- Hi Jeff -
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- This is from Raymond Shadis of the New England Coalition...
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- A 50cm (20 inch) return pipe, last inspected in 1996
(not inspected since construction in 1976 according to some reports) suddenly
burst scalding workers in the Mihama Unit 3 turbine hall.
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- Four workers were killed; seven were hospitalized. One
remains in serious condition.
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- Company spokesmen said that the failed pipe was scheduled
for inspection in November. A quality control manager said that it was
due for ultra-sonic inspection on August 14th.
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- When new, the pipe walls measured 10 millimeters in thickness
(.4 inches). At the time the pipe burst, it measured just 1.4 millimeters
(.056 inches, thinner than a penny, almost as thin as a dime).
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- High-pressure water or wet steam erodes the interior
of power of plant piping and pipes must be inspected for wear periodically.
(Through the industry, the phenomenon is termed, " erosion-corrosion.")
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- A deputy plant manager said that they "had never
expected such rapid corrosion."
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- A similar fatal incident took place in the United States
in 1986 (12-09-86) when a return line burst at the Surry Nuclear Power
Station in Virginia.
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- Both Surry and Mihama are pressure water reactors. Mihama
started commercial operation on December 1, 1976 and has a licensed out
put of 826 megawatts (electric).
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- The inescapable lesson of the Mihama experience is that:
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- the industry does not understand as much about erosion-corrosion
and the possibility of accelerated wear rates as it thought; therefore
surveillance and wear calculations must be made many times more conservative
than what they are today, both Mihama and Surry incidents happened in plants
that were not given the extra stress and wear of extended power uprates,
that ENVY appears to be cruising for an accident by placing cost-conservation
ahead of safety conservation, and just saying that it "can't happen
here" will not prevent the next tragedy. From our point of view, such
hubris will only mean that the next accident will not be an accident; rather
it will be an eventuality.
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