Energy Conversion and Management 72 (2013) 27–32

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Energy Conversion and Management

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Preliminary study on plutonium and minor actinides utilization inthorims-nes minifuji reactor

0196-8904/$ - see front matter � 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.enconman.2013.03.005

⇑ Corresponding author. Tel.: +62 222500834; fax: +62 222506452.E-mail address: awaris@fi.itb.ac.id (A. Waris).

Abdul Waris ⇑, Very Richardina, Indarta Kuncoro Aji, Sidik Permana, Zaki Su’udNuclear Physics & Biophysics Research Division, Department of Physics, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung, Indonesia

a r t i c l e i n f o a b s t r a c t

Article history:Available online 11 April 2013

Keywords:MSRMiniFUJIReactor grade PuWeapon grade PuMinor actinidesCriticality

Molten salt reactor (MSR) design has been chosen as one of the Generation IV nuclear energy systems,since it has many merits such as proliferation resistance, resource sustainability, and safety improve-ment. Recently, a concept which called as thorium molten salt nuclear energy synergetic (THORIMS-NES) was being proposed for the safe and sustainable nuclear industry. THORIMS-NES miniFUJI reactoris a small power MSR which originally considers Th/233U or Th/Pu as main fuel. In this study, the utiliza-tion of Pu and minor actinides (MA) in 25 MWth and 50 MWth miniFUJI reactors has been evaluated. Thereactor grade plutonium and weapon grade plutonium are employed in the present study. The criticalityfor 25 MWth of miniFUJI can be accomplished by loading 8.76% of reactor grade Pu & MA (RGPuMA), and3.96% of weapon grade Pu & MA (WGPuMA) in fuel, respectively. While, for that of 50 MWth, the reactorcan attain its criticality with 9.16% and 4.36% of RGPuMA and WGPuMA, correspondingly. The neutronspectra become harder with the lower grade of fissile plutonium vector as well as the increasing of Puand MA contents in loaded fuel salt.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

The Oak Ridge National Laboratory (ORNL) of USA has devel-oped molten salt reactors (MSRs) in 1960s [1]. At that time, thereare two types of MSR were developed in parallel, namely a moltensalt reactor experiment (MSRE) and a molten salt breeder reactor(MSBR). Recently, several countries such as: US, Russia, France,Korea, Japan, and China are developing many conceptual designsof MSR.

Since it has many good points such as safety improvement, pro-liferation resistance, resource sustainability, ability to be used forhydrogen production due to it can operate at high temperature(>650 �C), and waste burning [2,3], MSR design has been selectedas one of the six Generation IV nuclear power systems. MSR hasno chance for high power surges due to online refueling and smallexcess reactivity, which in turn enhances the safety aspect of MSR[2]. Natural Thorium (232Th) can undergo the radiative capturereaction to generate the artificial fissile nuclide 233U after succes-sive beta decays, as shown in the following process.

nþ 232Th! 233Th !22 min

233Paþ b!27d

233U þ b

Thorium–233U fuel cycle will produce 232U, a 2.6 MeV gammaemmiter. These later two aspects provide the resource sustainabil-ity and the proliferation resistance advantages of MSR [2].

Nowadays, a thorium molten salt nuclear energy synergetic(THORIMS-NES) concept was being proposed for the safe and sus-tainable nuclear industry [2]. The THORIMS-NES concept consistsof three stages. The first stage is the building of the miniFUJI reac-tor, a small 10 MWe power reactor that may be developed during7 years. The construction of the 100–300 MWe FUJI reactor, a tho-rium molten salt reactor planned to go online in 12–14 years is thesecond stage. The last stage is the setting up of regional breedingand chemical processing centers with production of 233U by tho-rium spallation in AMSB (accelerator molten salt breeder) [2].

The original miniFUJI reactor design considers Th/233U or Th/Puas main fuel. In agreement with the recently suggestion to avoidthe separation of Pu and minor actinides (MA), in the presentstudy, the utilization of Pu and MA in miniFUJI reactor will be eval-uated. The reactor grade plutonium and the weapon grade pluto-nium are employed in this study. In addition, two values of thethermal power output of miniFUJI reactor will be investigated,namely: 25 MWth and 50 MWth, respectively. These two thermaloutputs may be considered as 10 MWe and 20 MWe, correspond-ingly, by assuming that the thermal efficiency of miniFUJI reactoris about 40%.

