Safety study and human factor assessment of end-shield draining event for 220MWe Indian PHWRs

In Indian PHWRs (Pressurized Heavy Water Reactors), one of the major functions of the end-shield cooling system is to maintain temperature across the end-shield components uniform and thereby minimizing thermal stresses. Safety analysis considers draining of water from end-shield cooling system as one of the postulated event. In the PSA (Probabilistic Safety Analysis) Level-l study, failure to manually shut-down the reactor following this event was found to be one of the major contributors to Severe Core Damage. The deterministic and probabilistic studies as detailed in the paper, realistically evaluate contribution of the postulated event of end-shield draining in core damage and make a major input to Risk Informed Decision Making.