The ageing and poisoning of charcoal used in nuclear power plant air cleaning systems

This paper describes an investigation aimed at identifying the relative importance of oxidative ageing and hydrocarbon poisoning in the overall weathering of both potassium iodide (KI) and triethylene diamine (TEDA) impregnated charcoal used in filters on air cleaning systems. Preliminary results on oxidative ageing show a marked dependence of the KI material on relative humidities above 40% and to a lesser extent on temperature. The TEDA material on the otherhand showed no such dependence at least up to 50 deg. C. Hydrocarbon poisoning is shown to affect both impregnant types to the same extent but the TEDA material due to its higher initial performance shows the greater resistance to poisoning. No one type of hydrocarbon species appeared to be significantly more deleterious than the rest and even with loadings up to 5% hydrocarbon some useful methyl iodide adsorption capability is retained. A laboratory investigation of the combined effect of oxidation and poisoning up to 2,000 hours showed the superior performance of TEDA charcoal. However translating these results to operating plant and extrapolating to an operating time of one year it is clear that even TEDA charcoal filters would require the use of a guard bed designed to remove airborne organic species. The work has shown that the observed deterioration of charcoal filters on air cleaning systems can be accounted for by the combined effect of oxidative ageing and hydrocarbon poisoning in the case of both KI and TEDA impregnated charcoals