The development of modern design and reference core neutronics methods for the PBMR - abs72

The Pebble Bed Modular Reactor (PBMR) introduces several challenges for core neutronic methods. The particulate fuel is highly heterogeneous with a random distribution within the fuel pebbles and requires unique methods to calculate the effects of fuel resonance self-shielding. In addition, the flow of fuel through the core is specific to the PBMR, again requiring specialised methods to model refuelling. This paper describes developments to the ANSWERS core neutronics codes to treat the specific heterogeneity and fuel cycle features of the PBMR. ANSWERS provides both a reference calculational route, provided by the MONK Monte Carlo code (Reference 1), and a fast deterministic route for design calculations, provided by the WIMS9 modular code scheme (Reference 2). This paper describes some of the main developments implemented in the MONK and WIMS codes to treat PBMRs as well as presenting an inter comparison of the results obtained from the deterministic and Monte Carlo treatments as a first level of validation. (authors)