Evaluation of Hydrogen Release, Dispersion and it's Management in Containments of Indian PHWRs Under Accident Conditions

Abstract

An evaluation has been made regarding generation and dispersion of hydrogen in containment of the 235 MWe Indian PHWR under postulated accident conditions. For this purpose, metal water reaction between hot fuel clad and steam, and radiolysis of water are considered. For evaluating hydrogen release from metal water reaction, a postulated accident involving loss of coolant simultaneous with unavailability of ECCS has been considered. Radiolysis is based on interaction of beta and gamma energy from fission products with water in coolant and suppression pool, as well as with moderator water. Evaluation of dispersion of hydrogen in containment indicates that initially, the hydrogen concentration in the vault in which LOCA break takes place, is high. So is the steam concentration, with the result that detonability limit is not crossed, although flammability limit is crossed for a few minutes. In the rest of the containment, the hydrogen concentration due to metal water reaction stays below the flammability limits. However, over a period of days, concentration may build up due to radiolysis, requiring measures for disposal of hydrogen . Proposed features for management of hydrogen in the containment include (i) arrangement for mixing within the primary containment, and (ii) containment venting/scavaging provisions.