September 2002
TEPCO suspected of rigging data
The Daily Yomiuri, September 26, 2002
By Yomiuri Shimbun[Posted 26/09/2002]
In what is considered far more grave than the recent series of cover-ups at Tokyo Electric Power Co. (TEPCO) nuclear power plants, the company is now suspected of falsifying key data concerning the safety of a radioactivity containment system at one of its reactors, The Yomiuri Shimbun learned Wednesday.
According to documents obtained by The Yomiuri Shimbun and revelations by the people involved, TEPCO fabricated readings of airtightness of the containment building -data of key importance to nuclear safety- at one of its six reactors at the Fukushima No. 1 plant in Fukushima Prefecture in 1992.
The containment building is referred to by experts as a "final-stage fort" to prevent radioactivity from being discharged from a reactor in the event of a nuclear accident. A high level of airtightness is a prerequisite for keeping the containment capability of the reactor intact and is one of the priority items in the government safety checkups for nuclear reactors.
Revelations emerged in recent weeks of a spate of cover-ups at TEPCO nuclear power plants in connection with cracks in reactor shrouds and in pipes carrying primary cooling water in reactors. Inspections of such reactor components are listed as "voluntary checkups" under the nuclear safety regulations.
In light of the importance of the airtightness of containment buildings, checkups of the buildings and reports of the findings to the government are included in statutory items in regular inspections under the Electric Utility Law.
As it is the most important system to prevent radioactivity from being discharged into the environment, its checkups are in the "Rank A" category, the highest-ranking inspection under the law, according to the experts. They said the latest revelations are expected to exacerbate public distrust of TEPCO, while bringing into question the professional ethics of the nuclear power technicians involved.
The containment building is a huge steel container about 32 meters high. It houses the nuclear reactor in a separate pressurizer container, and both are housed in a 44-meter-high reactor building.
The falsification of the airtightness data occurred following a regular inspection of the reactor in June 1992, sources said on condition of anonymity.
To ensure the airtightness of a containment building exceeds government safety standards, checkups are conducted by pouring nitrogen gas into the buildings to enhance their internal pressure to about three times the atmospheric pressure.
Technicians then track changes in the pressure readings for six hours to determine the gas leakage rate, the experts said.
A degree of leakage is unavoidable, since containment buildings are linked to a large number of pipes, from which they said very small amounts of gas may escape.
Under the government regulations, the maximum permissible level of leakage is set at 0.45 percent of the building's entire cubic volume per day.
During the statutory regular checkups of the No. 1 reactor of the Fukushima No. 1 plant, however, airtightness readings found in tests carried out by a TEPCO subsidiary were fluctuating from 0.3 to 2.5 percent a day, according to the sources.
Anxious about the implications of the unstable readings, TEPCO officials at the plant and nuclear power plant manufacturers decided to falsify the readings to make them appear much the same as previous tests, they said.
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