in the core and blanket. Due to less MA production inthe core, the incineration rate dominates the net production

of 238Pu for all burnup intervals. The net production of 238Puand 242Pu remains negative for all burnup intervals. The netproduction of 240Pu remains positive mainly due to 239Pu upto the end of irradiation.

The generation of even-mass-number Pu isotopes in theblanket has the same tendency as the 0th cycle of the P3

recycling option except in the 1st cycle of 238Pu generation.The major contributor is �� decay of 238Np at the beginningof irradiation, and � decay of 242Cm dominates the accumu-lation of 238Pu at the end of irradiation due to a highercontent of the 241Am isotope.(2) DB Option (Closed-MA Cycle)

For the next cycle, Pu produced from the blanket is usedas MOX fuel in the core, and all MAs produced in the coreand all remaining MAs in the blanket are mixed together forMA doping in the blanket. This option can be described asclosed-MA cycle. The fraction of MAs doped into the blan-ket is kept constant at 5wt%.

As shown in Table 6, Pu and MA accumulations in thecore of the 1st cycle have a similar tendency to that of theDA option. After the 1st cycle, the 238Pu and 242Pu isotopicfractions are gradually reduced by cycling, while 239Pu,241Pu, and 240Pu fractions increase. The major MA isotopesproduced in the core of the 1st cycle are 237Np and 243Am,since the fuel only has a small amount of 241Pu. After the 1st

cycle, 237Np becomes the major MA isotope produced in thecore owing to reduced 242Pu content and increased 241Pucontent in the fuel by increasing the number of cycles.

During multicycling, the contents of 237Np and 241Amisotopes in the blanket are reduced, while the contents ofhigher-mass-number MA isotopes increase compared with

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Fig. 11 Pu composition in the core of DA option: (a) 1st cycle and(b) 10th cycle

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Fig. 10 Pu composition in the blanket of DA option: (a) 1st cycleand (b) 10th cycle



the contents at the 0th cycle. The fraction of even-mass-number Pu isotopes produced in the blanket is almost thesame as the one at the 0th cycle.

The major contributor nuclides in the generation of even-mass-number Pu isotopes of the DB option has the sametendency as that of the DA option in the core and the blanketexcept that 238Pu accumulation of the 1st cycle in the blankethas the same tendency as the 0th cycle of the P3 recyclingscheme.(3) DC Option (Closed-Cycle FBR)

In this option, all the Pu produced in the blanket and theremaining Pu in the core are used as MOX fuel for the nextcycle. All MAs produced in the core are mixed together withall remaining MAs in the blanket for the next cycle. Thisoption is described as closed-cycle FBR. The MA fractiondoped into the blanket is kept constant at 5wt%.

The 238Pu isotopic fraction in the core increases duringmulticycling, while it drops in the blanket. MAs produced inthe core contain 241Am and 243Am as the major isotopes thatcome from �� decay from 241Pu and neutron capture reac-tion of 242Pu. During multicycling, reduced 238Pu and 242Puaccumulations in the blanket result from a decrease in con-tent of 237Np and 241Am isotopes, and an increase in 243Am

content give a much more significant effect on the prolifer-ation resistance compared with the slight increase in 240Puaccumulation.

Figures 14 and 15 show the major contributor nuclidesin the generation of even-mass-number Pu isotopes of theDC option in the core and blanket. In the core, � decay of242Cm dominates the accumulation of 238Pu with a smallportion coming from �� decay of 238Np at the end ofirradiation. Neutron capture reaction of 241Pu dominatesthe 242Pu generation during multicycling. The net produc-tion of 238Pu and 242Pu remains negative up to the equi-librium cycle and the net production of 240Pu remains posi-tive due to 239Pu neutron capture reaction. In the blanket, �decay of 238Np dominates the accumulation of 238Pu withsome portion coming from � decay of 242Cm. The netproduction of 238Pu remains positive up to the end of irra-diation. In the case of 240Pu generation, the major contrib-utor is � decay of 244Cm at the beginning of irradiation, and239Pu dominates at the end of irradiation with some portioncoming from � decay of 244Cm. Production of 242Pu at allburnup intervals is mainly due to electron capture of 242Amrather than 241Pu neutron capture reaction and � decay of246Cm.

