ROSA/LSTF experiment on a PWR station blackout transient with accident management measures and RELAP5 analyses

Takeda, Takeshi ; Otsu, Iwao 

An experiment on a PWR station blackout transient with accident management (AM) measures was conducted using the ROSA/LSTF under an assumption of non-condensable gas inflow to primary system from accumulator tanks. The AM measures considered are SG secondary-side depressurization by fully opening safety valves in both SGs with start of core uncovery and coolant injection into the secondary-side of both SGs at low pressures. The primary pressure started to decrease when the SG primary-to-secondary heat removal resumed soon after the SG secondary-side coolant injection. The primary depressurization worsened due to the gas accumulation in SG U-tubes after accumulator completion. The RELAP5 code indicated remaining problems in the predictions of the SG U-tube collapsed liquid level and primary mass flow rate after gas ingress. The SG coolant injection flow rate was found to significantly affect the peak cladding temperature and the ACC actuation time through RELAP5 sensitivity analyses.