Comparative Studies on Plutonium and Minor Actinides Utilization in Small Molten Salt Reactors with Various Powers and Core Sizes

Available online at www.sciencedirect.com ScienceDirect

Energy Procedia 71 ( 2015 ) 62 – 68

The Fourth International Symposium on Innovative Nuclear Energy Systems, INES-4 Comparative studies on plutonium and minor actinides utilization in small molten salt reactors with various powers and core sizes

Abdul Warisa,*, Indarta Kuncoro Ajib, Syeilendra Pramudityaa, Novitriana, Sidik Permanaa, DQG=DNL6X¶XGa

aNuclear Physics and Biophysics Research Division, Department of Physics, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung, Jl. Ganesa 10 Bandung 40132 Indonesia bDepartment of Physics, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung, Jl. Ganesa 10 Bandung 40132 Indonesia

Abstract

Molten salt reactor (MSR) has many advantages such as safety improvement and ability for waste burning. In the present study, the use of plutonium and minor actinides (MA) in small MSRs with various powers and core sizes has been investigated. For the small MSRs with 50 MWth, 100 MWth, 150 MWth, 200 MWth, and 250 MWth of power output, the criticality condition can be achieved if the reactor grade plutonium and MA content in loaded fuel are 7.56%, 6.76%, 6.56%, 6.56%, and 6.56%, respectively. The plutonium and MA utilization in small MSR results in the hardening of neutron spectrum compared to that of the standard 25 MWth miniFUJI MSR with Th-233U fuel. Furthermore, the neutron spectra become harder with the augmenting of Pu and MA contents in loaded fuel as well as the increasing of the output power.

© 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license © 2014 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/3.0/). Selection and peer-review under responsibility of the Tokyo Institute of Technology. Selection and peer-review under responsibility of the Tokyo Institute of Technology

Keywords:MSR; reactor grade plutonium; minor actinides; criticality;neutron spectrum

1. Introduction

Molten salt reactor (MSR) designs have been promoted as one of the six Generation IV nuclear power systems

* Corresponding author. Tel.: +62-22-2500834; fax: +62-22-2506452. E-mail address:[email protected]

1876-6102 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Selection and peer-review under responsibility of the Tokyo Institute of Technology doi: 10.1016/j.egypro.2014.11.855 Abdul Waris et al. / Energy Procedia 71 ( 2015 ) 62 – 68 63 since they have many merits such as amongst others are the safety, ability to be used for hydrogen production due to it can operate at high temperature, and waste burning capability [1-2]. MSR has a small excess reactivity and the refuelling process can be conducted online so that it has no possibility for high power surges, which in sequence improves the safety performance [1]. Nowadays, several countries are developing many conceptual designs of MSR. They are USA, Russian Federation, France, Japan, and China, commonly within the Generation-IV International Forum (GIF) [3]. Generally, the MSR reactor designs consider Th/233U or Th/Pu as main fuel. Currently, from the nuclear proliferation point of views, some experts suggest to stay away from the separation of plutonium and minor actinides (MA). In addition, the plutonium and MA recycling in thorium based reactor is an interesting solution for the nuclear wastes management since it will produced smaller amount of high level nuclear waste (HLW) [4]. Preliminary study on plutonium and minor actinides utilization in small molten salt reactor, namely miniFUJI reactor has been conducted. The miniFUJI reactor has the core height and diameter of 2.0 m and 2.0 m, respectively. In this previous study, 25 MW and 50 MW of the thermal power output of miniFUJI reactor have been investigated. The power density of core are 3.98 W/cc and 7.96 W/cc for the 25 MW and 50 MW thermal power output, correspondingly. Since this reactor works in continuous mode with the liquid fuel, the difference of the power density can be assumed to be adjusted by changing the the flow rate of the fuel salt. By supposing that the thermal efficiency of miniFUJI reactor is about 40%, these two thermal outputs can be regarded as 10 MWe and 20 MWe, respectively [5]. In the present study, the comparative study on plutonium and minor actinides utilization in small molten salt reactors with various power and core sizes will be conducted. Only the reactor grade plutonium is employed in this study.

