Sulphur ingress into Hinkley Point 'B' AGR and its effect on carbon monoxide oxidation

Measurements of sulphur (present as carbonyl sulphide COS) in the Hinkley Point 'B' AGR coolant gas circuits following commissioning, indicated concentrations up to 400 vpb. This was substantially higher than that found in WAGR and Magnox coolants and, in view of the known susceptibility of nickel and chromium to attack by sulphur, the possibility of enhanced corrosion of the high nickel and chromium steels within the reactor circuit was suggested. Based largely on WAGR experience, a maximum tolerable COS concentration of 35 vpb was recommended by corrosion specialists. This paper deals with the work carried out to determine, and remove, the major source of sulphur and the methods adopted to reach the recommended maximum level. In addition the interaction of sulphur and sulphur control with the operation of the catalytic carbon monoxide converter (recombination unit) is discussed. (author)