Quake-hit nuclear power station faces grave problems; seismic shock 3.6 times greater than design criterion

   The earthquake (magnitude: 6.8 on the Richter scale) that occurred under the seabed off Niigata Prefecture on July 16 directly hit the Kashiwazaki-Kariwa Nuclear Power Station, one of the world’s largest nuclear power plants that has seven reactors with a total output of 8,210 megawatts.

   At the TEPCO (Tokyo Electric Power Co.) power station site, the seismic shock reached 3.6 times more than anticipated at the time of its design (see table).

   Local residents expressed deep anxiety over the safety of the plant. “Radioactive substances were already released into the sea and air. TEPCO’s policy of releasing limited information has increased our distrust. We have pointed out the possible existence of active faults close to the power station, but TEPCO has denied it. Unless TEPCO discloses all information and we become fully confident of their policies, it is absolutely unacceptable to resume the operation of the plant,” said Nakazawa Yoichi, a 58-year-old resident.

   The hypocenter of the earthquake was located nine kilometers north of the power station at a depth of 17 kilometers. An analysis jointly conducted by the Meteorological Agency, Tokyo University, and the National Research Institute for Earth Science and Disaster Prevention found that the fault that caused the earthquake may well extend to directly below the power station site.

   When the earthquake occurred at 10:13 a.m., Units No. 3, No. 4, and No. 7 were in operation and No. 2 was starting up, and all suffered emergency shut-downs because of the shock. The other three units were not in operation due to inspections.

   In less than two minutes, a fire broke out at a transformer installed outside Unit No. 3. It was the first time that a fire broke out at a nuclear power plant due to an earthquake.

   At Unit No. 6, water spilled over from a pool storing used nuclear fuel located inside the nuclear reactor building, and the radioactive water flowed out to the sea. Radioactive substances were also released into the air.

   As of July 21, TEPCO reported a total of 63 incidents, including malfunctions and damage of equipment.

   TEPCO must conduct a thorough investigation and fully disclose the information.

   It was exposed once again that Japan’s nuclear power plants are not adequately designed to withstand earthquakes.

   TEPCO on its website stated, “We have confirmed that there is no active fault underneath the site” and put a map showing locations of nuclear power stations and active faults. The map failed to show even the fault that caused the earthquake.

   In March, a strong earthquake registering a magnitude at 6.7 on the Richter scale occurred close to Hokuriku Electric Power Co.’s Shika Nuclear Power Plant and caused a shock stronger than anticipated. The active fault that caused the quake also was unknown.

   Power companies have explained that earthquakes cannot damage nuclear reactors since they are installed on bedrock and that the shock will be half or one-third of the shock on normal ground. The government has accepted their argument.

   Despite their claim, the grounds on which nuclear reactors are installed shook far more violently than the design criteria anticipated.

   It is said that the Japanese archipelago has entered an active seismic period, the first such period since nuclear power plants were built.

   It is urgently needed to drastically review nuclear power plants’ anti-earthquake measures. The Chubu Electric Power Co. Hamaoka Nuclear Power Plant (Shizuoka Pref.) needs to be shut-down since it is located in the hypocentral region of the Tokai earthquake, a great earthquake expected to occur in the near future.

Table: Observed maximum seismic acceleration (upper) and Design-basis

 acceleration (lower) at Kashiwazaki-Kariwa Nuclear Power Station (Unit: Gal)

- Akahata, July 19, 20 & Sunday Edition, July 22, 2007