Nuclear Regulatory Commission (NRC) guidance for Subsequent License Renewal (SLR) applicants is provided in the NUREG-2191. Specifically, Section X.M1 of the NUREG-2191 includes guidance for aging management programs (AMP) which has two aspects related to fatigue analyses, one that verifies the continued acceptability of existing analyses through cycle counting and the other that provides periodically updated evaluations of the fatigue analyses to demonstrate that they continue to meet the appropriate limits. In addition, the NUREG-2191 provides requirements to account for reactor water environment by deriving cumulative fatigue usage (CUF) including environmental effects (CUFen) in component fatigue analyses for a set of sample critical components for the plant outlined in NUREG/CR-6260. Furthermore each applicant is required to determine plant-specific component locations in the reactor coolant pressure boundary that may be more limiting than those considered in NUREG/CR–6260. This paper presents a methodology to identify plant-specific primary equipment component locations that are potentially more limiting than the locations identified in NUREG/CR-6260, through a detailed review and ranking of the analyses of record (AORs) for a plant. The ranking approach implemented in this methodology assesses the level of technical rigor required to derive the CUF values and provides a means to appropriately compare CUF values within the same transient section. This paper also illustrates how this methodology was applied for a recent license renewal application.
As plants apply for 80 year licensure (subsequent license renewal), the United States Nuclear Regulatory Commission (U.S. NRC) has queried the nuclear power plant industry to investigate the impact of neutron embrittlement (radiation effects) on the reactor pressure vessel (RPV) structural steel supports due to extended plant operation past 60 years. The radiation effects on RPV supports were previously investigated and resolved as part of Generic Safety Issue No. 15 (GSI-15) in NUREG-0933 Revision 3 [1], NUREG-1509 [2] (published in May 1996), and NUREG/CR-5320 [3] (published in January 1989) for design life (40 years) and for first license renewal (20 additional years). The conclusions in NUREG-0933, Revision 3 stated that there were no structural integrity concerns for the RPV support structural steels; even if all the supports were totally removed (i.e. broken), the piping has acceptable margin to carry the load of the vessel. Nevertheless, for plants applying for 80 year life licensure, the U.S. NRC has requested an evaluation to show structural integrity of the RPV supports by accounting for radiation embrittlement (radiation damage) for continued operation into the second license renewal period (i.e. 80 years). The RPV support designs in light water reactors are grouped into one of five categories or types of supports: (1) skirt; (2) long-column; (3) shield-tank; (4) short column; and (5) suspension. In this paper, two of these RPV support configurations (short column supports and neutron shield tank) will be investigated using fracture mechanics to evaluate the effect of radiation embrittlement of the structural steel supports for long term operations (i.e. 80 years). The technical evaluation of other support configurations will be provided in a separate technical publication at a future date.
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