EQ6 Calculation for Chemical Degradation of Pu-Ceramic Waste Packages: Effects of Updated Materials Composition and Rates
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| CAL-EDC-MD-000003_MOL.19990928.0235.pdf (3.91 MB) | 3.91 MB |
The Monitored Geologic Repository (MGR) Waste Package Operations (WPO) of the Civilian Radioactive Waste Management System Management and Operating Contractor (CRWMS M&O) performed calculations to provide input for disposal of Pu-ceramic waste forms. The Pu- ceramic (Refs. 1 and 2) is designed to immobilize excess plutonium from weapons production, and has been considered for disposal at the potential Yucca Mountain site. Because of the high content of fissile material in the ceramic, the waste package (WP) design requires special consideration of the amount and placement of neutron absorbers, and the possible loss of absorbers and fissile materials over geologic time. For some WPs, the corrosion-allowance material (CAM) and the corrosion-resistant material (CRM) may breach (Ref. 3, Section 10.5.1.2), allowing the influx of water. Water in the WP will moderate neutrons, increasing the likelihood of a criticality within the WP; and the water may, in time, gradually leach the fissile components and neutron absorbers out of the WP, further affecting the neutronics of the system.
This study presents calculations of the long-term geochemical behavior of WPs containing Pu- ceramic disks arranged· according to the "can-in-canister" concept. The cans containing Pu- ceramic disks are embedded in canisters filled with high-level waste (HLW) glass (Ref. 1). The objectives of this calculation were to determine:
• The extent to which criticality control material, suggested for this WP design, will remain in the WP after corrosion/dissolution of the initial WP configuration (such that it can be effective in preventing criticality).
• The extent to which fissile plutonium and uranium will be carried out of the degraded WP by infiltrating water (such that internal criticality is no longer possible, but the possibility of external criticality may be enhanced).
• The nominal chemical composition for the criticality evaluations of the WP design, and to suggest the range of parametric variations for additional evaluations.
