Experimental investigation of sagging and ballooning in LOCA for Indian PHWR

In a nuclear reactor Loss of Coolant accident (LOCA) considers wide range of postulated damage or rupture of pipe in the heat transport piping system. In the case of LOCA with/without failure of emergency core cooling system in a Pressurised Heavy Water Reactor (PHWR), the Pressure Tube (PT) temperature could rise significantly due to fuel heat up and gross mismatch of the heat generation and heat removal in the affected channel. The extent and nature of deformation is important from reactor safety point of view. Experimental set-ups have been designed and fabricated to simulate sagging (downward deformation) and ballooning (radial deformation) of PT for 220 MWe Indian PHWRs. It is observed that sagging initiates at a temperature around 450° C. Contact between PT and Calandria Tube (CT) occurs at around 585° C. At 60 bar internal pressure and initial heat up rate of 2.37° C/sec, ballooning of PT initiates at a temperature around 520° C. The PTCT contact is found to take place at 640° C temperature. The structural integrity of PT is retained (no breach) for all the experiments. The PT heatup is found to be arrested after the contact between PT and CT, thus establishing moderator acting as an efficient heat sink for IPHWRs.