2. Methodology

Design parameters of miniFUJI reactor is presented in Table 1.Active core consists of several hexagonal assemblies with thereflector is made of graphite. The boron carbide is used both for

Table 1Specification of miniFUJI.

Physics parameters Specification

Thermal power 25 and 50 MWt

Core geometryHeight 2.00 mDiameter 2.00 m

FuelTypes Molten saltComposition: LiF, BeF2, ThF4, (PuMA)F3

Inlet temperature 840 KOutlet temperature 980 KLifetime 20 years

Table 2Composition of fuel for reactor grade plutonium.

LiF (%) BeF2 (%) ThF4 (%) PuMAF3 (%)

71.78 16.00 3.06–6.26 5.96–9.16

Table 3Composition of fuel for weapon grade plutonium.

LiF (%) BeF2 (%) ThF4 (%) PuMAF3 (%)

71.78 16.00 7.86–11.06 1.16–4.36

Table 4Reactor grade plutonium vector (%).

238Pu 239Pu 240Pu 241Pu 242Pu

1.58 57.76 26.57 8.76 5.33

Table 5Minor actinides vector (%).

237Np 241Am 243Am 242Cm 243Cm 244Cm 245Cm 246Cm

42.25 47.57 8.50 0.32 0.01 1.26 0.07 0.01

Table 6Weapon grade plutonium vector (%).

238Pu 239Pu 240Pu 241Pu 242Pu 241Am

0.01 93.80 5.80 0.13 0.02 0.22

28 A. Waris et al. / Energy Conversion and Management 72 (2013) 27–32

neutron absorber and reactor shielding [2]. The core height anddiameter are 2.0 m and 2.0 m, respectively. In this preliminarystudy, for the thermal power of 25 MW and 50 MW the exactlysame reactor size and geometry have been chosen. The power den-sity of core are 3.98 W/cc and 7.96 W/cc for 25 MW and 50 MWthermal power output, respectively. Since this reactor operates incontinuous mode with the liquid fuel, the difference of the powerdensity can be assumed to be adjusted by changing the flow rate ofthe fuel salt. The detail discussion regarding the flow rate of MSRcan be found in Ref. [4]. Even though, MSR can be operated contin-uously, the lifetime of reactor of about 20 years has been employedin this proxy study, due to the graphite lifetime. Fig. 1 shows therelation between power, lifetime of graphite and core radius ofMSR, which has been taken from Refs. [5,6]. This figure is mostlymatch with the design parameters of 25 MWth miniFUJI. However,for 50 MWth reactor, Fig. 1 looks misleading due to the previousassumption on the reactor size and the power density. To replacethe graphite, the miniFUJI reactor should be shut down when thegraphite achieves its time limit due to cracking and/or swelling [6].

It should be noted that the neutronics aspect is the main consid-eration in the present study. The neutronics cell calculation [4] wasperformed by using PIJ (collision probability method code) routineof SRAC 2002 code [7], with nuclear data library is JENDL-3.2 [8].The SRAC code with JENDL-3.2 library consists of 107 energygroups, where 48 thermal groups and 74 fast groups with 15 over-lapping groups.

The composition of fuel salt is tabulated in Tables 2 and 3. Thetotal fraction of LiF and BeF2 in the fuel salt is fixed at 87.78%, whilethe total fraction of ThF4 and PuMAF3 is 12.22%. In the present pa-per, the fraction of PuMAF3 to the total fraction of ThF4 and PuMAF3

is varied to evaluate the criticality of miniFUJI reactor. The compo-sition of fuel for the reactor grade Pu with MA, and the weapongrade Pu with MA are also presented in Tables 2 and 3,correspondingly.

Fig. 1. Relation between power, lifetime of graphite and core radius of MSR [5,6].

