Over the years, the nuclear power industry and the U.S. Nuclear Regulatory Commission (NRC) have conducted many studies to evaluate the safety of U.S. used fuel pools. Logically, the concern about the safety of U.S. used fuel pools increased following the 2011 earthquake that affected the Fukushima Daiichi Nuclear Plant in Japan.
All of the used fuel rods from more than five decades of electricity production at U.S. nuclear energy facilities are stored in used fuel storage pools or above-ground dry storage containers. When fuel is removed from the reactor, it is stored under water in fortified concrete, stainless steel-lined pools. The water helps cool the fuel and shields workers and the environment from radiation. After cooling in the used fuel storage pool, assemblies may be moved into robust steel and concrete dry storage containers also built to withstand extreme conditions such as earthquakes and tornadoes.
Multiple layers of safety systems ensure the cooling water level is maintained even during extreme events such as hurricanes, earthquakes and floods. Although the pool’s water level at the Fukushima Daiichi plant was sufficient, plant personnel assumed the worst and made many attempts to add water to the pool, including dropping water from helicopters. These actions distracted the site from addressing the main problem of damaged reactors.
Following the incident in Japan, the NRC ordered U.S. nuclear power plants to add instrumentation to their used fuel pools. That way, if an accident occurs plant staff would be able to tell if the pools need attention. The ultimate goal of instrumentation is to keep the public safe by helping plant staff properly prioritize their accident response.
Although U.S. reactors already monitor a small fraction of the water level in the used fuel pool, this system may not work if power is lost, as it was at Fukushima, and can’t provide advance warning of low water levels.
The NRC’s order requires U.S. reactors to be able to tell whether water is at or above certain levels. The highest level means enough water is available for the normal cooling system to work, while the lowest level is still enough to cover the fuel, but warns staff to begin adding more water to the pool. The NRC order also requires plant staff to be able to read these levels from a location away from the pool, such as in the main control room.
U.S. plants must install the new instruments no later than two refueling cycles after submitting plans to the NRC or by the end of 2016, whichever comes first. All U.S. plants, including Duke Energy plants, submitted their instrumentation plans in February 2013. The NRC recently issued interim evaluations so plants can order equipment and move forward with installing the instruments.
Shortly after the incident at Fukushima, the NRC staff also assessed whether a severe earthquake could damage used fuel pools of the same reactor type as Fukushima to the extent of uncovering the fuel and whether this should warrant expediting moving used fuel from wet pools to dry storage.
The study results found that this type of used fuel pool is very likely to withstand severe earthquakes without leaking and that reducing the volume of used fuel in storage pools would be of minimal value. Based on this study and previous studies, the NRC staff concluded that used fuel pools adequately protect public health and safety.