2. Methodology

Design parameters of studied small molten salt reactors are presented in Table 1. The thermal power outputs are 56.3 MW, 102.1 MW, 150.0 MW, 200.1 MW, and 253.2 MW. The power density of cores for all five reactors are exactly same, that is 3.98 W/cc. The corresponding core diameters are 3.0 m, 3.3 m, 4.0 m, 4.0 m, and 4.5 m, respectively. Moreover, the equivalent core heights are 2.0 m, 3.0 m, 3.0 m, 4.0 m, and 4.0 m, correspondingly. Although, MSR can be operated endlessly, due to the graphite lifetime, the lifetime of reactor of about 20 years has been used in this study. To replace the graphite, the reactors should be shut down when the graphite accomplishes its time bound due to swelling and/or cracking [6].

Table 1 Specification of studied MSRs Physics Parameters Specification Thermal power (MW) 50; 100; 150; 200; 250 Power density (W/cc) 3.98 Core geometry: Height (m) 2.0; 3.0; 3.0; 4.0; 4.0 Diameter (m) 3.0; 3.3; 4.0; 4.0; 4.5 Fuel Types molten salt Composition: LiF, BeF2, ThF4, (PuMA)F4 Inlet temperature (K) 840 Outlet temperature (K) 980 Lifetime (y) 20

It should be noted that the neutronics aspect is the main consideration in the present study. The neutronics cell calculation [7] was performed by using PIJ (collision probability method code) routine of SRAC 2002 code [8], with nuclear data library is JENDL-3.2 [9]. The SRAC code with JENDL-3.2 library consists of 107 energy groups, where 48 thermal groups and 74 fast groups with 15 overlapping groups. The fuel salt composition is presented in Table 2. The total fraction of LiF and BeF2 in the fuel salt is fixed at 87.78%, while the total fraction of ThF4 and PuMAF4 is 12.22%. In the present paper, the fraction of PuMAF4 to the 64 Abdul Waris et al. / Energy Procedia 71 ( 2015 ) 62 – 68

total fraction of ThF4 and PuMAF4 is varied to evaluate the criticality of reactors. The composition of the reactor grade Pu with MA in fuel is also presented in Table 2.

Table 2 Composition of fuel for reactor grade plutonium

LiF (%) BeF2 (%) ThF4 (%) PuMAF4 (%) 71.78 16.00 4.66 ± 7.06 5.16 - 7.56

Table 3 Reactor grade plutonium vector (%) 239 240 241 242 238Pu Pu Pu Pu Pu

1.58 57.76 26.57 8.76 5.33

Table 4 Minor Actinides vector (%) 241 243 242 243 244 245 246 237Np Am Am Cm Cm Cm Cm Cm 42.25 47.57 8.50 0.32 0.01 1.26 0.07 0.01

Tables 3 and 4 presents the isotopic vector compositions of the reactor grade plutonium, and the minor actinides, recpectively. These isotopic compositions have been derived from the spent fuel composition of the 3 GWth of pressurized water reactor (PWR) with 33 GWd/t burnup, 33 tons of annual loaded uranium oxide fuel, and 10 years cooling [10]. Because of the reference [10] offers only two data for curium isotopes, namely 243Cm and 244Cm, the detail isotopic composition of curium isotopes have been taken from the other reference [11], based on the fact that the mass ratio of MA and Pu in the PWR spent fuel is 1: 9 [12].

3. Results and Discussion

Figure 1 shows the effective multiplication factor (k-eff) as a function of burnup for the thermal power output of: (a) 50 MW, and (b) 100 MW, respectively. As shown in these figure, the reactors can achieve their criticality with the Pu & MA composition in the fuel of 7.56% or more for MSR with 50 MWth of power and at least 6.76% for MSR with 100MWth of power, correspondingly. The maximum obtained burnup for the 20 years of lifetime is 16.7 GWd/ton and 17.7 GWd/ton, respectively. One of the good points of MSR is a capability to incinerate the nuclear waste. This evidence is obviously revealed in the figure. The effective multiplication factor as a function of burnup for 150 MWth and 200 MWth of power are ilustrated in Figure 2a and 2b, in that order. As can be seen in these figures, the reactors can realize their criticality with the Pu & MA composition in the fuel of 6.56% or more for both MSR with 150MWth and 100MWth of power output. The maximum obtained burnup is 17.8 GWd/ton for 20 years of lifetime. Figure 3a demostrates the effective multiplication factor as a function of burnup for 250MWth. This figure reveals that the reactor can accomplish its criticality with the Pu & MA composition in the fuel of 6.56% or more. The maximum obtained burnup is 17.8 GWd/ton for 20 years lifetime. Moreover, Figure 3a demostrates the comparison of the effective multiplication factor as a function of burnup for all evaluated reactors with 7.56% of Pu & MA in loaded fuel. The higher output power reveals the larger effective multiplication factor for the same PU & MA composition in fuel. The maximum obtained burnup for the 20 years of lifetime slightly increases with the augmenting of the power output. Abdul Waris et al. / Energy Procedia 71 ( 2015 ) 62 – 68 65

