From page 48 of the full report at http://web.mit.edu/nuclearpower/
Also note they said more than 1 core damage before 2050 is unaccceptable,
there were 3 cores destroyed just last year - we've already passed what they considered acceptable.
And there will be more.
What is the expected frequency of accidents
today with the currently operating nuclear
plants? There are two ways to determine the frequency
of accidents: historical experience and
Probabilistic Risk Assessment.7 Since the beginning
of commercial nuclear power in 1957,
more than 100 LWR plants have been built and
operated in the U.S., with a total experience of
2679 reactor-years through 2002. During this
time, there has been one reactor core damage
accident at Three Mile Island Unit 2. The core
damage frequency of U.S. reactors is therefore 1
in 2679 reactor-years on average.
Probabilistic Risk Assessment (PRA) identifies
possible failures that can occur in the reactor,
e.g., pipe breaks or loss-of-reactor coolant flow,
then traces the sequences of events that follow,
and finally determines the likelihood of their
leading to core damage. PRA includes both
internal events and external events, i.e., natural
disasters. Expert opinion using PRA considers
the best estimate of core damage frequency to
be about 1 in 10,000 reactor-years for nuclear
plants in the United States. Although safety
technology has improved greatly with experience,
remaining uncertainties in PRA methods
and data bases make it prudent to keep actual
historical risk experience in mind when making
judgments about safety.
With regard to implementation of the global
growth scenario during the period 2005-2055,
both the historical and the PRA data show an
unacceptable accident frequency. The expected
number of core damage accidents during the
scenario with current technology8 would be 4.
We believe that the number of accidents expected
during this period should be 1 or less, which
would be comparable with the safety of the current
world LWR fleet. A larger number poses
potential significant public health risks and, as
already noted, would destroy public confidence.
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