[en] Thorium fuels have been much discussed over the past few years as a replacement for uranium in main-line power reactors, or in special systems to consume minor actinides or unwanted stocks of plutonium. Less attention has been paid to the reprocessing. Existing knowledge is a useful basis for a tentative scheme to reprocess thorium fuels, but the reasons for favouring thorium, the types of fuel in which it is most likely to be used, and external circumstances with their consequent requirements have all changed since the early work was performed. The amount still to be done should not be under-estimated. (author)

[en] This paper briefly summarizes the state of the art on the study of thorium at the CEA and its projected use in pressurized water reactors. The advantages and drawbacks of thorium for the nuclear cycle are examined. Studies carried out in France are reviewed, major findings are recalled and possible future orientations for inert matrix fuels are presented. (author)

[en] The paper describes the status of work on pyrocarbon-binder spherical fuel elements with thorium dioxide-base fuel for HTGR. Basic flow charts of manufacturing fuel microspheres, coated particles and spherical fuel elements are described. Results of investigations into the main characteristics of fuel elements and their constituents, including their operation under reactor irradiation conditions, are discussed. Some special features of the technology of pyrocarbon-bound (U,Th)O₂ - base spherical FE are presented and reports the results from studies of their main characteristics. (author)

[en] The official policy of Japanese government concerning nuclear energy is to pursue ²³⁸U-Pu fuel cycle. On one hand, a large number of university professors, together with some of the research staffs of Japan Atomic Energy Research Institute (JAERI), has performed several research projects on the thorium fuel cycle as the future nuclear energy with the support of Grant-in-Aid for Scientific Research by the Ministry of Education, Science and Culture. These projects ended in 1993,but several activities have been continued after that. (author)

[en] A molten salt reactor (MSR) based on ²³³U-Th cycle has a positive feature from the standpoint of neutron economy, and it has been studied in Japan to utilize the MSR for the incineration of minor actinides (MA) produced in light water reactors (LWR). Therefore, Japan has proposed to study a MSR in the frame of the IAEA co-ordinated research project on the 'Potential of thorium-based Fuel Cycles to Constrain Plutonium and to Reduce Long-term Waste Toxicities'. It is important to study the basic character of the reactor with simple model especially for the purpose of comparison with other type of reactors. This report presents the results of the benchmark calculation and the effect of fuel volume ratio for the burnup characteristics. (author)

[en] The value of an innovation depends on the urgency of problems or deficiencies that it is intended to overcome, on its effectiveness in doing so, and inversely on the costs and any new difficulties that it raises. Thus industry sees no net benefit in thorium simply as a substitute for uranium except perhaps in certain areas such as India, since a general shortage is not expected for several decades. Interest is directed more at the property of thorium in generating hardly any transuranic elements apart from a little neptunium; using it would minimize additions to inventories of these elements, or increase net rates of consumption in schemes to incinerate them. (author)

[en] Brazilian systematic investigations on the use of thorium fuel cycles in nuclear power reactors started in 1965. During the 60's and early 70's the work was mainly concentrated on the thorium utilization in heavy water reactors (HWRs). This work was performed in the framework of a cooperation agreement with the, French CEA. In the frame of the International Nuclear Fuel Cycle program, Brazil started in 1979 an R and D program on the thorium utilization in pressurized water reactors (PWRs), within the scope of a Brazil-German cooperation agreement. This program lasted for almost ten years. The activities of both programs wore performed at the CDTN nuclear technology development center, in Belo Horizonte. More recently two Brazilian institutions restarted again investigations on the thorium fuel cycle. At CNEN, work is being pursued to further investigate the possible utilization of thorium in a PWR (Angra 1). The purpose of the paper is to comment briefly the main results of the past work and to give emphasis on the description of the recent results and new plans related to the work on thorium utilization in power reactors. (author)

[en] India is a country with limited deposits of uranium and large deposits of thorium. This fact ensures that India's nuclear power program cannot be totally uranium based the way it today is in most countries that have gone for nuclear power. Therefore, almost from the beginning of India nuclear power program, some effort has always been expended towards developing the technology of the thorium cycle. This has included fuel cycle studies, technology development, inpile irradiations and health physics aspects. A complete study of thorium cycles in various reactor types led to the conclusion that heavy water reactors were second only to molten salt reactors in this respect. HWR then, was the natural option for India. Currently India is working on the design of an advanced heavy water reactor (AHWR), specially designed with thorium in mind. In this paper, the results of a few interesting studies involving the recycling of plutonium with thorium in PHWR are presented. (author)

[en] The main objective of the present design is to use thorium based fuel for an efficient incineration of excess weapon grade plutonium. A heterogeneous, seed-blanket (SBU) fuel assembly design was adopted. The main design approach is to use plutonium as a seed fuel providing neutrons to a subcritical blanket loaded mainly with thorium. The seed subassembly fuel consists of Pu/Zr metal alloy and the blanket subassembly fuel consists of Th-Pu-U mixed oxide. The plutonium provides a fissile component, while natural uranium part is added to denature (dilute) the ²³³U built-up in thorium. This design is usually designated as the Radkowsky Thorium Fuel (RTF). A simulation of an 'equilibrium' cycle demonstrated the feasibility of the RTF design with an efficient plutonium incineration. Advantages of thorium-based SBU assembly design in compliance with the standard PWR control system requirements are also demonstrated. (author)

[en] The advantages of HTR module pebble bed reactor and thorium fuel cycles are discussed in this paper. In order to reduce plutonium stockpiles, the thorium fuel cycles are used for HTR module, and plutonium is used as fissile material. The equilibrium core is calculated and analysed for the case of the different heavy metal loading and enrichment. For the case of more than 11 g heavy metal per sphere has a negative temperature coefficient, and the maximum temperature of fuel elements under regular operation and loss of coolant accident is lower than 1500 deg. C. Therefore the feasibility of above scheme is studied. (author)