By Brian Wheeler, Editor
The world watched on March 11, 2011, as the earthquake-caused tsunami rolled onto the shores of eastern Japan and directly into the six-unit, 4,600 MW Fukushima Daiichi nuclear power plant. The 9.0 magnitude Tohoku earthquake, one of the largest ever recorded, triggered a tsunami that overwhelmed the power plant. More than 20,000 people either lost their lives or are still considered missing. Another 100,000 were displaced from their homes.
The total cost of damage is expected to near $220 billion. In total, 14 nuclear power units along the coast of Japan were affected by the earthquake and tsunami. Both the Onagawa and the Tokai stations were safe from the looming disaster at Fukushima due to the height of these plants.
When the tsunami hit the Fukushima plant, Units 4, 5 and 6 were already in a cold shutdown state in various stages of refueling. As large as the earthquake was, the units that were operating at full power, Units 1, 2 and 3, shut down as they were designed to, even though the design basis at Fukushima Daiichi was for earthquakes with magnitude of 8.2 or below.
The problem was not the earthquake. When the tsunami struck the plant, the cooling systems for Units 1 through 4 were rendered inoperable as backup generators were disabled. The plant was designed for a tsunami of roughly 5.7 meters, or about 19 feet. The tsunami triggered by the earthquake is believed to have been as tall as 48 feet. Due to the diesel generators being placed below grade, the critical equipment was lost when the flooding began resulting in the inability to bring the reactors to a safe, cool shutdown. This led to the fuel melting at Units 1 through 3 and serious damage to Unit 4. In December 2011, all reactors entered into a cold shutdown state.
Now, one year later, the plant looks as it did on the day of the disaster, according to those who have been to the site.
“I have to admit that it’s still rather fragile,” Fukushima Daiichi plant chief Takeshi Takahashi told The Associated Press during a tour in March. “Even though the plant has achieved what we call ‘cold shutdown conditions,’ it still causes problems that must be improved.”
Japan’s Prime Minister Goshi Hosono has proposed new regulations for Japan’s reactors that would limit the operation to 40 years. Japanese regulation gives reactors an initial 30-year lifetime with additional 10-year extensions. The Japanese government has said it is revising seismic and tsunami safety standards for facilities.
According to a paper from the Carnegie Endowment for International Peace, the disaster at Fukushima could have been prevented if the operators, the Tokyo Electric Power Co., or TEPCO, and the Nuclear and Industrial Safety Agency would have taken the proper steps.
|A satellite image of the Fukushima Daiichi nuclear power plant after the earthquake and tsunami. Photo courtesy DigitalGlobe.|
“The plant would have withstood the tsunami had its design previously been upgraded in accordance with state-of-the-art safety approaches,” according to the paper.
The paper’s authors, James M. Acton and Mark Hibbs, both senior associates for Carnegie’s Nuclear Policy Program, said moving emergency power supplies to higher ground or into watertight bunkers could have possibly saved the equipment; one of several steps they said were overlooked.
“In the final analysis, the Fukushima accident does not reveal a previously unknown fatal flaw associated with nuclear power,” the authors wrote. “Rather, it underscores the importance of periodically reevaluating plant safety in light of dynamic external threats and of evolving best practices, as well as the need for an effective regulator to oversee this process.” TEPCO is now focused on decommissioning activities. Japan’s science ministry has committed up to $57 billion in research funds for the upcoming fiscal year to help decommission the Fukushima reactors, a process that could last 40 years. According to the Nuclear Energy Institute, a consortium made up of Hitachi General Electric Nuclear Energy, Mitsubishi Heavy Industries and Toshiba will determine how to locate fuel debris inside Units 1, 2, and 3, and how to fill the pressure vessels with water. Funds will also be used to investigate possible corrosion of the units after sea water was pumped into them in March 2011 for cooling.
|Debris removal takes place on Jan. 5, 2012. Photo courtesy TEPCO.|
Just days after the tsunami, Shaw Group representatives were in Tokyo at the offices of Toshiba. Shaw, with Toshiba, presented a 10-year plan to TEPCO to help bring the plant to a stable condition. TEPCO did come up with a plan which encompassed many of the elements Shaw and members of their team had presented to the utility.
