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Statement of Need: This rulemaking would codify alternative requirements for ECCS at nuclear power reactors by using risk information to refine ECCS requirements based on the likelihood of pipe breaks of various sizes. The rule would divide all coolant piping breaks currently considered in emergency core cooling requirements into two size groups: Breaks up to and including a "transition" size, and breaks larger than the transition size up to the largest pipe in the reactor coolant system. Selection of the transition size was based upon pipe break frequency estimates and associated uncertainties. Because pipe breaks in the smaller size group are considered more likely, they would be analyzed using existing criteria for ensuring that the reactor core stays cool during and after an accident. Larger breaks are considered less likely and would be analyzed with less conservative methods. Plants would still have to mitigate the effects of breaking the largest pipe and maintain core cooling. Under the draft final rule, power plant operators could make plant design changes that could enhance safety and/or provide operational benefits. The rule includes risk acceptance criteria to ensure that modified designs would continue to provide adequate protection of public health and safety.

Alternatives: The alternative is for the NRC not to issue these requirements. The alternative would not allow operators of nuclear power plants to have the increased design and operational flexibility that would be allowed by these risk-informed requirements.

Anticipated Costs and Benefits: There are no costs or benefits associated with this alternative rule for licensees who choose not to implement it. For the licensees who do choose to comply with the alternative requirements, if they request to increase power generation at their facilities and eliminate the need for fast-starting of emergency diesel generators, they would need to invest an estimated overall total of approximately $445 to $1,221 million (in 2008$ @ 3 percent discount rate) for plant modifications and staff support. Total estimated NRC cost associated with implementing the alternative requirements and reviewing licensees' design change requests at these facilities would be approximately $22 to $24 million (in 2008$ @ 3 percent discount rate). Substantial net benefits would result after subtracting both licensee and NRC costs from the benefits that licensees would obtain from making these plant modifications. The total cumulative net benefits are estimated to range from $279 to $2,876 million (in 2008$ @ 3 percent discount rate).

Risks: The rule would allow plant design and operational changes which could result in small but acceptable increases in risk. Specific acceptance criteria for risk increases are contained in the rule which limit overall risk increases to very small amounts. Allowable risk increases under this rule are consistent with the current risk increase guidelines specified in Regulatory Guide 1.174, "An Approach for Using Probabilistic Risk Assessment in Risk-informed Decisions on Plant-Specific Changes to the Licensing Basis."