TEPCO urged to cut risk of radioactive water leak
Japan’s nuclear regulator has urged the operator of the crippled Fukushima Daiichi nuclear power plant to reduce the risk of leaking of highly radioactive water from the facility into the sea, in case of another tsunami.
About 60,000 tons of such water is believed to have pooled in reactor buildings at the plant. The operator, Tokyo Electric Power Company, or TEPCO, is injecting water into the buildings to cool melted nuclear fuel, and groundwater is flowing into their basements.
The Nuclear Regulation Authority instructed TEPCO at a meeting on Tuesday to urgently study measures to lower the amount and radiation levels of the water.
The authority proposed 2 measures to TEPCO. One is building more tanks to store the water, even though the plant has about one thousand tanks. The other is treating the water using a system designed to filter out radioactive material, and circulating the water in a cooling system.
NRA member Toyoshi Fuketa said the utility cannot keep the water in the buildings forever. He said TEPCO should handle the water problem either along with that of other radioactive water or first of all.
Following the NRA’s instruction, TEPCO is to report the results of its study at a meeting next month or later.
State minister rules out sarcophagus option
Japan’s state minister for industry has ruled out the option of sealing off disabled reactors at the Fukushima Daiichi nuclear plant with a Chernobyl-style sarcophagus.
Tokyo Electric, the operator of the crippled Fukushima Daiichi nuclear power plant, has released a document during a lawsuit brought by over 40 shareholders which reveals the utilities acknowledgment that tsunami defenses at the plant were not adequate.
The internal document from 2008 noted that TEPCO executives had agreed that it would be “indispensable” to further build up coastal defenses for the plant in order to protect against a tsunami larger than had previously been recorded.
The utility has asserted that it could not have foreseen a tsunami of the size or magnitude that hit the plant in March 2011, that it had done everything it could to protect the nuclear power plant, took every available precaution against a tsunami, and has used that defense to protect itself from litigation.
This positioning by TEPCO has allowed the utility to argue that it is not responsible for the triple meltdown, but the internal document casts a definitive shadow over that claim.
Insiders from the nuclear industry in Japan have come forward since 2011 and claimed that TEPCO and the federal regulators ignored warnings of larger-than-expected tsunami in northern Japan for years. By ignoring these warnings, TEPCO delayed implementing countermeasures, including but not limited to increasing the height of protective wave barriers or removing the critical emergency backup diesel generators from the basements of the reactor buildings to higher ground.
In 2004, Kunihiko Shimazaki, a former professor of seismology of the University of Tokyo, warned that the coast of Fukushima could experience tsunamis more than double the estimates of federal regulators and TEPCO. His assertions were dismissed as “too speculative” and “pending further research.”
At a nuclear engineering conference in Miami in July 2007, Tokyo Electric researchers led by Toshiaki Sakai presented a paper which concluded that there was a 10% chance that a tsunami could test or overwhelm the defense at the Fukushima Daiichi nuclear power plant in the next 50 years.
Engineers from TEPCO confirmed Shimazaki’s concerns in 2008, when they produced three unique sets of calculations that revealed tsunami waves up to 50 feet tall could hit the Fukushima Daiichi nuclear power plant. The utility sat on the information for nearly a year before handing it over to federal regulators and didn’t reveal the 50-foot wave calculation until March 7th, 2011, but by then it was too late.
In hindsight, it can now be seen that TEPCO scientists realized by at latest 2004 that it was indeed quite probable that a giant tsunami could overcome the defenses at the Fukushima Daiichi nuclear power plant — defenses which were based on engineering assumptions that dated back to the plant’s design in the 1960s.
In the weeks following the nuclear disaster in 2011, former Japanese Prime Minister Naoto Kan pointed out the weaknesses in TEPCO’s tsunami defense concisely when he told the Japanese Parliament “It’s undeniable their (Tokyo Electric’s) assumptions about tsunamis were greatly mistaken. The fact that their standards were too low invited the current situation.”
