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 keff. 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.