Testing and implementation of LEU+ 6% enriched UO2 fuel at The PULSTAR reactor

Abstract

The PULSTAR reactor is a light water moderated and cooled, UO2 fueled reactor featuring both 4% and 6% enriched fuel assemblies. The PULSTAR was operated for over 40 years with 4% enriched assemblies. Originally designed to demonstrate key reactor concepts in the 1970s, the PULSTAR now serves as a hub of research opportunities. Recently, the PULSTAR has successfully demonstrated methods for licensing and operations with higher enriched fuel in a typical light water reactor configuration. Using MCNP, a model was developed and benchmarked against historical core loadings of the PULSTAR. Key reactivity contributions as well as kinetic effects were simulated. From this model, predictive calculations were completed to demonstrate the compliance of operations, with 6% enriched assemblies, to all required technical specifications. Based on the results, the PULSTAR reactor license was successfully amended to include both 4% and LEU+ 6% enriched assemblies. Results from three core loadings from 2017 to the present demonstrate the adherence of the PULSTAR to its technical specifications and the related US NRC regulations, while operating with LEU+ 6% enriched fuel. Operational experience with these new mixed enrichment cores continues to show excellent agreement between the predicted and observed reactor behavior. The precedent set by the simulations and operations with the PULSTAR’s mixed enrichment cores can be beneficial to the planned introduction of higher enriched (LEU+) fuel in the light water commercial reactor (LWR) fleet in the US and worldwide.