MAXUS® Corrosion Performance in Spent Fuel Pool Environments After 3 Years of 5-year Accelerated Corrosion Testing

Many commercial nuclear reactor spent fuel pool storage racks and storage and transportation packages incorporate neutron absorber material to ensure sub-criticality margin. Boron is widely credited in criticality safety analyses as a neutron absorber as it is cost effective with properties that are well documented and accepted by regulatory bodies. Neutron absorbers are usually formed in sheets, and placed within a support structure between fuel assemblies.One key performance concern regarding metal-based neutron absorbers used in spent fuel pools is uniform and localized corrosion that may have an adverse impact on neutron absorbing isotope areal density.MAXUS®, a three-layer aluminum-boron carbide neutron absorber metal matrix composite material, is currently qualified for use in spent fuel pool storage to maintain criticality safety vis-à-vis 10CFR50, 10CFR50.68, and 10CFR70.24. The authors identified PWR and BWR spent fuel storage pool corrosion factors facing aluminum-based, boron-10 (10B) neutron absorber material performance. These factors include water temperature, pH and dissimilar materials. Further, the authors identified MAXUS® production methods used to address these factors, such as the use of Al-Mg alloy for the material’s clad to not only prevent loss of 10B from the aluminum boron carbide core but also to prevent blistering and peeling through metallurgical bonding of the clad and core by diffusion of Mg into the core during production. Finally, MAXUS® is being tested in simulated PWR and BWR spent fuel pool environments to confirm its corrosion resistance.Testing of MAXUS® involves a 5-year spent fuel pool accelerated corrosion environment. The elevated temperature of the test baths at the end of 3 years simulates over 50 years of in-service performance at 27o C (80o F). Post-immersion measurements of MAXUS® include: microscopic visual examinations, physical dimension comparison to pre-characterized test samples and neutron attenuation measurements of a variety of MAXUS® 10B areal densities and spent fuel rack structure bi-metallic couplings.The 1st and 2nd year measurements of 10B areal density were found to unchanged within the measurement uncertainties. This paper shall show that the most recent 3rd year measurements of MAXUS® demonstrate life of plant (including extended decommissioning storage) efficacy as a spent fuel storage rack neutron absorber.