The Tokyo Electric Power Co. (TEPCO) covered up an incident
in which air from a reactor discharge pipe was tainted with
leaked plutonium and other radioactive substances, an
anti-nuclear activist group has said.
TEPCO has been scandalized for hiding the discovery of
cracks at its nuclear plants, however the leakage of plutonium
and other chemicals had not been revealed.
Members of the Osaka-based anti-nuclear group told the
press Wednesday that a TEPCO informer sent them e-mail in late
September and later copies of secret inside documents
detailing the leakage.
The internal documents show that nuclear substances were
detected at the outlet of a 120-meter-long discharge pipe
attached to two reactors in the Fukushima No. 1 nuclear plant
from 1979 to 1981.
TEPCO officials have admitted they detected the leaked
radioactivity, but tried to justify their failure to announce
"We didn't report the leakage to national government
authorities because the concentration of radioactivity at the
edge of the plant was only less than one 10,000th of the
government regulation amount," one of the officials said.
"Outside the plant, the amount of radioactivity discharged was
also less than the minimum level."
The level of radioactivity detected was up to 30 times the
lowest detectable value of a Geiger counter.
The official explained that several fuel rods at the
reactors cracked during the period allowing nuclear substances
to leak and contaminate the air in the reactor pipe.
Kunikazu Noguchi, a radioactivity expert at Nihon
University, said that TEPCO must voluntarily explain what
exactly was leaked and to what extent workers were exposed to
the nuclear substances.
"Generally no counters can detect such radioactivity
because normally the amount (found at the outlet of discharge
pipes) is below the minimum detectable level of counters at
nuclear power plants," Noguchi said. "Therefore, the fact that
such substances were detected is abnormal."
The nuclear substances found are generally called "alpha
nuclides" as they discharge alpha rays.
This is the first revelation of alpha nuclides leaking into
the air at a nuclear power plant, although such substances
were leaked at a reprocessing factory in Tokai, Ibaraki
Prefecture, during a major accident in 1997. (Mainichi
Shimbun, Oct. 24, 2002)