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[en] Aiming at building up the scientific and technical foundation for the development of the thorium fuel cycle, we carried out a cooperative fundamental study on this cycle as a promising energy source in and after the next century by the support of Grant-in-Aid for Scientific Research by the Ministry of Education, Science and Culture of Japanese Government from April 1988 to March 1993. In this cooperative research program, the following subjects were assigned: (1) Nuclear data for the thorium fuel cycle, (2) Design study of Th/U-233 fuelled reactors, (3) Critical experiments of these reactors and their analyses, (4)Preliminary works for fusion-fission hybrids with thorium, (5) Thorium fuel development; new thorium fuels and thorium fuel irradiation, (6) Molten salt technology, (7) thorium fuel reprocessing, and (8) Radiation safety for the thorium fuel cycle. Important results of this cooperative study from (1) to (3) are briefly reviewed. (Author)
[en] Dynamic fuel cycle simulation codes model evolving nuclear fuel cycles, and calculate nuclides inventories and material flows in each unit of the cycle. In the nuclear fuel cycle simulation code CLASS (Core Library for Advanced Scenario Simulation), a Fuel Loading Model (FLM) builds a fresh fuel fulfilling the reactor criticality requirement, depending on the available fissile material. Then, a mean cross-sections predictor calculates the mean cross-sections required to perform the fuel depletion in a short calculation time. This work focuses on the elaboration of these models in the case of a PWR-MOXEUS fuel (MOX on Enriched Uranium Support), which allows plutonium mono-recycling and multi-recycling in PWR. These models are built using neural networks. These predictors are trained on a databank composed of 1000 PWR infinite assembly depletion calculations performed using the software MURE (MCNP Utility for Reactor Evolution) based on the transport code MCNP (Monte-Carlo N Particle). Several databanks are tested and the performance of the resulting predictors are compared. The FLM predicts the plutonium content, and potentially the uranium enrichment, required in the fresh fuel. This model is based on a calculation of the infinite multiplication factor performed with an accuracy close to MCNP statistical error. Mean cross-sections prediction allows a deviation lower than 5% on main plutonium isotopes at 75 GWd/t compared to the fuel depletion reference calculation. PWR MOXEUS models are also tested on a balancing scenario. The complex evolution of MOXEUS fresh fuel isotopic composition during the scenario is highlighted. Furthermore, equilibrium fresh fuel isotopic vectors are compared to another study on an equilibrium MOXEUS multi-recycling strategy calculation, showing a good general agreement.
[en] The National Academy of Sciences (NAS) has declared that the large and growing stocks of plutonium from weapons dismantlement in the U.S. and the former Soviet Union FSU are a ''clear and present danger'' to peace and security. Moreover, the opinion of some experts that plutonium of any isotopic blend is a proliferation threat has been well publicized, heightening the concern that plutonium produced in the civilian fuel cycle is itself a proliferation threat. Assuring that separated plutonium, from dismantled warheads as well as from civilian power programs, is under effective control has (again) become a high priority of U.S. diplomacy. One pole of the debate on how to manage this material is to declare it to be a waste, and to search for some way to dispose of it safely, securely, and permanently. The other pole is to view it as an energy resource and to safeguard it against diversion, putting it into active use in the civilian power program. The ultimate choice cannot be separated from the long-term strategy for use of peaceful nuclear power. Continued use of a once-through fuel cycle will lead to an ever-increasing quantity of excess plutonium-requiring safeguarding. Alternatively, recycling the world's stocks of plutonium in fast reactors, contrary to common misconception, will cap the world supply of plutonium and hold it in working inventories for generating power. Transition from the current-generation light water cooled reactors (LWRs) to a future fast-reactor-based nuclear energy supply under international safeguards would, henceforth, limit world plutonium inventories to the amount necessary and useful for power generation, with no further excess production. (author)
[en] Breeder reactors are considered as a unique tool for fully exploiting natural resources. Fast breeder reactors based on thorium fuel can enhance inherent safety. Fluoride salt has good performance as a coolant in high-temperature nuclear systems. However, there is some doubt about the fuel breeding ability using fluoride salt coolant for fast spectrum due to its moderating ability. The aim of this study was to choose a proper fluoride salt mixture for Liquid-salt-cooled Solid-fuel Fast Reactor (LSFR) based on thorium-uranium fuel and give parametric studies to provide a design window for flexible self-sustaining core design. Infinite assembly model was used to analyze the salt selection from five candidate fluorides for fast spectrum as coolant. Combining neutron balance analysis with linear least squares fitting method based on 0D model, parametric studies at the neutron balance equation unique solution with burn-up for several parameters such as fuel volume fraction, removing fission gases process, total neutron losses and power density were presented in this paper. It was found that BeF2-NaF was a promising coolant in the five candidate fluoride salt mixture. This study proved that the design of a self-sustaining core for fluoride-salt-cooled fast breeder based on thorium fuel is achievable. A design window was found in the definition of a self-sustaining core for various fuel volume fractions and neutron loss fractions. Core design and fuel management strategy will be given in future.
