ML20214A864
| ML20214A864 | |
| Person / Time | |
|---|---|
| Site: | Braidwood  |
| Issue date: | 10/07/1986 |
| From: | AFFILIATION NOT ASSIGNED |
| To: | |
| References | |
| OL-I-ROREM-158, NUDOCS 8705190630 | |
| Download: ML20214A864 (3) | |
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'87 W?.' 12 P 7 :44 of this review by the Architect / Engineer, the discrepancy documentation will be l
returned to the BCAP Task Force. The BCAP Task Force will determine, in !!ght of the Architect / Engineer analysis, what further' iris;iections, if any, are indicated.
All discrepancies (whether design-significant or non-design-significant) will also be designated as nonconformances (NCRs) and will be processed in accordance with the existing Quality Assurance systems and approved procedures. This includes appro-priate corrective actions for removing the discrepant condition and trend analysis for identification of programmatic deficiencies, if any Corrective actions on the NCRs, however, will be completed only after review of the discrepancy for design significance.
The Commonwealth Edison Quality Assur'ance Department will overview these activities to assure that the actions taken are appropriate.
It should be understood that the objective of the CSR is to demonstrate with high.
confidence that there are no programmatic design-significant discrepancies in the construction of the plant. The sample selection and expansion criteria described in the next section will fulfill this objective.
1.
CSR Sample Selection Criteria The objective in this element of the BCAP is to establish a sample size which will support conclusions regarding the quality of the plant with high confidence.
For a large population, it is we!! recognized that if no defects are found in a sample of 60, a conclusion can be supported with 95% confidence that at least 95% of the total population is defect free. Similarly, if a sample size of 315 is found to be defect free, a conclusion can be drawn with 95% confidence, that at least 99% of the total population is defect free. These two statements have a firm foundation in statistics if the sample selection process is' random and the population is homogeneous.
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Since the work activities in the plant are non-homogeneous, it is not appropriate I
to utilize a rigorous statistical sampling approach for the CSR. Therefore, the size of the sample as well as the factors applied in selecting specific sample items will be determined by the application of engineering judgment.
In this regard the selection cf specific sample items within the specific i
construction categories of Appendix A will not be random. P.ather, the selection process will be biased toward a greater likelihood of detecting design-significant discrepancies by emphasizing areas of plant constrcction which have greater potential for discrepancies and areas of the plant or systems which are more critical to the proper performance of the plant safety functions. The CSR sample 1
will include representative examples of the. accessible and recreatable safety-related construction work performed by each contractor. The sample will include contractor work for the total time period over which the contractor performed the activity on site.
1 Even though the populations of the construction categories are not homogeneous, engineering judgment indicates that sample sizes in the range of those discussed i
earlier in this section will support a conclusion about the quality of the work, with high confidence. This engineering judgment is based upon the conservatism of the sampling bias and the large number of categories into which the reinspection program will be divided. The sample sizes selected for the work categories will be at least as great as those which would be suggested for a random sampling of a homogeneous population to conclude with 95% confidence that at least 95% of the population is defect free. In most cases, the CSR sample size selected will be significantly larger in order to develop a representative sample over the time period that the work was originally performed. Samples of this size, which are 4.
found to have no design-significant discrepancies, support a conclusion with high confidence that there are no programmatic design-significant discrepancies in the entire population of that construction activity. Furthermore, it,should be noted that the number of inspection points will generally be much greater than the sample size. For example, if the sample size utilized for cable pan hangers is 200, the reinspection could involve as many as 1,500 cable pan hanger welds and 3,000 or more attribute inspection points.
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All considerations influencing the sample selection, both with respect to the total I
number of items included in the sample and also the selection of specifc items within the sample, will be properly documented.
2.
CSR Sample Expansion Criteria Discrepancies identified in the performance of the CSR wi!! be evaluated by the Architect / Engineer for design significance. The evaluation will reference, when applicable, design calculations which were performed to support this analysis.
All discrepancies, including those determined to be non-design-significant, will be documented and processed as nonconformances (NCRs) in accordance with the existing QA procedures.
This includes appropriate corrective actions for removing the discrepant condition and trend analysis for identification of programmatic deficiencies, if any.
The design-significant discrepancies will be evaluated by the BCAP Task Force and the Architect / Engineer for identification of probable root cause or causes.
For example, root causes for welding discrepancies may. include welde'r qualification, weld procedure misapplication, defective welding metal, a faulty welding machine, inspector error or lack of training and weldability of base material.
Based on the identification of root cause(s) of a design-significant discrepancy, a determination will be made of the population of items which may be affected by the root cause(s). This population will be identified by a review of the installation and inspection documentation. This population will then be subjected to further inspections.
1 Some root causes may be, by observation or analysis, found to bd nongeneric and therefore unique. In such cases, further inspections may not be appropriate.
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