Chernobyl Nuclear Accident Congressional Hearings Transcript

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longer, as in U.S. light water reactors, and that decreases the quality
of the plutonium that is in the plant.
Senator Domenici. Thank you, very much.
Thank you, Mr. Chairman.
The Chairman. Thank you, Senator Domenici.
Senator Melcher.
Senator Melcher. Mr. Denton, the staff of the Commission has
estimated that out of the 100 nuclear plants in this country, there
is a 45-percent chance of a core meltdown. Just so we understand
what that likelihood is, does that 45 percent mean that you flip a
coin 100 times, and 50 times it is going to come up heads? What
does it mean?
Mr. Denton. I don't think the number itself is too meginingful.
Senator Melcher. What does it mean?
Mr. Denton. It is assuming that all the plants have about the
same management capabilities and maintain their plant at about
the same level, and have, good drug abuse programs in place, and
that therefore, you could treat all the class of reactors as cookiecutter
imitations of each other. That you truly have a random statistical
type basis.
What that number was based on were the 15 or 16 probablistic
risk studies that have been done since TMI, taking sort of the average
number and assuming that the same number applies to all the
plants, and that we are not effective in trying to reduce the probability
through our regulatory systems and other pressures that we
bring on the utilities.
It is my goal to try to reduce it at individual plants as low as we
can.
The real secret at preventing, accidents, I think
Senator Melcher. What does the 45-percent chance mean? My
next question will get into how safe people feel about nuclear
plants. But this is one item and if it means 50-50, that is what I
am asking. Does it or does it not?
Mr. Denton. Let me tell you what it does mean and how we got
it. We originated an average number for the probability of a TMItype
event based on analytical studies. That number turned out to
be about 1 chance in 10,000, roughly.
If you assume that we have 100 plants, and you run 20 years,
and you run through the math, you can come up that somewhere
in the U.S. population of reactors, in the next 20 years, there would
be a 45-percent change of another accident such as TMI occurring.
Senator Melcher. Did the staff suggest that it was a core meltdown,
or the chance of one occuring? Were they not looking at a
chance of a core meltdown?
Mr. Denton. No, we were looking at a TMI-type occurrence.
Senator Melcher. But not a core meltdown.
Mr. Denton. That number does not assume that containment
would fail.
The Chairman. Would the Senator yield?
Senator Melcher. Yes, I would be glad to.
The Chairman. There was a core meltdown at TMI, was there
not?
Mr. Denton. Yes, partial.
The Chairman. Partial. All right.