The Nuclear Regulation Authority failed to conduct on-site inspections to determine if safety equipment cables were installed separately from other cables at nuclear power plants during the safety screening process required for the restart of reactors, it was learned Saturday.
The revelation came to light when it was recently revealed that safety cables at nuclear facilities, including Tokyo Electric Power Co.’s Kashiwazaki-Kariwa plant in Niigata Prefecture, were not separated from other cables, a violation of the new nuclear safety standards introduced in July 2013.
The nuclear safety watchdog’s oversight also includes cables installed for reactors that have already passed safety screenings, including those at Kyushu Electric Power Co.’s Sendai plant in Kagoshima Prefecture.
At all seven reactors at the Kashiwazaki-Kariwa plant, many safety-related cables, including those used to transmit data from water meters and for water injection operations, were found combined with other cables. The seven units are all boiling-water reactors.
The new safety standards, drawn up after the triple reactor meltdown in March 2011 at Tepco’s crippled Fukushima No. 1 nuclear plant, call for the separation of safety cables from others to prevent possible fire damage.
The NRA only became aware of the problem at the Kashiwazaki-Kariwa plant when it received a report from Tepco in September.
Similar issues were discovered at other boiling-water reactors, including the No. 3 and No. 4 reactors at Tepco’s Fukushima No. 2 nuclear plant and the No. 4 reactor at Chubu Electric Power Co.’s Hamaoka plant in Shizuoka Prefecture.
According to NRA officials, the safety of cables is confirmed through the application documentation submitted by power companies, with no visual checks conducted on the ground.
In pre-restart reactor inspections, the NRA does not check to see if safety cables are separated, although inspections are done for fire-extinguishing and other equipment, the officials added.
At the Kashiwazaki-Kariwa plant, the problem cables were first found under the central control rooms for the No. 1 to No. 7 reactors.
The NRA then asked other power companies with boiling-water reactors to check and report if they had similar issues. Power utilities with pressurized-water reactors were also asked to report.
At the Kashiwazaki-Kariwa reactor, mixed cables were found in areas outside the central control rooms.
“At present, we can’t deny the possibility that other cables are mixed at pressurized-water reactors, but how to handle the problem has yet to be decided,” an official at the NRA said. “First, we’ll analyze the report from Tepco.”
Of pressurized-water reactors in Japan, the No. 1 and the No. 2 reactors at the Sendai power plant resumed operations in August and October, respectively.
The No. 3 and No. 4 reactors at Kansai Electric Power Co.’s Takahama plant in Fukui Prefecture, and the No. 3 reactor at Shikoku Electric Power Co.’s Ikata plant in Ehime Prefecture have also passed NRA safety screenings.