[en] Highlights: •We model 7 different steady-state electro-nuclear scenarios. •We make a comparison between these scenarios at different points of the fuel-cycle. •Low breeding capacity of thorium-fuel in PWR leads to no significant gain. •Pu-recycling in homogeneous assemblies leads to high Pu inventory, even using Th. -- Abstract: The possible delay of decades for the deployment of fourth generation reactors brings up new issues. First, the possibility of higher tension on uranium mining motivates the research of a better use of resources in PWR. Second, countries like France which are storing spent MOX fuels containing plutonium in prediction of starting FBR could have to adapt their plutonium management strategy. Different options and different types of uranium and thorium based fuels in PWR have been studied using the MURE core. The steady-state of all considered strategies is calculated taking into account the whole nuclear cycle, allowing a precise description of the fuel composition and behavior at each step. The study is made in the most similar strategy of fuel reprocessing and allows a real comparison of U and Th cycles. It shows the low breeding capacity of thorium-fuel in PWR that leads to no significant gain on resource consumption. Moreover multireprocessing plutonium on thorium matrix implies to reprocess it in dedicated ThPu assemblies in order to be able to recover 233U. This leads to high plutonium concentrations. The global comparison, that takes into account the whole fleet, between plutonium recycling on depleted uranium or thorium based fuel is then not such favorable for thorium in terms of total plutonium inventories in the fleet at steady state. The same effect is observed for americium production.
[en] In order to construct a sustainable society, it is necessary to consider fairness beyond generations and between countries. It is expected that Asian countries continue growing their economy and will result consuming more energy. More CO2 emission is not acceptable. Nuclear power has many advantages for reducing CO2 emission. However, it still has concerns of nuclear proliferation, radioactive waste and safety. It is necessary to overcome these concerns if nuclear power is expanded to Asian countries. Thorium utilization as nuclear fuel will be an opening key of these difficulties because thorium produces less plutonium, less radioactive waste. Safety will also be enhanced. The use of molten-salt reactor (MSR) triggered by plutonium supply from ordinary light water reactor (LWR) with uranium fuel will allow implementation of thorium fuel cycle with electricity capacity of about 446 GWe around at 2050. The other important sector in a view of sustainability is transportation. Transportation is essential for economy growth. Therefore it is inevitable to reduce CO2 emission from transportation sector. Electric vehicle (EV) will be used as a major mobility instead of gasoline engine cars. Rare-earth materials such as neodymium and dysprosium are necessary for producing EV. These materials are expected to be mined from Asian countries. It is often obtained with thorium as by-product. Thorium has not been used as nuclear fuel because it is not good for nuclear weapon and it does not have fissionable isotopes. Recent global trend of nuclear disarmament and accumulation of plutonium from uranium fuel cycle can support starting the use of thorium. Thorium utilization will help both to provide clean energy and to produce rare-earth for clean vehicle. These will create new industries in developing Asian countries. An international collaborative framework can be established by supplying resource from developing countries and supplying technology from developed countries. “THE Bank (THorium Energy Bank)” is proposed here as one part of such a framework.
