Publications Details
Improbability of Nuclear Criticality When Disposing of Transuranic Waste at the Waste Isolation Pilot Plant
Nuclear criticality was eliminated from performance assessment calculations for the Waste Isolation Pilot Plant (WIPP), a repository for waste contaminated with transuranic (TRU) radioisotopes, located in southeastern New Mexico, based on arguments presented in this article. After disposal and following an inadvertent human intrusion into the repository (an event that must be considered because of safety regulations), there is no credible mechanism to counteract the natural tendency of the material to disperse during transport. Physical constraints on concentrating fissile material include low initial solid concentration of fissile material, small mass of fissile material transported over 10,000 yr, and insufficient physical compaction; hydrologic constraints include the limited amount of brine available to transport fissile material. Geochemical constraints on concentrating the fissile radioisotopes include lack of sufficient adsorption and conditions conducive to precipitation. Hence, the probability of nuclear criticality is low. Furthermore, before a criticality would have the potential to affect human health—assuming that a criticality could occur—it would have to either (1) degrade the ability of the repository to contain radioactive waste or (2) produce significantly more radioisotopes than originally present. Neither of these situations can occur at the WIPP; thus, the consequences of a criticality are also low.