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  • Hindawi Publishing CorporationScience and Technology of Nuclear InstallationsVolume 2013, Article ID 674638, 5 pageshttp://dx.doi.org/10.1155/2013/674638

    Research ArticleTransmutation Strategy Using Thorium-Reprocessed FuelADS for Future Reactors in Vietnam

    Thanh Mai Vu and Takanori Kitada

    Division of Sustainable Energy and Environmental Engineering, Graduate School of Engineering, Osaka University,2-1 Yamadaoka, Suita-shi, Osaka 565-0871, Japan

    Correspondence should be addressed toThanh Mai Vu; m-vu@ne.see.eng.osaka-u.ac.jp

    Received 30 May 2013; Revised 18 July 2013; Accepted 18 July 2013

    Academic Editor: Arkady Serikov

    Copyright 2013 T. M. Vu and T. Kitada. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.

    Nuclear power is believed to be a key to the energy security for a developing country like Vietnam where the power demandingincreases rapidly every year. Nevertheless, spent nuclear fuel from nuclear power plants is the source of radiotoxic and proliferationrisk. A conceptual design ofADSutilizing thorium fuel as a based fuel and reprocessed fuel as a seed for nuclear waste transmutationand energy production is proposed as one of the clean, safe, and economical solutions for the problem. In the design, 96seed assemblies and 84 blanket assemblies were inserted into the core to make a heterogeneous subcritical core configuration.Introducing thorium fuel into the core offers an effective way to transmute plutonium and minor actinide (MA) and gain energyfrom this process. Transmutation rate as a function of burnup is estimated usingMCNPX 2.7.0 code. Results show that by using theseed-blanket designed ADS, at 40GWd/t burnup, 192 kg of plutonium and 156 kg of MA can be eliminated. Equivalently, 1 GWthADS can be able to transmute the transuranic (TRU) waste from 2GWth LWRs. 14 units of ADS would be required to eliminateTRUs from the future reactors to be constructed in Vietnam.

    1. Introduction

    Demand for power is rising as Vietnams economy expands.Electricity demand growth has been 14% per annum and isexpected to be 15% per annum by 2015 and then slowing by2020, though other figures suggest 10% per annum. In orderto improve the energy security, the government has approvedthe nuclear power development plan in Vietnam. Due to theplan, 2000MWe nuclear power plant at Phuoc Dinh in theNinh Thuan province should be online by 2020. A further2000MWe was planned at Vinh Hai nearby, followed by afurther 6000MWe by 2030. A high demand scenario wouldgive 8000MWe in 2025 and 15,000MWe (10% of total) in2030 at up to eight sites in five provinces [1]. As demonstratedin detail later, from 2025 with 8000MWe, about 170 tons ofspent fuels (of which 3 tons is TRUs and long-life fissionproducts (LLFFs)) is produced every year. It will extend to120 tons of TRUs and LLFFs after 40 years of operation. Ingeneral, the spent nuclear fuel (SNF) is cooled in the waterpools where the short half-life isotopes decay to safer leveland decay heat drops; then, it can be stored at dry facilities.

    Thus, reducing the amount of waste and minimizing theamount of radiation release to the environment are always anissue. With inherent safety feature and waste transmutationpotential and capability of converting fertile fuel to fissile fuelwithout exposing the radiotoxic material to the environment[2], accelerator-driven system (ADS) which helps to burnTRU waste from spent fuel and produce energy at the sametime can be a good candidate for the next few decadestechnology in Vietnam.

    Thorium with its abundance is gaining a considerableattention as the fuel candidate to replace uranium fuel.When choosing the based fuel for the system, taking intoaccount the ability of eliminating large amount of TRU wastesince the production of these elements in thorium cycle issignificantly reduced compared with the uranium cycle andenergy gaining from this process, thorium is an appropriatecandidate to be the based fuel in the ADS system. To start thefission reaction, reprocessed fuel (Pu +MA) is loaded into thecore as seed and thus transmuted.

    In this paper, conceptual designs of ADS for transuranicwaste transmutation and power generation utilizing thorium

  • 2 Science and Technology of Nuclear Installations

    140700140 1407070 140 700

    Target

    Fuel pin

    Shielding

    Reflector

    Thorium fuel assembly

    Reprocessed

    fuel assembly

    150

    0

    150Target

    Figure 1: Vertical and horizontal sectional views of the seed-blanket ADS design (scale is given in cm).

    blanket and reprocessed fuel as a seed are proposed. TheADS configuration and the calculation code are describedin Section 2. Calculation results and the elimination strategyfor TRU are discussed in Section 3. Finally, summarizing theresults, conclusions are remarked in Section 4.

