Struggling against earthquake aftershocks, devastating floodwaters and debris, employees at Tokyo Electric Power Co.’s (TEPCO) Fukushima Daini nuclear energy facility safely shut down all four of the facility’s reactors within days of the historic 9.0-magnitude earthquake and tsunami that struck on March 11. The facility is located only seven miles southwest of its sister plant, Fukushima Daiichi, and produces enough electricity to power roughly three million homes and businesses in Japan.
When the earthquake struck, the Fukushima Daini facility automatically shut down safely as designed. However, it went into a state of emergency following the tsunami when water damage disrupted heat removal systems in three of the four reactors.
TEPCO reactor operators were able to quickly bring reactor 3, which had retained its heat removal function, into stable condition in a matter of hours. Meanwhile, other employees worked feverishly around-the-clock to reestablish heat removal capability in the other three reactors and finished stabilizing them by March 15.
A key distinction between the post-disaster conditions at Fukushima Daini and Fukushima Daiichi was that off-site power was available at the Daini facility, whereas the Daiichi plant suffered a complete loss of electricity, including backup generators and, eventually, emergency batteries needed to power reactor cooling systems. Fukushima Daini workers were able to tap into electricity from a 500-kilovolt-transmission line – a key lifeline – to power a water injection system that helped cool the reactors as they shut down.
Kenji Tateiwa, TEPCO’s manager for nuclear power programs, said that while adding water to the Fukushima Daini reactors was successful, heat needed to be removed from the recirculating water to keep the reactors in safe condition and bring them into cold shutdown. Since much of the equipment critical to this process was rendered inoperable by the tsunami, plant management had to acquire replacement equipment quickly.
“It was extremely challenging to conduct a plant walk-down with special safety measures in the midst of ensuing tsunami alerts and darkness. However, based on this inspection, we were able to put together a recovery strategy with clearly-defined priorities,” explained Fukushima Daini’s Site Vice President Naohiro Masuda.
TEPCO officials arranged for equipment, including motors and cables, to be sent via truck from its Kashiwazaki-Kariwa plant, located more than 200 miles away. The one-two punch of the earthquake and tsunami destroyed or damaged several major roads, making the equipment difficult to deliver, but the truck succeeded in reaching the facility. Using a helicopter from Japan’s Self Defense Force, TEPCO also flew in a motor from a Toshiba factory in southern Japan to help restore cooling capability.
Workers also had to restore power by laying more than five miles of heavy electrical cables by hand, a painstaking process that typically requires machinery. This process would have typically taken 20 people two months to complete, but the workers at Fukushima Daini accomplished this task in just one day. There was a large amount of debris strewn throughout the facility’s 370 acres that workers had to remove while trying to restore electricity.
“TEPCO civil engineers and other workers cleared debris in the darkness; during significant earthquake aftershocks while tsunami alerts were still in effect,” said Tateiwa.
Tateiwa visited TEPCO’s emergency response center in Tokyo and saw first-hand the difficult task of managing information and emergency response at both Fukushima facilities. TEPCO’s emergency response center relied on video conferencing with staff from the company’s nuclear facilities, along with the regional headquarters in Fukushima prefecture to communicate and properly allocate resources.
Fukushima Daini’s staff managed the events in March in accordance with the facility’s emergency response procedures and staffing was an important consideration.
“Officials allocated employees with operating experience in the control rooms and people with an engineering background were staffed in the emergency response center,” said Tateiwa. “They were in constant communication so that the engineers knew how to best support the operators.”
TEPCO has kept the four reactors at Fukushima Daini in cold shutdown condition since March. The company has added backup equipment and new layers of safety to the facility so that it will be better prepared to withstand another earthquake or tsunami.
Evaluating Lessons Learned
After the Fukushima Daini reactors had been stabilized for several weeks, TEPCO asked the Palo Alto, Calif.-based Electric Power Research Institute (EPRI) to independently review and inspect the facility for earthquake and tsunami damage and to evaluate the company’s plans for improving plant safety. (For more on EPRI’s post-Fukushima activities, click here.)
The review team visited the facility in May and found the earthquake didn’t damage any safety-related structures or systems. However, the tsunami significantly damaged the facility’s heat exchanger buildings, which provide cooling capability to the reactors. EPRI identified short- and long-term recommendations for improving the plant’s ability to withstand extreme events. Many of the short-term recommendations already have been completed.
Key lessons learned from both Fukushima nuclear energy facilities are being shared and incorporated by nuclear plant operators around the world. According to Fukushima Daini’s plant manager, Shinichi Kawamura, three key takeaways have emerged from the facility’s response to the natural disaster:
- Senior leaders at every level made their expectations clear from the beginning and held employees accountable for fulfilling their roles and responsibilities, allowing them to effectively manage the organization throughout the crisis. Kawamura identified this as the most important lesson from his experience at Fukushima Daini in March.
- The facility’s Emergency Operating Procedures (EOPs) were essential in guiding reactor operators to safely stabilize each of Fukushima Daini’s four reactors. “By having procedures in place before this event and maintaining thorough understanding of these procedures through continuous training, we were able to quickly begin recovery efforts and modify them as needed,” said Kawamura. “The EOPs enabled our employees to clearly understand their responsibilities and to know which actions took priority, saving precious time during the recovery process.” Every nuclear power plant operator in the United States also has EOPs in place to respond to a wide variety of extreme events, including earthquakes.
- Plant management successfully prioritized recovery and response activities, determining the most important equipment that needed to be provided by TEPCO headquarters to replace critical systems that were destroyed by the tsunami. This saved time and was critical in recovering key safety components.
“This experience reminds us of the importance of the alliance between the U.S. nuclear energy industry and Japan,” said Tateiwa. “The U.S. nuclear energy industry was the first to come to Tokyo to support TEPCO, and the Institute of Nuclear Power Operations has stationed a team that we can rely on for industry guidance. They have been extremely supportive. We’d like to share our lessons learned so that we can make nuclear power plants in both countries, and around the world, even safer.”