Filters Used in Post Accident Containment Clean Up System for Indian PHWRs

Abstract

The standardized Indian Pressurized Heavy Water Reactor (PHWR) design incorporate several notable features to minimize the release of radioactive materials under accident conditions. Three of these Engineered Safety Features (ESF) use activated charcoal as the medium for retention of radio iodines. These systems are : i) Primary Containment Filtration and Pump Back (PCFPB) System to clean up the primary containment atmosphere by removing particulate and Iodine isotopes in various forms so that long term release from containment following an accident can be controlled to a very low value. This will help to initiate depressurization of the primary containment if necessary without appreciable loading on the primary containment controlled discharge system. ii) Primary Containment Controlled Discharge PCCD) System to initiate controlled depressurization of the Primary Containment if warranted for management of the accident. iii) Secondary (SCFRP) release secondary pressure. Purge level of the negative Containment Filtered Recirculation and System to prohibit/minimise the ground by multipass filtered recirculation containment atmosphere and maintain a These three systems make important contribution in controlling the radiological consequences following an accident in the reactor system. However, the high filtration efficiency charcoal is offset by the problems associated with the post adsorption temperature rise in absence of forced cooling. It may be possible to reduce the iodine loading to a more easily manageable level by providing a suitable iodine prefilter. The preliminary studies carried out in this area indicate possibility of use of lead exchanged zeolite as an iodine prefilter.