Simulation tests of BWR non-LOCA transients using the TBL

In the last decade, a large number of experiments have been performed in order to understand the thermal-hydraulic response in a boiling water reactor (BWR) under postulated loss of coolant accident (LOCA) conditions. These experimental results showed that the core cooling effect under the LOCA conditions was significantly affected by three-dimensional and multi-bundle phenomena after emergency core cooling systems (ECCSs) started. Also, the peak cladding temperature (PCT) during the LOCA was kept below a specific value of the licensing acceptance criteria, 1473 K (1200deg C). These key results of the experiments were incorporated into a computer code, SAFER, which was developed for the BWR LOCA/ECCS analyses under the cooperative studies of Hitachi Ltd, Toshiba Co., and General Electric Co. (GE). In a couple of years, the experimental study of multi-bundle phenomena was extended into the area of off-normal and non-LOCA transients. Thermal-hydraulic responses during boiling transition were studied using the TBL (Two Bundle Loop) test facility with two full-length bundles. The experimental results showed that interaction and feedback effects between the bundles were expected to be unaffected by core cooling during the typical off-normal and non-LOCA transients. Also, the SAFER showed good predictions for hydraulic responses in the bundles and temperature transients of the rod surfaces. (orig.)