In the weeks after the Fukushima nuclear plant was destroyed by a triple meltdown in March 2011, the plant’s owner turned to three of Japan’s largest construction companies for a quick fix to store radiated water that was pooling in the disaster zone.
The result was a rush order for steel tanks supplied by Taisei Corp, Shimizu Corp and Hazama Ando that were relatively cheap and could be put together quickly, according to the utility and three people involved in the project.
The tanks, which stand as tall as a three-storey building, were shipped in pieces and bolted together as makeshift repository for the cascade of water being pumped through the reactors of Fukushima every day to keep fuel in the melted cores from overheating.
The bolted tanks were sealed with resin and designed to last until about 2016 – long enough to buy time for Tokyo Electric Power, or Tepco, to work out a more permanent solution. But at least one of the tanks has already failed, leaking 300 tonnes of highly radioactive water that may have seeped into a drainage ditch and into the Pacific Ocean.
The discovery of the leak – which Tepco said on Friday was the fifth from the same type of tank – prompted Japan’s first declaration of a nuclear incident since a 9.0 magnitude earthquake and tsunami triggered reactor meltdowns and hydrogen explosions that spewed radiation around Fukushima in 2011.
It has also focused attention on the uncomfortable end-game for the radiated water collecting at Fukushima.
Some 330,000 tonnes of contaminated water – enough to fill more than 130 Olympic swimming pools – has been pumped into storage pits and above-ground tanks at the crippled facility.
The sheer scale of the build-up has prompted some experts and officials to warn that in order to focus on containing the most toxic waste, less contaminated water will have to be dumped into the sea.
“Think about it in simple terms. If you don’t release the water, there’s nowhere to store it. So we also think it may have to be released,” said Shinichi Nakayama, deputy director of the Nuclear Safety Research Center at the Japan Atomic Energy Agency and a member of a regulatory panel on Fukushima’s problems.
Before the latest leak, Toshimitsu Motegi, Japan’s minister of trade and industry, and Shunichi Tanaka, the top nuclear regulator, both indicated support for releasing water with low levels of radiation from Fukushima. No one has given any timeframe for such a move….
Officials say the immediate priority is to figure out why the bolted storage tank failed less than two years since it was installed. They are also looking at adjusting plans for the more than 400,000 tonnes of additional water storage Tepco plans to build by 2016.
When Tepco commissioned the first bolted tanks the advantage was the relative speed with which contractors could finish the job just a few hundred meters from the wrecked reactor building. “These could be quickly built,” said Masayuki Ono, a manager at Tepco’s nuclear division. …
Taisei, which built the structure around Japan’s newest reactor at Tomari in Hokkaido in 2009, was heavily involved in the construction of the Fukushima tanks, according to three people involved, who asked not to be named. Workers and engineers at Fukushima have been put on an “emergency” footing to work on the storage tanks this week, they said. …
There are 350 of the bolted-style tanks in place at Fukushima, and another 710 welded tanks, a more expensive design that takes longer to assemble. Nuclear Regulation Authority Commissioner Toyoshi Fuketa said on Friday that regulators also needed to examine the environmental risks posed by any failures of those tanks, especially in cases where they have been lined up directly on the ground rather than a concrete foundation.
Tepco plans to more than double the current storage capacity by 2016, but doesn’t have a plan beyond that point. The math is daunting. The utility has to find space for an additional 400 tonnes of radioactive water each day because of the need to keep the reactors cool for the next seven years. …
What is strange is that there have been designs since the 1950s for reactors that shut down automatically if they start to overheat. The TRIGA Mark III is this type of design, I believe.
The TRIGA reactor uses uranium zirconium hydride (UZrH) fuel, which has a large, prompt negative fuel temperature coefficient of reactivity, meaning that as the temperature of the core increases, the reactivity rapidly decreases. Because of this unique feature, it has been safely pulsed at a power of up to 22,000 megawatts,. TRIGA was originally designed to be fueled with highly enriched uranium, but in 1978 the US Department of Energy launched its Reduced Enrichment for Research Test Reactors program, which promoted reactor conversion to low-enriched uranium fuel.
The Fukushima recators were all the old Mark I design, as are many others in service. The designers of the Mark III were frustrated that their new safe design was ignored due to a political decision, if I recall correctly from a tour of a historic atomic reactor sight in Nevada.
The Fukushima Daiichi reactors are GE boiling water reactors (BWR) of an early (1960s) design supplied by GE, Toshiba and Hitachi, with what is known as a Mark I containment.
We should require that all reactors be swapped with types that shut down (due to the physical design) if they start to overheat.