Environmental Impact Statement - radioactive monticello

Environmental Impacts of Postulated Accidents
5.2.1 Introduction
This section presents a summary of the SAMA evaluation for Monticello conducted by NMC,
and described in the ER, and the NRC's review of this evaluation. The details of the review are
described in the NRC staff evaluation that was prepared with contract assistance from
Information Systems Laboratories, Inc. The entire evaluation for Monticello is presented in
Appendix G.
The SAMA evaluation for Monticello was conducted with a four-step approach. In the first step
NMC quantified the level of risk associated with potential reactor accidents using the
plant-specific probabilistic safety assessment (PSA) and other risk models.
In the second step NMC examined the major risk contributors and identified possible ways
(SAMAs) of reducing that risk. Common ways of reducing risk are changes to components,
systems, procedures, and training. NMC initially identified 40 potential SAMAs for Monticello.
NMC screened out 24 SAMAs 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
other factors, leaving 15 SAMAs.
In the third step NMC estimated the benefits and the costs associated with each of the
remaining SAMAs. Estimates were made of how much each SAMA could reduce risk. Those
estimates were developed in terms of dollars in accordance with NRC guidance for performing
regulatory analyses (NRC 1997a,b). The cost of implementing the proposed SAMAs was also
estimated.
Finally, in the fourth step, the costs and benefits of each of the remaining SAMAs were
compared to determine whether the SAMA was cost-beneficial, meaning the benefits of the
SAMA were greater than the cost (a positive cost-benefit). NMC found seven SAMAs to be
potentially cost-beneficial in the baseline analysis, and three additional SAMAs to be potentially
cost-beneficial when alternative discount rates and analysis uncertainties are considered (NMC
2005a).
NMC recognized that a combination of low-cost SAMAs can provide much of the risk reduction
associated with higher-cost SAMAs, and may act synergistically to yield a combined risk
reduction greater than the sum of the benefits for each SAMA if implemented individually.
Since the ER was submitted, NMC has implemented six SAMAs, and reassessed the value of
the remaining SAMAs. Implementation of the six SAMAs reduces the benefit of the remaining
SAMAs such that only one SAMA remains potentially cost-beneficial.
August 2006 5-5 NUREG-1437, Supplement 26 I