CORROSION OF BORATED STAINLESS STEEL IN WATER AND HUMID AIR Prepared for U.S. Nuclear Regulatory Commission Contract NRC–02–07–006 Prepared by

ii Borated stainless steel alloys are one of the most commonly used neutron absorber materials for criticality control in spent nuclear fuel disposal containers or dry storage canisters. Borated 304 stainless steels are similar to conventional Type 304 stainless steels except that they contain a boron addition, which imparts a much higher thermal neutron absorption cross section than other austenitic stainless steels. This work investigated the corrosion behavior of borated stainless steel in water and humid air environmental conditions. In this study, borated 304B4 and 304B5 stainless steels were exposed to the liquid and vapor (i.e., humid air) phases of simulated groundwater at 60, 75, and 90 °C [140, 167, and 194 °F] for about 3 months. The posttest specimens were analyzed to determine general corrosion rates and occurrence of localized corrosion. It was found that some specimens exposed to humid air at 75 and 90 °C [167 and 194 °F] suffered pitting corrosion, but pitting corrosion was not observed at 60 °C [140 °F] or from the liquid exposure at 75 and 90 °C [167 and 194 °F]. The pits were circular, and the surface near the pitted area was stained. The maximum pit depth was about 70 µ