Effectiveness of SFP Spray Cooling during Loss of Coolant Accidents

For a large Spent Fuel Pool (SFP) loss of coolant accidents, properly sized SFP spray can slowdown or possibly preclude fast heat-up of spent fuel. The MELCOR 2.1 model of NPP Krsko pool was developed and tested for cases of loss of cooling accidents. The simple spray system with spray nozzles distributed at specified location at the top of the pool was added to the model. Different loss of coolant rates where studied for different fuel heat loadings, and different openings and flow rates of the spray nozzles. Traditionally, spray nozzles able to produce larger diameter droplets are used close to the fuel locations with higher heat loadings. According to preliminary results, spray nozzles that will be installed are able to limit or delay long-term heat-up of the spent fuel, but in the case of late actuation it is possible to have temporary high oxidation rates and corresponding production of hydrogen.