Global competition for energy resources and tougher controls on greenhouse gas emissions have made Japan reliant on nuclear power. While the government and regional power utilities are quick to associate the word “safety” with atomic energy, several fatalities, accidents, coverups and earthquake threats have damaged the industry’s image.
This is the first in a series asking whether, in the wake of July’s massive quake just 9 km from the world’s largest nuclear plant, it still makes sense for such a seismically active country to rely so much on the power of the atom.
Hiroaki Koide of Kyoto University warns that a major earthquake near the Hamaoka Nuclear Power Plant in Shizuoka Prefecture could trigger destruction on the scale of the 1986 Chernobyl disaster and cause millions of casualties.
And despite the government’s repeated assurance that the July 16 magnitude-6.8 temblor that hit Niigata Prefecture caused no severe damage to the Kashiwazaki-Kariwa nuclear power plant, the reactor expert reckons nothing is absolute when it comes to atomic plant safety.
“The (damage) at Kashiwazaki could have been much worse,” said Koide, an assistant professor at Research Reactor Institute. “The reported troubles only proved this country’s policies need to change.”
The risk of operating nuclear power plants in a quake-prone country are manifest in Japan. With four tectonic plates sliding around under the archipelago and at least 2,000 active and identified fault lines, all of Japan’s 55 nuclear reactors, as well as nuclear fuel storage and other atomic-related sites, are under constant earthquake threat.
Whether these facilities are sufficiently quake-resistant, however, is a question that experts and government officials are split over.
The Kashiwazaki-Kariwa plant, the world’s largest in terms of output at 8.21 million kw, shut down at 10:13 a.m. July 16 just seconds after being hit by the temblor, which registered a rare upper 6 on the 7-level Japanese intensity scale.
The fault line that triggered the quake released a seismic energy wave 2 1/2 times more powerful than some parts of the plant were designed to withstand.
What subsequently happened at the plant — the fire, ceiling crane damage and water leaks containing low-level radioactive waste — was referred to as minor trouble by Tokyo Electric Power Co., the plant’s operator, and the Ministry of Economy, Trade and Industry, which oversees nuclear facilities in Japan.
A four-member team from the International Atomic Energy Agency that inspected the plant over four days in August said in a report that a visual inspection found no significant damage to its seven reactors, concluding the plant safely shut down at the time of the quake. The team, however, was unable to visually inspect the reactor cores.
But Koide argued that if the fault line, which was underestimated as a risk by Tepco, had been just a little bit closer, the reactors could have been damaged.
It was “sheer luck” that the plant was spared from a catastrophic accident and radiation release, he claimed.
Time bomb in Hamaoka
Koike is now worried about the Hamaoka plant in Shizuoka Prefecture, which is in a region where government experts in January forecast an 87 percent chance of a magnitude-8 earthquake striking within the next 30 years.
The fallout from a nuclear meltdown at Hamaoka could easily reach Tokyo, Koide said, warning that millions would be exposed to radiation and its effects could linger for generations.
Although the Hamaoka plant is designed to withstand a magnitude-8 quake, no one can promise that a seismic shock won’t defeat its design and that the reactors will shut down and cool off properly, he said.
“We judge that (our disaster-prevention protocols) worked properly” in the Kashiwazaki-Kariwa plant’s case, said Hitoshi Sato, deputy director general for nuclear safety at the Nuclear and Industrial Safety Agency, an arm of METI. “But some may attribute it to luck, because the quake was indeed stronger than the maximum level estimated in the plant’s design.”
Quake-resistance for nuclear plants is based on a government guideline drafted in 1981. It requires utilities to research active fault lines within a 30-km radius of any new power plant site and to conduct detailed examinations within a 5-km radius.
The plant must then be designed to withstand the maximum seismic shock that could possibly be caused by an earthquake occurring along the active fault lines. They also must be designed to resist quakes that could be generated by unknown fault lines as well.
The plants must be able to withstand a magnitude-6.5 earthquake with an epicenter within 10 km of the facility. Japan’s 55 reactors are all designed to survive such a quake. But the Niigata quake was much stronger.
Whether the July 16 quake was caused by a previously unidentified fault line is not yet known, but it has been confirmed that the seismic shock exceeded the plant’s design limits.
Sato said nuclear plants are built to avoid heavy damage even if quakes exceed the maximum estimate. But he did not know what the extra margin of safety was.
“There is always an unexpectedly strong earthquake. We are dealing with nature. It would be a lie if we say our guideline is sufficient,” he said. “The bottom line is we should learn from the experience of larger-than-expected quakes” and continue to reduce risk.
Last year, the government revised the 1981 guideline to reflect seismic findings from the magnitude-7.3 Great Hanshin Earthquake of 1995 and other major temblors.
To prepare for a major quake caused by an unidentified fault, the new guideline would require nuclear plants to beef up their quake resistance by roughly 20 percent, Sato estimated, adding that the number differs for each plant, depending on local conditions.
Since the Hamaoka plant sits near one of the four known tectonic plates, it must now be reinforced, and other utilities are re-examining the active fault lines around their plants to calculate new quake-resistance levels. Both the research and the new earthquake-resistance estimates will be examined by the government.
The whole process, including reinforcement, will take two to three years to complete, Sato said.
Chubu Electric Power Co. voluntarily began reinforcing the Hamaoka plant in 2005, increasing the cement in its foundation and inserting supports around its pipes. The work will cost up to ¥10 billion, a Chubu Electric official said.
Meanwhile, Mitsuhiko Tanaka, a former Hitachi group engineer involved in building Tepco’s Fukushima No. 1 Nuclear Power Plant, said he was worried about restarting the Kashiwazaki plant.
“Theoretically, it is natural to think that the power plant equipment underwent irreversible changes in their composition,” said Tanaka, who joined an antinuclear energy campaign after quitting Hitachi in 1977.
Invisible damage looms
Tanaka explained that damage perceivable only through microscopic examination probably occurred in the reactor pressure vessel, piping or containment vessel at the plant.
Such difficult to detect damage can considerably weaken a power plant, but Tanaka said he feared Tepco might skip the microscopic tests needed to evaluate the damage and put priority on restarting the plant following superficial nondestructive testing.
“I fear that the government will just glance through some of the reports supplied by Tepco, hold short discussions with experts and make a decision to reactivate the Kashiwazaki plant,” he said.
Sato of NISA said the government and Tepco will examine the seven reactors at the plant and seriously discuss whether they can be used again. “In the worst case, they may need to be rebuilt,” he said.
Despite the chance that an unidentified fault line could bring a severe quake at any given spot in Japan, Haruo Yamazaki, a seismological geology expert at Tokyo Metropolitan University, said he supports the nuclear power industry.
“In a way, nuclear power plants are a necessary evil,” said Yamazaki, who has worked in the Nuclear Safety Commission at the Cabinet Office.
“Nuclear meltdowns are terrifying, but so is a power shortage. The only way to handle the issue is to improve regulatory guidelines for the facilities.”