Agency begins probe into TEPCO data manipulation case.
(EDS: RECASTING WITH ADDITIONAL INFO, CHANGING DATELINE)
The Nuclear and Industrial Safety Agency began yet another probe Wednesday into Tokyo Electric Power Co.'s (TEPCO) cover-up of defects at nuclear plants following allegations that the utility manipulated data during government inspections in 1992.
Earlier revelations of the scandal involved TEPCO's voluntary facility checks, raising doubts about the firm's attitude toward safety, but the latest revelation regarding government checks could undermine the state's nuclear safety assurances as a whole.
In a separate development the same day, TEPCO said its inspectors have found cracks in 242 of the 282 stainless steel pipes sending water into a control rod at the No. 3 reactor of the Fukushima No. 1 nuclear plant in Fukushima Prefecture, northeastern Japan.
Regarding the new probe, TEPCO allegedly forced the company which was undertaking the June 1992 routine checks of the No. 1 reactor of the Fukushima No. 1 nuclear plant to inject oxygen in order to cover up instability of air sealing by the reactor's container, sources close to the case said.
The air tightness of a reactor container is the last resort in preventing an accident from turning serious through a radiation leak. Sealing tests are thus a top priority in the government's safety inspections of nuclear plants.
Inside, the steel container is depressurized so that the different pressure prevents radioactive leakage in the event of an accident.
Sealing tests are usually carried out at the last phase of government inspections by infusing nitrogen and checking changes in the internal pressure every six hours over 24 hours to see how much gas leaks through bolts and valves.
With one government inspector overseeing, the tests concerned showed the rate of leakage was 0.12% of the entire gas volume, well within the 0.45% limit permissible for a day.
''It's usually unthinkable that oxygen could be injected into a reactor container during inspections by a government inspector,'' a TEPCO spokesperson said.
''But as long as there is an allegation, we will thoroughly examine the facts in contact with the manufacturer'' which undertook the actual tests.
As for the newly found cracks, TEPCO said there was no water leakage at the No. 3 reactor of the Fukushima No. 1 nuclear plant, which has been temporarily shut down due to a regular safety checkup.
The company believes the cracks were caused by chloride erosion and is studying countermeasures, it said.
The company announced on Aug. 22 that it had found cracks in 36 of the pipes during the checkup that started in July, and that it would check other pipes as well.
The announcement was made prior to the revelations on Aug. 29 that TEPCO, Japan's largest power utility, had covered up the existence of cracks and other damage at 13 nuclear reactors located in the Fukushima No. 1, No. 2 and Kashiwazaki-Kariwa plants during the 1980s and 1990s.
TEPCO admitted to some of the cover-ups and said its chairman and president would resign as a result.