Recent studies in nuclear power plant safety. (2) Experimental studies on heat transfer to core spray

A multirod fuel assembly was spray-tested to evaluate the feasibility and performance of a core spray cooling system to remove decay heat from the reactor core in the event of a loss-of-coolant accident. The test assembly consisted of 16 identical heat rods of 12 mm diameter, about 3 m effective heating length and 6 kW heat output per rod arranged in a square lattice inside a 71 x 71 mm stainless steel channel. The range of test variables covered included flow rates up to 30 l/min, heat fluxes up to 4 x 10⁴ kcal/hr-m² and system steam pressures ranging from 0 to 6.5 kg/cm²g. The results of the experimental data can be summarized as follows: (1) Sprayed water particles did not flow down into the channel as envisaged, obstructed by the upward steam flow induced by the vacuum created by spray cooling of the steam above the channel. (2) The heater was cooled quite strongly by this up-flowing steam, and high values of heat transfer coefficient were observed. (3) Correlation of the spray cooling data was within 20% using a McAdams equation for the steam. (author)