ML082490728
| ML082490728 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 09/25/2008 |
| From: | Markley M Plant Licensing Branch IV |
| To: | Entergy Operations |
| Markley, M T, NRR/DORL/LP4, 301-415-5723 | |
| References | |
| TAC MD6897, TAC MD6898 | |
| Download: ML082490728 (8) | |
Text
September 25, 2008 Vice President, Operations Arkansas Nuclear One Entergy Operations, Inc.
1448 S.R. 333 Russellville, AR 72802
SUBJECT:
ARKANSAS NUCLEAR ONE, UNITS 1 AND 2 - RELIEF REQUEST ANO-CISI-001 RE: ALTERNATIVE FOR CONTAINMENT INSERVICE INSPECTION INTERVAL (TAC NOS. MD6897 AND MD6898)
Dear Sir or Madam:
By letter dated September 27, 2007, as supplemented by letter dated July 23, 2008, Entergy Operations, Inc. (Entergy, the licensee) submitted to the U.S. Nuclear Regulatory Commission (NRC) a relief request for approval of a proposed alternative (ANO-CISI-001) to the Arkansas Nuclear One, Unit 1 and 2, Containment Inservice Inspection (CISI) interval. Specifically, Entergy requested alternatives to the American Society of Mechanical Engineers Boiler and Pressure Vessel Code,Section XI, 1992 Edition and 1992 Addenda, Subsections IWL-2421(a) and IWL-2421(b) respectively, with regard to examination interval for the containment tendons.
The NRC staff completed its review of the subject request for alternative. Based on the enclosed safety evaluation, the NRC staff determined that the alternative inspection interval proposed by the licensee will provide an acceptable level of quality and safety. Therefore, pursuant to paragraph 50.55a(a)(3)(i) of Title 10 of the Code of Federal Regulations, the NRC staff authorizes the use of ANO-CISI-001.
If you have any questions regarding the SE, please contact Alan B. Wang at (301) 415-1445.
Sincerely,
/RA/
Michael T. Markley, Chief Plant Licensing Branch IV Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-313 and 50-368
Enclosure:
Safety Evaluation cc w/encl: See next page
- NLO w/comments OFFICE NRR/LPL4/PM NRR/LPL4/LA DE/EMCB/BC OGC NRR/LPL4/BC NRR/LPL4/PM NAME AWang GLappert KManoly SUttal (**)
MMarkley AWang MMarkley for DATE 9/12/08 9/7/08 9/12/08 9/22/08 9/25/08 9/25/08
Arkansas Nuclear One (6/19/08) cc:
Senior Vice President Entergy Nuclear Operations P.O. Box 31995 Jackson, MS 39286-1995 Vice President, Oversight Entergy Nuclear Operations P.O. Box 31995 Jackson, MS 39286-1995 Senior Manager, Nuclear Safety
& Licensing Entergy Nuclear Operations P.O. Box 31995 Jackson, MS 39286-1995 Senior Vice President
& Chief Operating Officer Entergy Operations, Inc.
P.O. Box 31995 Jackson, MS 39286-1995 Associate General Counsel Entergy Nuclear Operations P.O. Box 31995 Jackson, MS 39286-1995 Manager, Licensing Entergy Operations, Inc.
Arkansas Nuclear One 1448 SR 333 Russellville, AR 72802 Section Chief, Division of Health Radiation Control Section Arkansas Department of Health and Human Services 4815 West Markham Street, Slot 30 Little Rock, AR 72205-3867 Section Chief, Division of Health Emergency Management Section Arkansas Department of Health and Human Services 4815 West Markham Street, Slot 30 Little Rock, AR 72205-3867 Pope County Judge Pope County Courthouse 100 W. Main Street Russellville, AR 72801 Senior Resident Inspector U.S. Nuclear Regulatory Commission P.O. Box 310 London, AR 72847 Regional Administrator, Region IV U.S. Nuclear Regulatory Commission 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011-8064
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELIEF REQUEST ANO-CISI-001 ENTERGY OPERATIONS, INC.
ARKANSAS NUCLEAR ONE UNIT, 1 AND 2 DOCKET NO. 50-313 AND 50-368
1.0 INTRODUCTION
By letter dated September 27, 2007 (Agencywide Document Access and Management System (ADAMS) Accession No. ML072910229), as supplemented by letter dated July 23, 2008 (ADAMS Accession No. ML080270197), Entergy Operations, Inc. (Entergy, the licensee) submitted to the U.S. Nuclear Regulatory Commission (NRC) a relief request for approval of a proposed alternative (ANO-CISI-001) to the Arkansas Nuclear One (ANO),
Units 1 and 2, Containment Inservice Inspection (CISI) interval. Entergy submitted the request to employ an alternative inspection interval for the pre-stressed concrete containment systems of ANO. The licensee currently examines ANO under the provision of Subsection IWL-2420 of Section XI of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) (Reference 3 and 5). The licensee is requesting NRC staff approval for invoking the inspection interval of Subsection IWL-2421, Sites with Two Plants. This safety evaluation addresses the acceptability of this relief request.
