No abstract available

[en] A study has been made of the feasibility of converting the 5-MW TR-2 reactor at CNAEM to use fuel with uranium enrichment of <20% (LEU) instead of its current 93% enriched (HEU) fuel. The criteria applied in judging the merits of the various LEU options used were: 1) fuel cycle costs must not be substantially increased relative to those with HEU fuel; 2) flux levels, or activation rates, at irradiation positions must not be reduced by more than 20% relative to those for the HEU core; and 3) adequate safety margins must be maintained. The study concentrated on LEU fuel design using U³O⁸-Al fuel meat with a uranium density in the range 2.3 to 3.0 g/cm₃ in the fuel meat with meat thickness varying between 0.9 and 1.00 mm, the number of plates in the LEU element being reduced from 23 in the HEU element to 19 to 20 to maintain adequate cooling. Fuels within this density range are expected to be commercially available within the next two years. From the results of the study it appears to be feasible to safely operate the TR-2 reactor using LEU fuel without increased fuel cycle costs or decreased performance using U²O⁸ fuels with densities in the 2.3 to 3.0 gU/cm₃ range. (author)

No abstract available

[en] Historically space reactors flown or designed for the U.S. and Russia used Highly Enriched Uranium (HEU) for fuel. HEU almost always produces a small and lighter reactor. Since mass increases launch costs or decreases science payloads, HEU was the natural choice. However in today's environment, the proliferation of HEU has become a major concern for the U.S. government and hence a policy issue. In addition, launch costs are being reduced as the space community moves toward commercial launch vehicles. HEU also carries a heavy security cost to process, test, transport and launch. Together these issues have called for a re-investigation into space reactors the use Low Enriched Uranium (LEU) fuel.

[en] In research reactors, highly enriched uranium (HEU) is used as fuel for their purposes of operation. However, the United States strongly required in 1977 that these HEU should be replaced by low enrichment uranium (LEU) of 20% or less, or even in unavoidable cases, it should be replaced by medium enrichment uranium (MEU). INFCE (International Nuclear Fuel Cycle Evaluation) which started its activity just at that time decided to discuss this problem in the research reactor group of No. 8 sectional committee. Japan has been able to forward the work, taking a leading part in the international opinion because she has taken the countermeasures quickly. INFCE investigated the problem along the lines of policy that the possibility of reducing the degree of enrichment should be limited to the degree in which the core structures and equipments of research reactors will be modified as little as possible, and the change of fuel element geometry will be done within the permissible thermohydrodynamic capacity, and concluded that it might be possible in near future to reduce the degree of enrichment to about 45% MEU, while the reduction to 20% LEU might require considerable research, development and verification. On the other hand, the joint researches by Kyoto University and ANL (Argonne National Laboratory) and by Japan Atomic Energy Research Institute and ANL are being continued. IAEA has edited the guidebook (IAEA-TECDOC-233) for reducing the degree of enrichment for developing countries. (Wakatsuki, Y.)

[en] A new concept of High Flux Reactor with Solid Coolant (HFRSC) is presented. Due to application of high temperature moving fuel with significant heat capacity, used to accumulate energy generated in the reactor core, it is possible to overcome technological and physical barriers limiting the values of neutron fluxes in case of traditional reactor design. For HFRSC MEU or LEU is a natural choice to ensure essential temperature coefficient of reactivity. Application of water in the reactor core only as a moderator creates an opportunity to avoid pressurized circuit and place reactor into pool with all the advantages both for reactor safety and easy access to experimental facilities. A comparison with traditional high flux research reactor concept (ANS) is presented. (author)

[en] In the last decade research reactor operators have focused mainly on the issues of disposal of spent research reactor fuel and the development of high density fuels. The safe supply of fresh uranium did not receive as much attention. This is surprising since the United States - who was the main supplier for LEU and HEU since the late 1950's - stopped supplying non-US research reactors with enriched uranium a decade ago. The reason for this stop of supply is described in this paper. This paper explains how research reactors in the E U continued to operate during the last decade, in spite of the fact that their primary supply source had not provided LEU and HEU over the same period. (author)

[en] An attempt was carried out to handle the neutronic and burn-up calculation of a 10 Mw MTR-core with a view to convert its fuel from highly (93%) to medium enriched uranium (30%), keeping its performance power level and availability unchanged. At present this technique has been widely reported in literature, in view of its importance in safeguards and non-proliferation of fissile fuel. A benchmark study of a hypo technical model reactor suggested by IAEA was considered for the convert of its 93% fuel into both 45% and 20% enrichment figures. WIMS-D4 code was employed to generate the cross-sections data om conjunction with DAIXY code to carry out the multigroup diffusion calculation. 27 tabs.; 44 figs.; 24 refs

[en] Use of enriched uranium as reactor fuel necessitates its handling in various forms. For purposes of planning and organising radiation protection measures in enriched uranium handling facilities, it is necessary to have a basic knowledge of the radiation status of enriched uranium systems. The theoretical variations in beta activity and energy with U²³⁵ enrichment are presented. Depletion is considered separately. Beta activity build up is also studied for two specific enrichments, in respect of which experimental values for specific alpha activity are available. (author)

[en] Under the U.S.-Russian HEU agreement, approximately 500 tons of highly enriched uranium (HEU) from large-scale dismantlement of former Soviet nuclear warheads will be transformed into products not usable in nuclear weapons. According to the agreement, Russian facilities will convert and blend down HEU to low-enriched uranium (LEU) fuel for nuclear reactors. However, HEU is vulnerable to insider diversion during processing operations. The paper describes the principal HEU diversion vulnerabilities at the plant, and recommends a strong internal preventive safeguards system. 27 refs., 2 figs., 1 tab