Development of an advanced core analysis system for boiling water reactor designs

A core analysis system has been developed for the recent advanced designs of boiling water reactors. This system consists of a fuel assembly analysis code VMONT and a three-dimensional core simulator COSNEX. To cope with heterogeneous structures found in the recent high-performance fuel, VMONT employs a Monte Carlo neutron transport calculation method. COSNEX is based on a three-group nodal expansion method to treat spectral interactions among fuel assemblies. Both codes are vectorized to meet timing requirements as design tools. The analysis system is verified by the tracking of recent plant operations. Although the analyzed cores are highly heterogeneous in the multienrichment configuration, the system gives sufficient accuracy both in critical eigenvalues and thermal power distributions.