New quake info has nuclear-plant operators scrambling to strengthen facilities, but official standards are out of date. `There is a larger possibility of a major earthquake hitting the Hamaoka plant than at any other nuclear plant in the world.'KIYOO MOGI Earthquake expert

When the No. 1 and No. 2 reactors at the Hamaoka nuclear plant in Omaezaki, Shizuoka Prefecture, were built in the 1970s, it was not known that a major earthquake might hit directly under the site.

Now it is.

In fact, there's an 84 percent probability that a Tokai-region earthquake measuring 8 on the Richter scale could strike there during the next 30 years, scientists say.

Incredible though it may seem, the Chubu Electric Power Co. went ahead and built three more reactors at the Hamaoka plant even though officials by then were aware of the potential hazard.

Now, to stave off disaster, the company is gearing up to strengthen the structure of the five reactors at the Hamaoka plant.

It is a three-year project, already beset by a particularly nerve-racking problem. Guidelines on what is needed to shore up the facility are woefully out of date.

Current quake-resistant guidelines for nuclear plants were compiled in 1978. After the Great Hanshin Earthquake hit in 1995, many experts pleaded for revisions that took into account the latest knowledge about earthquakes. Already a decade has passed since the Kobe temblor that left more than 6,400 people dead-and nothing has been done to improve safety standards for nuclear plants.

The Nuclear Safety Commission has spent the past three years revising quake-resistant building standards for nuclear reactors, but has yet to issue its final report.

Chubu Electric Power officials essentially decided they could not wait. To cover themselves, they have ratcheted up their reinforcements way beyond what they think might be proposed as standard guidelines.

Currently, to gain government approval, nuclear plants must be constructed to withstand a certain projected earthquake motion.

The calculated earthquake motion for the Hamaoka nuclear plant is projected at 600 gals. (A gal is a unit for expressing the horizontal acceleration of earthquakes.) The 600 figure is the highest for any nuclear plant in Japan.

Chubu Electric Power officials are proceeding with reinforcement plans by raising their projected earthquake motion to 1,000 gals. Officials say strengthening the plant to that level would give them about an additional 30 percent leeway in design terms.

At this point, reinforcing the metal framework of the exhaust ducts and the support mechanism for piping is expected to cost 80 billion yen for the five reactors, with the work to be completed by spring 2008.

Details of the actual reinforcement work still have to be worked out.

The Nuclear Safety Commission asked Chubu Electric Power officials to explain the company's plans to the subcommittee handling the revision of the quake-resistant guidelines. However, company officials said they still did not have technological information worthy of reporting to the subcommittee.

Local conditions were largely behind the company's decision to announce its plans to reinforce the Hamaoka nuclear plant even though the technological details had not been hammered out, experts say.

Recent incidents at Hamaoka have sparked public dismay about general plant safety.

After piping in the No. 1 reactor was damaged in 2001, the Yoshida municipal assembly was one of many that passed a resolution calling on Chubu Electric Power to mothball the No. 1 and No. 2 reactors.

In 2003, a citizens group filed a lawsuit seeking an injunction on operations at the plant.

Kiyoo Mogi, a professor emeritus at the University of Tokyo and former chairman of the Coordinating Committee for Earthquake Prediction, has long opposed continued operation of the Hamaoka nuclear plant.

``There is a larger possibility of a major earthquake hitting the Hamaoka plant than at any other nuclear plant in the world,'' Mogi said. ``Unless a scientific explanation can be given for why the level of reinforcement work is required, it cannot be said to be sufficiently safe.''

The No. 1 reactor is still not back online. Moreover, cracks have been found in the shrouds that surround the cores of the No. 1 and 2 reactors. The shrouds now have to be replaced.

Industry experts said the decision to reinforce the plant was likely made partly as a means of placating local community doubts about safety.

Meanwhile, officials of other electric power companies are taking a wait-and-see approach to the guideline revisions.

One reason for the difficulty in revisions is the lack of consensus on the gal figure to be used as a standard.

However, the Central Disaster Management Council has come up with an estimated earthquake motion of 395 gals should a Tokai earthquake hit as predicted.

Unexpected earthquakes are another reason for the lack of progress in revising the guidelines.

For example, an earthquake that hit western Tottori Prefecture in 2000 had a 7.3 magnitude on the Richter scale. Moreover, that quake occurred in a region where active faults had not been discovered.

According to Katsumi Ebisawa, who heads the structural safety analysis group at the Japan Nuclear Energy Safety Organization, temblors measuring 6.5 on the Richter scale have an earthquake motion of 370 gals.

Given the possibility that an active fault may have been overlooked, Ebisawa said there is a need for nuclear plants to raise their minimum projections for earthquakes to those with a magnitude of 6.8 and earthquake motion of 450 gals.

Also, there has been no consensus on what to do about a new assessment method known as probabilistic safety appraisal, which calculates the probability of damage to the reactor core caused by an earthquake.

Some members of the Nuclear Safety Commission want that method incorporated into the revised guidelines; others see it as a supplementary tool.

Mitsumasa Hirano, a member of the Nuclear Safety Commission subcommittee working on the quake revisions, favors incorporating the probabilistic safety appraisal.

``Presenting risk probabilities to the public will help gain an understanding from them on the level of risk they are willing to endure,'' Hirano said. ``How to incorporate that method into the safety restrictions is one of the major focal points of the revision process.''(IHT/Asahi: February 22,2005)