DISPOSABILITY OF LOADED U.S. DUAL-PURPOSE CANISTERS FROM A CRITICALITY STANDPOINT

This paper assesses the feasibility of direct disposal of loaded dual-purpose canisters (DPCs) from a criticality standpoint by evaluating attributes that could be credited to justify that the DPCs remain subcritical over a repository performance period. This study investigates the uncredited criticality margin associated with actual fuel loading compared with the regulatory licensing design basis limits and evaluates the percentage of DPCs that remain subcritical solely based on the uncredited criticality margin. Additionally, the reactivity impact of dissolved groundwater species, such as chlorine, is studied to approximately quantify the amount of dissolved species needed to maintain subcriticality where the uncredited criticality margin based on an as-loaded calculation is insufficient to maintain subcriticality alone over the repository performance period. The preliminary study of a small subset of 179 DPCs (of approximately 2000 loaded nationwide) at five reactor sites shows that 87% of these as-loaded DPCs may be able to demonstrate subcriticality over the repository performance period when fully flooded and with a complete loss of neutron absorber materials from the basket. The preliminary study also indicates that chlorine concentrations of approximately 14,000 ppm would be sufficient to maintain subcriticality for the other 13% of this subset of DPCs.