This paper summarises recent experimental results from a programme that was carried out to investigate the effects of radiation on the anaerobic corrosion of carbon steel, in relation to the overpack that will be used in the Belgian supercontainer concept for radioactive waste disposal. Anaerobic corrosion rates of carbon steel were measured by monitoring hydrogen evolution using manometric gas cells and an autoclave and the corresponding electrochemical behaviour was investigated by measuring open circuit potential, linear polarisation resistance and alternating current impedance. The test medium was alkaline simulated pore water, at c-irradiation dose rates of 0 and 25 Gy h 21 , temperatures of 25 and 80uC and chloride concentrations of 0 and 100 mg L 21 . The anaerobic corrosion rates exhibited a slow decline due to the formation of magnetite. Good agreement was found with weight loss measurements. A dose rate of 25 Gy h 21 had a negligible effect on gas generation rates.

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In the UK, most intermediate level radioactive waste is packaged in stainless steel containers. It is important that containers should maintain their integrity for extended periods of storage prior to final disposal. A prototype 4 metre box fabricated from 304S11 stainless steel was monitored at an inland rural building for over twelve years to gain experience in monitoring environmental conditions and corrosion during storage. A wide range of different types of aerosol particles were observed on the surfaces and in the air. They contained corrosive ions such as chloride, as well as other anions such as sulfate and nitrate. The chloride deposition rate was between 0.1 and 4 mg cm À2 yr À1 depending on the orientation and location of the surface, with a chloride/sulfate ratio ranging from~0.3À2. The temperature and relative humidity typically ranged from 0À30ºC and 40À90%, respectively. The greatest degree of corrosion developed on the base of the box, which had elevated chloride concentrations (10À140 mg cm À2 ). However, there was little evidence of corrosion propagation on the surface of the box and no evidence of stress corrosion cracking. The average pit propagation rates on a 316L coupon mounted next to the 4 m box were <1 mm yr À1 .

In the Belgian supercontainer concept, a carbon steel overpack will surround high-level waste and spent fuel containers and be encased in a cementitious buffer material. A programme of research has been carried out to investigate and measure the rate of anaerobic corrosion of carbon steel in an artificial alkaline porewater that simulates the aqueous phase in the cementitious buffer material and also in solid cement matrices. This paper highlights the main features of the programme and presents some recent results from the analysis of several samples, including two 20-year-old steel in cement samples, which showed that under anoxic conditions there is no localised corrosion or incorporation of iron into the surrounding cement, even in the presence of 20 000 ppm chloride in the porewater.

Abstract. This paper describes recent results from an investigation of the effects of -radiation on the anaerobic corrosion of carbon steel in cement, in relation to the Belgian Supercontainer Concept for radioactive waste disposal. Anaerobic corrosion rates were measured by monitoring hydrogen evolution and the corresponding electrochemical behaviour was investigated by measuring open circuit potential and linear polarisation resistance. The test medium was alkaline simulated porewater, at -irradiation dose rates of 0 and 25 Gy hr −1 , temperatures of 25• C and 80• C and chloride concentrations of 0 and 100 mg/l. The effects of radiation on the corrosion behaviour were found to be small.