2015 June 12 « nuclear-news

Gov’t OKs long-term Fukushima cleanup plan despite unknowns

TOKYO —The Japanese government on Friday approved a revised 30- to 40-year roadmap to clean up the wrecked Fukushima nuclear plant, but many questions remain.

The plan, endorsed by cabinet members and officials, delays the start of a key initial step — the removal of spent fuel in storage pools at each of the three melted reactors — by up to three years due to earlier mishaps and safety problems at the plant.

Three of the plant’s six reactors melted following the 2011 earthquake and tsunami. The fourth, which was offline and had no fuel in the core at the time of the accident, suffered damage to its building, and its fuel storage pool was emptied late last year.

Despite the delay, experts need to locate and study melted fuel inside the reactors and develop robots to start debris removal within six years as planned.

Experts believe melted fuel had breached the reactor cores and mostly fell to the bottom of the containment chambers, some possibly sinking into the concrete foundation.

The plant operator, Tokyo Electric Power Co, has conducted limited surveys of the reactors using remote-controlled robots.

The roadmap says the initial plan to repair damage in the containment chambers and fill them with water to conduct debris removal underwater is more technically challenging than previously thought, and alternative plans need to be studied.

Radiation levels at the reactors remain high and the plant is still hobbled by the massive amount of contaminated water.

Some of the uncertainties and questions:

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THE FUEL RODS: Kept cool in storage pools on the top floor of each of the three reactors, they need to be removed to free up space for robots and other equipment to go down to the containment chambers. The 1,573 units of fuel rods – mostly used but some of them new – are considered among the highest risks at the plant, because they are uncovered within the reactor building. To remove them, the building roofs must be taken off and replaced with a cover that prevents radioactive dust from flying out. Each building is damaged differently and requires its own cover design and equipment. The government and plant operator TEPCO hope to start the process in 2018, three years later than planned.

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THE MELTED FUEL: Once the spent fuel rods are out of the way, workers can turn their attention to what is expected to be the hardest part of the decommissioning: Removing the melted fuel from the three wrecked reactors. The biggest questions are where the melted fuel is and in what condition. Radiation levels are too high for humans to approach. Based on computer simulations and a few remote-controlled probes, experts believe the melted fuel has breached the cores and fallen to the bottom of the containment chambers, some possibly seeping into the concrete foundation.

A plan to repair the containment chambers and fill them with water so that the melted fuel can be handled while being kept cool may be unworkable, and experts are now studying alternative methods. How to reach the debris – from the top or from the side – is another question. A vertical approach would require robots and equipment that can dangle as low as 30 meters (90 feet) to reach the bottom. Experts are also trying to figure out how to get debris samples out to help develop radiation-resistant robots and other equipment that can handle the molten fuel.

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CONTAMINATED WATER: The plant is still plagued with massive amounts of contaminated water – cooling water that must be added regularly, and subsequently leaks out of the reactors and mixes with groundwater that seeps into the reactor basements. The volume of water grows by 300 tons daily. TEPCO runs it through treatment machines to remove most radioactive elements, and then stores it in thousands of tanks on the compound. Water leaks pose environmental concerns and health risks to workers. Nuclear experts say controlled release of the treated water into the ocean would be the ultimate solution.

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RADIOACTIVE WASTE: Japan currently has no plan for the waste that comes out of the plant. Under the roadmap, the government and TEPCO are supposed to compile a basic plan by March 2018. Waste management is an extremely difficult task that requires developing technology to compact and reduce the toxicity of the waste, while finding a waste storage site is practically impossible considering public sentiment. This raises serious doubts about whether the cleanup can be completed within 40 years.

Source: JapanToday

http://www.japantoday.com/category/national/view/govt-oks-long-term-fukushima-cleanup-plan-despite-unknowns

June 12, 2015 Posted by dunrenard | Japan | decommissioning, Fukushima Daiichi | Leave a comment

Contaminated waste water in Fukushima: the unending horror

This is what passes for good news from Fukushima Daiichi, the Japanese nuclear power plant devastated by meltdowns and explosions after a cataclysmic earthquake and tsunami in 2011: By the end of last month, workers had succeeded in filtering most of the 620,000 tons of toxic water stored at the site, removing almost all of the radioactive materials.

