LARGE LOCA ANALYSIS OF INDIAN PRESSURIZED HEAVY WATER REACTOR - 220 MWe

Loss Of Coolant Accident (LOCA) in a Pressurized Heavy Water Reactor (PHWR) leads to coolant expulsion in a primary heat transport system resulting in depressurization and possible core voiding. This results in deterioration of cooling conditions in reactor channels and increase in power before reactor shutdown, leading to higher fuel temperatures. Coolant expulsion rates during LOCA are dictated by critical flow conditions governed by initial plant conditions prior to the accident, break geometry, location of break, etc. In addition the PHWR s have positive void- coefficient of reactivity for coolant resulting in reactor power rise in earlier part of LOCA, when the stored heat of the fuel has yet not been removed. If, in addition heat transfer to the coolant drops sharply, very high fuel surface temperatures are expected. This paper describes analysis carried out for header break LOCA. I. THE PRIMARY HEAT TRANSPORT SYSTEM The primary heat transport (PHT) system of a standardized 220 MWe Indian PHWR consists of number of parallel channels in figure-of-eight loop configuration, with one pair of steam generators and pumps in each leg of the loop. Out of the total 306 fuel channels in the Kaiga APS, flow through 153 channels is from South to North and the flow direction in the remaining 153 channels is from North to South. A schematic of the primary heat transport system is shown in Fig.1.