TEPCO’s Kashiwazaki Kariwa nuclear power plant in Niigata was discovered to have concerning structural damage to the Unit 6 reactor building.
The damage was discovered in the support pilings beneath the large garage building attached to the Unit 6 reactor. One piling had significant
damage, broken rebar, and some disconnection to the upper concrete. Other pilings had varying levels of lesser damage. Japan’s nuclear regulator,
the NRA plans to do on-site inspections by early next year. The current assumption is that this damage was caused by the 2007 earthquake that caused widespread damage and a mandatory shut down of the plant.
Garage building attached to the Unit 6 reactor building.
Piling locations beneath the garage building.
The garage building (circled) is seen in this press photo.
Neither TEPCO nor the NRA’s reports discuss the potential structural integrity of support pilings for other buildings in this section of the plant grounds.
Unit 7’s garage building was noted to have newer updated construction beneath it. Beyond this mention, the risk for similar problems elsewhere at the
plant is not currently known. Neither report was clear about what caused TEPCO to excavate and inspect under the Unit 6 garage building in the first place.
There have been concerns since at least the 2007 earthquake about an active fault line under the plant. It was noted at the time that the plant design was engineered to withstand a maximum of a 6.5 earthquake. The 2007 earthquake was a 6.8. This 2007 report from The Guardian documents a number of failures and incorrect disclosures by TEPCO that were later admitted to being worse than initially admitted.
The new NRA report cites that the number 8 pillar beneath the garage building is the most damaged.
The images and diagram below show the damage to the top of the pillar.
Number 8 pillar under the unit 6 garage building. 7 of the 18 rebar tie sections are damaged, 11 are distorted.
The 7 flagged points in blue have separation from the concrete tie-in above. All points have a distortion in the same direction.
A wider view of the number 8 pillar that is documented to be the most severely damaged.
TEPCO has focused on conditions at the Unit 6 and 7 reactors at Kashiwazaki Kariwa as their best chance to gain approval to restart any of their nuclear reactors in Japan. The plant is the largest nuclear plant in Japan, hosting 7 reactor units. The older units at the plant with no plans to be restarted could provide an important opportunity for forensic research into reactor construction design and real-world earthquake resistance. This finding at Unit 6 may also raise questions about the safety of operating Units 6 or 7 in the future and the potential for more unseen foundation damage.
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