Accelerated Corrosion Tests to Evaluate the Long-Term Performance of BORAL® in Spent Fuel Pools

Neutron absorber materials are used to increase storage capacity in spent fuel pools (SFPs) while maintaining criticality safety margins. BORAL®—a neutron absorber material commonly used in SFPs—is a metal matrix composite containing boron carbide (B4C) and Al-1100 mixture. The aluminum (Al) cladding, which is on both sides of the core, serves as a protective barrier. Al cladding is susceptible to corrosion, which is observed in the form of pitting and/or blistering. EPRI has several ongoing projects to evaluate the long-term performance of neutron absorber materials and monitoring approaches. EPRI’s accelerated corrosion test project started in 2013 as a five-year project and concluded in 2018. For this project, different vintages of BORAL® were placed in test baths representing PWR and BWR water chemistry and test were conducted at elevated temperatures. Over 200 coupons representing different vintages and encapsulation conditions were placed in the test baths. Typically, SFP water temperature varies from 27°C to 38°C (80°F to 100°F). The corrosion rate is accelerated by conducting the tests at elevated temperatures, with test baths maintained at 91°C (196°F) to simulate corrosion effects representing more than 60 years of operation. Furthermore, to evaluate the corrosion under worst conditions, the protective cladding material was intentionally removed for some of the coupons. Every year, a number of coupons had been removed and analyzed to determine long term performance. In this paper, an overview of EPRI’s accelerated corrosion test project and results from the Year 1 to Year 5 of the test results will be presented.