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Tokyo Electric Power Co. has radioactive water problems at its crippled Fukushima No. 1 nuclear plant that seem uncontainable, as seen in the latest case to beset the utility: tanks used to store highly tainted water that was used to cool its melted reactors but now must be safely stored are leaking.
The plant, part of which was built on filled-in land, also faces the risk of liquefaction if another big temblor hits.
The tank leaks come as Tepco struggles to halt the flow, some 300 tons a day, of highly radioactive groundwater into the Pacific, where it is believed wreaking environmental havoc.
And the groundwater problem will probably dog Tepco over the next four decades or so as it tries to scrap and entomb the spent fuel from reactors 1 to 4 and the melted fuel inside units 1 to 3.
A key to minimizing the exposure of groundwater to the highly radioactive coolant water leaking into the basements of the buildings housing the crippled reactors is to learn the courses the groundwater takes from the landward mountains to the sea under the plant, experts say.
“Figuring out the flow of the groundwater is vital, as it will help spot where the sources of contamination are and stop it from spreading further in the future,” said Atsunao Marui, a groundwater expert and principal senior researcher at the National Institute of Advanced Industrial Science and Technology, a Tokyo- and Ibaraki-based semi-public research body.
At the moment, Tepco has a rough idea of where the groundwater is flowing.
About 1,000 tons of groundwater flows from the mountains under the complex daily, and about 400 tons of it penetrates the basement walls of the buildings housing reactors 1 to 4 of the six-reactor plant, thus mixing with the highly radioactive coolant water leaking from the containment vessels.
The remaining 600 or so tons apparently flows to the sea and Tepco suspects about half of it gets contaminated somewhere else under the plant.
But the exact paths the groundwater takes have yet to be pinpointed.
Tepco compiled a groundwater flow simulation for an Aug. 12 meeting with experts from the Nuclear Regulation Authority, but the utility said the simulation was inaccurate.
According to Marui, the simulation was not difficult to draw up, but Tepco needs to collect more data from a wider area, even outside the plant, where it doesn’t have monitoring wells to check groundwater flows.
’If the government is really planning (to take a step forward to reducing the tainted groundwater), it needs to (support Tepco in) widening the monitoring points to outside the plant,’ including from the source of the groundwater and the mountainside, said Kazunari Yoshimura, an expert in water-related matters, who runs Global Water Japan, a water-consulting company.
To reduce the amount of groundwater flowing under the reactor buildings, Tepco dug a number of wells on the nearby mountains and plans to pump the water up before it has a chance to mix with radioactive water.
Aware of Tepco’s struggles, Prime Minister Shinzo Abe said earlier this month that taxpayer money will be pumped into a project to build barriers around the reactor buildings to prevent tainted groundwater from flowing to the sea.
Considering Tepco will have to deal with radioactive groundwater for about 40 years until the reactors are safely neutralized, getting accurate data about the groundwater, including the amount, depth and detailed flow paths, is essential if it is to take effective measures, said Yoshimura, who has advised Tepco on the problem.
Tepco must be aware that more monitoring wells need to be built but it is probably hesitant to do so outside the complex, in part because it lacks manpower, Yoshimura said.
The large volume of groundwater flowing under the plant is creating another problem – the possibility that the land it stands on will liquefy if another major earthquake hits.
The east side of the reactor buildings, in an area close to the sea where land was filled in, appears more vulnerable to liquefaction. Marui said the reclaimed land consists of clay and crushed rocks, through which water can easily pass.
Tepco recently injected liquid glass into the filled land, thereby forming an underground barrier to help prevent groundwater from reaching the sea.
Due to technical reasons, the barrier had to be built 1.8 meters below ground, meaning tainted groundwater can flow to the sea above it. Tepco officials believe that is happening now.
And because the wall is blocking a certain amount of groundwater, the level of groundwater has risen in the fill area, raising the risk of liquefaction if and when another earthquake hits, Tepco said. However, the plant’s turbine buildings are likely to withstand any earthquake because they are built on the bedrock, it said.
