Best-Estimate Plus Uncertainty Analysis of 37-Element CANDU Fuel Safety Margins

Abstract

A novel method of reliability analysis was implemented to determine the safety margin that exists for the 37-element CANDU fuel. The approach follows the principle of 'best estimate plus uncertainty (BEPU),' where probability of failure to meet a performance criterion is adapted as a measure of safety against consideration of uncertainties. In this study, fuel performance was predicted using the industry standard code, ELESTRESS, which models fuel behavior during steady-state operation. The outputs of the code were assessed against failure criteria derived from industry norms to determine the probability of failure. In total, 10⁵ independent iterations were made for each of 12 radially divided zones of a 480-channel CANDU reactor modelled after the Darlington Nuclear Generating Station cores. The manufacturing parameters of the fuel were adapted from data provided by Cameco Corporation. The uncertainty quantification and sensitivity analysis was conducted using a surrogate model developed using polynomial chaos expansion.