23/04 Nuclear experts say Fukushima accident was avoidable

2011/04/23

A group of 16 nuclear safety experts has issued proposals for preventing a recurrence of the Fukushima No. 1 nuclear power plant accident, saying that "relatively inexpensive improvements, detectable by more extensive analysis beforehand" may have prevented it altogether.

The joint statement by experts representing 11 countries, including the United States, Russia, India and Sweden, was presented to the International Atomic Energy Agency.

In the statement titled "Never Again: An Essential Goal for Nuclear Safety," experts also recommended that future nuclear power plants be located away from "areas of extreme natural and manmade hazards." The translation of the statement was posted on April 19 by the Japan Atomic Industrial Forum on its website with its original English version.

Among its recommendations, the group says that plants built to earlier safety standards should be given renewed attention.

"In light of the common mode failure of redundant safety systems (electric power) caused by the tsunami at Fukushima, authorities should ask to what extent this failure and other common mode failure vulnerabilities in operating plants might be revealed by current technology."

This would include refining safety requirements for future nuclear power plants to ensure that their "backup cooling systems are able to operate for a long enough time following complete loss of on-site and off-site power."

Another area the experts highlight is the need for special attention to go into training of plant personnel.

They recommend that countries with nuclear power plants "should establish centers to train specialists for nuclear technology."

"Top professionals involved in nuclear power generation should not only 'know what' and 'know how' but also 'know why' in order to deliver difficult and critical decisions in time to deal with unforeseen circumstances."

The statement also proposes that new international frameworks could be created, such as an "international regulatory agency entrusted with issuing international safety standards and performing compulsory inspections."

The nuclear safety experts include Harold Denton, a former director of the U.S. Nuclear Regulatory Commission's Office of Nuclear Reactor Regulation and former President Jimmy Carter's adviser at Three Mile Island during the 1979 accident; Pierre Tanguy, former inspector general of nuclear safety, Electricite de France; and Nikolai Steinberg of Ukraine, former chief engineer at the Chernobyl nuclear power plant.

10/04 Expert: Residences should be moved to higher ground

Yasushi Kaneko / Yomiuri Shimbun Staff Writer

The government should consider moving residents living in low-lying costal areas to higher ground, according to a specialist in coastal engineering.

Waseda University Prof. Tomoya Shibayama has inspected the areas affected by the tsunami caused by the March 11 earthquake via helicopter. "More than half of the breakwater in Kamaishi, Iwate Prefecture, was destroyed by the tsunami, and the one in Ofunato was no longer visible," he said.

Towns on the Sanriku coast have long experience with tsunami, including notable tsunami caused by domestic earthquakes in 1896 and 1933, as well as one following a quake in Chile in 1960. According to Shibayama, these tsunami measured about four meters at the tallest at Onagawacho, Miyagi Prefecture.

The March 11 tsunami in the town, however, was more than four times this height, he said, and came with force of dozens of tons per square meter, similar in strength to the 2004 Indian Ocean tsunami that killed more than 230,000 people.

Tsunami after the March 11 earthquake were much bigger than those anticipated in disaster action plans made by towns on the Sanriku coast, effectively rendering their protective measures meaningless, Shibayama said. "It's clear now that breakwaters and seawalls don't do much to protect residential areas from tsunami," he said.

To preserve regional communities, local governments should consider revising their land-use programs and move low-lying residential areas near the sea to higher ground, Shibayama said.

The village of Ultogia, Samoa, was hit by the 2009 tsunami and about a month later, neighborhoods near the sea began moving to higher ground. "In Japan, the central and prefectural government should take the initiative [and implement similar policies] because of the difficulty of coordinating the rights [of the affected parties]," he said.

The central and local governments also need to increase the tsunami size their disaster action plans are predicated on and revise evacuation plans based on even larger tsunami, he said.

The central government's tsunami guidelines stipulate that citizens should seek refuge on the third floor or higher of buildings built of reinforced concrete. However, according to officials of Minami-Sanrikucho, Miyagi Prefecture, people on the roof of a four-story building said the tsunami reached their knees, about 15.5 meters above the ground.

