suspected of rigging data
The Daily Yomiuri, September 26, 2002
By Yomiuri Shimbun
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