ML15218A151
| ML15218A151 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 10/30/1997 |
| From: | Labarge D NRC (Affiliation Not Assigned) |
| To: | Mccollum W DUKE POWER CO. |
| References | |
| TAC-M99779, TAC-M99780, TAC-M99781, NUDOCS 9711140138 | |
| Download: ML15218A151 (8) | |
Text
Octob@30, 1997 Mr. W. R. McCollum Vice President, Oconee Site Duke Energy Corporation P. 0. Box 1439 Seneca, SC 29679
SUBJECT:
REQUEST FOR ADDITIONAL INFORMATION - PROPOSED AMENDMENT TO CHANGE THE STEAM GENERATOR TUBE INSPECTION SURVEILLANCE PROGRAM - OCONEE NUCLEAR STATION, UNITS 1, 2, AND 3 (TAC NOS.
M99779, M99780, AND M99781)
Dear Mr. McCollum:
By letter dated October 20, 1997, Duke Energy Corporation requested an amendment to the Technical Specifications for the Oconee Nuclear Station Units 1, 2, and 3. The amendment proposes the use of a reroll process to repair the degraded steam generator tubes in a tubesheet. The technical basis for the reroll process is stated in Topical Report BAW-2303P, Revision 2. To complete its review, the staff requests additional information as described in the enclosure.
Sincerely, ORIGINAL SIGNED BY:
David E. LaBarge, Senior Project Manager Project Directorate 11-2 Division of Reactor Projects - 1/11 Office of Nuclear Reactor Regulation Docket Nos. 50-269, 50-270, 50-287 DISTRIBUTION 1164cketFild COgIe,RII
Enclosure:
Request for Additional Information PUBLIC PRush PDII-2 RF JJohnson,RII cc w/encl: See next page CBeardslee JTsao Document Name: G:\\OCONEE\\OCO99779. RAI To receive a copy of this document, indicate In the box: "C" = Copy without attachmentlenclosure "E" = Copy with attachmentlenclosure "N"= No copy
- concurrence by Beardslee (via EMail)
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/97 OFFICIAL RECORD COPY 9711140138 971030 PDR ADOCK 05000269 I
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 October 30, 1997 Mr. W. R. McCollum Vice President, Oconee Site Duke Energy Corporation P. 0. Box 1439 Seneca, SC 29679
SUBJECT:
REQUEST FOR ADDITIONAL INFORMATION - PROPOSED AMENDMENT TO CHANGE THE STEAM GENERATOR TUBE INSPECTION SURVEILLANCE PROGRAM - OCONEE NUCLEAR STATION, UNITS 1, 2, AND 3 (TAC NOS. M99779, M99780, AND M99781)
Dear Mr. McCollum:
By letter dated October 20, 1997, Duke Energy Corporation requested an amendment to the Technical Specifications for the Oconee Nuclear Station Units 1, 2, and 3. The amendment proposes the use of a reroll process to repair the degraded steam generator tubes in a tubesheet. The technical basis for the reroll process is stated in Topical Report BAW-2303P, Revision 2. To complete its review, the staff requests additional information as described in the enclosure.
Sincerely, David E. LaBarge, Senior Project Manager Project Directorate 11-2 Division of Reactor Projects - III Office of Nuclear Reactor Regulation Docket Nos. 50-269, 50-270, and 50-287
Enclosure:
Request for Additional Information cc w/encl: See next page
Oconee Nuclear Station cc:
Mr. Paul R. Newton Mr. J. E. Burchfield Legal Department (PBO5E)
Compliance Manager Duke Energy Corporation Duke Energy Corporation 422 South Church Street Oconee Nuclear Site Charlotte, North Carolina 28242 P. O. Box 1439 Seneca, South Carolina 29679 J. Michael McGarry, Ill, Esquire Winston and Strawn Ms. Karen E. Long 1400 L Street, NW.
