[3K06-09] Criticality Analysis of Fuel Debris 2

[3K07] Improvement of criticality calculation speed in fuel debris falling down in water

*Takuya Miura¹, Jun Nishiyama¹, Toru Obara¹ (1. Tokyo Tech)

Keywords:Criticality safety, Monte Carlo calculation, Speed up, STGM, Fuel debris

In the analysis of criticality accidents during fuel debris retrieval in Fukushima Daiichi NPSs, because of a large amount of fuel debris, it needs a lot of computational time. When applying the statistical geometry model, STGM to Monte Carlo calculations, fuel debris particles are positioned probabilistically along neutron paths based on fuel debris volume ratio in each region. In the calculations, if the number of divisions is small, the accuracy of k-eff becomes lower. On the other hand, if the number of divisions is large, computationally expensive. In this study, using the region joint algorithm which combines regions whose volume ratio are close, it is clarified that it is possible to speed up the criticality calculation with enough accuracy.