COMPARISON OF U₃Si₂ AND U-10Mo LEU-FUELED REACTOR CORES FOR THE PRECONCEPTUAL NIST NEUTRON SOURCE DESIGN

抄録

The National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR) is one of the primary U.S. national research facilities that hosts thousands of visiting domestic and international scientists/researchers for various research projects. The National Bureau of Standards Reactor (NBSR) has been operational more than 50 years, but due to increasing outage times and costly maintenance, a new replacement reactor, namely the NIST Neutron Source (NNS), is being planned by the NCNR to replace the aging NBSR. The preliminary conceptual design of the NNS core was based on Material Test Reactor (MTR) plate type U-10Mo fuel; however, due to recent difficulties and unknown timeline for the certification of U-10Mo fuel in the U.S., NCNR is investigating the possibility of using low-enriched uranium silicide dispersion (U₃Si₂/Al) as alternative fuel material. In this paper, the neutronics performance of low-enriched U₃Si₂/Al fuel and U10Mo fuel are compared with the objective of identifying the dimensions of U₃Si₂/Al fuel plates that can yield similar neutronics behavior to the current U-10Mo fuel plates without modifying overall assembly size. Hence, the main objective of the NNS is to provide neutrons for the two cold sources located around the core, and the current compact core design delivers more neutron intensity and brightness for the cold neutron sources. Neutron transport analyses follow an optimization process for minimizing the difference between the k_∞ of the silicide plates to the U-10Mo, maximizing the coolant channel thickness and ²³⁵U content inside the assembly. Results show correlations between the fuel-to-coolant area ratio and the reactivity worth characteristics of the U-10Mo and U₃Si₂/Al plates in the NNS.