The isotopic vector compositions of the reactor grade pluto-nium, and the minor actinides are listed in the following Tables 4and 5, respectively. These isotopic compositions have been takenfrom the spent fuel composition of the 3 GWth of pressurizedwater reactor (PWR) with 33 tons of annual loaded uranium oxidefuel, 33 GWd/t burnup, and 10 years cooling [9]. Since the Ref. [9]offers only two data for curium isotopes, namely 243Cm and 244Cm,the detail isotopic composition of Curium isotopes have been de-rived from the other Ref. [10], based on the fact that the mass ratioof MA and Pu in the PWR spent fuel is 1:9 [11].

In case of the reactor grade plutonium, the idea for not separat-ing Pu and MA can be accomplished practically. However, since theweapon grade plutonium is separated from the spent fuel interimstorage site, this scenario can be adopted only theoretically. Theisotopic vector compositions of the weapon grade plutonium ispresented in Table 6 [12]. As can be seen from this table, 241Amis also included in WGPu. The isotopic composition of MA in theweapon grade Pu with MA fuel is exactly same as in Table 5, so thatthe total fraction of isotopic composition of 241Am for this case isslightly different compared to the that of the reactor grade Pu withMA case.

3. Results and discussion

Fig. 2 shows the effective multiplication factor (k-eff) as a func-tion of burnup for 25 MWth of miniFUJI, where (a) for the reactorgrade Pu with MA (RGPuMA), and (b) for the weapon grade Pu withMA (WGPuMA), respectively. As can be seen from the figures, thecriticality condition of miniFUJI reactor can be obtained for 8.76%of RGPuMA, and 3.96% of WGPuMA, correspondingly. This factmeans that 25 MWth of miniFUJI reactor can be loaded with atleast 8.76% of RGPuMA, and 3.96% of WGPuMA in loaded fuel.

0.85

0.9

0.95

1

1.05

1.1

1.15

1.2

2000 4000 6000 8000 1 104 1.2 104 1.4 104 1.6 104 1.8 104

PuMA 5.96%PuMA 6.36%PuMA 6.76%PuMA 7.16%PuMA 7.56%PuMA 7.96%PuMA 8.36%PuMA 8.76%PuMA 9.16%

Effe

ctiv

e m

ultip

licat

ion

fact

or (k

-eff)

Burnup (MWd/ton)

0.8

0.85

0.9

0.95

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1.05

1.1

2000 4000 6000 8000 1 104 1.2 104 1.4 104 1.6 104 1.8 104

PuMA 1.16%PuMA 1.56%PuMA 1.96%PuMA 2.36%PuMA 2.76%PuMA 3.16%PuMA 3.56%PuMA 3.96%PuMA 4.36%

Effe

ctiv

e m

ultip

licat

ion

fact

or (k

-eff)

Burnup (MWd/ton)

(a) (b) Fig. 2. K-eff for 25 MWth miniFUJI MSR, (a) for RGPuMA, (b) for WGPuMA.

0.85

0.9

0.95

1

1.05

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1.15

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4000 8000 1.2 104 1.6 104 2 104 2.4 104 2.8 104 3.2 104 3.6 104

PuMA 5.96%PuMA 6.36%PuMA 6.76%PuMA 7.16%PuMA 7.56%PuMA 7.96%PuMA 8.36%PuMA 8.76%PuMA 9.16%

Effe

ctiv

e m

ultip

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fact

or (k

-eff)

Burnup (MWd/ton)

0.8

0.85

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1.05

1.1

4000 8000 1.2 104 1.6 104 2 104 2.4 104 2.8 104 3.2 104 3.6 104

PuMA 1.16%PuMA 1.56%PuMA 1.96%PuMA 2.36%PuMA 2.76%PuMA 3.16%PuMA 3.56%PuMA 3.96%PuMA 4.36%

Effe

ctiv

e m

ultip

licat

ion

fact

or (k

-eff)

Burnup (MWd/ton)

(a) (b) Fig. 3. K-eff for 50 MWth miniFUJI MSR, (a) for RGPuMA, (b) for WGPuMA.

A. Waris et al. / Energy Conversion and Management 72 (2013) 27–32 29

The lifetime of the core that is 20 years corresponds to the maxi-mum burnup of about 18.3 GWd/ton.

