ANALYSIS OF STEAM-GENERATOR U-TUBE RUPTURE AND INTENTIONAL DEPRESSURIZATION IN LOBI-MOD2 FACILITY

LOBI-MOD2 results from an experimental investigation of a steam generator tube rupture (SGTR) with no active emergency core cooling system (ECCS) available are presented. The characteristic system response, following a three-tube break occurring during normal full power operation, is analysed. Thermal-hydraulic data for a phenomenological understanding of natural circulation, the reflux condenser heat transport mode and core dry-out at high primary pressure are provided. The importance of the availability of the ECCS for the SGTR mitigation is outlined by comparing the above mentioned data to the results of a second LOBI test on SGTR with the same break area but with the standard ECCS in operation. The effectiveness of a new recovery procedure, starting from highly degraded core scenarios, is also examined. It relies on intentional primary system fast depressurization through the pressurizer relief valves and passive accumulator injection. Primary passive feed and bleed for the long term cooling can improve the safety criteria for the design of nuclear power plants (NPPs).