PREVENTION POSSIBILITY OF NUCLEAR POWER REACTOR MELTDOWN BY USE OF HEAT PIPES FOR PASSIVE COOLING OF SPENT FUEL

In Japan, following a major earthquake, a 15-metre tsunami disabled the power supply and cooling of three Fukushima Daiichi reactors, causing a nuclear accident on 11 March 2011. All three cores largely melted in the first three days. The accident was rated 7 on the INES (International Nuclear Event Scale) scale, due to high radioactive releases in the first few days. After two weeks the three reactors (units 1-3) were stable with water addition but no proper heat sink for removal of decay heat from fuel. By July they were being cooled with recycled water from the new treatment plant, and reactor temperatures had fallen to below 80oC at the end of October, and official 'cold shutdown condition' was announced in mid December. In this paper, the nuclear power plant No. 4 at Fukushima was chosen for the analysis - thermal power 2,381 MW; electrical power 784 MW; 658 spent fuel bundles (39,456 spent fuel rods); spent fuel water pool volume 1,400 tonnes. Detail analysis of various heat pipe design cases to determine the best design concept in terms of cooling power, construction and cost are presented. The best design when considering thermal safety margin and cost is the heat pipe cooling 0.9 MW; 1,662 heat pipe modules; water temperature will reach to peak 68 °C after 75 hours, and will be saturated at 50 °C after 2,000 hours. The estimated cost for complete heat pipe cooling system is about 2.16 Millions USD.