Preparation and safety testing of Fast reactor Fuels and Targets

Abstract

Fast reactor driver fuels are based on MOX with a high Pu content. They can be prepared by classical powder metallurgy, but suffer from potential heterogeneities in the Pu distribution, and significant quantities of dust have to be managed in the processing gloveboxes. In contrast, sol gel and infiltration routes offer appealing alternatives especially, if minor actinides are to be included for their transmutation in fast reactor systems. As the processes rely on well controlled liquid to solid conversion steps, resulting in particles in the 20-150 µm size range, dust is no longer an issue for their handling. Furthermore, excellent solid solutions can be obtained by such liquid processing routes. X –ray diffraction is a good means to check the longer range order, but the absolute quality can solely be provided by Magic Angle Spinning (MAS) NMR. A detailed study on the (U,Np)O2 system has shown that the metal atoms around the oxygen atoms are randomly distributed.

Fast reactor fuels must fulfil a variety of specifications on pellet diameter, Pu homogeneity, and grain size. The oxygen to metal ration must be less than 2.00 to ensure that the oxygen potential is sufficiently low to avoid internal oxidation of the cladding. In addition, all fast reactor fuels must be compatible with the reactor coolant. The typical tests to ensure this criterion are usually achieved by heating the fuels in the appropriate coolant for 50 hours at pre-selected temperatures, usually the highest temperature in the core, or at higher temperatures to exacerbate any chemical interaction effects. We will report here on the results determined for MOX interaction with lead bismuth eutectic and with MOX fuels with Na at elevated temperatures.