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Fig. 13 Blanket diagrams of the DA option: (a) contributors to238Pu production, (b) contributors to 240Pu production and (c)contributors to 242Pu production

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Fig. 12 Core diagrams of the DA option: (a) contributors to 238Puproduction, (b) contributors to 240Pu production and (c) contrib-utors to 242Pu production



(4) DD Option (Hybrid LWR-FBR)Since MA doping in the blanket can serve as an MA

burner and as MA producer in the core, the amount ofMAs in the system decreases with the cycle number. A smallamount of MAs fed from outside (LWR spent fuel) is neededto provide a constant 5wt% into the blanket. This option iscalled the hybrid LWR-FBR.

In this option, 241Am and 243Am are the major MA iso-topes produced in the core. In the core, the 238Pu fractionincreases significantly at the 1st cycle, then increases slowlyuntil the 5th cycle, and after that, it is not changed until the10th cycle. The 242Pu isotopic fraction decreases duringmulticycling while the 240Pu isotopic fraction is almost thesame as the one at the 0th cycle. The MA composition in theblanket during multicycling has the same tendency as the 0th

cycle except for the 242mAm isotope.The major contributor nuclides in the generation of even-

mass-number Pu isotopes of this option have the same ten-dency as the DC option.

3. Attractiveness of Pu in the Cycle OptionsFigure 16 show attractiveness in the core and blanket at

the end of irradiation during multicycling, normalized byattractiveness of 239Pu isotope, compared with several cri-

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1

Fig. 15 Blanket diagrams of the DC option: (a) contributors to238Pu production, (b) contributors to 240Pu production and (c)contributors to 242Pu production

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Fig. 16 Attractiveness of Pu (a) in the core and (b) in the blanket

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Fig. 14 Core diagrams of the DC option: (a) contributors to 238Puproduction, (b) contributors to 240Pu production and (c) contrib-utors to 242Pu production



teria of Pu categorization proposed in the literature.8–10)

Without the addition of MAs, the Pu attractiveness in theblanket is very high at the early time of irradiation, and itdecreases with increasing irradiation time due to the 240Puproduction. However, even at the end of irradiation, it stillcan be categorized as standard material for NEDs.

In the core of the 0th cycle, even 238Pu content from LWRspent fuel is less than 6wt%, and with this evaluation func-tion, both criteria are satisfied due to a high 240Pu isotopicfraction. Utilization of Pu derived from the blanket with high239Pu isotope content as fuel in the core (XA option) makesthe Pu attractiveness higher than that of the REF case, andboth criteria are still not satisfied. In the XC option, the Puattractiveness of the core increases with the number ofcycles even it still satisfies both criteria. As DeVolpi18)

mentioned, reactor-grade Pu still has potential to be con-verted to explosive devices. Therefore, in the present paper,technical efforts to reduce more of the proliferation resist-ance of Pu have been undertaken by denaturing Pu with MAtransmutation.

In the P3 recycling options, the Pu attractiveness de-creases by more than one order of magnitude compared withthat without MA doping due to the 238Pu production by MAtransmutation. In general, the Pu attractiveness of each op-tion of the P3 recycling scheme satisfies both criteria. TheDA option makes the Pu attractiveness fluctuate, dependingon composition of MAs produced in the core. The Pu at-tractiveness slightly increases with the number of cycles forDB, DC, and DD options. However, the DB option has theleast Pu attractiveness in the core as well as in the blanket.

VI. P3 Fuel Cycle System

It was shown above that the P3 recycle scheme optionsenhance the proliferation resistance of Pu fuel due to theconcentration of even-mass-number Pu isotopes, and thisfeature could be enhanced by more addition of MAs.

