Corrosion of research reactor aluminum clad spent fuel in wet storage

This paper gives an overview of activities carried out at IPEN, Brazil, in the IAEA-sponsored Coordinated Research Project (CRP) "Corrosion of Research Reactor Al-clad Spent Fuel in Water" and in the Latin American regional project on "Management of Spent Research Reactor Fuel". In both projects Al alloy coupons in various configurations were exposed to the spent fuel storage pool of the IEA-R1 reactor for various times and then examined. Pitting was the main form of corrosion and pit distribution on coupons revealed the marked influence of settled solids. The AA6061 and AA1050 alloy coupons withdrawn after 2 years were stained with a layer of Bayerite caused by an increase in the average pool water temperature. This observation-part of a normal sequence of activities within the project-enabled reactor operations to explain the perplexing change in color of most in-reactor Al alloy components. It exemplified advantages of conducting a corrosion surveillance program. Analysis of sediments obtained from the pool revealed that the main constituents were oxides of aluminum, iron, silicon, and calcium. Coupons of the Russian alloy SZAV, pitted more inside crevices compared to the alloy AA6061. The former pitted more when coupled with stainless steel. Alloy grain orientation also influenced pitting. Coupons of rolled AA6061 alloy pitted more than coupons made from extruded AA6061 alloy. Details about the spent fuel storage facilities in IPEN and the water purification systems of the IEA-R1 research reactor (RR) are also presented.