1.15 1.2

PuMA 5.16% PuMA 5.16% PuMA 5.56% PuMA 5.56% PuMA 5.96% PuMA 5.96% 1.15 1.1 PuMA 6.56% PuMA 6.56% PuMA 6.76% PuMA 6.76% PuMA 7.16% PuMA 7.16% PuMA 7.56% PuMA 7.56% 1.1 1.05

1.05

1 Effective multiplication factor factor (k-eff) multiplication Effective Effective multiplication factor factor (k-eff) multiplication Effective 0.95 0.95

0.9 0.9 4 4 4 4 4 2000 4000 6000 8000 1 10 1.2 10 1.4 10 1.6 10 1.8 10 2000 4000 6000 8000 1 104 1.2 104 1.4 104 1.6 104 1.8 104 Burnup (MWd/ton) Burnup (MWd/ton)

(a) (b)

Figure 1 Effective multiplication factor for MSR with power of: (a). 50 MWth, (b). 100 MWth

1.2 1.2

PuMA 5.16% PuMA 5.16% PuMA 5.56% PuMA 5.56% PuMA 5.96% 1.15 PuMA 5.96% PuMA 6.56% 1.15 PuMA 6.56% PuMA 6.76% PuMA 6.76% PuMA 7.16% PuMA 7.16% PuMA 7.56% PuMA 7.56% 1.1

1.1

1.05

1.05 1 Effective multiplication factor factor (k-eff) multiplication Effective Effective multiplication factor factor (k-eff) multiplication Effective 1 0.95

0.9 0.95 4 4 4 4 4 2000 4000 6000 8000 1 10 1.2 10 1.4 10 1.6 10 1.8 10 2000 4000 6000 8000 1 104 1.2 104 1.4 104 1.6 104 1.8 104 Burnup (MWd/ton) Burnup (MWd/ton)

(a) (b)

Figure 2 Effective multiplication factor for MSR with power of: (a). 150 MWth, (b). 200 MWth

The neutron spectra of MSR for 50 MWth and 100 MWth of power output are presented in Figures 4a and 4b, respectively. The neutron spectra become harder with the increasing of Pu and MA contents in loaded fuel. 66 Abdul Waris et al. / Energy Procedia 71 ( 2015 ) 62 – 68

1.2 1.2

PuMA 5.16% 50MWt PuMA 7.56% PuMA 5.56% 100MWt PuMA 7.56% PuMA 5.96% 150MWt PuMA 7.56% 1.15 PuMA 6.56% 200MWt PuMA 7.56% PuMA 6.76% 250MWt PuMA 7.56% 1.15 PuMA 7.16% PuMA 7.56%

1.1

1.05 Effective multiplication factor factor (k-eff) multiplication Effective Effective multiplication factor factor (k-eff) multiplication Effective 1.05 1

0.95 1 2000 4000 6000 8000 1 104 1.2 104 1.4 104 1.6 104 1.8 104 2000 4000 6000 8000 1 104 1.2 104 1.4 104 1.6 104 1.8 104 Burnup (MWd/ton) Burnup (MWd/ton)

(a) (b)

Fig ure 3 Effective multiplication factor for MSR with power of: (a). 250 MWth, (b). Comparison for PuMA 7.56%

0.07 0.07

PuMA 5.16% PuMA 5.16% 0.06 PuMA 5.56% 0.06 PuMA 5.56% PuMA 5.96% PuMA 5.96% PuMA 6.56% PuMA 6.56% PuMA 6.76% PuMA 6.76% 0.05 PuMA 7.16% 0.05 PuMA 7.16% PuMA 7.56% PuMA 7.56%