After numerous false starts and technical glitches, most of the stored water has been run through filtration systems to remove dangerous strontium-90, as well as many other radionuclides. TEPCO, the Japanese utility that operates the power plant, trumpeted the achievement: “This is a significant milestone for improving the environment for our surrounding communities and for our workers,” said Naohiro Masuda, TEPCO’s chief decommissioning officer, in a press release.

But it’s not quite so easy to bounce back from a nuclear disaster of this scale. For one thing, don’t take TEPCO’s statement too literally: No one is living in the “surrounding communities”—they’re far too contaminated for human habitation. Furthermore, the filtered water is still full of tritium, a radioactive version of hydrogen. (When two neutrons are added to the element, it becomes unstable, prone to emitting electrons.) Tritium bonds with oxygen just like normal hydrogen does, to produce radioactive “tritiated water.” It’s impractical—or at least extremely difficult and expensive—to separate tritiated water from normal water.

Hence TEPCO’s dilemma—which gets bigger by the day.The enormous volume of water comes from the ongoing need to keep the three melted-down reactor cores cool. More than four years after the disaster, pumps still must pour a constant stream of water into the pressure vessels that contain the radioactive cores. But the meltdowns and explosions rendered those vessels leaky, so TEPCO collects the water that seeps out, as well as rainwater that flows down the hills and through the shattered buildings.

TEPCO has been filling fields with vast arrays of storage tanks to cope with the accumulating water. The company’s 40-year plan for decommissioning the plant calls for the construction of an underground “ice wall” to freeze the soil around the reactor buildings and divert rainwater, and for plugging the leaks in the buildings. But TEPCO has run into problems with the ice wall—the underground tunnels carrying coolant haven’t gotten cold enough to sufficiently freeze the surrounding ground—and the more long-term solution of plugging the reactor buildings’s leaks is still a distant goal. In the meantime, TEPCO keeps building tanks.

Some experts, including the eminently respectable IAEA, have suggested that TEPCO may have to simply dump the tritium-contaminated water into the ocean. Tritium traditionally hasn’t been considered very dangerous to human health. Although tritiated water can reach all parts of the body, like normal water, it’s also expelled quickly from the body, like normal water. If released into the ocean, the contaminated water would quickly be diluted, and it wouldn’t bioaccumulate in fish (unlike strontium-90, for example, which is taken up by bones).

But is tritiated water really so harmless? It’s currently getting a second look from regulators in the United States. Last year, the EPA announced plans to review safety standards for tritiated water, which has leaked from many a nuclear plant. As this excellent Scientific American article explains, there’s considerable uncertainty over whether the stuff is more dangerous than we previously thought.

The amount of tritium in Fukushima Daiichi’s water is not negligible. The World Health Organization’s standard for tritium in drinking water is 10,000 becquerels per liter (34 ounces). According to Mayumi Yoshida, a TEPCO communications officer, Fukushima’s stored water contains between 1 and 5 million becquerels per liter. Yet Yoshida noted that operational nuclear power plants around the world discharge water with a much higher level of tritium than that.

Does that imply that the company is considering discharging its water into the sea, I asked? “Nothing has been decided but to keep storing at the site,” Yoshida said. “We will discuss thoroughly with the government, the oversea and domestic experts, the fishermen, and the surrounding residents, which way would be the safest and the best for everyone, before deciding anything.”

It’s hard to imagine that those discussions will be productive. Releasing the water into the ocean sounds like a non-starter in Japan’s Fukushima prefecture, where fishermen are already furious with TEPCO. Fishing has been suspended around the coastal Fukushima Daiichi plant since the accident, and repeated leaks of radioactive water have angered the fishing associations still further.

If the water can’t be released as-is for political reasons, TEPCO’s only options are to keep building tanks or to accept its extremely difficult and expensive fate, and figure out how to remove the last bit of nuclear taint from its enormous holdings of problematic water.

Source: DiaNuke.org