A Review of Corrosion Considerations of Container Materials Relevant to Underground Disposal of High-Level Radioactive W
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A Review of Corrosion Considerations of Container Materials Relevant to Underground Disposal of High-Level Radioactive Waste in Belgium Bruno Kursten1 and Frank Druyts1 1 SCK•CEN, The Belgian Nuclear Research Centre Waste and Disposal Department Boeretang 200 B-2400 Mol, Belgium ABSTRACT The underground formation that is currently being considered in Belgium for the permanent disposal of high-level radioactive waste and spent fuel is a 30-million-year-old argillaceous sediment (Boom Clay layer). This layer is located in the northeast of Belgium and extending under the Mol-Dessel nuclear site at a depth between 180 and 280 meter. Within the concept for geological disposal (multibarrier system), the metallic container is the primary engineered barrier. Its main goal is to contain the radioactive waste and to prevent the groundwater from coming into contact with the wasteform by acting as a tight barrier. The corrosion resistance of container materials is an important aspect in ensuring the tightness of the metallic container and therefore plays an important role in the safe disposal of HLW. The metallic container has to provide a high integrity, i.e. no through-the-wall corrosion should occur, at least for the duration of the thermal phase (500 years for vitrified HLW and 2000 years for spent fuel). An extensive corrosion evaluation programme, sponsored by the national authorities and the European Commission, was started in Belgium in the mid 1980's. The main objective was to evaluate the long-term corrosion performance of a broad range of candidate container materials. In addition, the influence of several parameters, such as temperature, oxygen content, groundwater composition (chloride, sulphate and thiosulphate), γ-radiation, ... were investigated. The experimental approach consisted of in situ experiments (performed in the underground research facility, HADES), electrochemical experiments, immersion experiments and large scale demonstration tests (OPHELIE, PRACLAY). Degradation modes considered included general corrosion, localised corrosion (pitting) and stress corrosion cracking. This paper gives an overview of the more relevant experimental results, gathered over the past 25 years, of the Belgian programme in the field of container corrosion. INTRODUCTION Currently, approximately 55% of the total electricity production in Belgium arises from nuclear power plants [1]. Part of the inventory of high-level radioactive waste (HLW), including spent nuclear fuel (SF), discharged from one test reactor (BR2) and seven commercial nuclear reactors is temporarily being stored either under water in special ponds or in dry concrete structures. For more than 30 years, the Belgian nuclear research centre (SCK•CEN) has been involved in the development of a safe long-term solution for the permanent disposition of this
waste. This research has been performed under the supervision of the Belgian Agency for Radioactive Waste and Enriched Fissile Materials (NIRAS/ONDRAF). The favoured approach for dealing with HLW/SF is deep unde
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