0.04 0.04

0.03 0.03 Relative flux per unit lethargy per unit flux Relative Relative flux per unit lethargy per unit flux Relative 0.02 0.02

0.01 0.01

0 0 0.01 1 100 104 106 0.01 1 100 104 106 Energy (eV) Energy (eV)

(a) (b)

Figure 4 Neutron spectra for MSR with power of: (a). 50 MWth, (b). 100 MWth

The similar trend of the neutron spectra also happens for MSR with 150 MWth, 200 MWth, and 250 MWth of power outputs, as shown in Figure 5a, 5b, and 6a. These facts may due to the higher total fissile plutonium content as well as higher concentration of absorber (such as 238Pu and 240Pu) in the reactor grade plutonium.These facts have also been reported in the references regarding the plutonium and/or minor actinides utilization in thermal reactor which result in the hardening of the neutron spectrum [13-15]. Abdul Waris et al. / Energy Procedia 71 ( 2015 ) 62 – 68 67

0.07 0.07

PuMA 5.16% PuMA 5.16% 0.06 PuMA 5.56% 0.06 PuMA 5.56% PuMA 5.96% PuMA 5.96% PuMA 6.56% PuMA 6.56% PuMA 6.76% PuMA 6.76% 0.05 0.05 PuMA 7.16% PuMA 7.16% PuMA 7.56% PuMA 7.56%

0.04 0.04

0.03 0.03 Relative flux per unit lethargy per unit flux Relative Relative flux per unit lethargy per unit flux Relative 0.02 0.02

0.01 0.01

0 0 0.01 1 100 104 106 0.01 1 100 104 106 Energy (eV) Energy (eV)

(a) (b)

Figure 5 Neutron spectra for MSR with power of: (a). 150 MWth, (b). 200 MWth

0.07 0.07

PuMA 5.16% 0.06 PuMA 5.56% 50MWt PuMA 7.56% 0.06 PuMA 5.96% 100MWt PuMA 7.56% PuMA 6.56% 150MWt PuMA 7.56% PuMA 6.76% 200MWt PuMA 7.56% 0.05 PuMA 7.16% 0.05 250MWt PuMA 7.56% PuMA 7.56% Th-U 25MWt U-233 1.16%

0.04 0.04

0.03 0.03 Relative flux per unit lethargy per unit flux Relative

0.02 lethargy per unit flux Relative 0.02

0.01 0.01

0 0 4 6 0.01 1 100 10 10 0.01 1 100 104 106 Energy (eV) Energy (eV)

(a) (b)

Figure 6 (a) Neutron spectra for MSR with power of 250 MWth, (b) Comparison for PuMA 7.56% and Th-233U fueled MSR

Figure 6b demonstrates the neutron spectra comparison of the all evaluated reactors with the plutonium and minor actinides content in fuel is 7.56%. In addition to these, for the perspective, the neutron spectrum of the 25 MWth Th - 233U fueled miniFUJI MSR with 1.16% of 233U (instead of PuMA) also presented in Figure 6b. Clearly from this figure, Pu and MA utilization in MSR results in the hardening of neutron spectrum compared to that of the 68 Abdul Waris et al. / Energy Procedia 71 ( 2015 ) 62 – 68

25 MWth miniFUJI MSR with Th-233U fuel. Moreover, the neutron spectra become slightly harder with the boosting of the output power.

4. Conclusions

The study on plutonium and minor actinides utilization in small molten salt reactors with various thermal power outputs and core sizes has been carried out. For the reactor with 50 MWth, 100 MWth, 150 MWth, 200 MWth, and 250 MWth of power output, the criticality condition can be realized for 7.56%, 6.76%, 6.56%, 6.56%, and 6.56% of reactor grade plutonium and MA content in loaded fuel, correspondingly. The utilization of plutonium and MA in small MSR gives the hardening of neutron spectrum compared to that of the standard 25 MWth miniFUJI MSR with Th-233U fuel. Moreover, the neutron spectra become harder with the raising of plutonium and MA contents in loaded fuel as well as the increasing of the output power.

Acknowledgements

This study is supported by Institut Teknologi Bandung (ITB) research grant 2013 and Indonesian Ministry of Education and Culture, Directorate General of Higher Education (DGHE) Competitive Research Grant 2013.

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