Burnup Credit Experiences with the GA-4 Cask

General Atomics (GA) is developing two legal weight truck casks for shipping spent fuel from both pressurized water reactors (PWRs) and boiling water reactors (BWRs). The GA-4 (4 PWR) and GA-9 (9 BWR) casks are high-capacity legal weight truck casks designed to transport light water reactor spent-fuel assemblies. The GA-9 cask can meet the criticality safety requirements using the “fresh fuel” assumption. To maintain a capacity of four PWR spent-fuel assemblies, the GA-4 cask uses burnup credit as part of the criticality control for initial enrichments >2.9 wt% ²³⁵U. Using the U.S. Department of Energy Burnup Credit Program as a basis, GA has performed burnup credit analysis for the GA-4 cask. The approach to calculating the minimum burnup requirement takes into account all of the key parameters affecting k_eff. It is based on technically sound principles and conservatively increases the burnup requirement for a given enrichment to account for all uncertainties and biases associated with the calculations.