The effective multiplication factor as a function of burnup for50 MWth of miniFUJI is presented in Fig. 3, where (a) for the reac-tor grade Pu with MA and (b) for the weapon grade Pu with MA, inthat order. As shown in these figures, the reactor can achieve itscriticality with the Pu & MA composition in the fuel of 9.16% ormore and at least 4.36% for RGPuMA and WGPuMA, correspond-ingly. The maximum obtained burnup for 50 MWth of miniFUJI is36.7 GWd/ton, about twice of that of 25 MWth of miniFUJI. Thedoubling of maximum burnup value for 50 MWth compared tothat of 25 MWth is due to the twofold of the power density. De-spite the safety is not to be considered in this preliminary study,Figs. 2 and 3 also exhibit that WGPuMA case reveals the lowerreactivity swing compared to that of RGPuMA case.

The neutron spectra for 25 MWth of miniFUJI is presented inFig. 4. SRAC 2002 code can generate several kinds of neutron fluxes.However, the neutron spectra that used in this paper are the neu-

tron fluxes multiplied by the volume of the i-radial region (R-re-gion) and the lethargy width of the energy group-g. Here, tworadial regions, one for the fuel salt and the other for the graphitemoderator has been utilized. As mentioned before, 107 of energygroups has been employed in this study. This is the reason forusing the ‘‘relative flux per unit lethargy’’ terminology in the pres-ent paper. The neutron spectra become harder for the reactor gradeplutonium compared to that of the weapon grade plutonium.Moreover, the neutron spectra become harder with the increasingof Pu and MA contents in loaded fuel. The similar trend of the neu-tron spectra also happens for 50 MWth of miniFUJI, as shown inFig. 5. These facts may due to the higher total fissile plutoniumcontent as well as higher concentration of absorber (such as238Pu and 240Pu) in the reactor grade plutonium cases comparedto that of the weapon grade cases. These evidences have also beenreported in the references regarding the plutonium and/or minoractinides utilization in thermal reactor that result in the hardeningof the neutron spectrum [13–16]. On top of that, the neutron spec-

0

0.01

0.02

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0.01 1 100 104 106

PuMA 5.96%PuMA 6.36%PuMA 6.76%PuMA 7.16%PuMA 7.56%PuMA 7.96%PuMA 8.36%PuMA 8.76%PuMA 9.16%

Rel

ativ

e flu

x pe

r uni

t let

harg

y

Energy (eV)

0

0.01

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0.01 1 100 104 106

PuMA 1.16%PuMA 1.56%PuMA 1.96%PuMA 2.36%PuMA 2.76%PuMA 3.16%PuMA 3.56%PuMA 3.96%PuMA 4.36%

Rel

ativ

e flu

x pe

r uni

t let

harg

y

Energy (eV)

(a) (b) Fig. 4. Neutron spectra for 25 MWth miniFUJI MSR, (a) for RGPuMA, (b) for WGPuMA.

0

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PuMA 5.96%PuMA 6.36%PuMA 6.76%PuMA 7.16%PuMA 7.56%PuMA 7.96%PuMA 8.36%PuMA 8.76%PuMA 9.16%

Rel

ativ

e flu

x pe

r uni

t let

harg

y

Energy (eV)

0

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PuMA 1.16%PuMA 1.56%PuMA 1.96%PuMA 2.36%PuMA 2.76%PuMA 3.16%PuMA 3.56%PuMA 3.96%PuMA 4.36%

Rel

ativ

e flu

x pe

r uni

t let

harg

y

Energy (eV)

(a) (b)Fig. 5. Neutron spectra for 50 MWth miniFUJI MSR, (a) for RGPuMA, (b) for WGPuMA.

0

0.01

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0.01 1 100 104 106

RGPuMA 25MW 8.76%RGPuMA 50MW 9.16%WGPuMA 25MW 3.96%WGPuMA 50MW 4.36%Th-U 25MW 1.16%

Rel

ativ

e flu

x pe

r uni

t let

harg

y

Energy (eV)

Fig. 6. Comparison of neutron spectra for criticality of miniFUJI MSR.

