Reliability of core exit thermocouple for accident management action during SBLOCA and abnormal transient tests at ROSA/LSTF

Suzuki, Mitsuhiro; Nakamura, Hideo  

Presented in the paper are experimental results on general performance of core exit thermocouple (CET) to detect core overheat for accident management (AM) action. Thirteen tests simulating small break loss-of-coolant accident (SBLOCA) and abnormal transient are studied by using the Large Scale Test Facility (LSTF) which is a full-height, full-pressure and 1/48 volumetric-scaled PWR model. Clarified are as follows, (1) general CET performance with certain delay in time and temperature rise from core overheating in most cases, (2) one common reason of the delay due to cooling effects of metal structures in core and core exit, (3) an indication of superheat instead of its temperature necessary for significantly high or low pressure transients, (4) no CET heat-up in case of large water fall-back from hot legs and in addition, discussion on applicability to PWR is presented.