Since the core-utilized Pu with high contents of 239Pu and238Pu isotopes as a fuel during multicycles replaces Pu fromLWR spent fuel, an affect on the required Pu mass and Puenrichment in the MOX fuel can be expected. Figure 17(a)shows the 239Pu isotopic fraction dependence on the requiredPu mass for loading to obtain the same burnup, normalizedby that of the 0th cycle. The options that utilize only Pu fromthe blanket have lower required Pu mass for loading thanthat of a mixture of Pu from the core and blanket due to ahigh content of the 239Pu isotope. The smallest mass is forthe XA option, which only needs less than 80wt% of therequired Pu mass for loading at the 0th cycle, and the biggestone is for the DC option, 101wt%. In general, the requiredPu mass for loading gradually falls with the number ofcycles owing to increased 239Pu isotopic fraction.

The Pu enrichment in the MOX fuel is defined as the ratioof the amount of required Pu for loading to that of MOX fuel(U-Pu) to obtain the same burnup. As shown in Fig. 17(b),the Pu enrichment in the MOX fuel also gradually decreaseswith the number of cycles. The XA option requires only21wt% Pu enrichment, while the DC option requires at most27wt% Pu in the MOX fuel.

The mass balance of the system that is briefly explained inthis section is especially for the hybrid LWR-FBR (DDoption). The mass balance of the system is calculated basedon basic LWR fuel cycle incorporating 1GWe class PWRloaded with 3.3% 235U fuel, followed by 3 years of coolingtime, which provides Pu and MAs in the first cycle of the P3

recycling scheme. The supply of a small amount of MAs iscontinued in the hybrid LWR-FBR (DD option) to providea constant 5wt% MAs. Table 7 shows example Pu and MAmass balances of DC and DD options. For the DC option(closed-cycle FBR), the amount of MAs at the 10th cycledecreases to 50wt% compared with the 0th cycle of P3

recycling. The required Pu mass for loading DD option islarger than that for the DC option at the 10th cycle.

The discharged MA composition is different from the oneinitially fed to the reactor. For the current approach, the MAdoping fraction of the DD option (5wt%) is taken to beconstant, i.e., the composition exemplified in Table 3. ThisMA doping scheme is illustrated in Fig. 18(a). Figure 18(b)shows the required MA feeding from LWR spent fuel anddischarged MAs, normalized by that of the 0th cycle. Theresults show that the equilibrium can be realized after 10 fullcycles. At the 10th cycle, the required MA feeding is about8wt% of their initial loading in the 0th cycle, but it increasesto 36wt% of that in the 1st cycle mostly due to decreases inthe amount of MAs produced in the core. The required MAfeeding is about 72.4 kg per year per reactor at the 10th

cycle. Considering that, in Japan, the amount of MAs dis-charged is 850 kg/year in 2010,19) about two P3 FBRs withthe addition of 5wt% MAs in the blanket of a 714MWthclass reactor can thus be supplied by domestic spent fuel atthe initial introduction of FBR. In the equilibrium cycle, this

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Fig. 17 (a) The required Pu mass for loading and (b) Pu enrich-ment



is equivalent to the amount for 28 reactors, one reactor onlyneeds 30 kg of MAs from LWR spent fuel in the equilibriumcycle.

VII. Conclusions

The present paper investigated the possibility of denatur-ing Pu with consideration of multicycling of Pu and MAs inFBRs. Two types of Pu and MA multicycle schemes werechosen, the conventional scheme, based on multicycling ofPu only, and the P3 recycling scheme, based on multicyclingof Pu and MAs. The calculation results showed that all fourconsidered options of the P3 recycling scheme with theassumption of 5wt% MAs doped into the blanket signifi-cantly enhanced the proliferation resistance of Pu.

