Advancements on Spent Fuel Pools through Passive Cooling

This project addresses the Fukushima accident where spent fuel pools lost forced cooling and overheated. Although fuel was never uncovered in the accident, it was just a matter of time before boil-off and rapid evaporation would have led to exposed fuel and consequent fuel melting. A system has been designed to use the radiation of the spent fuel to power back-up circulation pumps to cool the pool water. Exposed spent nuclear fuel rods can emit strong damaging radiation, particularly gamma rays, and can quickly lead to a significant safety concern. Therefore, the goal of this project is to utilize gamma rays from the spent fuel to maintain the spent fuel pool below boiling temperature in the case of a similar accident. It is proposed to install solar cells within the fuel racks to produce electric power to operate circulation pumps. Solar cells are optimized for visible light. Gamma rays or other photons with energy greater than the band gap of the solar cell semiconductor will generate charge carriers and therefore enable a current, but energy greater than the band gap is lost. In addition, the interaction cross section for gamma rays decreases with increasing energy resulting in many of the photons penetrating without interaction. These problems can be solved by using a scintillator similar to those used in radiation detectors. Plastic Scintillators will be used for this project. Sodium iodide and cesium iodide yield high levels of visible light in response to gamma ray bombardment and could be used with solar cells, but plastic and glass scintillators can be used as well and are more robust and less expensive. Both solar cells and scintillators are inefficient, but the pool radiation level is intense, and there is room for thousands of solar cells. These solar cells are designed and meant to provide as much cooling as possible in the event of complete station blackout. This external system could be applied to all existing nuclear power plants, and contribute to preventing uncovering of spent fuel in a complete station blackout.