Method research and engineering validation of the improved homogenization for the heavy reflector in VVER

Compared with the traditional Cartesian PWR design, the heavy reflector, composed of larger amount of iron and less moderator, is an important feature of the VVER reactor. This structural feature would result in two different neutronics characteristics: first, less moderator would harden the neutron spectrum and make more adjoint reflector-node correlated; second, larger amount of iron within harden neutron spectrum may lead to notable resonance phenomenon for the structure–material isotopes. Therefore, the above neutronics characteristic would introduce corresponding challenges to the homogenization method for the heavy reflectors. In order to provide more accurate few-group homogenized parameters, an improved homogenization method has been proposed. As method verification, a two-dimensional VVER benchmark has been simulated, with the reference values provided by the Monte-Carlo code. Moreover, the improved homogenization method has been applied to the real VVER-1000 reactor operated in China, validating the simulation values of the key parameters with corresponding measurement values.