Stability of γ-UMo Nuclear Fuel Alloys by Thermal Analysis

Abstract

The development of a nuclear fuel for research reactor applications must take into account the non-proliferation of nuclear grade materials for weapons requirements, according to the Reduced Enrichment of Research and Test Reactors RERTR program. To minimize a potential problem with the use of high enriched fuels, i.e., the production of Pu and its possible utilization in nuclear weapons, several reactors have been converted their fuels from high to low enrichment. It is now acceptable a level of less than % of U .However, to compensate for the resultant loss of power, fuel densities must be raised and, thus, a new class of fuels, mainly the metallic ones, is under development. Those fuels are replacing the current oxides and silicides, and the most promising candidate has emerged from the binary system U-Mo, gamma phase stabilized, according firstly to the confirmation of its good behavior under fabrication and irradiation conditions, observed in several in pile tests performed over the years [ ]. Compositions of and wt. % molybdenum are considered to be the most promising for the gamma-stabilized uranium fuels. γUMo fuels can be used in two main configurations in fuel plates. If mixed as metallic powder in aluminum powder matrix, they are called dispersion fuels. The other way, a foil of γUMo is co-rolled with the aluminium cladding to achieve metallic bonding. In this configuration, they are called monolithic fuels. Since in the fabrication process, mainly in the rolling of the fuel plates, temperature is needed to ensure metallurgical stability, formation of new compounds can be observed [ ]. For example, it was observed that, for the U-Mo-"l system, compounds of γUMo "lx, ≤x≤ have some deleterious results over the fuel plate´s performance, due to the production of new uranium phases. Most of the new phases have low

Relation between Gamma Decomposition and Powder Formation of <i>γ</i>-U8Mo Nuclear Fuel Alloys via Hydrogen Embrittlement and Thermal Shock

“…On the basis of the classical time-temperature-transformation diagrams for the binary uranium-molybdenum system, and based on the results of stability under aluminum and oxygen [11] [22], it can be suggested that compositions near or between γ-U7.5Mo and γ-U8Mo are the most gamma stable, in terms of reactions with the aluminum matrix. Since their behaviors under irradiation, according to previous works [8]- [10] [23] are almost the same in the range of 5% to 8% Mo addition.…”