Oct 4, 2014
Tokyo Electric Power Co. has warned its stricken Fukushima No. 1 nuclear plant could be hit by tsunami as high as 26.3 meters.
The deluge would likely cause seawater to mingle with the radiation-tainted water accumulating in the basements of the reactor buildings at the six-unit plant, allowing 100 trillion becquerels of cesium to escape, according to an estimate that Tepco revealed Friday at a meeting of the Nuclear Regulation Authority.
Tepco said a tsunami of that size occurs once every 10,000 to 100,000 years.
The Fukushima No. 1 plant, more than 40 years old, was crippled by the March 2011 earthquake and tsunami after waves as high as 15.5 meters inundated the facility, knocking out all power and disabling the vital backup cooling systems for reactors 1 to 4, triggering three core meltdowns.
Tepco also said the nearby Fukushima No. 2 nuclear plant, which is nearly as old as Fukushima No. 1, could be hit by tsunami of up to 27.5 meters, but that its idled reactors and fuel pools would not be damaged by such an event.
Source: Japan Times
October 04, 2014
By TSUYOSHI NAGANO/ Staff Writer
A tsunami of 26 meters would inundate the already-stricken Fukushima No. 1 power plant, causing a huge amount of radioactive substances to spill into the sea, according to Tokyo Electric Power Co.’s updated estimates.
The crippled plant’s operator told a Nuclear Regulation Authority commission Oct. 3 that it raised its projected tsunami height to 26.3 meters–nearly double its previous estimate--and increased the scale of the largest potential earthquake by 1.5 times.
According to the new estimate, if such a towering tsunami struck the facility, hundreds of trillions of becquerels of cesium-137 could be released into the ocean from the basements of reactor buildings.
Currently, nuclear plant operators across Japan are making efforts to receive permission to resume operations of reactors that have remained or were put offline after the nuclear crisis started in March 2011.
Other utilities have been raising the scale of the highest possible tsunami for individual plants to meet stricter safety standards introduced following the Fukushima disaster. But TEPCO had not revised its height estimate for tsunami because the new safety standards do not apply to the Fukushima No. 1 plant reactors, which are scheduled to be decommissioned.
However, due to the unique risk factors at the plant, including destroyed reactor buildings and accumulating contaminated water, the NRA demanded that TEPCO review its tsunami forecast and countermeasures.
TEPCO’s latest estimate assumed a scenario in which a tsunami of 26.3 meters triggered by an earthquake of 900 gals struck the coast at the north end of the facility. A gal is a unit of gravitational acceleration. TEPCO’s previous report assumed a strongest possible quake of 600 gals.
Some of the plant’s reactors are at the southern part of the plant, where the elevation is 10 meters above sea level. Reactors in the north lie on land 13 meters above sea level.
Tsunami of 15.5 meters struck the southern coastal area following the magnitude-9.0 earthquake in 2011.
Projecting a succession of smaller tsunami at a maximum height of 14 meters may inundate the nuclear power plant, TEPCO erected 14-meter-tall temporary levees at some areas in the south following the disaster.
However, the latest estimate shows that the highest potential tsunami exceeds the height of the land and levees. Such a deluge would thus swamp the reactor buildings, where highly contaminated water has accumulated, causing the release of radioactive substances.
In the new forecast, TEPCO said storage tanks for radioactive water would not be affected by such a tsunami because they are situated on higher ground. It also said damaged reactor buildings could withstand the potential strongest quake of 900 gals.
To minimize the impact of the estimated 26.3-meter tsunami, TEPCO said it will reduce the vast quantity of radioactive water accumulating on site instead of raising the height of the levees to block tsunami.
According to TEPCO officials, the amount of tainted water estimated to spill into the ocean could be reduced to 30 percent by filling in trenches near reactors, where a large quantity has accumulated.
The NRA is not expected to demand TEPCO raise the height of levees, as there is no equipment around the reactor buildings that could cause critical damage in the event of inundation. However, the nuclear watchdog plans to check the appropriateness of TEPCO’s latest estimate and proposed countermeasures.
Source: Asahi Shimbun