Environmental Impact Statement - radioactive monticello

Environmental Impacts of Postulated Accidents
As shown in Table 5-3, internal flood events initiated by FPS and SW pipe breaks are the
dominant contributors to CDF. Loss of offsite power and other transient initiators contribute
about 6 percent of the CDF.
In the ER, NMC estimated the dose to the population within 50 mi of the Monticello site to be
approximately 38 person-rem per year. The breakdown of the total population dose by
containment release mode is summarized in Table 5-4. Containment failures within the late
time frame (greater than 6 hours following declaration of a general emergency) and early time
frame (less than 6 hours following declaration of a general emergency) provide similar
contributions to the population dose risk at Monticello.
Table 5-4.
Breakdown of Population Dose by Containment Release Mode
Population Dose
Containment Release Mode (person-rem(s) per year) % Contribution
Late containment failure 20.4 54
Early containment failure 17.6 46
Intact containment Negligible Negligible
Total 38 100
(a) 1 person-rem per year = 0.01 person-Sv per year
The NRC staff has reviewed NMC's data and evaluation methods and concludes that the quality
of the risk analyses is adequate to support an assessment of the risk reduction potential for
candidate SAMAs. Accordingly, the staff based its assessment of offsite risk on the CDFs and
offsite doses reported by NMC.
5.2.3 Potential Plant Improvements
Once the dominant contributors to plant risk were identified, NMC searched for ways to reduce
that risk. In identifying and evaluating potential SAMAs, NMC considered insights from the
plant-specific PSA, SAMA analyses performed for other operating plants that have submitted
license renewal applications, as well as SAMAs that could further reduce the risk of the
dominant internal fires. NMC identified 40 potential risk-reducing improvements (SAMAs) to
plant components, systems, procedures and training.
Twenty-four SAMAs were removed from further consideration because they are not applicable
at Monticello due to design differences, require extensive changes that would involve
implementation costs known to exceed any possible benefit, or exceed the dollar value
associated with completely eliminating all internal and external event severe accident risk at
Monticello. The remaining 16 SAMAs were subjected to further evaluation. During the second
phase of the evaluation, NMC screened out one additional SAMA based on risk insights and
August 2006 .' 5-7 NUREG-1437, Supplement 26 I