LEU+ Pellets in Westinghouse Electric Sweden’s nuclear fuel factory : Criticality safety analysis of the nuclear fuel factory in Västerås

Sammanfattning

Today the maximum allowed enrichment in uranium pellets created at Westinghouse Electric Sweden’s (WSE) nuclear fuel factory is 5%. The market is currently moving towards higher enrichment in its nuclear fuel for its benefits with energy security, such as higher energy density, and economics. The aim with this project is to investigate the possibility of using Westinghouse Electric Company’s nuclear fuel pellets LEU+ ADOPT produced in Springfield, United Kingdom, with a weight enrichment of up to 8% safely in WSE’s factory in Västerås. These pellets would be used to produce fuel assemblies with higher enrichments compared to production of today. The analysis will be made using Monte-Carlo N-Particle Transport Code (MCNP) version 6.2. MCNP is a Monte-Carlo based program that can calculate values with the use of mathematical equations to model systems in the factory. The value calculated in this project is the neutron multiplication factor keff. With the keff value a conclusion can be made whether the system will have an uncontrolled chain fission reaction or not during an accident scenario. If the keff value is too high, modifications to the model are needed to decrease the keff value to a safe level. In this project three different accident scenarios were analyzed, and all were unsafe with the increased uranium in the pellets before modifications were made. However, with modifications to the systems by reducing conservative margins and introducing neutron absorbers to the system a critically safe model was achieved.