"Residents need to evacuate to areas about 18 meters high, equivalent to a building's sixth floor," Shibayama said.

(Apr. 10, 2011)

01/04 N-plant has long road ahead / Experts: Decommissioning Fukushima reactors to take decades

The Yomiuri Shimbun

Nuclear experts predict it will take decades to complete the decommissioning of the Nos. 1 to 4 reactors at the Fukushima No. 1 nuclear power plant.

Tokyo Electric Power Co. Chairman Tsunehisa Katsumata said Wednesday the company will decommission the four reactors, but the most pressing task at the moment is how to dispose of the huge quantity of water that has become contaminated with radioactive materials after being used to cool the reactors. Just disposing of this water will take a long time.

An estimated 13,000 tons of contaminated water has accumulated in trenches--tunnels used for maintenance of the reactors. A large quantity of contaminated water also has to be extracted from the basements of the reactors' turbine buildings, although the exact amount is unknown.

If the contaminated water can be removed, it will pave the way to reactivating the reactors' original cooling systems, which can lower the temperature of the reactor cores more efficiently than the methods now being employed.

Currently, however, workers at the plant are stymied by the contaminated water. They cannot even connect power cables outside the plant to the reactors' control systems.

It may be impossible to restore power to the reactor control systems if internal radiation levels are so high workers cannot repair the machinery, or if the contaminated water cannot be removed.

If water continues to leak, external tanks for temporarily storing it may become full. Workers and experts have said new facilities to store the contaminated water must be secured as soon as possible.

If all the contaminated water can be removed, the reactors then must be put in what is called cold shutdown to prevent the further discharge of large quantities of radioactive substances and bring the reactors into a stable state.

Cold shutdown means all control rods have been inserted into the reactors to stop nuclear fission chain reactions, and the coolant water inside the reactors is below 100 C.

Usually the temperature needs to be lowered further to remove fuel rods for regular checks or decommissioning.

"If the original cooling systems can be activated through a power supply from outside the plant and coolant water circulated, cold shutdown can be achieved in a day or two," Prof. Kenichiro Sugiyama of Hokkaido University said.

But it will likely take a few more years for the nuclear fuel rods to be cool enough to be removed from the reactors to decommission them.

On the other hand, if the current method--putting coolant water into the reactors with makeshift pumps--continues to be used, the situation may become more serious.

"Although the nuclear fuel would cool gradually, it would take at least several months to achieve cold shutdown," said Toru Ebisawa, a former associate professor of Kyoto University's Research Reactor Institute.

This would mean using more water, which would increase the amount of contaminated water.

Overall, it will take decades to complete the process of decommissioning the reactors.

The Japan Atomic Power Co.'s Tokai plant in Ibaraki Prefecture was the first commercial nuclear power plant in Japan to begin being decommissioned. The plant ended commercial operations in 1998, and the decommissioning process is scheduled to end in 2021.

In the decommissioning process, fuel rods are removed and workers wait for levels of radioactivity to fall. During that time, power generators and other equipment with low levels of radiation contamination are decommissioned first.

In the final stage, reactors' steel containers and other equipment are cut into pieces and buried deep underground. At the Tokai plant, heat exchangers and other parts are now being removed.

But in the case of the Fukushima No. 1 nuclear power plant, in which reactors and buildings were damaged, it is doubtful whether the normal process of decommissioning will be possible.

Shojiro Matsuura, former chairman of the Nuclear Safety Commission, said, "This time, much more time and effort will be needed to lower radiation contamination levels. Twenty or 30 years probably won't be enough."

In the 1979 Three Mile Island accident in the United States, it took a month to achieve cold shutdown and six to seven years to remove melted fuel rods.

Fourteen years later, U.S. authorities declared the decommissioning process complete. Part of the nuclear fuel could not be recovered and remained in the reactors.

(Apr. 1, 2011)