Numerical investigation of the random arrangement effect of coated fuel particles on the criticality of HTTR fuel compact using MCNP6. (May 2017) - Ho, Hai Quan
Highlights: HTTR fuel with randomly distributed CFPs was modeled. Criticality calculation for a pin cell model was performed by MCNP6. The effect of the random model given by MCNP6 on the kinf of HTTR fuel was negligible. The explicit random model showed a lower kinf than that of the uniform model at 30% packing fraction. The lower uranium enrichment, the greater the difference of kinf. Abstract: This study investigated the random arrangement effect of coated fuel particles (CFPs) on the criticality of the fuel compact of the high-temperature engineering test reactor (HTTR). A utility program coupled with MCNP6, namely the realized random packing (RRP) model, was developed to explicitly model the random arrangement of CFPs in a specified fuel compact of the HTTR. The criticality and neutronic calculations for a pin cell model were performed using the Monte Carlo MCNP6 code with ENDF/B-VII.1 neutron library data. The reliability of the RRP model was confirmed by the insignificant variance of the infinite multiplication factor (kinf ) among 10 different random arrangements of the CFPs. Next, the criticality of the RRP model was compared with those of a non-truncated uniform packing (NUP) model and an on-the-fly random packing (ORP) model, which is a stochastic geometry capability in MCNP6. The results indicated that there was no substantial difference between the NUP and ORP models. However, the RRP model presented a lower kinf (by about 0.32–0.52%Δk/k) than the NUP model. In addition, the difference in kinf was increased as uranium enrichment decreased. Investigation of the 4-factor formula showed that the difference in kinf was predominantly a result of the resonance escape probability, with the RRP model showing the smallest value.