Effects of Core Spray Cooling at Stationary State after Loss of Coolant Accident

Abstract

In order to determine the conditions under which core spray cooling can be effective after loss of coolant accident, spray cooling experiments have been conducted on a heater assembly at low heat fluxes corresponding to the decay heat following a reactor shut-down. A series of tests have been made at atmospheric pressure using two kinds of 36-rod heater assemblies (15 mm O.D. sheathed heaters arranged in 119 mm square channels, 1,500 mm and 2,500 mm heated length). The following results were obtained: The heaters are cooled either by water a film of water streaming down its surface or by fog-flow and radiation to surroundings. The rate of flow along any single rod did not generally deviate much from the value of the total channel flow rate multiplied by the ratio of cross [sectional areas between single rod and total channel, but the smallest value was about 0.4 of this average. So long as the heat transfer surface is covered by water, the surface temperature is close to the saturation temperature. Once the covering film is dried up, the heat flux becomes related to the temperature of the wall above that of saturation by the equation The dry-out is caused either by progressive evaporation of the falling film (applicable to the range of the channel flow rates up to 400 kg/hr at 20°C water) or by “choking” (or flooding) with the ascending flow of steam generated in the channel (range of the channel flow rates above 400kg/hr at 20°C water). © Taylor & Francis Group, LLC.