ROSA/LSTF test and RELAP5 code analyses on primary feed-and-bleed operation during total loss-of-feedwater transient of PWR

Abstract An experiment was conducted using the rig of safety assessment/large-scale test facility (ROSA/LSTF), which simulated the primary feed-and-bleed operation during a total loss-of-feedwater transient of a pressurized water reactor. The primary feed-and-bleed operation included coolant injection from high-pressure injection (HPI) system into cold legs and the full opening of a power-operated relief valve (PORV) of pressurizer (PZR). In the LSTF test, the primary and steam generator (SG) secondary-side pressures were maintained, respectively, at around 16 MPa and 8 MPa by cycle opening of the PORV and of the SG relief valve until the start of the PORV full opening. Coolant behavior in the PZR affected the primary depressurization. The RELAP5/MOD3.3 code predicted well the overall trends of the major thermal hydraulic responses observed in the LSTF test, and indicated insufficient predictions of primary pressure, primary coolant distribution, and accumulator flow rate. The sensitivity analysis results clarified the primary pressure, the core collapsed liquid level, and the cladding surface temperature are largely influenced by the combination of the HPI total flow rate, the onset timing of the PORV full opening, and the PORV flow area within the defined calculation conditions.