Assistant Attorney General Washington, DC 20005 North Carolina Department of Justice Mr. Robert B. Borsum P. 0. Box 629 Framatome Technologies Raleigh, North Carolina 27602 Suite 525 1700 Rockville Pike Mr. G. A. Copp Rockville, Maryland 20852-1631 Licensing - ECO5O Duke Energy Corporation Manager, LIS 526 South Church Street NUS Corporation Charlotte, North Carolina 28242-0001 2650 McCormick Drive, 3rd Floor Clearwater, Florida 34619-1035 Mr. Richard M. Fry, Director Division of Radiation Protection Senior Resident Inspector North Carolina Department of U. S. Nuclear Regulatory Environment, Health, and Commission Natural Resources 7812B Rochester Highway 3825 Barrett Drive Seneca, South Carolina 29672 Raleigh, North Carolina 27609-7721 Regional Administrator, Region II U. S. Nuclear Regulatory Commission Atlanta Federal Center 61 Forsyth Street, S.W., Suite 23T85 Atlanta, Georgia 30303 Max Batavia, Chief Bureau of Radiological Health South Carolina Department of Health and Environmental Control 2600 Bull Street Columbia, South Carolina 29201 County Supervisor of Oconee County Walhalla, South Carolina 29621
Request for Additional Information Steam Generator Tube Reroll Repair Amendment Oconee Nuclear Station Units 1, 2, and 3 Duke Energy Corporation By letter dated October 20, 1997, Duke Energy Corporation (the licensee) requested an amendment to the Technical Specifications (TS) for the Oconee Nuclear Station Units 1, 2, and 3. The amendments propose the use of a reroll process to repair the degraded steam generator tubes in the tubesheet. The technical basis for the reroll process was stated in Topical Report BAW-2303P, Revision 2.
A. Questions Related to TS Changes
- 1.
The submittal does not specify the exact length of the rerolling and associated measurement uncertainties. The staff has accepted references to technical reports in which the length of the reroll is specified. However, in this case, three reroll lengths (1 inch, 1-5/8 inches, and 1.14 inches) are discussed in Topical Report, BAW-2303P.
As a result, it is not clear which of the above reroll lengths would be applicable.
Therefore, the staff requests that the reroll length and uncertainties be specified in the TS, or, a revised BAW-2303P, Revision 2, be referenced in the TS that includes a regulatory acceptable reroll length and uncertainties.
- 2.
Previous implemention of alternative repair criteria for the tubes in the tubesheet such as reroll or F* have included requirements to reinspect all repaired tubes at each refueling outage to verify that the cracks have not progressed in the repaired region.
Experience with rerolling applications at other pressurized water reactors (PWRs) indicates that rerolled joints may be more susceptible to stress corrosion cracking than original roll expansions. In addition, Section 6.1 of the topical report states that the expected life of rerolled joints is uncertain. Therefore, continued inservice inspection requirements are needed in the TS to monitor the integrity of repaired tubing. Discuss the bases for not reinspecting rerolled tubes at each future refueling if there is no plan to inspect rerolled tubes.
- 3.
To remain consistent with the staffs position on alternate tube repair criteria and methods that have been incorporated at other facilities, the TS need to incorporate a new leakage limit from each steam generator to be equal or less than 150 gallons per day.
- 4.
It is not clear to the staff whether reroll will be applied to the degraded tubes in the upper or lower tubesheet. In the cover letter, the licensee implies that the reroll will be applied to the tubes in the upper tubesheet. However, the topical report (Figure 5.3) shows that reroll may be applied to the tubes in the upper and lower tubesheets. Also, the qualification presented in BAW-2303P does not appear to apply to rerolled joints in the lower tubesheet because it seems that the presence of tubesheet crevice impurities and Enclosure
-2 the observation that such impurities were in the lower tubesheet crevice were not accounted for in the qualifications testing.
If the amendment is to applicable to rerolls in the lower tubesheet, provide additional technical justification for applying rerolls in the lower tubesheet area, including adjustments to axial pullout joint strength and leakage integrity. Otherwise, modify the amendment or propose a license condition to exclude rerolling repairs in the lower tubesheet.
- 5.
The staff notes that, as presently proposed, existing indications in the tubes that will be rerolled would still be counted toward the C-1, C-2, and C-3 classification of inspection results in future inspections. If this is not desired, provisions need to be addressed in a revised submittal.
- 6.
