ML16161A269
| ML16161A269 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 09/15/1997 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML16161A268 | List: |
| References | |
| NUDOCS 9709260357 | |
| Download: ML16161A269 (6) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.225T0 FACILITY OPERATING LICENSE DPR-38 AMENDMENT NO. 2251O FACILITY OPERATING LICENSE DPR-47 AND AMENDMENT NO.222TO FACILITY OPERATING LICENSE DPR-55 DUKE ENERGY CORPORATION OCONEE NUCLEAR STATION, UNITS 1. 2. AND 3 DOCKET NOS. 50-269, 50-270, AND 50-287
1.0 INTRODUCTION
By letter dated October 30, 1996, and supplemented by letters dated April 22, July 2, September. 3, and September 4, 1997, Duke Energy Corporation (the licensee -formerly Duke Power Company) submitted a request for changes to the Oconee Nuclear Station, Units 1, 2, and 3, Technical Specifications (TS). The requested changes would revise the Reactor Building Structural Integrity TS regarding the tendon surveillance program. The letters dated April 22, July 2, September 3, and September 4, 1997, provided clarifying information that did not change the initial proposed no significant hazards consideration determination.
The purpose of the proposed amendments is to change the tendon surveillance program by adopting Regulatory Guide (RG) 1.35, Revision 3. RG 1.35, Revision 3, which stipulates that tendon lift-off tests be performed on randomly selected tendons, instead of repeatedly on the same tendons, as required by the existing tendon surveillance TS. In addition, RG 1.35, Revision 3, contains guidance concerning the acceptability of the tendon forces by requiring that the tendon lift off forces be within limits established on the basis of the prescribed lower limit (PLL). It also prescribes the actions to be taken when the lift-off forces are below the specified limit.
In order to assure that the trend of the lift-off force will not go below the minimum required tendon force for each group of tendons before the next surveillance, it is necessary to specify the minimum required values (MRVs) for each of the tendon groups. RG 1.35, Revision 3, refers to RG 1.35.1 for guidance in establishing PLLs and MRVs. By adopting RG 1.35, Revision 3, the licensee will use the criteria stipulated therein for the tendon surveillance programs at the three Oconee units.
2.0
Background
By letters dated October 11, 1995, and March 14 and July 30, 1996, the licensee submitted the results of the previous tendon surveillance tests and resulting graphs for the MRVs. By letter dated March 14, 1996, the licensee committed to perform a re-analysis of the containment structure in order to establish more accurate tendon group MRVs, and to evaluate the causes of any loss of 9709260357 970915 PDR ADOCK 05000269 P
2 prestresses in excess of the PLLs computed during the original plant design, because the existing PLLs have been shown to be inaccurate. Therefore, the licensee will establish new PLLs as part of the containment reanalysis.
The change to the surveillance program will allow the licensee to obtain new inspection data, which will be used to enhance the level of knowledge of the current state of the Reactor Building Post Tensioning System and the ability to predict the future state of the system.
3.0 EVALUATION The NRC staff has reviewed the licensee's proposed change and the following is the staffs evaluation of the proposed change.
3.1 Modification of the Tendon Test Program Presently, in Section TS 4.4.2.1, Tendon Surveillance, the tendons to be inspected by lift-off force testing are preselected and fixed, that is, the same tendons are inspected by lift-off tests for all of the surveillances. The surveillance program consists of periodic inspections of nine predesignated tendons; three horizontal, three verticle, and three dome tendons on each unit. One of the three tendons in each group is detensioned and retensioned for wire sample removal on a rotational basis. The acceptability of the tendon lift-off test depends on whether the force-time trend line extends below the lower bound of the predicted design band. Presently there are no stipulations as to what actions should be taken for such a condition. The licensee has reported that because of repeated detensioning and retensioning, one dome tendon (2D28) in Unit 2 and one hoop tendon (51 H9) in Unit 1 have been damaged to the extent that they will be precluded from future lift-off tests. This raises questions as to whether the information from the lift-off of fixed tendons can be used to truly represent the tendon forces in the group of tendons. The results of the recent sixth tendon inspection for Unit 3 show low tendon forces, which can be attributed mostly to the repeated testing of the same tendons. Thus, experience has shown that long-term wear on the pre-selected sample tendons, caused by repetitive surveillance tests, can adversely affect the quality of the observed surveillance data.