Before the nuclear crisis started on March 11, 2011, Tepco pumped up about 850 tons of groundwater per day from sub-drains to prevent it from flowing under the complex.
It recently started pumping groundwater from under the fill area to reduce the accumulation.
“(Tepco) is seeing a danger that the area near the sea might become like mud, so it is pumping up the groundwater,” said Marui.
Yoshimura of GWJ said if a another big quake hits the Fukushima plant, there is a risk that the highly radioactive water that is presently flooding the basements of the reactor buildings could flow out and further contaminate the groundwater.
Kazuaki Nagata, Japan Times Staff Writer, August 20, 2013
Tank at No. 1 lost 300 tons of radioactive water — Tepco claims barrier keeping leaked toxins from the Pacific
About 300 tons of highly radioactive water had leaked from a tank at the damaged Fukushima No. 1 nuclear power plant as of Tuesday afternoon, Tokyo Electric Power Co. said.
Tepco claims none of the water, which had been used to cool its stricken reactors and is highly radioactive, has flowed directly into the Pacific, apparently contained by a 30-cm-high waterproof concrete barrier surrounding dozens of tanks, including the leaking No. 5 tank. But some of the water may have been absorbed into the ground, joining with already tainted groundwater.
Where the leak is occurring in the tank, which is bolted together and has sealed seams, remains elusive, however, even after workers finished pumping water from inside the barrier Tuesday afternoon.
Rain was forecast across much of the Tohoku region, including Fukushima, Tuesday afternoon.
The pump is powerful enough to keep water from flowing over the 30-cm-high barrier fence, even if rainfall is heavy, Tepco executive and spokesman Masayuki Ono said at a news conference, adding: “We apologize again for causing anxiety among the public.”
The Nuclear Regulation Authority released a preliminary assessment of a level 1 incident on the eight-notch international severity scale for nuclear accidents.
The amount of beta rays being emitted by radioactive materials in the leaked water, including strontium, was 80 million becquerels per liter, Tepco said.
At 9:50 a.m. Monday, Tepco workers on patrol found a pool of at least 120 liters of highly contaminated water thought to have escaped from concrete barrierÅfs drain valves. The valves had been opened to drain rainwater.
The radiation level measured around 50 cm above the toxic water stood at about 100 millisieverts per hour, Tepco said.
Exposure to 100 millisieverts increases the incidence of death by cancer by 0.5 percent, according to the International Commission on Radiological Protection. It is also the legal upper limit for a nuclear worker over five years.
On Tuesday, Tepco said the water level in tank No. 5 had dropped by 3 meters, meaning about 300 tons of contaminated water had been lost. From Monday to Tuesday, about 10 tons were lost, indicating this amount may have leaked every day over the past 30 days, a senior Tepco official told The Japan Times.
“So far, we had four similar (tank) leakage cases. The problem this time is that we didn’t detect it for as long as 30 days,” the official said.
All five leaks were in temporary water tanks made of steel plates bolted together with waterproof packing to seal the seams. In contrast, welded steel tanks are more watertight.
The temporary tanks are supposed to be replaced or repaired every five years.
Tepco has set up more than 1,000 huge above-ground water tanks to hold the ever-increasing amounts of highly contaminated coolant water. It must inject water to cool the melted nuclear fuel inside the damaged reactors.
Of those tanks, 350 are temporary, according to Tepco.
Ono stressed that the cause of the leak has not been determined, adding that Tepco has used temporary tanks of this type for about two years.
It started using the first tanks of this type on Dec. 12, 2011.
A temporary tank can be set up in just over a week. Although Tepco acknowledges welded steel tanks are more robust, it plans to set up more temporary tanks to contain the contaminated water at the plant.
Reiji Yoshida, Japan Times Staff Writer, August 20, 2013
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