RELAP5 code study of ROSA/LSTF experiment on a PWR station blackout (TMLB') transient

Takeda, Takeshi ; Nakamura, Hideo  

One of abnormal transient tests was conducted with the ROSA/LSTF simulating a PWR station blackout transient with the TMLB scenario in 1995. Influences of AM measure and coolant injection conditions into SG secondary-side onto core cooling were clarified as RELAP5 code parameter study of the LSTF test. SG secondary-side depressurization as the AM action was initiated by fully opening the safety valve in the loop without pressurizer (loop-B) with the incipience of core uncovery, while coolant was injected into the SG-B at low pressures. The AM action and the coolant injection with larger flow rate would contribute to maintain core cooling by accumulator system actuation. In the test, long-term single-phase natural circulation continued until liquid level formed in hot leg. The primary-side fluid temperatures in SG U-tubes indicated non-uniform flow distribution including reverse flow at different timings. Core uncovery by boil-off took place, while the primary pressure was kept high.