30 A. Waris et al. / Energy Conversion and Management 72 (2013) 27–32

tra of the 25 MWth and 50 MWth of miniFUJI reactors with RGPu-MA are similar. The last facts also occurs for the 25 MWth and50 MWth of miniFUJI reactors with WGPuMA. Fig. 6 shows theneutron spectra comparison of the four evaluated cases of miniFUJIMSR when the criticality condition are achieved. The four casesmean: the 25 MWth of miniFUJI with RGPuMA, 50 MWth of mini-FUJI with RGPuMA, 25 MWth of miniFUJI with WGPuMA, and50 MWth of miniFUJI with RGPuMA, respectively. In addition tothese four cases, the neutron spectrum of the 25 MWth Th–233Ufueled mini FUJI MSR with 1.16% of 233U (instead of PuMA) alsopresented in Fig. 6. The added spectrum demonstrates the proofthat the original thermal neutron (graphite moderated) MSR hasa soft neutron spectrum.

One of the issues regarding the MSR is a capability to incineratethe nuclear waste. Fig. 7 shows the number densities of Pu and MAin the reactor core during the lifetime for the 25 MWth of miniFUJIreactor with (a) 9.16% of RGPuMA and (b) 4.36% of WGPuMA,respectively. Almost no significant change of number density ofPu and MA can be observed from this figure. For RGPuMA casethere is small decrement of number density for 241Pu and 244Cm,

1018

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1021

1022

0 1000 2000 3000 4000 5000 6000 7000 8000

Th-232

Np-237

Pu-238

Pu-239

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#/cc

)

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1017

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Th-232Np-237Pu-238Pu-239

Pu-240Pu-241Pu-242Am-241

Am-243Cm-244Cm-245

Nuc

lide

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ty in

reac

tor (

#/cc

)

Time (day)

(a) (b) Fig. 7. Number density of Pu and MA for 25 MWth, (a) for RGPuMA, (b) for WGPuMA.

A. Waris et al. / Energy Conversion and Management 72 (2013) 27–32 31

as well as a minor increasing of number density for 241Am and245Cm. The trend for WGPuMA case is more interesting. The num-ber density of several Pu isotopes, namely: 238Pu, 241Pu, and 242Puincreases drastically. Therefore, these evidences may in contradic-tory with the above issue. However, from the spent fuel stockpile,especially plutonium stockpile’s point of view, the data in Figs. 2and 3 may become facts that the MSR can consume or burn muchmore nuclear waste. For instance, at least 8.76% of RGPuMA is re-quired to achieve the criticality of 25 MWth of miniFUJI MSR, com-pared to only 1.16% of 233U in Thorium–233U fuel of 25 MWth ofminiFUJI MSR.

Fig. 8 shows the change of the number density of 233U in thecore during the lifetime for the 25 MWth of miniFUJI reactor with9.16% of RGPuMA and 4.36% of WGPuMA. The increasing of thenumber density of the produced 233U for WGPuMA is much largercompared to that of RGPuMA. This data may become the reason forthe big difference of the required isotopic fuel composition ofRGPuMA compared to that of WGPuMA for criticality of miniFUJIreactor.

0

5 1018

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U-233 RG-25MWU-233 WG-25MW

Nuc

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e (#

/cc)

Lifetime (day)

Fig. 8. Number density of 233U in 25 MWt miniFUJI.

4. Conclusions

Pu and MA utilization in 25 MWth and 50 MWth of miniFUJIMSRs have been studied. For 25 MWth of miniFUJI, the criticalitycondition can be realized for 8.76% of RGPuMA, and 3.96% ofWGPuMA, correspondingly. While, for that of 50 MWth, the reactorcan reach its criticality with 9.16% and 4.36% for RGPuMA and forWGPuMA, respectively. The neutron spectra become harder withthe increasing of Pu and MA contents in loaded fuel as well asthe lower grade of fissile plutonium vector. The production rateof 233U in the reactor during the lifetime for the WGPuMA fuel ismuch larger compared to that of the RGPuMA fuel.

Acknowledgements

This study is supported by Institut Teknologi Bandung (ITB) Re-search Grant 2012 and Indonesian Ministry of Education and Cul-ture, DGHE Competitive Research Grant 2012.

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