[en] Highlights: • Simulations include HTTR, VHTR, DB-MHR and LS-VHTR systems. • The systems were simulated with the codes SCALE 6.0, ORIGEN 2.1, WIMSD-5, MCNP5 and MCNPX 2.6.0. • Analyses were focused on the neutronic evolution and fuel composition during burnup. • The adopted methodologies confirmed the codes capabilities to simulate specific situations. - Abstract: This paper presents the results of studies developed at the Department of Nuclear Engineering of the Universidade Federal de Minas Gerais – Brazil (DEN-UFMG) on the use of reprocessed fuels and combined thorium fuel cycles. These studies involved simulations of Very High Temperature Reactor (VHTR), Liquid-Salt-Cooled Very High-Temperature Reactor (LS-VHTR), High Temperature Engineering Test Reactor (HTTR) and Deep Burn Modular Helium Reactor (DB-MHR) systems and the analyzes focused mainly on the neutronic evolution of the systems and fuel composition during burnup using models developed with established nuclear code systems such as SCALE 6.0 (KENO-VI/ORIGENS), MCNPX 2.6.0, MCNP5, ORIGEN 2.1, and WIMSD-5. The results show that the adopted methodologies of studies confirmed the capabilities of the codes to simulate specific situations in steady state or transient operating conditions.
[en] This paper presents a concept of the dual tier system consisting of the existing light water reactor (LWR) plants and sodium-cooled fast reactor (SFR) for transuranics (TRU) burning for the purpose of downsizing the required SFR. In this system, Pu is combusted by the LWR at first and then the remaining Np, Am, and Pu are destructed by the SFR. The iteration number of Pu combustion by the LWR is chosen to be twice owing to the sodium void reactivity limitation of $6. As a result of combustion calculation, the twice Pu burning of LWR lessens the TRU amount by 27% and changes the composition significantly. Moderator pins of zirconium hydride are deployed to the SFR fuel subassembly so as to enhance TRU burning and reduce the sodium void reactivity. The nuclear calculation found that the core characteristics become similar to the conventional SFR due to the moderator: the sodium void reactivity remains still $4 and the Doppler coefficient becomes −6 × 10−3 Tdk/dT. This study concludes that this dual tier strategy can downsize the required SFR to approximately 40% of the single tier system of SFR with TRU conversion ratio of 0.6.
[en] The use of thorium fuel in current PWRs in a once-through fuel cycle is an attractive option due to potential advantages such as high conversion ratio and low minor actinide generation. The current neutronics assessments indicate that the thorium fuel cycle could supplement the current uranium–plutonium fuel cycle to improve operational performance and spent fuel consideration in current PWRs without core and subassembly modifications. Neutronics safety parameters in the PWR cores with the thorium fuels are within the range of current PWRs. The PWR cores with thorium fuels have significantly higher conversion ratios which could enable efficient fuel utilization. Further, it is shown that the use of thorium as a fertile material can reduce minor actinide generation and the radio-toxicity of spent fuels. In considerations related to proliferation resistance, the results of the current analyses show no significant difference between the studied thorium fuels and the standard oxide fuel for the assumed characteristics and burnup levels.
[en] Highlights: • We simulated 4 different future nuclear fuel cycle scenarios. • The ADS and FRs impact on the future Chinese nuclear fuel cycle is studied. • The partition and transmutation option is compared against the simple reprocessing. • The MA cycle, Pu flow and spent fuel cycle are assessed. - Abstract: The civil nuclear energy deployment in China is important for future “Nuclear Renaissance” of China and worldwide. Compared to the other nations that developed their nuclear power energy system in last century, China can take advantage of the research and mistakes made by those states with regards to the back-end of the nuclear fuel cycle (NFC). The spent fuel accumulated by decades of operations of civil nuclear power is today a big burden for the nuclear industry. China must carefully plan the NFC for a sustainable development of the nuclear energy with special consideration to closing the fuel cycle. The present paper addresses the NFC option and implication of a LWR reactors scenario development and of a fast reactor park developed after 2035 and 2050, and covers the historical development of nuclear energy in China (i.e. from the first criticality of the first reactor) to the year 2100. The paper studies the partition and transmutation strategy with the use of accelerator driven system (ADS) to burn the MA to understand the ADS impact on the NFC and to estimate the number and the necessary deploying schedule of the ADS reactors to limit the minor actinides stock build up. The code INFCIS developed by the International Atomic Energy Agency (IAEA) is used in the present study.