By Brian Wheeler, Editor
A satellite image of the Fukushima Daiichi nuclear power plant after the earthquake and tsunami. Photo courtesy of DigitalGlobe.
The ongoing crisis at the Fukushima Daiichi nuclear power plant in Japan could be brought under control within the next six to nine months, according to a plan put together by the plant’s operator, Tokyo Electric Power Co. (TEPCO). The company said that “By bringing the reactors and spent fuel pools to a stable cooling condition and mitigating the release of radioactive materials, we will make every effort to enable evacuees to return to their homes and for all citizens to be able to secure a sound life.”
Using its plan, TEPCO set two steps as the first targets. In the first step, radiation within and around the plant must take a steady decline. TEPCO expects the decline in radiation could take three months. But to achieve Step 1 the company said it must overcome two “critical” issues. It must prevent hydrogen explosions inside the primary containment vessel (PCV) in Units 1, 2 and 3. Cooling the reactor by injecting fresh water into the reactor increases the chance of steam condensation, raising concerns of potentially triggering a hydrogen explosion. Because of this, TEPCO will inject nitrogen gas into each unit’s PCV to keep the concentration of hydrogen and oxygen below flammability levels. TEPCO said it also must prevent the release of contaminated water with high radiation levels outside of the site boundary from Unit 2.
After achieving this multi-part first milestone, TEPCO hopes to have the release of radioactive materials under control and for the radiation dose to be “significantly held down.” TEPCO plans to complete the second step within three to six months.
In mid-May, TEPCO revised this plan after they discovered that the damage at Units 1-3 is more severe than they expected and could possibly suffer a meltdown. The revised plan will delay a step to fill the reactors with water to cool the fuel, since the company has found that the containment vessels are leaking. TEPCO had already begun filling Unit 1, but the discovery of the leak has led to tens of thousands of gallons of water leaking into the reactor building basement, according to Nikkei.
Under the revised plan, TEPCO is planning to recycle the contaminated water already in the complex. Nikkei reported that efforts are underway to build a water treatment facility and an air-based cooling system.
“Cold shutdown will be achieved without filling the reactors with water,” a Nuclear Industry Safety Agency official told the Japanese media outlet.
TEPCO workers have been trying to fill up the basement rooms of the reactor buildings with cement to plug leaks. But due to the hazardous working environments they have been unsuccessful as of yet. Still, TEPCO remains firm on its plan to have the reactors in safe shutdown in six to nine months.
A Long Time Coming
The process of dismantling the reactors at Fukushima is just getting started.
|Damage caused by the tsunami taken on April 11.Photo courtesy of TEPCO.|
In April, Hitachi—which supplied one of the plant’s six reactors—submitted a long-term plan to TEPCO to decommission the Fukushima Daiichi reactors once TEPCO has them cooled and in safe shutdown. Working with General Electric, Exelon Corp. and Bechtel Corp., Hitachi said the plan would include removing the fuel rods from the reactors and spent fuel pools, cleaning the contaminated facilities, disposing of all nuclear waste and dismantling the reactors and buildings.
Hitachi spokesman Masanao Sato told Nikkei News that such a process could take “about 30 years” to complete.
Hitachi has sent more than 300 employees to the site to help with reestablishing electricity supplies to the power station, cooling of the reactor pressure vessels and pools for spent fuel and draining water from the turbine buildings and tunnels.
Toshiba, which supplied two reactors as the main contractor and jointly supplied two others with GE at the complex, also submitted a long-term decommissioning plan. With help from the Babcock and Wilcox Co., the Shaw Group Inc. and Westinghouse Electric, Toshiba said its plan could take at least 10 years to accomplish.
“Over the last month we have been refining the comprehensive plan that would really take the site from its current status to a 10-year process to bring it to safe shutdown, put radiological materials in the appropriately safe places and get the site to the point where significant response activities are no longer needed,” said Jeffrey Merrifield, senior vice president of Shaw’s Power Group.
damage inside the unit 2 Control room taken on march 26. courtesy of TEPCO.
Merrifield said one of the first issues the team must address is radiological protection. The Shaw Group, with assistance from Bamp;W, Westinghouse and Toshiba, is placing radiological detection devices near the plant itself as well as in the area surrounding it, including parts of the evacuation zone.
The team has proposed clearing debris that currently rests around the units, especially around Units 3 and 4 which suffered hydrogen explosions. The team must figure out how to remove the contaminated debris, some of which is from secondary containment, to clear the way for workers to receive a lower dose of radiation when making their way into the site. Merrifield said they must gather the debris, bring down the roofline of Units 1, 3 and 4 and try to get the debris out of spent fuel pool so they can begin to clarify water in those pools.
“There has to be a wise, accelerated and well-crafted plan to move the material out of the spent nuclear fuel pools now and placed into a proper storage containment,” said S. Robert Cochran, president of the Babcock amp; Wilcox Technical Services Group Inc.
No approach has been approved for the spent fuel. After an option is approved, infrastructure to support the option must be put in place as well as the regulatory framework.
“We have to make sure that any long term option is done in a way that the Japanese will be comfortable with the outcome,” said Cochran.
|Workers perform grid line connection work to offsite power grid on March 18. Photo courtesy of TEPCO.|
Before the fuel can be moved it first must be cooled in accord with the long-term plan to have the reactors in a safe condition. One way to achieve this is to create a closed-loop cooling system and eliminate large volumes of contaminated water that is currently around the plant. As a Louisiana-based company that helped pump out New Orleans following Hurricane Katrina, Merrifield said the Shaw Group has experience that Japan may lack. Japan has not had a major radiological contamination event in its civilian nuclear history. Also, Japan has not decommissioned any major nuclear facilities.
“Working in a salt water environment is not new to us,” he said.
A conference takes place April 15 at the Emergency Response Headquarters to discuss the situation at Fukushima Daiichi. Photo courtesy of TEPCO.
Numerous challenges remain. One is that there are different situations with each of the six reactors at Fukushima Daiichi. Hydrogen explosions have left Units 1, 3 and 4 heavily damaged, so workers must approach them carefully. Units 1, 2 and 3 all had salt water injected into the vessels to help cool them. That water, with the ensuing corrosion, has put those reactors in a state that they likely will never again operate. Units 5 and 6 were both partially defueled at the time of the March 11 earthquake and tsunami and were in cold shutdown. Merrifield said in theory those two reactors could possibly operate again, although the decision is a political one for the Japanese government to decide.
“From a technical standpoint, you could restart the reactors. From a political and social decision, it is unclear what decision will happen for those two units.”
Bamp;W and the Shaw Group continue to move experts in and out of Japan. Both had been asked to provide quick- turnaround items that could help line up technology and resources in the U.S. to handle immediate needs in Japan. Cochran said his company has provided a series of technical papers and access to some in the U.S. vendor community to assist Toshiba and, ultimately, TEPCO and Japan itself.
“Clearly it is an unusual event to have a 9.0 earthquake combined with a tsunami,” he said. “Certainly there are challenges in any environment. Given the nature of devastation there would always be challenges.”
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