2.0 REGULATORY EVALUATION
In a Notice published in the Federal Register (61 FR 41303), dated August 8, 1996, the NRC modified Title 10 of the Code of Federal Regulations (10 CFR) 50.55a, to incorporate by reference Subsections IWE and IWL of Section XI of the ASME Code. Subsection IWE and IWL provide the requirements for inservice inspection (ISI) of steel and concrete containments. Subsection IWL of Section XI of the ASME Code provides the requirements for ISI of Class CC (concrete containments) of light-water cooled power plants.
A licensee may, however, propose alternatives to requirements of the regulation pursuant to 10 CFR 50.55a(a)(3), which states, in part, that alternatives to the requirements of paragraphs (c), (d), (e), (f), (g) and (h) may be used, when authorized by the NRC, if (i) the proposed alternatives would provide an acceptable level of quality and safety or, (ii) compliance with the specified requirements would result in hardship or unusual difficulty without a compensatory increase in the level of quality and safety.
The licensee requested relief from the requirements of Subsection IWL-2421 of Section XI of the ASME Code regarding the specified inspection interval for its ANO, Units 1 and 2.
The NRC staffs findings with respect to authorizing the proposed alternative are discussed in the following sections.
3.0 TECHNICAL EVALUATION
3.1 Code Requirements In Section XI of the ASME Code, Subsection IWL-2421, Sites with Two Plants, paragraph (a) allows the use of IWL-2421 paragraph (b) examination requirements if both containments utilize the same pre-stressing system, if they are essentially identical in design, if the post-tensioning operations for the two containments were completed not more than two-years apart, and if both containments are similarly exposed to or protected from the outside environment.
3.2 Specific Relief Request In lieu of meeting the IWL-2420(a) examination requirements, Entergy proposes to use the examination requirements of IWL-2421(b) without meeting the specific two-year (24-month) criteria of IWL-2421(a). This two-year criteria was established by the ASME Code to ensure, to the extent practical, that when using the IWL-2421 rules, the two containments in a two-unit site would be essentially identical.
The licensee proposes to use 37 months (the actual duration between the completion of ANO, Units 1 and 2, post-tensioning operations) as meeting the 24-month requirement of IWL-2421(a).
3.3 Licensees Basis for Relief In Reference 1, the licensee stated that the containment designs of ANO, Units 1 and 2, are essentially identical structures, using the same pre-stressing design, located on one site and were constructed by the same contractor in a continuous manner. Furthermore, the environmental conditions to which the containments were exposed or protected were also virtually identical. The submittal states there are no safety or technical concerns with regard to age related degradation because of extending the post-tensioning period inspections 13 months beyond the ASME Code 24-month requirement. The licensee stated that the 13-month period is insignificant when compared to the life of the structures. For these reasons, Entergy states that no appreciable benefit is gained by overly frequent examination of the ANO containments post-tensioning systems and the proposed alternative will provide an acceptable quality level of quality and safety in accordance with 10 CFR 50.55a(a)(3)(i).
The licensee also noted that the NRC staff has approved similar post-tensioning period relief requests for Farley Nuclear Plant and Palo Verde Nuclear Generating Station.
3.4 Staff Evaluation of Relief Request The NRC staff agrees with the licensees assessment regarding the similarity of the two respective containments pre-stressing designs and the exposure to similar environmental effects. Thus, the focus of the NRC staff technical evaluation was to examine the similarities and differences in the behavior of the two containments and the potential effect of the additional 13-month time period between post-tensioning operations.
The NRC staff requested the licensee to provide summaries of the containment inspection reports for ANO, Units 1 and 2. In the letter dated July 23, 2008, Entergy provided ANO, Unit 1, summaries for the 1-, 3-, 5-, 10-, 15-, 20-, 25-and 30-year inspections. The inspection summaries identified a range of issues consisting of: discontinuous wires, high nitrate levels in the sheath filler samples, wires which did not meet minimum strength testing requirements, concrete cracks in the area surrounding bearing plates, and exposed reinforcing steel. In each instance where a deficiency was identified, the licensee performed an evaluation which ultimately determined that the infraction did not impact the overall structural integrity of the containment system. In essence, each of the issues identified were minor or insignificant relative to the performance of the containments intended function. It should be noted that the inspection summaries consistently identified the acceptability of the containment components.
As a part of the 15-year inspection for ANO, Unit 1, the licensee performed a regression analysis for the measured lift-off forces of the containment buildings tendons. At the time of the 15-year inspection, the NRC staff performed a review of the evaluation and concluded that no abnormal degradation had occurred in the post-tensioning system. Furthermore, during the 30-year surveillance, the licensee again performed a regression analysis of the ANO, Unit 1 tendons. This analysis predicted that the pre-stressing forces in the hoop, vertical, and dome tendons would all remain in excess of the minimum required tendon forces throughout the remainder of the current 40-year plant license.
