Effect of operating conditions on the retention of ruthenium tetroxide (RuO4) by different solid traps
Résumé
Mitigation of gaseous RuO4 is an important issue in nuclear safety in order to reduce potential radiological consequences, either in the context of severe accident arising on pressurized water reactors (oxidizing conditions) or in reprocessing plants (loss of cooling of fission product storage tanks). For the first time, RuO4 trapping was compared using three kinds of materials acting as solid traps: a functionalized MOF UiO-66-NH2, an amine-modified silica and a commercial cerium dioxide. Different experimental conditions of temperature, humidity and gas composition were investigated in order to mimic those prevailing under accident conditions at filtered containment venting system (FCVS) level or in ventilation ducts (gas mixture). At 50 °C, the efficiency of UiO-66-NH2 for RuO4 trapping was both very high in dry gas and in presence of steam with decontamination factor (DF) in the range 10 4-10 5. Under more severe conditions, the retention performances slightly decrease, especially when NO2 was present in the feed gas due to some poisoning of adsorption sites. In presence of amino-modified silica, breakthrough of RuO4(g) occurred at an earlier stage due to its inferior adsorption capacity but the performances of the trap did not deteriorate in presence of steam and NO2 in gas mixture. Under similar conditions, cerium dioxide showed no retention of RuO4(g).
