Laboratory Corrosion Tests on Candidate High-Level Waste ContainerMaterials : Results from the Belgian Programme

摘要

The Belgian SAFIR-2 concept foresees the geological disposal of conditioned high-levelradioactive waste in stainless steel containers and overpacks placed in a concrete gallerybackfilled with Boom clay or a bentonite-type backfill. In addition to earlier in situexperiments, we used a laboratory approach to investigate the corrosion properties ofselected stainless steels in Boom clay and bentonite environments. In the SAFIR-2 concept,AISI 316L hMo is the main candidate overpack material. As an alternative, we alsoinvestigated the higher alloyed stainless steel UHB 904L. Our study focused on localisedcorrosion and in particular pitting. We used cyclic potentiodynamic polarisationmeasurements to determine the pit nucleation potential ENP and the protection potential EPP.The evolution of the corrosion potential with time was determined by monitoring the opencircuit potential in synthetic claywater over extended periods.In this paper we present and discuss some results from our laboratory programme, focusingon long-term interactions between the stainless steel overpack and the backfill materials. Wedescribe in particular the influence of chloride and thiosulphate ions on the pitting corrosionbehaviour. The results show that, under geochemical conditions typical for geologicaldisposal, I.e. [Cl-] ～ 30 mg/L for a Boom clay backfill and [Cl-] ～ 90 mg/L for a bentonitebackfill, neither AISI 316L hMo nor UHB 904L is expected to present pitting problems. Animportant factor in the long-term prediction of the corrosion behaviour however, is therobustness of the model for the evolution of the geochemistry of the backfill. Indeed, atchloride levels higher than 1000 mg/L, we predict pitting corrosion for AISI 316L hMo.