Core spray and bottom flooding effectiveness in the BWR/6. Licensing topical report

A core heatup model is used to calculate the thermal response of the fuel assembly cladding in a General Electric BWR after a postulated loss-of-coolant accident. An extensive series of emergency core cooling tests was conducted to determine the modifications necessary to make the current model appropriate for calculations of the temperature response in an 8 x 8 bundle. Fifty tests were conducted with a full-scale, electrically heated, stainless-steel-clad mockup of a BWR/6 fuel bundle. Rod-to-rod and rod-axial power variation in the tests were very similar to those in the BWR/6 assembly. Transient simulations of the emergency cooling phase of the loss-of-coolant accident were conducted over a wide range of bundle power, coolant flow rate, and cladding temperature at the start of emergency cooling. Using the conservative Interim Acceptance Criteria assumptions, the maximum BWR/6 fuel cladding temperatures are calculated to be less than 16000F. With realistic assumptions, the maximum calculated temperature is approximately 7000F. Test temperatures higher than 16000F were obtained by starting bottom flooding at times significantly later than those appropriate for the BWR/6 accident. Therefore, the test conditions conservatively bounded the BWR/6 loss-of-coolant accident. The General Electric core heatup model was modified to match the test geometry and the test conditions, and the model was used to predict the thermal response of the test bundle. Predictions of maximum bundle temperature in BWR/6 accident simulations ranged from 300F below to 1000F above the recorded test maximum bundle temperatures. Therefore, the modified core heatup model is considered appropriate for use in BWR/6 loss-of-coolant calculations. It is concluded that no further confirmatory testing is required to demonstrate the adequacy of the model for application to 8 x 8 fuel geometry