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Tokyo Electric Power Co. (TEPCO) called Thursday for new quake-resistant standards that are five times higher than current levels for its Kashiwazaki-Kariwa Nuclear Power Plant in Niigata Prefecture.

The Niigata Chuetsu-oki Earthquake, which struck offshore last July, sent fierce seismic jolts directly below the nuclear plant, causing extensive damage. As a result, the facility's seven reactors were shut down.

Using earthquake-resistance design guidelines revised in 2006, TEPCO factored in the new data gained from observations of that temblor to calculate the estimated intensity. It concluded that greater earthquake-proofing was needed.

Specifically, it was stated that the bedrock under Reactors 1 through 4 must be secured against temblors 5.1 times stronger than believed safe to date, with the area under the No. 5 to 7 reactors to be reinforced by 2.6 times the present strength.

In the interests of safety, TEPCO intends to equip the facility with quake-resistance capabilities above and beyond these revamped estimates, with the reinforcement work to commence next month. While all Kashiwazaki-Kariwa reactors are currently shut down for inspection, these latest findings further complicate any plans to resume operations.

Why have the estimated values of the seismic shocks that these facilities must withstand surged to such a degree?

For one, the new guidelines were used to carry out detailed studies of the active faults in the vicinity of the plant.

Rigid estimates were likewise made of the scale of quakes caused by those faults. Precise methods for computing the swaying likely to stem from fault movements were also devised.

Besides that, observation data from the Niigata Chuetsu-oki Earthquake and other seismic activity determined that the geological strata beneath the nuclear plant zone also possesses characteristics that amplify earthquake vibrations.

Estimates of seismic waves based on the new earthquake-resistance design guidelines for other nuclear plants around the country were completed this past spring. The findings forced the operators of all facilities to make upward revisions in their forecasts of shocks--the largest being 1.6 times the previous level.

The five times greater resistance required at Kashiwazaki-Kariwa certainly stands out.

This series of modifications also clarified the fact that lengthy active faults pass directly beneath the Kansai Electric Power Co.'s Mihama Nuclear Power Plant and the Japan Atomic Energy Agency's Monju fast-breeder reactor--both located in Fukui Prefecture.

In short, the educated judgments of seismic intensity applied to the original construction of these and other nuclear plants have proved to be easygoing.

One lesson to be learned is that seismology is a science in which new discoveries occur daily, with rapid advances also continuing to be made in fault surveys and other technical fronts. The key premise, therefore, must be that seismic estimates will need to be updated from here on as well.

Power companies and others in the industry play down the fear factor, insisting that nuclear power plants are designed with proper leeway to handle earthquake activity. However, when the Kashiwazaki-Kariwa figures are added to the seismic estimates, it is obvious that all nuclear plants in Japan are frittering away whatever such leeway they may have had.

When thinking of earthquake-proof engineering, it is vital to realize that new grounds for concern will continue to emerge hand in hand with progress made in research.

In an earthquake-prone nation like Japan, no further time should be wasted in making reinforcements to restore the leeway necessary to ensure safe and trustworthy nuclear power generation.

--The Asahi Shimbun, May 23(IHT/Asahi: May 24,2008)