    2. Calculations

    2.1. Seed and Blanket Thorium-Reprocessed Fuel ADS. Themodel of ADS used in this simulation was conducted fromthe typical fast neutron spectrum, lead-bismuth accelerator-driven transmutation system inTrellue research [3].Neutronsare produced from the spallation reaction by bombarding1GeV proton beam into the LBE cylindrical target. In thesubcritical core, the fuel rods are introduced in the oxideform and contained in hexagonal assemblies. 180 fuel assem-blies are loaded into the cylindrical core of 140 cm radius.However, instead of loading the whole core with reprocessedfuel as in original design, in this study, 96 seed assembliesof reprocessed fuel and 84 blanket assemblies of thoriumfuel were inserted into individual regions.This heterogeneousapproach will help to simplify the fuel assembly fabrica-tion and in-core fuel management. By spatially separatingthe fertile and fissile materials, ideally, there would be nocompetition for neutron absorption between them; thus, thecapture rate in fertile fuel would be optimized, and 233Uconversion ratio in the blanket could be enhanced. Thebreeding 233U from thoriumwill compensate the burnt TRUsin the reprocessed fuel, thus reducing the reactivity swing.The thorium blanket assemblies are placed at the periphery ofthe core in order to improve the neutron economy. Sodium isemployed as coolant of the system. Figure 1 shows the verticaland horizontal sectional views of the seed-blanket ADS.

    In the calculations, Pu and MA are recovered from thereprocessing scheme assumed in Tsujimoto research [4].

    Table 1: Fuel composition of thorium and reprocessed fuel.

    Nuclides Number density (atoms/b-cm)Reprocessed fuel

    235U 4.177 07236U 9.462 08237Np 1.332 03238Pu 1.605 04239Pu 2.587 03240Pu 1.149 03241Pu 5.154 04242Pu 3.306 04241Am 9.092 04242Am 1.594 06243Am 3.607 04243Cm 8.384 07244Cm 1.037 04245Cm 1.224 05246Cm 1.311 0616O 1.490 2

    Thorium fuel232Th 2.1641 2Gd 9.2607 816O 4.3282 2

    From that, the spent PWR fuel of 45GWd/t burnup wasreprocessed after 7 years cooling, and MA and Pu wererecovered using PUREX and MA is enriched for enhancedMA burning. The initial content of thorium and reprocessedfuel is determined in order to achieve the initial eff of 0.959.The isotopic composition of thorium and reprocessed fuel isshown in Table 1.

  • Science and Technology of Nuclear Installations 3

    Table 2: Performance characteristics of the ADS.

    Core diameter (cm) 280Core length (cm) 300Fuel pin radius (cm) 0.315Pin pitch (cm) 0.89Cladding thickness (cm) 0.031Thorium assemblies/reprocessed fuel assemblies 84/96Thorium weight/reprocessed fuel weight 2.45/1LBE target radius (cm) 15.0Accelerator current (mA) 1330Spallation yield (n/s) 30Power output (MWth) 840Cycle length (days) 430Radial power peaking factor at BOC 2.50Axial power peaking factor at BOC 1.21Radial power peaking factor at EOC 2.09Axial power peaking factor at EOC 1.20Void coefficient at BOC (102 k/k) 7.53Burnup (GWd/MT) 40eff

    BOC 0.9591 0.0012EOC 0.8983 0.0012

    Burnup reactivity swing 0.0634

    2.2. Code. MCNPX is an extension of MCNP-4B andLAHETwith the improvement of physics simulationmodels;extension of neutron, proton, and photonuclear libraries to150MeV; and the formulation of additional variance-reduction and data-analysis techniques [5]. MCNPX withENDF/B-VII.0 library [6] was used for evaluation in thisproblem. Burnup capability is performed via linked processinvolving steady-state flux calculations by MCNPX andnuclide depletion calculation by CINDER90 [7]. However,MCNPX is unable to take into account the flux from externalsource during burnup calculation [2]. Therefore, eff andfuel evolution results are obtained under kcode modeapproximately. As long as the external source would not besufficient to drive the system towards criticality, the resultsare reasonable to discuss the transmutation capability of thesystem.

    3. Results and Discussion

    3.1. TRU Waste Transmutation. In order to investigate theneutronics characteristics and transmutation potential of theseed and blanket thorium-reprocessed fuelADS, theMCNPXcode was employed for the calculation using the core config-uration illustrated in Figure 1. Performance characteristics ofthe core are shown in Table 2.

    Neutron energy spectra for different regions in ADS coreare demonstrated in Figure 2. It clearly shows the dominationof neutron in the fast energy range. The 3 keV resonanceof sodium coolant is the reason to cause the flux drop atthat region. The fast spectrum system is advantageous foractinide transform since the actinide fission to capture ratio

    1.0E + 08

    1.0E + 10

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    1.0E

    08

    1.0 E

    07

    1.0E

    06

    1.0E

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    1.0E

    04

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