The events at Fukushima unveiled an important lesson to the nuclear industry on the need to remotely monitor water temperature and levels in used fuel storage pools during an extended loss of power. In particular, when power was lost at Japan’s Fukushima Daiichi reactors, the systems the plant relied on to monitor the used fuel pools were inoperable. That loss led some to erroneously conclude that there was no water in the spent fuel pool at reactor 4—a conclusion that was later proven to be false.
The industry supports the Nuclear Regulatory Commission’s (NRC) recommendation that U.S. nuclear energy facilities enhance used fuel pool monitoring instrumentation. The storage pools protect used fuel rods under 40 feet of water to allow radioactivity in the fuel to safely decrease. Adding backup monitoring equipment enables operators to know when they need to take action to maintain water level and temperature of used fuel storage pools in the unlikely event that installed systems have been disabled.
By monitoring used fuel pools from remote locations, operators are able to prioritize actions, if needed, when a nuclear energy facility endures an extreme event. The industry is pursuing post-Fukushima safety enhancements that take into account differences in plant designs, locations and vulnerabilities. The process for monitoring used fuel storage pools is no exception. Placing monitoring equipment in diverse locations and training operating crews to respond to extreme events on a case-by-case basis will further safeguard used fuel.
In the months since Fukushima, the industry has taken steps to ensure that used fuel storage pools are adequately cooled and protected at all times. In addition to enhancing backup sources of cooling water, the industry immediately sought to provide additional information to operating crews regarding water temperature in storage pools.
Just weeks after the accident, the Institute of Nuclear Power Operations (INPO), the industry’s own watchdog body, required U.S. plant to know how long it would take the used fuel pools to reach 200oF. INPO also required plants to ensure that the water temperature would remain below 200°F for at least 72 hours following the loss of active cooling. U.S. plants have the ability to maintain cooling water to a used fuel storage pool in the event of a loss of power–well before it becomes a safety issue.
The new INPO requirement proved useful after the East Coast earthquake in August. Operators at the North Anna Power Station in central Virginia could easily check the storage pool logs to know that the pools were not in any danger of overheating immediately following the earthquake.
“The North Anna example demonstrates the value of providing accurate spent fuel pool information to plant operators,” said Steven Kraft, NEI’s senior director for Fukushima regulatory response. “We will further enhance the safety of our spent fuel pools by providing this additional instrumentation.”
Used fuel storage pools are robust steel and concrete structures capable of maintaining cooling water levels and protecting used fuel rods even under the most extreme circumstances. If electrical power is interrupted for any reason, backup systems and procedures are in place to ensure that cooling water is supplied to the pools.
Even when the sources of cooling water to the storage pools at Fukushima were temporarily interrupted, there was ample time to ensure that the fuel was safely maintained. The heat generated by used fuel causes a slow increase in water temperature and evaporation, giving operators days to implement backup safety procedures in the event of a problem.
The U.S. nuclear industry ensures each day that used fuel is safely stored and protected. Following the 9/11 terrorist attacks, the industry made substantial safety enhancements at all nuclear plants, including improving the ability to keep used fuel storage pools cool in an emergency. The post-9/11 enhancements, combined with the additional installation of remote monitoring instrumentation, will layer precaution on top of precaution to mitigate the effects of any potential disruption.