Transmutation Studies With Sodium Cooled Fast Reactor

Long-lived High Level Wastes (LHLW) arising from nuclear energy production process will constitute potential hazard to environment in a long term. Therefore, the safe disposal of LHLW is very important to the large-scale and sustainable development of nuclear energy. LHLW mainly comprises long-lived minor actinides (MA) and long-lived fission products (LLFP). Nuclear power is being developed rapidly since near term in China, and, along with the increasing installed nuclear capacity, we have to face to the problem of accumulated MA and LLFP. Partitioning and transmutation (P&T) technology is, in principle, capable to reduce the mass and the radiotoxicity inventory of LHLW. MA and LLFP can be destructed effectively in sodium cooled fast reactor (SFR), which has been operated successfully in some countries, and using SFR to transmute some long-lived nucleus is also one of hot research areas worldwide. This thesis studies the related neutronics problems of MA and LLFP transmutation in SFR.Firstly, by using China Demonstration Fast Reactor (CDFR) as a reference core, the fundamental neutronics characteristics of MA transmuted in SFR are investigated systematically, comprising influences on core performance and evaluation of MA transmutation efficiency. Core performance will be affected significantly by the addition of MA into SFR fuel, which limits MA percentage in fuel heavey metal (HM), while, on the other hand, MA transmutation support ratio is proportional to MA fraction in fuel. It can be said that this is the inherent conflict between MA transmutation and core safety issues. Though MA could be largely added into the blanket, the transmutation efficiency is much lower. When considering MA net destruction, incineration (MA is destructed into fission products, including fission of the daughter nucleus of MA capture reaction) is more important than capture reaction. The general rule of the parameters representing MA incineration effect is concluded in this thesis as MA burning efficiency is in direct proportion to the product of heavy metal burnup and MA burning efficiency factor, while MA burning specific consumption is only in direct proportion to MA fission share, where MA burning efficiency factor is defined as MA fission share divided by MA initial mass percentage in HM.Based on the above basic analysis, different MA transmutation manners in SFR are further studied, including transuranics (TRU) from PWR spent fuel recycled in oxide or TRU-U-Zr metal fuelled CDFR as an entirety without separation of MA and Pu, MA heterogeneous transmutation in CDFR as target sub-assemblies (SA) with IMF fuel or the target SA placed in CDFR blanket to replace all the blanket SA, and MA transmutation in dedicated burner reactors. High MA transmutation efficiency can be obtained by heterogeneous transmutation with IMF fuel, but IMF fuel can not be loaded largely into CDFR core and the locations of target SA should be optimized. For the dedicated MA burner, high MA transmutation support ratio can be achieved, but the core safety performance is weakened. The strategy of TRU wholly recycled in SFR is more promising for MA transmutation due to the less impact on core performance (less penalty on core safety parameters and breeding capability), while in this strategy, after the equilibrium of MA percentage in TRU is realized, the overall MA inventory in nuclear fuel cycle is only in direct proportion to the overall installed capacity of nuclear power plant. From the scenario analysis of future MA inventory in China, the result proves that, compared with the only development of PWR or standard CDFR fast reactor, TRU wholly recycled in CDFR can effectively control the accumulated amount of high radiotoxic MA in China along with the development of nuclear power in large-scale, while can also produce enough industry Plutonium to meet the requirement of nuclear fuel breeding.Finally, the thesis also studies the feasibility of utilizing neutrons leaking from fast reactor core to transmute LLFP (Tc-99 and I-129). The research results demonstrate that these leaking neutrons can be used to destruct LLFP effectively by properly slowing down. A certain impact on core performance, however, will be brought by introducing LLFP transmutation SA into core radial reflector, and the impact is closely related to the locations and components of LLFP transmutation SA. LLFP transmutation efficiency will be affected largely by moderator materials and moderating manners.