Although the principle focus was to bring the reactors to a cold shutdown state, the contaminants on-site and in the water had to be addressed. There was a significant amount of sea and fresh water that was injected into the reactors. Containment buildings, turbine halls and other connected facilities flooded.
As a Louisiana-based company that is familiar with water-based environments, Shaw, with Toshiba, began assisting TEPCO by designing a purpose-built treatment system to treat water and decrease contaminant levels.
“We found that we could help address the issue of water management,” said Jeffrey Merrifield, senior vice president of Shaw’s Power Group.
|Inspection of the main steam isolation valve inside containment at Unit 4. Photo courtesy TEPCO.|
Shaw, along with specialized contractors from the U.S., constructed shielded containers that possessed specialized resins to capture contaminants. Millions of gallons of water were passed through these filtration systems after they were operational in August 2011.
“On one end water had very large amounts of contaminants. The other end was water stripped of those contaminants,” said Merrifield. “We really put into place a system that can be used to treat those massive volumes of water and it has been a resounding, albeit quiet, success.”
Operating at about a 98 percent capacity factor, Merrifield said this system was also designed and built rapidly. A project of this magnitude can take years, yet the team was able to deploy the system at Fukushima in a matter of months. TEPCO currently has about 160,000 cubic meters of removed water stored in tanks on-site.
Today, about 3,000 workers are at Fukushima Daiichi assisting in the recovery efforts. According to TEPCO’s strategy for the decommissioning of the plant, steps 1 and 2 have been completed as Phase 1 is just beginning.
“The utility is not moving as rapidly on removing the fuel from spent fuel pools, or completing other remedial activities at the site, as we had once envisioned,” said Merrifield.
The Japanese government has been very focused on providing remediation to decrease the amount of radiation in towns and villages surrounding the plant so people may return to what is left.
|IAEA’s fact-finding team gathers information from the Fukushima Daiichi site to share with the global nuclear industry. Photo courtesy IAEA.|
Working with the U.S. Department of Energy, the Environmental Protection Agency and the U.S. Army Corps of Engineers on hazardous waste projects, Shaw also can assist the Japanese government in moving citizens back to their towns.
“We are very familiar with the kind of steps you need to take to remediate soil, remediate water, de-contaminate houses and things of that nature,” said Merrifield. “It is those same types of skill sets that we hope to utilize in Japan to help them move through this a whole lot quicker.”
To prevent radioactive material from entering the sea, TEPCO over the next four months plans to cover about 17 acres of the seabed near the cooling water intake systems with a two-foot-thick mixture of cement and clay. To keep emissions down, a cover has been installed over the top of Unit 1 and TEPCO plans to do the same on both Units 3 and 4 this year.
TEPCO is also considering the use of an underwater robot to get a view inside the containment of reactors 1 through 3. Repairing the vessels so the fuel can be removed is a process that could last two years under TEPCO’s strategy. This could be the most difficult task ahead for TEPCO. Japan has never decommissioned a nuclear power facility. Merrifield said they have taken down research reactors.
To share expertise and knowledge of lessons learned between global operators and governments, the International Atomic Energy Agency and the World Association of Nuclear Operators said they are revising their partnership. The two organizations will coordinate more closely on peer reviews and safety of individual plants and discuss ways to further improve information sharing.
“One of the lessons of Fukushima is the need for strong and effective communication between governments, regulators and nuclear operators,” said IAEA Director General Yukiya Amano. “By working more closely together, we can help to ensure that practical experience is properly shared to reinforce nuclear safety everywhere.”
Lessons will continue to be learned from the Fukushima disaster, as they were in the case of Chernobyl and Three Mile Island. Since the disaster, regulatory authorities from 23 different countries have contributed information on national response activities and stress tests reports. To help defend against natural disasters, the U.S. nuclear industry has developed a strategy known as the diverse and flexible coping strategy, or FLEX. This strategy will address the main problem at Fukushima, the loss of power to cooling systems.More Power Engineering Issue Articles
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