Abstract
Nuclear criticality safety evaluations commonly take credit for neutron-absorbing materials. The normal practice for validating the calculational process to develop safety limits and margins of safety is to compare the safety case models with calculations of various critical experiments of a similar composition. Because there is a lack of critical experiments with various relevant neutron-absorbing materials mixed with fissile material, a new approach is being developed. This new approach uses small amounts of these credited materials in a critical assembly and assesses their worth and neutron energy spectral characteristics using absorption reaction rates. This approach is proposed as a new method for nuclear data validation. The assessment will involve measured central reactivity worth in a critical or near-critical assembly and subsequent comparison with calculated values from Monte Carlo computer analyses. Additionally, four configurations are proposed which replace fuel rods in the driver region with absorber rods. These configurations will allow for examination of the effects of the material in a more thermalized spectrum experiment selection in these scenarios. This paper presents some case studies examining the impact of these changes on some hypothetical safety analysis systems.
This paper documents the detailed design portion of the critical experiment design process, focusing on development of a capability to test epithermal/ intermediate energy cross sections for materials using the 7uPCX critical experiment facility. Tantalum is specified as the test material to be examined.
