Development of Monte Carlo-based pebble bed reactor fuel management code

ABSTRAC
A fuel management code for pebble bed reactors (PBRs) based on the Monte Carlo method has been
developed in this study. The code, named Monte Carlo burnup analysis code for PBR (MCPBR), enables
a simulation of the Once-Through-Then-Out (OTTO) cycle of a PBR from the running-in phase to the
equilibrium condition. In MCPBR, a burnup calculation based on a continuous-energy Monte Carlo code,
MVP-BURN, is coupled with an additional utility code to be able to simulate the OTTO cycle of PBR.
MCPBR has several advantages in modeling PBRs, namely its Monte Carlo neutron transport modeling,
its capability of explicitly modeling the double heterogeneity of the PBR core, and its ability to model
different axial fuel speeds in the PBR core. Analysis at the equilibrium condition of the simplified PBR
was used as the validation test of MCPBR. The calculation results of the code were compared with the
results of diffusion-based fuel management PBR codes, namely the VSOP and PEBBED codes. Using
JENDL-4.0 nuclide library, MCPBR gave a 4.15% and 3.32% lower
k
eff
value compared to VSOP and PEBBED,
respectively. While using JENDL-3.3, MCPBR gave a 2.22% and 3.11% higher
k
eff
value compared to VSOP
and PEBBED, respectively. The ability of MCPBR to analyze neutron transport in the top void of the PBR
core and its effects was also confirmed.