By MARTIN FACKLER, New York Times, June 5, 2013
TOKYO — The operator of the stricken Fukushima nuclear plant said Wednesday that it had found a leak in one of the hundreds of steel tanks used to store radioactive water at the plant, raising renewed questions about the company’s ability to handle the plant’s cleanup.
The discovery comes a day after the operator, the Tokyo Electric Power Company, or Tepco, admitted that it had found cesium particles in groundwater flowing into the Fukushima Daiichi plant, reversing its earlier assertion that the water was uncontaminated.
The company stressed that the size of the tank leak was small — the equivalent of about a quart had dripped out so far, it said — and that the level of radioactivity in groundwater was within safe levels. However, the problems are the latest in a string of mistakes and mishaps that have added to mounting criticism of the government’s decision to leave the tricky cleanup in the hands of Tepco, the company that many say allowed the triple meltdown two years ago to happen in the first place.
Recently, Tepco has struggled to deal with tens of millions of gallons of contaminated, toxic water at the plant, which must be stored in the large steel tanks that now occupy virtually every available bit of space there. The amount of radioactive water has continued to grow as groundwater has flowed at a rate of 100,000 gallons per day into the basements of the damaged reactor buildings. This contaminated water must be drawn off every day to prevent it from overwhelming makeshift systems that cool the melted reactors.
The company has installed a new filtering system that it says removes every type of radioactive particle but one, tritium. Still, that leaves it no choice but to keep storing the water rather than dumping it.
Wednesday’s leak underscored the risks of doing so at the plant, where a larger spill might potentially reach the nearby Pacific Ocean. The leaking tank had just been installed to store toxic water from an underground storage pond that needed to be emptied after it, too, sprang a leak.
Faced with growing public alarm over the water crisis, the government last week ordered Tepco to stop the influx of groundwater by freezing soil around the reactor buildings, a novel plan that calls for creating a wall of underground ice. The company has also planned to reduce the influx by pumping some of the groundwater into the sea before it reaches the buildings and becomes contaminated.
However, the pumping plan needs the approval of residents and commercial fishermen in areas outside the evacuation zone immediately around the plant, who have been slowly regaining their livelihoods since the meltdowns spewed radiation over northeastern Japan. The company had been offering them reassurances that the water to be dumped contained no radioactive particles that could further contaminate the ocean.
Those plans could now be jeopardized by Tuesday’s admission that the groundwater in fact does contain cesium, a byproduct of the meltdowns. The company, which conceded that it had erred in previous tests, said it had found up to 0.39 becquerels of radioactive cesium 137 per liter of water, an amount that is far below Japan’s safety level for drinking water of 10 becquerels per liter.
Still, it may be enough to scuttle or at least put on hold the company’s plan to pump groundwater into the sea. Just last week, the company sought to persuade local fishing cooperatives by telling them that levels of cesium in the groundwater were so low that they could not be detected. Those reassurances were met with intense skepticism by fishermen who, even before Tuesday’s admissions, said they no longer trusted any assertions made by Tepco.
Background:
June 6 2013
by Gordon Edwards
See Akio Matsumura’s excellent blog at http://tinyurl.com/m9rasxx.
Large volumes of radioactively contaminated water are being produced every day from the stricken Fukushima Dai-ichi Nuclear Station in Japan. News reports tell of leaking underground tanks and the hasty construction of more and more storage tanks above ground. Here’s why this is all happening, two years after the disastrous 2011 accident.
(1) When nuclear fuel is used in a nuclear reactor or an atomic bomb, the atoms in the fuel are “split” (or “fissioned”) to produce energy. The fission process is triggered by subatomic particles called neutrons. In a nuclear reactor, when the neutrons are stopped, the fission process also stops. This is called “shutting down the reactor”.
(2) But during the nuclear fission process, hundreds of new varieties of radioactive atoms are created that did not exist before. These unwanted radioactive byproducts accumulate in the irradiated nuclear fuel — and they are, collectively, millions of times more radioactive than the original nuclear fuel.
(3) These newly created radioactive materials are classified as fission products, activation products, and transuranic elements. Fission products — like iodine-131, cesium-137 and strontium-90 — are the broken pieces of atoms that have been split. Activation products — like hydrogen-3 („tritium“), carbon-14 and cobalt-60 — are the result of non-radioactive atoms being transformed into radioactive atoms after absorbing one or more stray neutrons. Transuranic elements — like plutonium, neptunium, curium and americium — are created by transmutation after a massive uranium atom absorbs one or more neutrons to become an even more massive atom (hence “transuranic”, meaning “beyond uranium”).
(4) Because of these intensely radioactive byproducts, irradiated nuclear fuel continues to generate heat for years after the fission process has stopped. This heat (“decay heat”) is caused by the ongoing atomic disintegration of the nuclear waste materials. No one knows how to slow down or shut off the radioactive disintegration of these atoms, so the decay heat is literally unstoppable. But decay heat does gradually diminish over time, becoming much less intense after about 10 years.
(5) However, in the early years following a reactor shutdown, unless decay heat is continually removed as quickly as it is being produced, the temperature of the irradiated fuel can rise to dangerous levels — and radioactive gases, vapours and particles will be given off into the atmosphere at an unacceptable rate.
(6) The most common way to remove decay heat from irradiated fuel is to continually pour water on it. Tepco is doing this at the rate of about 400 tons a day. That water becomes contaminated with fission products, activation products and transuranic elements. Since these waste materials are radiotoxic and harmful to all living things, the water cannot be released to the environment as long as it is contaminated.
(7) Besides the 400 tons of water used daily by Tepco to cool the melted cores of the three crippled reactors, another 400 tons of ground water is pouring into the damaged reactor buildings every day. This water is also becoming radioactively contaminated, so it too must be stored pending decontamination.
(8) Tepco is using an „Advanced Liquid Processing System“ (ALPS) that is able to remove 62 different varieties of radioactive materials from the contaminated water — but the process is slow, removal is seldom 100 percent effective, and some varieties of radioactive materials are not removed at all.
(9) Tritium, for example, cannot be removed. Tritium is radioactive hydrogen, and when tritium atoms combine with oxygen atoms we get radioactive water molecules. No filtration system can remove the tritium from the water, because you can’t filter water from water. Released into the environment, tritium enters freely into all living things.
(10) Nuclear power is the ultimate example of the throwaway society. The irradiated fuel has to be sequestered from the environment of living things forever. The high-quality materials used to construct the core area of a nuclear reactor can never be recycled or reused but must be perpetually stored as radioactive waste. Malfunctioning reactors cannot be completely shut off because the decay heat continues long after shutdown. And efforts to cool a badly crippled reactor that has melted down result in enormous volumes of radioactively contaminated water that must be stored or dumped into the environment.
No wonder some have called nuclear power “the unforgiving technology”.
Gordon Edwards.