Hydrogen combustion in an MCO during interim storage (fauske and associates report 99-14)

Abstract

ApprovalDesignator sNQ ED-7400-172-2 (05/96) GEF097 8-5Zero Comment Record dispositions based on FAI/98-113, which was a draft for review of scope and content, and it also includes an internal FA1 review in compliance with project requirements.

Spent Nuclear Fuel (SNF) Project Product Specification

“…The transient calculations in Plys and Duncan (1998b) indicate that 70% of the maximum pressure for a worst case MCO occurs 10 years after the start of storage in the CSB. Therefore, a maximum time of 10 years was selected for mechanically sealed MCOs based on increasing the design pressure safety margin for the interim storage time when an MCO is projected to approach the maximum pressure.…”

“…This allocation has been used as the basis for evaluating MCO pressurization and gas compositions during storage. Therefore, any future modification of this limit requires reanalysis of the stored MCO pressure and gas composition (see Plys and Duncan 1998b). Section 4.6.3.3.7 describes the overall basis for allocating water to different constituents that may exist in an MCO during storage.…”

“…This analysis, demonstrating that formation of a flammable gas mixture is precluded over the 40 year storage period in the CSB, is based on an initial backfill gas that is essentially pure helium. Sherrell and Pajunen (1999) determined that an initial backfill gas composition of 99.5% helium would not impact the results and conclusions of Plys and Duncan (1998b). Therefore, the MCO void space gas composition is specified as greater than or equal to 99.5% helium.…”

“…Plys and Duncan (1998b) indicates that a maximum internal MCO pressure of 61.7 psig is anticipated over a 40 year storage time period, based on a transient analysis of radiolytic gas generation, fuel corrosion, dehydration of fuel corrosion products, and oxygen gettering. Therefore, while the mechanically sealed MCO is suitable for containing the projected pressure buildup, the welded cover cap provides a significant increase in the safety margin between the anticipated internal pressure and the MCO design pressure.…”

“…The oxygen concentration in an MCO is limited to 4 vol% to prevent developing a flammable gas mixture during interim storage (Plys and Duncan 1998b). Oxygen gettering by uranium metal is projected to maintain oxygen concentrations at less than 4 vol% in an MCO for all potential combinations of MCO loadings and decay heat.…”