ML120820098
| ML120820098 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 03/22/2012 |
| From: | Balwant Singal Plant Licensing Branch IV |
| To: | Harrison A South Texas |
| Singal, B K, NRR/DORL, 301-415-301 | |
| Shared Package | |
| ML120820096 | List: |
| References | |
| RR-ENG-3-08, TAC ME8159 | |
| Download: ML120820098 (3) | |
Text
REQUEST FOR ADDITIONAL INFORMATION RELIEF REQUEST RR-ENG-3-08 REPAIR OF VALVES IN THE ESSENTIAL COOLING WATER SYSTEM SOUTH TEXAS PROJECT, UNIT 2 DOCKET NO. 50-499 By letter dated March 12, 2012, (Agencywide Document Access Management System (ADAMS)
Accession No. ML12079A034), STP Nuclear Operating Company (the licensee) submitted for U.S. Nuclear Regulatory Commission (NRC) review and approval Relief Request (RR)
RR-ENG-3-08 at South Texas Project (STP), Unit 2. The licensee requested relief from IWA-5250 of Section XI of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code. To complete its review, the NRC staff request for the following additional information.
- 1. General The NRC and the ASME Code provide guidance concerning temporary repairs in NRC Generic Letter 90-05, Guidance for Performing Temporary Non-Code Repair Of ASME Code Class 1, 2, and 3 Piping, (ADAMS Accession No. ML031140590) and ASME Code Case 513-3, Evaluation Criteria for Temporary Acceptance of Flaws in Moderate Energy Class 2 or 3 Piping,Section XI, Division 1, with condition specified in NRC Regulatory Guide 1.147, Revision 16, Inservice Inspection Code Case Applicability, ASME Section XI, Division 1 (ADAMS Accession No. ML101800536). The NRC staff notes that this guidance has not been included in the RR under consideration. The NRC staff believes that failure to consider all the available guidance may result in temporary repairs which do not meet appropriate safety criteria. For each of the requirements contained in both the code case and GL 90-05, please identify whether the current RR a) meets the requirement; b) the requirement is not applicable; or c) how the current RR provides an acceptable level of safety.
- 2. Section 1. - Component for Which Relief is Requested 1.) Section 1.(d) discusses the indications found and describes these indications as through-wall dealloying with no cracks and no measurable leakage. Was any leakage noticeable and if so, please describe the leakage?
2.) Section 1.(d) describes the five indications found on Valve 2-EW-FV-6936 and multiple indications found on valve 2-EW-FV-9637. Please discuss if these indications were treated as a single defect and how they compared to the 3-inch critical flaw size stated in Section 6.4 of your request. If they were treated independently, please discuss the basis for making that assumption.
- 3. Section 4 - Reason for Request
- 1) This section discusses the reason for this request and states that the valves will be replaced following receipt of the replacement parts. The proposed duration presents regulatory ambiguity because it is not clear to the NRC staff the exact length of time the relief is requested. The licensee needs to provide the exact date beyond which the RR will be expired and no longer be effective. It is not clear to the NRC staff that the flaw evaluation in Section 6.4 of the RR demonstrates that the through wall flaw in the valve at the end of proposed duration would still be within the critical crack length of 3.0 inches. Please demonstrate that the flaw size in the subject valves at the end of duration period will be within the critical crack length of 3.0 inches.
- 2) Please demonstrate that appropriate actions have been taken to procure a replacement valve and address the concept of using a valve constructed from an alternate material on a temporary basis. If practical, please state the delivery dates for such valves.
- 4. Section 6.2 - Specific considerations 1.) This section describes how structural integrity of these valves will be monitored. It states that structural integrity and monitor frequency are re-evaluated if significant changes in the condition of the dealloying occur. Please provide the criteria that define significant changes in the condition of the dealloying.
2.) This section states that dealloying flaws are only detectable by visual examination once they have reached the piping surface. Please describe how the evaluation procedures account for the inside diameter (ID) degradation and its effect on the overall valve degradation. Please describe any inspection procedures that may be used to verify the ID degradation. If current inspection procedures cannot detect the extent of the ID dealloying, justify why a single linear indication that is part through wall for the complete circumference, and through-wall for the extent of the OD defects should not be assumed in the fracture analyses.
3.) Section 6.2, page 4, states that the affected valves will be inspected by a monthly walkdowns. ASME Code Case N-513-3, paragraph F requires that for through-wall leaking flaws, leakage shall be observed by daily walkdowns to confirm the analysis conditions used in the evaluation remain valid. Please explain why a monthly inspection is sufficient to ensure that the changes in flaw size or leak rate will not affect the structural integrity of the valves.
4.) The licensee stated that leakage from Essential Cooling Water (ECW) piping in the subject valve location flows to the mechanical auxiliary building sumps. The licensee further stated that sump level alarms are available to warn operator if leakage exceeds the sump pump capacity. This seems that the leak rate would have to be significant before the sump level alarms will annunciate in the control room. By such time, the crack may have been grown to a significant size such that the structural integrity of the pipe would be in question. Please discuss the leak rate and associate crack size in the ECW piping that would cause sump level alarm to initiate.
- 5. Section 6.4 - Flaw Evaluation 1.) This section describes the flaw evaluations completed in this effort. A critical crack length of 3.0 inches was determined for the through wall crack. Please provide details on the analyses conducted including the fracture mechanics procedures used and the material properties assumed.
2.) Please provide details on the basis for the 100 percent dealloyed tensile strength (30ksi). Please include the number of specimens tested, the data used to determine this value, and describe the experimental procedure used in its development. In addition, please discuss how 100% dealloyed material can leak yet have residual strength.
3.) A summary of fracture results from 4-inch nominal pipe sizes was used in the fracture analysis. Please provide additional details on the experiments used in the comparison and their applicability to the dealloyed valves in this request. Include details on the materials, geometry, loading conditions and flaw type.
4.) Please provide details on the allowable moment and stress calculations for both end loading and postulated pipe break stress.
5.) This section states that significant margin exists compared to the fracture analysis calculations. Please provide details on the fracture margin. The beginning of this section describes a 3-inch critical flaw size derived from experiments but does not estimate a margin.
- 6. Section 6.5 Augmented Inspection 1.) Indications have been found in similar valves in two of the three ECW loops. Please discuss the rationale for not implementing the augmented inspection on the similar valve in the third ECW loop.