MODELING AND ANALYSIS OF CORE-DEBRIS RECRITICALITY DURING HYPOTHETICAL SEVERE ACCIDENTS IN THE ADVANCED NEUTRON SOURCE REACTOR

This article discusses salient aspects of severe-accident-related recr iticality modeling and analysis in the Advanced Neutron Source (ANS) r eactor The development of an analytical capability that uses the KENO5 A-SCALE system is described, including evaluation of suitable nuclear cross-section sets to account for the effects of system geometry, mixt ure temperature, material dispersion, and other thermal-hydraulic cond itions. Benchmarking and validation efforts conducted with KENO5-SCALE and other neutronic codes and compared with critical experiment data are described. Potential deviations and biases resulting from the use of the 16-group Hansen-Roach library are shown. A comprehensive test m atrix of calculations to determine the reactivity of various hypotheti cal configurations that might arise, along with the effects of various parameters on that reactivity, is described. Strong dependencies oil geometry, material constituents, and thermal-hydraulic conditions are also discussed as well as the introduction of designed mitigative feat ures.