Generally, among MA nuclides, 237Np was shown to playthe largest role in building up Pu isotopes since higher-mass-number Pu isotopes were produced mainly from the succes-sive capture of 238Pu. Nevertheless, 242Cm and 241Am alsogave noticeable contributions. In the blanket, �� decay of238Np dominated the accumulation of 238Pu with a smallportion coming from � decay of 242Cm. In the case of 240Pu

generation, the major contributor was � decay of 244Cm atthe beginning of irradiation and 239Pu dominated at the endof irradiation. Production of 242Pu was mainly due to elec-tron capture of 242Am rather than 241Pu and � decay of246Cm.

Normalized attractiveness of Pu produced in the blanketdecreased by more than one order of magnitude comparedwith that of the REF case by MA transmutation. This func-tion showed that not only 238Pu but also other even-mass-number Pu isotopes would have an important role in thedenaturion of Pu due to noticeably large spontaneous fissionneutron generation. All four options of the P3 recyclingscheme satisfied both criteria, the criterion based onKessler’s proposal, 6% 238Pu content, and the criterion basedon Pellaud’s proposal, 30% 240Pu content with combinationof even-mass-number Pu isotopes. The present study indi-cated that the hybrid LWR-FBR (DD option) had constantPu attractiveness and simultaneously provided an alternativeway of managing MAs in the stockpiles of LWR spent fuel.The closed-MA cycle in FBR (DB option) had the smallestPu attractiveness in the core as well as in the blanket com-pared with other options. In addition, the P3 fuel cycle

Table 7 Example of Pu and MA mass balance

0th cycle of P3 recycling scheme 10th cycle of DC 10th cycle of DD

BOI EOI BOI EOI BOI EOI

Core Blanket Core Blanket Core Blanket Core Blanket Core Blanket Core Blanket

Mass (kg)

Pu 1729 0 1495 345 1672 0 1465 336 1690 0 1480 345

MA 0 906 30 821 0 441 11 398 0 906 11 821

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Fig. 18 (a) Annual MA doping and (b) mass balance of DD option



system consisting of Pu with high contents of 239Pu and238Pu isotopes including MAs was discussed. At the initialstate, two P3 FBRs with the addition of 5wt% MAs into theblanket of a 714MWth class reactor can be operated usingthe annually discharged spent fuel in Japan.

References

1) M. Saito, ‘‘Development of innovative nuclear technology toproduce protected plutonium with high proliferation resistance(P3-Project) (I),’’ Trans. Am. Nucl. Soc., 91 (2004), [CD-ROM].

2) Y. Peryoga, H. Sagara, M. Saito et al., ‘‘Inherent protection ofplutonium by doping minor actinide in thermal neutron spec-tra,’’ J. Nucl. Sci. Technol., 42[5], 442–450 (2005).

3) Y. Meiliza, M. Saito, H. Sagara, ‘‘Protected plutonium breed-ing by transmutation of minor actinides in fast breeder reac-tor,’’ J. Nucl. Sci. Technol., 45[3], 230–237 (2008).

4) J. V. Massei, A. Schneider, ‘‘The role of plutonium-238 innuclear fuel cycles,’’ Nucl. Technol., 56[1], 55–71 (1982).

5) J. C. Mark, ‘‘Explosive properties of reactor-grade plutonium,’’Sci. Global Security, 4, 111–128 (1993).

6) H. Matsunobu, T. Oku, S. Iijima et al., Data Book for Calcu-lation Neutron Yield from (a,n) Reaction and SpontaneousFission, JAERI 1324 (1991).

7) G. Kessler, ‘‘Plutonium denaturing by Pu-238,’’ The First Int.Sci. Technol. Forum on Protected Plutonium Utilization forPeace and Sustainable Prosperity, Tokyo, Japan, Mar. 1–3,2004 (2004).

8) G. Kessler, ‘‘Plutonium denaturing by Pu-238,’’ Nucl. Sci.Eng., 155, 53–73 (2007).

9) B. Pellaud, ‘‘Proliferation aspects of plutonium recycling,’’ J.Nucl. Mater. Manag., 31[1], 30–38 (2002).

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denaturing generated pu in fast breeder reactor blanket

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