BEHAVIOR OF AN INDIAN PHWR FUEL CHANNEL DURING A LARGE LOCA COINCIDENT WITH THE FAILURE OF ECCS - A NEW APPROACH

摘要

Large Break Loss of Coolant Accident (LOCA) in Pressurised Heavy Water Reactors (PHWRs) along with failure of Emergency Core Cooling System (ECCS) causes a near total voiding of the reactor core. In such situation the core experiences very low flow which leads to poor heat removal from the fuel bundles. The power excursion, stored heat and decay power can cause overheating and damage of the fuel pins as well as the pressure tube. A detailed thermal hydraulic analysis has been carried out for the maximum rated reactor channel. The analysis is carried out using the computer codes RELAP4/MOD6 and inhouse codes HFLOWR and HT/MOD4. The case analysed is for a double ended guillotine rupture of the Reactor Inlet Header (RIH), which is the biggest diameter pipe in the reactor piping network for 220 MWe Indian PHWRs. The analyses predict a contact of the Pressure Tube and the Calandria tube at an early stage of the transient. The mode of contact is due to the sagging of the Pressure Tube thus ensuring the heat removal from the reactor core to the moderarator system.