Photo/IllutrationThe Tomari nuclear power plant in the village of Tomari, western Hokkaido, seen from the town of Iwanai (Asahi Shimbun file photo)

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A possible active fault beneath the Tomari nuclear power plant in Hokkaido could prolong the government's screening process for a restart and deal a major financial blow to Hokkaido Electric Power Co., the plant's operator.

On Dec. 8, the Nuclear Regulation Authority (NRA) did not accept the assertion of Hokkaido Electric Power that no active fault existed in the compound of the plant. The NRA directed the utility to do additional research.

The ruling by the country’s nuclear watchdog will inevitably delay the screening process and hurt the utility, which had been counting on a restart to help its financial situation.

In the screenings, which are based on the new safety standards introduced after the 2011 Fukushima No. 1 nuclear plant crisis, faults that moved after the period between about 130,000 and 120,000 years ago are regarded as being active.

If active faults exist just below key facilities, such as nuclear reactor buildings, the reactors must be decommissioned. Even if active faults do not exist just beneath them, those facilities are required to have high quake-resistance capabilities if those faults exist in the compound.

In 2013, Hokkaido Electric Power applied to NRA to approve the restart of all three reactors at the Tomari nuclear power plant in western Hokkaido. In the NRA’s screenings, the company acknowledged that several faults exist in the compound of the plant.

However, the company asserted that those faults do not run through the layer of volcanic ash from about 200,000 years ago, which was found in the boring research at the time of construction of the No. 1 and the No. 2 reactors.

Based on the assertion, the firm insisted that those faults moved in the period earlier than 200,000 years ago and, therefore, are not active. The NRA accepted the statement at that time.

As the layer of volcanic ash was found only in the location of the boring research, however, the NRA also required the company to take boring samples in other places to support the assertion.

In response, the firm implemented boring research in six other sites in and outside the compound of the nuclear power plant. Then, the apparent layer of volcanic ash was not found in any of the six locations.

“We were very surprised because what should have been found was not found. It is certain that (the result) will have major influences on our screenings,” said NRA Chairman Toyoshi Fuketa.

In an NRA screening meeting on whether to approve a restart on Dec. 8, Hokkaido Electric Power repeated its assertion that faults that exist in the compound of the nuclear power plant are not active.

The claim was based on the result of the analysis of the “ingredients of volcanic ash” found in the same places and on the topographical features of the area in and around the plant.

“The assessment we have made so far is appropriate,” an official of the utility said in the meeting.

However, it failed to gain support as the NRA members cast doubts on the method used by the utility to determine when the faults were formed.

Hokkaido Electric Power said that it will show by late January the result of new research that uses a different method.

“We want to show the data (of the result) as early as possible,” an official of the utility said after the meeting.

In the meeting, the company also acknowledged that one of the faults that exist in the compound of the nuclear plant runs just below the key facilities of the No. 1 and the No. 2 reactors.

So far, the utility had not revealed details on the locations of facilities and their distances from the faults as part of anti-terrorism measures.

Meanwhile, if Hokkaido Electric Power is unable to present sufficient data for the restart of the nuclear power plant, it will suffer further financial setbacks.

Even if the operation of the Tomari nuclear power plant is suspended, the utility will need nearly 70 billion yen (about $616.3 million) in maintenance costs.

After the operations of all the three reactors at the plant were suspended in 2011 and 2012, the utility raised electricity rates by an average 7.73 percent (11 percent for companies) in 2013 and 15.33 percent (20.32 percent for companies) in 2014 to avoid deficits.

As a result, the electricity charges imposed by Hokkaido Electric Power have become the highest in Japan.