Chernobyl Nuclear Accident Congressional Hearings Transcript

267
QUESTION 10. (Continued) 3 -
indications that taken together serve as the basis for any
estimate of the likelihood of a core melt accident.
With regard to quantitative indications, the Commission has
previously stated that the most complete and recent PRAs suggest
.3
core-melt frequencies in the range of 10 per reactor year to
4 -4
10 per reactor year, with a typical value of 3x10 per reactor
year. Based on this latter value as an industry average and given
a population of 100 reactors operating over a period of 20 years,
the Commission has estimated the likelihood of a severe core melt
accident in the next 20 years to be 45 percent. (See the
Commission's response to Question 21(a) in the April 16, 1985
letter to Congressman Markey from Chairman Palladino.) The value
of 45 percent has been estimated by the Commission through the
- X t
formula P=l-e , where P is the cumulative probability of an
event occurring over time t, and x is the likelihood of the event.
-4
In this case, t equals 20 years and x equals 3x10 per reactor
year times 100 reactors.
The PRA estimates given above have substantial uncertainties that
span a factor of about 10 above and below the reported values. I
believe it is mandatory that consideration of these uncertainties
be factored into any application of such point estimates. Thus,
the cumulative probability of a core meltdown accident in the next
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