EQ6 Calculation for Chemical Degradation of Shippingport PWR (HEU Oxide) Spent Nuclear Fuel Waste Packages

The Monitored Geologic Repository (MGR) Waste Package Operations (WPO) of the Civilian Radioactive Waste Management System Management & Operating Contractor (CRWMS M&O) performed calculations to provide input for disposal of spent nuclear fuel (SNF) from the Shippingport Pressurized Water Reactor (PWR) (Ref. 1). The Shippingport PWR SNF has been considered for disposal at the proposed Yucca Mountain site. Because of the high content of fissile material in the SNF, the waste package (WP) design requires special consideration of the amount and placement of neutron absorbers, and the possible loss of absorbers and SNF materials over geologic time. For some WPs, the corrosion-allowance barrier and the corrosion- resistant material (CRM) may breach (Refs. 1 and 2), allowing the influx of water. Water in the WP will moderate neutrons, increasing the likelihood of a criticality event 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.