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information about Fukushima published in English in Japanese media info publiée en anglais dans la presse japonaise

Fault under Shika plant likely active

March 3, 2016


Fault under Shika nuclear reactor likely to be active: NRA expert panel



March 3, 2016 (Mainichi Japan)


The Shika Nuclear Power Plant is seen in Shika, Ishikawa Prefecture, on Nov. 2, 2011. (Mainichi)

An investigative panel of experts with the Nuclear Regulation Authority (NRA) compiled a new draft report on March 3 in which it says that a fault running just below the No. 1 reactor at the Shika Nuclear Power Plant in Ishikawa Prefecture is likely to be active.

In the report, the panel says, "It is reasonable to understand that the fault had moved." In its first draft report prepared in July 2015, the group of experts had pointed to the possibility of the fault being active.

The new regulatory standards adopted in the wake of the 2011 Fukushima nuclear disaster forbid construction of key facilities such as a nuclear reactor right above an active fault. Unless Hokuriku Electric Power Co., the operator of the Shika plant, can overturn the NRA expert group's conclusion, it will become increasingly likely that the No. 1 reactor will be decommissioned.

Furthermore, as for two other faults running right below a key facility of the No. 2 reactor that has been going through NRA safety screening, the draft report said, "There is a possibility that they had moved." Using as strong a language as what was used for the No. 1, reactor, the expert panel pointed out the possibility of the fault being active. Reactivation of the No. 2 reactor will likely be delayed substantially because there will be even a higher possibility of it being unable to clear the NRA screening process unless large-scale work such as relocation of its facilities is carried out.

The investigative panel is to draw up a formal report and submit it to the NRA. If Hokuriku Electric were to seek to reactivate the reactors, the NRA would conduct safety screenings on them again to determine whether the faults are active. If the faults are confirmed to be active after the screening, the No. 1 reactor is expected to be decommissioned.

Hokuriku Electric is planning to apply for NRA screening of the No. 1 reactor as well. In that case, attention will be focused on whether the utility will be able to show new data to overturn the NRA's final conclusion during the fresh round of screening by the nuclear watchdog.

There are three faults in question: the 780-meter-long "S-1" fault situated just below the No. 1 reactor; and the "S-2" and "S-6" faults just beneath cooling pipes for releasing sea water, extending a combined total of 550 meters. Hokuriku Electric had insisted that none of the faults are active. After compiling a draft report in July 2015 that said the possibility of the faults being active "cannot be denied," the NRA expert group heard the opinions of other experts.



Panel: Fault below Shika reactor may be active



A panel of scientists at Japan's nuclear regulator says a fault under a reactor at the Shika power plant in central Japan could slip in the future.

The conclusion could lead to the reactor's decommissioning, although the panel does not rule out additional study if fresh data are presented.

The panel of the Nuclear Regulation Authority met Thursday to discuss whether the fault right below the No.1 reactor at the plant in Ishikawa Prefecture is active or not.

A similar meeting last July came up with a draft assessment indicating the possibility of a shift of the fault in the future. The judgment was based on research conducted by the plant's operator, Hokuriku Electric Power Company, and other data.
But the panel members were later criticized by a group of other scientists for not presenting a full explanation, which led to the fresh meeting.

On Thursday, panel members reaffirmed that it makes sense to think the fault shifted during or after a geological period called the Late Pleistocene, between 120,000 and 130,000 years ago.

They agreed to retain the previous conclusion, which didn't rule out the possibility the fault could slip in the future. But they added that additional data on the fault is needed to make a more accurate assessment. The panel will report the results to the regulator.

New regulations adopted after the 2011 Fukushima Daiichi accident do not allow the construction of reactor buildings and other key nuclear plant facilities above faults that could slip in the future. The assessment could lead to scrapping of the No.1 unit.
The evaluation can be revised depending on the nature of additional data provided by the utility. Attention is focused on how the plant operator will respond to the conclusion and what decision the regulator will make.

The panel has also upheld its earlier assessment that another fault running beneath cooling pipes leading to the plant's No.1 and No. 2 reactors could distort the ground foundation in the future. The operator may be required to relocate or reinforce facilities.



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