The growth of surface oxygen complexes on the surface of activated carbon exposed to moist air and their effect on methyl iodide-131 retention

¹ Central Electricity Generating Board, Centrai Electricity Research Laboratories, Kelvin Avenue, Leatherhead, Surrey, UK.
² United Kingdom Atomic Energy Authority, Windscale Nuclear Power Development Laboratories, Sellafield, Cumbria,, UK.

Abstract

The formation of surface oxygen complexes, in the presence of moist air, on activated carbons used for methyl iodide-131 control in the nuclear industry is deleterious to trapping efficiency.

In this paper oxygen complex formation at different relative humidities was measured by both adsorption and desorption techniques and their effect on methyl iodide-131 retention at high humidity was evaluated.

It is concluded that oxygen groups form on different areas of the carbon surface depending on the relative humidity at which the carbon was equilibrated. Those forming on the micropore surface do not affect methyl iodide trapping performance whereas those on meso — and macropore surfaces are strongly inhibitive. Some evidence for differences in the chemistry of micro — and larger pore surfaces in coal-carbons is examined.

Résumé

La formation de complexes oxygénés à la surface de charbons actifs exposés à l'air humide a été mesurée par des techniques d'adsorption et de désorption et leur effet sur la rétention d'iodure de méthyle a été évaluée.

Les résultats montrent que les groupements oxygénés se forment sur des portions différentes de la surface du carbone suivant l'humidité relative à laquelle le carbone est exposé. Ceux qui se forment à la surface des micropores n'affectent pas la fixation d'iodure de méthyle, mais ceux qui se forment à la surface des meso — et macropores sont fortement inhibiteurs.