Instead of using nine fixed tendons (i.e., three from each group), 11 representative tendons (five hoop, three vertical, and three dome) will be selected randomly with one in each group to be kept unchanged for the subsequent inspection.
On the basis of the experience obtained to date, as described above, the licensee has proposed to change the present TS by adopting the inspection program that will comply with the guidance in RG 1.35, Revision 3. The staff agrees with the licensee that such a change should eliminate, as much as possible, the deficiencies in the present TS.
In response a staff request, the licensee incorporated the tendon surveillance interval start dates for each unit into TS Section 4.4.2.1 by supplement dated April 22, 1997. However, as explained in the
3 supplemental letter dated September 3, 1997, the licensee has determined that the date specified for Unit 1 of July 1, 1991, was overly conservative. This is the date that the Unit 1 Sixth Tendon Surveillance began, not the date the test was completed. Because portions of the test were carried over to the next refueling outage, the test was not completed until January 1, 1993. Therefore, this is the date that the licensee has determined should be used to determine the date when the Seventh Tendon Surveillance should be performed. The staff agrees that establishing the date as 5 years from January 1, 1993, rather than 5 years from July 1, 1991, is acceptable since it correctly reflects the interval between completion a test to completion of the next test. In addition, the test will be performed within the interval required by RG 1.35.
3.2 Establish the PLLs and Revise the MRVs Since the present tendon surveillance TS do not specify any PLL and do not use PLL, but instead uses MRV as an acceptability criterion, it is necessary for the licensee to establish the PLL for each group of tendons. RG 1.35 requires the comparison of measured tendon forces with the predicted forces of randomly selected tendons. The predicted forces at a given time are based on the measurement of the tendon forces during installation minus the losses in the tendon forces that were predicted to have occurred since that time because of material and structural characteristics.
Because of the various complex interacting phenomena involved, the chance is small that the measured tendon force will agree closely with the predicted value. Hence, RG 1.35 recommends the determination of the upper and lower bounds. The PLL is the lower bound. For each prestressed concrete containment, the upper and lower bounds should be determined before the initiation of the tendon surveillance program. Without the PLL, there is no basis to establish the 95 percent and 90 percent PLL limits as the criteria for the acceptance of the tendon force. If the tendon lift-off forces chronically cannot meet the criteria, then the lower bound should be revised or the tendons should be retensioned, depending on whether the lower bound is predicted to go below the MRV before the end of the plant life. If the containment design pressure is not changed, there should not be a major change in the MRVs provided during the staffs review of the sixth tendon surveillance of Unit 3.
On the basis of the above discussion, the licensee has committed in its July 2 and September 4, 1997, letters to the NRC to a license condition to include the revised PLL and MRV values in the Oconee Selected Licensee Commitment (SLC) Manual, which is Chapter 16 of the Oconee Updated Final Safety Analysis Report (UFSAR), and to submit those values to the staff, prior to the implementation of the TS. The staff needs this information to verify that the values are reasonable and that they properly reflect the method used to generate them.
In the letter dated October 30, 1996, the change proposed by the licensee to Specification 4.4.2.2.a.2 required that two additional tendons be checked for their prestressing forces if the measured prestressing force for the first-examined tendon is between the PLL and 90 percent of the PLL. However, as explained in their letter dated September 3, 1997, the licensee has recently determined that the proposed change does not conform to RG 1.35, Revision 3, Section 7.1.2. The RG requires that two additional adjacent tendons be checked for their prestressing forces if the
4 measured prestressing force for the first-examined tendon is between 95 percent of the PLL and 90 percent of the PLL. As a result, as Specification 4.4.2.2.a.2 is currently worded, adjacent tendons to the first-examined tendon would have to be examined unnecessarily if the first-examined tendon exhibited a prestressing force between 100 percent of the PLL and 95 percent of the PLL. This is overly conservative and could result in the examination of additional tendons beyond the requirements of RG 1.35, Revision 3.
