Tsuruga Nuclear Power Plant - Seismic Research Done in 2005, 2011 and 2012

Seismic Research Done in 2005, 2011 and 2012

On 5 March 2012, a group of seismic researchers revealed the possibility of a 7.4M (or even more potent) earthquake under the Tsuruga Nuclear Powerplant. Before this date, the Japanese governmental Earthquake Research Committee and Japan Atomic Power had calculated that the Urasoko fault under the plant, combined with other faults connected to it, was around 25 km long. and could cause a 7.2M quake and a 1.7 meter displacement. On top of this, the presence of the oceanic faults were not taken into account by NISA and JAP in the assessment of the safety of the Tsuruga nuclear power plant.

Analysis of sonic survey and other data provided by Japan Atomic Power analysed by a panel of experts of Nuclear and Industrial Safety Agency showed the presence of multiple faults existing within 2 to 3 km from the Urasoko fault. According to Yuichi Sugiyama, a member of this group of scientists, these faults were highly likely to be activated together, and this would extend the length of the Urasoko fault to 35 km.

Computer-simulations calculating the length of a fault based on its displacement, showed the Urasoko fault to be 39 km long, a result close to the length estimated by the sonic survey data, and the fault could cause some 5 meter displacement when activated together with other faults.

Sugiyama, the leader of this research group of the National Institute of Advanced Industrial Science and Technology, warned that – as other faults on the south side of the Urasoko fault could become activated together – "The worst-case scenario should be taken into consideration".

According to the experts, there were many other faults located under one reactor on the west side of the Urasoku fault that could also move simultaneously. If this would be confirmed, the location of the Tsuruga nuclear plant would be disqualified.

On 6 March 2012, NISA asked Japan Atomic Power Co. to reassess the worst-case scenario for earthquakes at the Tsuruga-nuclear power plant: what damage this could do to the buildings on the site, because the Urazoko fault, running around 250 meters from the reactor buildings, could have a serious impact on the earthquake resistance of the power plant. NISA was also planning to send similar instructions to two other nuclear power plant operators in the Fukui area: Kansai Electric Power Company, and Japan Atomic Energy Agency, because the Mihama Nuclear Power Plant and the Monju fast-breeder reactor could also be affected by a possible earthquake caused by the Urazoko fault.

A few weeks later, on 21 March 2012, was revealed that the results of sonic research done in 2005 were ignored by JAPCO and that this data was kept secret in 2008 from a NISA research team of experts.

After an on-site survey at four points of geological layers by a panel of geologists, on 24 April 2012, NISA did admit that the 35-km-long Urazoko fault that runs under the Tsuruga reactors could be active. The experts determined that an earthquake did happen there some 4,500 years ago and that the other fault (without a name) running right beneath reactor 2 could slip and cause critically damage to the reactor induced by an earthtquake caused by the Urazoko fault. By definition, a fault is "active" when it is believed to have caused a quake about 120,000 to 130,000 years ago or later. Japan Atomic Power was requested to produce a detailed assessment of the two faults under the reactors.

On 14 November 2012, the Nuclear Regulation Authority of Japan decided to conduct a field-survey on the Tsuruga-site to check the faults under and around the plant. On 1 December, and of necessary, 2 December, the investigative team lead by NRA Commissioner and seismologist Kunihiko Shimazaki and four other experts planned to examine the site to exclude that faults running directly underneath the two reactors might move in conjunction with the active Urazoko fault located only 250 meters from the buildings.

The result of these investigations was presented at a meeting of experts on 10 December 2012. The conclusion was that the "fault zone of crushed rock called D-1, located beneath the plant's No. 2 reactor, could move in conjunction with the Urazoko fault." Kunihiko Shimazaki, the NRA-commissioner at the head of the team, told at the meeting, "that what appeared to be an extended section of D-1 had moved as an active fault in the past, together with the movement of the Urazoko fault". Although some local residents were stunned by the NRA-led team's judgment, the mayor of Tsuruga, Mayor Kazuharu Kawase, said that the outcome was "very tough", but that additional investigations could possibly confirm the safety of the plants.

In a draft-report presented 28 January 2013, a panel of experts of the Japanese NRA again affirmed that the D-1 fault that runs under reactor No. 2 is likely to be geological active, because it could move in conjunction with the active Urazoko-fault located only some 250 meters from both the No. 1 and No. 2 reactor buildings. Although other outside experts will be asked to check the report "to improve" the contents, Kunihiko Shimazaki, NRA-member and panel head said : "We're not expecting to spend much time, but I can't tell at this moment by when (the review will finish)."

On 22 January 2013, officials of Japan Atomic Power Co. received a version of the draft assessment report on the geologic faults running under the reactor complex. This was just a week before the report was scheduled to be made public by an NRA-appointed panel. Although the leaked information was not secret, for it contained a summary of public discussions, the incident was rather an embarrassment for the NRA because it undermined its policy of transparency and neutrality. Japan Atomic Power Co. was eager to get the information, because it wanted to prepare its counter arguments in the discussions. Although no money was paid for it, Tetsuo Nayuki, the NRA-official involved, was fired, because he violated the strict NRA regulations that, to ensure transparency, forbid single NRA staff members to meet officials of nuclear power plant operators. On 1 February, Nayuki was transferred to his former post at the Ministry of Education, Culture, Sports, Science and Technology.

On Friday, 8 March 2013, Japan Atomic Power Co. presented its latest analysis based on its ongoing geological investigation at the plant to the NRA-panel. According to JAPCO, the D-1 was not active and there was no need to refer to K because it did move in earlier times. But although the content of the report could be improved in a way that it would be more comprehensible to the public, the NRA did not expect that the meeting would change earlier conclusions. At the next meeting of the panel, the report was expected to be finalized and submitted to the NRA. After this, the NRA would decide whether the reactors could be reactivated or not. In a statement, JAPCO was "extremely" disappointed that the panel had not taken into account the important data provided by the operator. JAPCO made a "strong request" for another possibility for discussions. On 19 April 2013, the NRA inspection team told JAPC that it would not accept the power company's refutation of the NRA-report, stating the high possibility of an active fault lying under reactor No. 2 reactor, because the arguments of the power company were unclear. Although a 24 April-meeting was planned for another hearing, it was unlikely that the NRA-team would alter its position.

On 15 May 2013, the experts appointed by the Nuclear Regulation Authority presented their final report. They concluded that the No. 2 reactor was located right above an active fault, which could undermine its safety. This made it more likely that this unit might be shut down permanently. The expected costs of this could easily lead to a bankruptcy of its owner.