The responsible use of calculational methods in nuclear criticality safety includes a determination of bias and bias uncertainty that may exist between the calculated results and reality. Such biases exist due to approximations used to model the real world, uncertainties in nuclear data, and approximations associated with the calculational method (e.g., Monte Carlo method). The bias and bias uncertainty are typically determined by using the modeling approximations, nuclear data, and calculational method to model well-known, usually critical, systems.

The Nuclear Regulatory Commission (NRC) Office of Regulatory Research (RES) has initiated a program to support effective implementation of burnup credit in the criticality safety assessment of transport and dry storage casks. The goal is to develop technical bases that can be used to provide criteria and guidance for use in licensing activities. The program is being conducted in a phased approach, with the initial focus on unresolved issues related to the use of actinide-only bumupcredit in transport and dry storage casks designed for spent fuel from pressurized-water reaciors (PWRs).