This analysis is prepared by the Mined Geologic Disposal System (MODS) Waste Package Development (WPD) department to provide an evaluation of the criticality potential within a waste package having some or all of its contents degraded by corrosion and removal of neutron absorbers. This analysis is also intended to provide an estimate of the consequences of any internal criticality, particularly in terms of any increase in radionuclide inventory. These consequence estimates will be used as part of the WPD input to the Total System Performance Assessment.

The Monitored Geologic Repository Waste Package Operations 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 Navy (Refs. 1 and , 2). The Navy SNF has been considered for disposal at the potential Yucca Mountain site. For some waste packages, the containment may breach (Ref. 3), allowing the influx of water. Water in the waste package may moderate neutrons, increasing the likelihood of a criticality event within the waste package.

The effects of radiation on the corrosion of various metals and alloys, particularly with respect to in-reactor processes, has been discussed by a number of authors (Shoesmith and King 1998, p.2). Shoesmith and King (1998) additionally discuss the effects of radiation of the proposed Monitored Geologic Repository (MGR) Waste Package (WP) materials. Radiation effects on the corrosion of metals and alloys include, among other things, radiolysis of local gaseous and aqueous environments lead to the fixation of nitrogen as NO, NO2, and especially HN03 (Reed and Van Konynenburg 1988, pp.