The MUST ADS Concept

The presented work is motivated by a French law regarding nuclear waste management. A new conceptual Accelerator Driven System (ADS) designed for the Minor Actinides (MA) transmutation has been assessed by numerical simulation. The MUltiple Spallation Target (MUST) ADS combines high thermal power (up to 1.4 GWth) and high specific power. A 30 mA and 1 GeV proton beam is divided into three secondary beams transmitted on three liquid lead-bismuth spallation targets. Neutron and thermalhydraulic simulations have been performed with the code MURE, based on the Monte-Carlo transport code MCNPX. A methodology has been developed to define characteristic of the MUST ADS concept according to a specific transmutation scenario. The reference scenario is based on a MA flux (neptunium, americium and curium) providing from European Fast Reactor (EPR) and a plutonium multireprocessing strategy is accounted for. The MUST ADS reference concept is a sodium cooled fast reactor. The MA fuel at equilibrium is mixed with MgO inert matrix to limit the core reactivity and improve the fuel thermal conductivity. The fuel is irradiated over five years. Five years of cooling and two years for the fuel fabrication are taken into account. The MUST ADS reference concept burns about 50% of the initial MA inventory during a complete cycle. In term of mass, up to 570 kg/year are transmuted in one concept. The methodology to design the MUST ADS and to calculate fuel composition at equilibrium is precisely described in the paper. A detailed fuel evolution analysis is performed and the reference scenario is compared to a scenario where only americium transmutation is performed. Keywords—Accelerator Driven System, double strata scenario, minor actinides, MUST, transmutation. I. CONTEXT AND MOTIVATION HE nuclear waste management R&D; priority axes in France are defined in the 1991 and 2006 law. The Accelerator Driven System (ADS) potential for Minor Actinides (MA) transmutation is being investigated in this framework. The present paper attempts to describe ADS influence on MA inventory in double strata scenarios. The nuclear plants stratum dedicated to electricity production generates MA which feeds ADS fleet stratum devoted to transmutation. J-B. Clavel is with Subatech, Subatomic physics and associated technology laboratory, 4 rue Alfred Kastler La Chantrerie BP 20722 44307 Nantes cedex 3, France (phone: +33 2 51 85 84 63; fax: +33 2 51 85 84 79; e-mail: [email protected]). N. Thiollière is with Subatech, Subatomic physics and associated technology laboratory, 4 rue Alfred Kastler La Chantrerie BP 20722 44307 Nantes cedex 3, France (phone: +33 2 51 85 86 42; fax: +33 2 51 85 84 79; e-mail: [email protected]). B. Mouginot is with Subatech, Subatomic physics and associated technology laboratory, 4 rue Alfred Kastler La Chantrerie BP 20722 44307 Nantes cedex 3, France (phone: +33 2 51 85 85 64; fax: +33 2 51 85 84 79; e-mail: [email protected]). To define the electricity generator stratum, two cases have been taken into account. On one hand, world nuclear power has been considered as constant, which implies that uranium reserves can provide the electricity needs. With this scenario, breeder reactors are not required and European Pressurized Reactor (EPR) can be used as the first stratum. On the other hand, a significant increase in global electricity production from nuclear energy is considered, which implies the use of fast breeder reactors leading to uranium saving. A major part of the long-term radiotoxicity of nuclear waste is due to the plutonium resulting from the used nuclear fuel. This implies a plutonium closed cycle strategy in the AM management. As a consequence, a plutonium multireprocessing into MOX fuel is taken into account for both cases. Figure 1 illustrates scenarios assessed in the present work. Fig. 1 Schematic drawing illustrating double strata scenario principle J-B. Clavel, N. Thiollière and B. Mouginot The MUST ADS Concept T TABLE I VARIABLES AND UNITS Symbol Quantity Units IV isotopic vector MA minor actinide FP fission product Keff multiplication factor ρ reactivity φMax maximum neutron flux inside the reactor core 1.cm.s φm mean neutron flux inside the reactor core 1.cm.s PMaxPin maximum pin thermal power 1 W Pm Total thermal power 1 W average fission energy 1 J → 6.2415096471204 .10 MeV σf fission cross section 1 b → 10−24 cm NN nuclei number Γff flux form factor Npin pin number per assembly NAss total fuel assembly number World Academy of Science, Engineering and Technology International Journal of Mathematical, Computational, Physical, Electrical and Computer Engineering Vol:6, No:3, 2012 351 International Scholarly and Scientific Research & Innovation 6(3) 2012 scholar.waset.org/1999.7/14900 In te rn at io na l S ci en ce I nd ex , P hy si ca l a nd M at he m at ic al S ci en ce s V ol :6 , N o: 3, 2 01 2 w as et .o rg /P ub lic at io n/ 14 90 0 The EFIT (European Facility for Industrial Transmutation) [1], [2] ADS concept is usually the reference for MA transmutation studies. The induced MA inventory in nuclear cycle (reactors, treatment and fuel fabrication factories) is large compared to transmutation in fast reactor scenarios [3]. Moreover, many ADS are needed to burn MA flux produced by the electricity strata. The MUST (MUltiple Spallation Target) ADS concept has been developed at Subatech Laboratory with the aim of avoiding those major drawbacks. MUST ADS consists of three spallation targets disposed inside a sub-critical core (Keff ~ 0.97). To produce the neutron flux required to maintain a constant number of fission inside the core, a high energy (1 GeV) and high intensity (~30 mA) proton beam is divided into three secondary beams transmitted the spallation targets. A three neutron sources concept provides a regular and high specific power inside the subcritical core. The MUST ADS is characterized by a higher thermal power between 1.2 GWth and 1.5 GWth. In addition, the irradiation time during which minor actinides are burned (cycle time) is extended up to five years. The following paper describes the methodology used to design the MUST ADS concept, including neutron and thermal-hydraulic calculations. II. SIMULATION TOOLS