As explained in their letter dated September 3, 1997, the licensee also proposed adding the word "adjoining" to the change proposed in the October 30, 1996, submittal to clarify that additional lift-off testing needs to be done only if two adjoining tendons' prestressing force falls below 95 percent of the PLL. As originally proposed, the specification could have been misinterpreted to imply that additional testing would be required based on the results of any two tendons, regardless of whether or not they were adjacent. This wording is consistent with RG 1.35, Revision 3.
3.3 Provisions for Detension and Retension Tendons The criterion for retensioning detensioned tendons is described in TS Section 4.4.2.2.c. The criterion incorporates the Regulatory Position (RP) 4.2 in RG 1.35, Rev. 3, for simultaneous measurement of tendon force and elongation and also RP 7.2 for determination of potential wire failure or wire slip at anchorages.
3.4 Other Areas of Inspection as Required in RG 1.35, Rev. 3 The following areas of inspection are adequately covered in the TS:
a) inspection of tendon wires for corrosion, cracks, and damage and testing of tendon wires for their strength; b) sheathing filler grease for presence of water, voids in grease, grease leakage on the exterior surface, chemical contents, and the amount of each; c) tendon anchorage and adjacent concrete surface for any abnormality; and d) the reactor building surface for the detection of large spall, severe scaling, cracking, and other surface deterioration or disintegration or grease leakage.
4.0
SUMMARY
On the basis of it's evaluation as presented above, the staff concludes that the changes to the TS as proposed by the licensee are acceptable since they comply with RG 1.35. It is also based on the licensee's commitment to make available to the staff the PLL and the MRV of tendon force for each group of tendons by including them in the Oconee SLC Manual, which is Chapter 16 of the Oconee UFSAR, before the forthcoming tendon inspection. This commitment is contained in a change to
5 Appendix C of the Oconee TS and was acknowledged in the licensee's letter dated September 4, 1997.
On August 8, 1996, the NRC published in the Federal Register (61 FR 41311) changes to 10 CFR 50.55a that invoked the requirements of the American Society of Mechanical Engineers (ASME)
Boiler and Pressure Vessel Code,Section XI, Subsections IWE and IWL. This rule change requires that utilities perform inservice inspections of containments in accordance with the 1992 Edition of the ASME Code, through 1992 Addenda (with specific exceptions and limitations). For Oconee this will require that surveillance tests be performed in a manner similar to that specified in RG 1.35, as approved by this amendment. In addition, the rule change allows utilities to take credit for Reactor Building Post-Tensioning System tests to satisfy the IWL provisions for a 5-year period from the effective date of the rule change for tests that were performed in accordance with RG 1.35 before the effective date of the rule change. However, Oconee has not yet performed tests in accordance with RG 1.35 and is not yet prepared to perform the tests in accordance with the ASME Code.
Therefore, this TS change also satisfies the Expedited Examination of Containment requirements contained in the rule change on an interim basis until final implementation of the rule change, which will occur within the five year period allowed for implementation of the Rule/ASME Code.
5.0 STATE CONSULTATION
In accordance with the Commission's regulations, the South Carolina State official was notified of the proposed issuance of the amendments. The State official had no comments.
6.0 ENVIRONMENTAL CONSIDERATION
The amendments change requirements with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 and change surveillance requirements. The NRC staff has determined that the amendments involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure.
The Commission has previously issued a proposed finding that the amendments involve no significant hazards consideration, and there has been no public comment on such finding (61 FR 64383 dated December 4, 1996). Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.
7.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that: (1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's
6 regulations, and (3) the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor: Chen P. Tan; David E. LaBarge Date:
September 15, 1997