Onagawa Nuclear Power Station Unit No. 2 Review for 6 years Where is the point? Feb 26, 12:59 pm
It has been about six years since the Tohoku Electric Power Company filed an application for a prerequisite for the restart of Onagawa Nuclear Power Station Unit 2 until the NRA finalized the inspection report. One of the reasons behind the Great East Japan Earthquake was the need for more careful discussions on nuclear power plants affected by the tsunami and shaking of the earthquake.
How to prepare for a huge tsunami
The biggest point of the examination was tsunami countermeasures.
In the Great East Japan Earthquake, a huge tsunami, 13 meters in height, stormed the Onagawa Nuclear Power Plant, causing seawater to enter from the intake and some of the emergency generators could not be used.
Based on these facts, Tohoku Electric Power has raised the maximum height of the supposed tsunami from 13.6 meters before the disaster to 23.1 meters, which is almost double.
The Onagawa NPS was built on a site approximately 15 meters above sea level, so the tsunami did not survive the site.However, in response to raising the assumption of the tsunami, Tohoku Electric Power newly added a length of approximately 800 He said he was planning to build a seawall 29 meters above sea level.
However, it was pointed out in the examination that if a huge seawall was created, the ground would sink due to its weight and the height would be insufficient.
For this reason, Tohoku Electric Power has shown measures to strengthen the ground by solidifying the ground with concrete so that the ground does not sink.
However, another point was pointed out that when the ground was strengthened, the phenomenon of damming the flow of groundwater occurred, causing water to accumulate in the ground of the site and causing liquefaction in the event of an earthquake.
In response, Tohoku Electric Power showed plans to reinforce equipment such as "wells" that pump up groundwater, and also to install backup equipment, and finally passed the review.
The tsunami needed a lot of related preparations.
Preparing for an earthquake
In addition, preparing for a major earthquake was also a point of judging.
The Onagawa Nuclear Power Plant is located closest to the epicenter of the Great East Japan Earthquake. For this reason, the largest earthquake was estimated based on the in-plate earthquake off Miyagi prefecture, which occurred as an aftershock of the Great East Japan Earthquake as a standard for earthquake resistance.
As a result, the expected maximum earthquake tremor has been significantly increased from 580 gal before the earthquake to 1000 gal.
Also, regarding the earthquake, the strength of the building was also the subject of the examination.
A total of 1130 small cracks with a width of less than 1 mm were found on the wall of the reactor building, the reactor building.
It is thought to be the effect of past earthquakes, including the Great East Japan Earthquake.
Tohoku Electric Power's analysis showed that the reinforced concrete inside the walls was more flexible than before the earthquake.
On that basis, Tohoku Electric Power conducted a simulation and experiment assuming the shaking of the earthquake, and as a result, evaluated that there was no effect on the soundness of the building itself as it was and reported.
The Regulatory Commission determined that Tohoku Electric Power's evaluation was appropriate, stating that the report "has been rigorously evaluated to withstand the anticipated earthquake."