Experimental study of the effect of carbon monoxide on the performance of passive autocatalytic recombiners

Abstract

Passive autocatalytic recombiners (PARs) have been implemented in water-cooled nuclear reactors to prevent hydrogen explosion during severe accidents. Carbon monoxide (CO) can also be produced in severe accidents from ex-vessel molten core–concrete interaction. Assessment of scenarios involving ex-vessel interactions requires additional attention to the contribution of CO to combustion loads in containments. The risk of CO combustion can be mitigated by catalytic oxidation of CO in parallel with hydrogen recombination; however, the PAR performance may be affected by catalyst poisoning by CO. Tests were performed to examine the PAR self-start behaviour, recombination rate and efficiency, and ignition induced by hot catalyst plates in the presence of hydrogen and CO mixtures. The experiments were conducted in a 120 m3 test facility with a full-sized PAR and in a lab-scale apparatus with catalyst coupons. These measurements demonstrate that the CO poisoning effect strongly depends on the temperature and gas compositions. CO appears to have no adverse effect on PAR recombination rate during operation. This paper presents select experimental results with a focus on the effect of CO on PAR self-start behaviour. These results will help to refine severe accident management guidelines.