Parallel channel effects and long-term cooling during emergency core cooling in a BWR/4

The effectiveness of the core spray cooling system and the low pressure coolant injection system during a design basis accident in a boiling water nuclear reactor (BWR) was investigated. This investigation considered a BWR/4 with both intact and broken jet pumps during the short-term and long-term core cooling of a postulated loss of coolant accident (LOCA). The experiments were performed in a special parallel channel effects (PCE) test section in which Freon-114 was used to simulate the conditions in a BWR/4. The PCE test section simulated the major regions of a BWR/4, namely: three heated parallel channels; a bypass channel; a bypass-to-channel leakage path; a jet pump; lower and upper plena; a steam separator and standpipe; and a downcomer. Extensive use of glass components in the PCE test section provided visual observation of the thermal-hydraulic phenomena. In order to fully simulate BWR/4 response during postulated LOCA events, the PCE test section used included two flow paths simulating jet pump breaks at the lower seal of the downcomer region and at the mixing section's slip joint. Detailed analyses were performed to simulate the proper bypass leakage flow, the countercurrent flow limitation at the upper tie plate, and the size of the jet pump break areas in the PCE test section. To insure proper scaling of the reflood rate, transient and steady-state analytical models were developed to predict the two-phase level in the core regions of a BWR/4 and the PCE test section