From High to Low Enriched Uranium Fuel in Research Reactors

Since the 1970's, global efforts have been going on to replace the high-enriched (over 90 percent 235U), low-density UAlx research reactor fuel with high-density, low enriched (below 20 percent 235U) replacements. This search is driven by the attempt to reduce the civil use of high-enriched material because of proliferation risks and terrorist threats. American initiatives, such as the Global Threat Reduction Initiative (GTRI) and the Reduced Enrichment for Research and Test Reactors (RERTR) program have triggered the development of reliable low-enriched fuel types for these reactors, which can replace the high enriched ones without loss of performance. Most success has presently been obtained with U3Si2 dispersion fuel, which is currently used in many research reactors in the world. However, efforts to search for a replacement with even higher density, which will also allow the conversion of some high flux research reactors that currently cannot change to U3Si2 (eg. BR2 in Belgium), have continued and are for the moment mainly directed towards the U(Mo) alloy fuel (7-10 w Mo). This paper provides an overview of the past efforts and presents the current status of the U(Mo) development.