In the letter dated July 23, 2008, Entergy provided ANO, Unit 2, inspection summaries for the 1-, 3-, 5-, 10-, 15-, 20-, and 25-year inspections. The reported conditions were similar to those identified in the Unit 1 reports. Namely, the licensee cited some discontinuous wires, mild corrosion, cracks in the concrete surrounding bearing plates, and some exposed reinforcing steel. Also similar to the behavior of ANO, Unit 1, all of the identified issues were minor or insignificant relative to the performance of the containments intended function.
It should be noted that prior to the NRC implementation of Section XI, Subsection IWE/IWL, of the ASME Code, the licensee was performing containment inspections under the guidance of Regulatory Guide (RG) 1.35, Inservice Inspection of Ungrouted Tendons in Pre-stressed Concrete Containment Structures. Under the provisions of RG 1.35, Rev. 2, only a visual surveillance was required for identical containment structures on one site, without environmental or other apparent differences, constructed in a continuous manner by the same contractor. For this reason, ANO, Unit 2, was able to receive credit for the inservice inspections performed on the reactor building tendons of ANO, Unit 1. The inference is clear that the NRC staff has accepted the behavior of one Unit to represent two essentially identical containments on the same site.
In a letter dated June 2, 2008 (ADAMS Accession No. ML080270197), the NRC staff also requested the licensee to provide records and evaluations of any water intrusion occurrences for the ANO, Units 1 and 2, post-tensioning ducts. The intent of this request was to verify that there were no gross differences between the behaviors of the two Units pertaining to water intrusion which could potentially lead to corrosion. In the Entergy letter dated July 23, 2008, the licensee provided information for both Units showing that no significant corrosion or intrusion had been recorded for either Unit during their respective surveillance periods.
The Code requirement associated with the 24-month limit between post-tensioning operations was initiated because post-tensioning forces decrease with time as a consequence of concrete shrinkage, concrete creep, and tendon stress relaxation. The regression line which predicts these effects is most often graphically expressed on a log-linear plot. The provision of a small time interval between two post-tensioning operations ensures that the age-related post-tensioning system behavior is approximately the same, allowing for the tendon population in both Units to be considered as one statistical population. An additional delay of 13 months (beyond the Code designation) will make little, if any, difference in the relative age-related behavior of the two containments.
In summary, the NRC staff finds that the licensees proposal that the behavior of the two essentially identical post-tensioned containment systems will not be affected by the additional 13-month period between post-tensioning operations is reasonable. This is supported by the similarity in the summaries of the surveillance reports and the overall condition of the containments, and the fact that the NRC staff has previously allowed the inspection of one unit to adequately represent the inspection of another unit. Thus, the inspection criteria of IWL-2421 is acceptable for implementation for ANO, Units 1 and 2, relieving the requirement for the post-tensioning operations of the Units to have been performed within a 24-month period. However, the NRC staff points out that as the behavior of the tendons in two Units comprise one population, any discrepancies discovered in one unit could be present in the second unit, and the licensee would need to evaluate the condition in the second unit.
4.0 CONCLUSION
The NRC staff has reviewed the justification provided by the licensee in support of the relief request for containment inspection interval associated with Section XI, Subsection IWL, of the ASME Code. The NRC staff concludes that the licensees proposed alternative of 37 months between post-tensioning operations of the two units is acceptable, in lieu of the 24-month code requirement, because this extended time period will not have an appreciable effect on the level of quality and safety which is currently associated with the containment integrity. Therefore, pursuant to paragraph 50.55a(a)(3)(i) of Title 10 of the Code of Federal Regulations, the NRC staff authorizes the use of the proposed alternative in ANO-CISI-001.
5.0 REFERENCES
- 1.
Letter dated September 27, 2007, from Dale E. James (Entergy Operations, Inc.) to USNRC with regard to Proposed Alternative for Containment Inspection Interval, Arkansas Nuclear One, Units 1 and 2 (ADAMS Accession No. ML072910229).
- 2.
Letter dated July 23, 2008, from Dale E. James (Entergy Operations, Inc.) to USNRC with regard to Response to Request for Additional Information, Proposed Alternative for Containment Inspection Interval, Arkansas Nuclear One, Units 1 and 2 (ADAMS Accession No. ML080270197).
- 3.
American Society of Mechanical Engineers, Boiler and Pressure Vessel Code, 1992 Edition,Section XI, Subsection IWL, Requirements for Class CC Concrete Components of Light-Water Cooled Plants, 1992 Addenda.
- 4.
U.S. Nuclear Regulatory Commission, Codes and Standards for Nuclear Power Plants; Subsection IWE and Subsection IWL (10 CFR part 50), Federal Register, Vol. 61, No. 154, August 8, 1996, pp. 41311 - 41312.
- 5.
American Society of Mechanical Engineers, Boiler and Pressure Vessel Code, 2001 Edition,Section XI, Subsection IWL, Requirements for Class CC Concrete Components of Light-Water Cooled Plants, 2003 Addenda.
Principal Contributor: B. Titus Date: September 25, 2008