Pressure Suppression Pool Hydrodynamic Effects in Containment System of Indian PHWRs

Abstract

The standard Indian PHWR design incorporates a pressure suppression type of containment system with a suppression pool. This containment design requires evaluation of structural loads arising from dynamic effects of steam-air mixture, being rapidly forced into the suppression pool during postulated LOCA events. The major effects to be considered include loads arising from (i) acceleration and ejection of water column from vent downcomers during the initial vent clearing stage followed by (ii) pool swell as influx of air into the pool lifts up and accelerate the slug of water above it, and subsequently, (iii) 'chugging loads' arising from unsteady condensation of steam in the pool. The analysis for vent clearing acceleration and pool swell is based on thermal hydraulic calculation using basic principles. With regard to chugging phenomena, based on published information on experimental studies, it ha~ been possible to conclude that Indian PHWR containments would not be susceptible to such loads owing to the presence of large fraction of air in the steam-air mixture. Analytical studies on chugging have also been initiated specifically for containment of 500 MWe reactors. Several inputs of steam flow rate history (obtained by multiplying the actual flow rate history by a factor ranging from 0.01 to 1.0) were considered to evaluate chugging loads. For flow rate too small (factor = 0.01) or too large (factor = 1.0) chugging did not occur.