PBR Pebble Sensitivity Analyses for Material Accountancy Purposes

Pebble bed reactors (PBR) are one of several advanced reactor designs being developed by multiple commercial entities. While there are many benefits to PBR, the fact that the fuel consists of thousands of relatively small pebbles creates material accountancy challenges. Modeling and simulation work is being conducted in an attempt to address this issue, but a fundamental challenge in opensource modeling is the ability to get precise data. Information such as uranium enrichment, densities, elemental compositions, and number of TRISO particles per pebble are all examples of key modeling parameters that could be proprietary, not yet defined, or vary due to limitations in manufacturing. Because of this, a fuel pebble in a generic PBR is modeled in MCNP6.2 and key modeling parameters varied to assess the impact of key metrics, such as criticality. This sensitivity analyses will allow other PBR opensource modelers to identify which parameters are of greatest importance in their models. Understanding and minimizing these sources of potential bias is essential in any material accountancy activities.