Condensation effects in large scale BWR safety experiments

Experiments addressing thermal hydraulic phenomena under Loss-of-Coolant-Accident (LOCA) conditions have been conducted in a full scale 30 degree sector mock-up of the Boiling Water Reactor (BWR). The test program included both steady pressure and transient LOCA simulation, at system pressure up to ten atmospheres, and covered both specific thermal hydraulic phenomena and system response under blowdown/refill/reflood performance. Two condensation effects observed in these experiments contributed to the effective system refill/reflood performance. Two condensation effects of particular interest are core spray injection leading to localized subcooling in the upper plenum that breaks down counter-current flow limiting at the top of the core, and low pressure coolant injection leading to subcooling in the lower plenum that reduces liquid flow out the jet pumps. Both of these effects augment plenum refill and core reflood. Other condensing effects identified and evaluated are evidenced by the coupling of upper plenum two-phase level with core spray injection location, and the periodic flooding and voiding of the guide tube region. Condensation effects do not lead to system performance instability or oscillation, and the phenomena are satisfactorily modeled by system analysis methods