Category Archives: Estimating Loss-of-Coolant Accident (LOCA) Frequencies Through the Elicitation Process

WILLIAM (BILL) GALYEAN

The approach taken by Bill Galyean is based on the total operating experience of U. S. commercial nuclear power plants. This experience consists of approximately 2,650 LWR-years with zero category-1 (> 100 gpm [380 lpm]) loss of coolant accidents. The average age of these plants is approximately 25 years, with a number of plants being 30-plus years old. During this […]

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Submitted by Joseph Conen of the BWR Owners Group

Comment: It is apparent that the panel has not given appropriate credit to the IGSCC mitigation measures for the NSSS stainless steel piping that the BWR owners have implemented since the early 1980s. For example, the second paragraph from bottom on page xvii states, in part: “.. .the biggest frequency contributors for each LOCA size tend to be systems having […]

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Benchmarking

A limited scope benchmarking exercise was performed to compare predicted weld failure rates with the reported service experience. The benchmarking was limited to NPS12 BWR reactor recirculation welds susceptible to IGSCC. Probabilistic fracture mechanics (PFM) calculations using the WinPRAISE computer code generated predictions about the weld failure rate for different assumptions about the normal operating stresses (cNO).18 Bayesian reliability analysis […]

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DESCRIPTION OF NON-PIPING DATABASE

DESCRIPTION OF NON-PIPING DATABASE H. 1 Background The non-piping database has been compiled with the intention that it will serve as one source of information supporting the development of estimates of LOCA frequencies attributable to non-pipe components. The data has been obtained from two primary sources. First, a search of LERs was made to identify those instances where failures[17] of […]

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GERY WILKOWSKI

The piping non-seismic LOCA evaluations were conducted for PWR and BWR piping separately from a bottom-up approach using reference cases for certain pipe systems in each type of plant. The reference cases were determined from a combination of the base case results supplied to the elicitation panel. The base cases supplied consisted of two independent PFM analyses, and two independent […]

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Combined LOCA Frequencies due to Reactor Vessel Failures

Tables I.4 and I.5 summarize and combine the above RPV LOCA frequency results for BWRs and PWRs, respectively. For BWRs, three RPV LOCA contributors are addressed: RPV vessel beltline region, large nozzles (6 through 28 inch diameter), and small penetrations (partial penetration welded nozzles, 4 inch in diameter or less, such as CRDs). The individual LOCA probability contributions for each […]

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Leak Rate Evaluation

When estimating RR-PRODIGAL leak rates through the final through wall defect in a pipe weld, evaluations were made using an elastic crack opening displacement (COD) analysis. However, it was felt that the uncertainties associated with assessing both the defect length around the pipe circumference as well as the COD needed for estimating the flow rate through the crack, were too […]

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