The proposed insert into the Bases section is inconsistent with the surveillance requirements in the TS. Specifically, TS 4.17.5.h, "Tube Inspection," states that the inspection is tube end to tube end. However, the proposed insert into the Bases states that the rerolled tubes do not need to be inspected in the degraded area because the degradation is outside the tube pressure boundary. The staff notes that the TS surveillance requirements themselves are the governing requirements for the inspection of once-through steam generator (OTSG) tubing, not the Bases statements. Therefore, inspections of the rerolled tubes would be required from tube end to tube end. Please clarify or modify the proposed insert into the TS Bases section and provide details on the extent of future inspections of rerolled tubing.
B. Questions Related to Topical Report. BAW-2303P. Revision 2
- 1.
On page 2-1, reroll is defined as a 1-inch long defect-free roll expansion beyond the MIriginal r!! expansio As stated in Section 3.2 of the report, spacers are used to achieve the proper depth of installed rerolls. However, It is not clear how the length of the reroll is defined and maintained constantly during installation.
(a)
How would the boundary of the reroll joint be defined if there are axial indications extended beyond the original roll transition region?
(b)
Provide the range of depths into the tubesheet for existing hardrolls for each of the Oconee Unit 1, 2, and 3 steam generators.
(c)
Discuss how the variability of the existing hardroll location for each tube will be accounted for in the installation to ensure an adequate hardroll length inboard of the original roll expansion-transition.
- 2.
On page 2-1, the report presented the double repair roll method and the single repair roll method.
(a)
To what tube would each method be applied?
-3 (b)
It seems that the qualification testing used a single rolled joint to attempt to demonstrate tube structural and leakage integrity. However, the topical report implies that both single and double rerolled joints are qualified and acceptable for use. The staff believes that the introduction of a second hardroll, as in the double reroll joints, between the original roll expansion and the rerolled joint may affect the initial reroll and potentially introduce an effect apparently not accounted for in the qualification testing. Discuss the basis for demonstrating the adequacy of double reroll joints using a single reroll as done in the qualification testing.
- 3.
Section 3.2 states that new roll expansions will be installed using a Delta plugging type tool head. In the qualification testing, the tube specimens were rolled using a modified roll.
(a)
The report does not state any specific requirements on the dimensions of the rerolling tool. Provide the type and dimensional requirements for the tooling proposed to install field rerolls.
(b)
Provide details on the differences between the rolling tool used in the qualification and the Delta plugging type tool head proposed for field rerolls.
(c)
Discuss the implications of these differences on the validity of the qualification testing.
- 4. Table 4.2 shows tube design operating loads for 40 years.
(a)
Clarify how the tube loads in table 4.2 were calculated. Were the calculated tube loads based on the tube being fixed on both ends or fixed on one end only (i.e.,
severed on the other end).
(b)
The staff notes that the axial loading on tubing varies across the tube bundle.
Discuss the conservatism of the values provided in Table 4.2 with respect to the limiting tubes in the Oconee OTSGs. The maximum tube axial load under main steamline break (MSLB) conditions, 2378 lb, appears inconsistent with the result of 3140 lb presented in BAW-10146. Provide additional information on the bases for the results provided in Table 4.2, and clarify this apparent discrepancy.
- 5.
Section 5.3 discussed the determination of tube radial contact stresses but did not provide details on (a) tube specimen material properties, (b) the rerolling procedure (e.g., installation torque), (c) mock-up block dimensions and materials, and (d) other factors that could affect the calculated radial tube stresses. Provide these additional details and discuss the conservatism for each of these factors in relation to the conditions and configuration of the Oconee OTSG tubes.
- 6.
The report, Table 5.2.2, shows various roll torque applied to test tubes. Table 5.2.3 shows the leak test results of the test samples. The leak results showed that the two test tubes with the highest roll torque (90 in-Ibs) experienced the lowest leak rate and the three test tubes with the low roll torques (71, 72, and 74 in-lbs) experienced
-4 relatively high leak rates. In the conclusion section, the report recommended a nominal installation torque of 90 in-lbs with a minimum of 70 in-lbs.
(a)
What would be the torque used in the field?
(b)
In light of the leakage results for the 70-in-lb torque, provide justification that a torque of 70 in-lbs would be acceptable in the actual rerolled joints.
(c)
Discuss how the field installation procedure ensures that the applied torque is achieved in practice and the means used to verify that the installation torque is at least this value.
- 7.
The higher the torque in the roll the smaller the leak. However, the higher the torque the more susceptible to stress corrosion cracking of the roll because of high stresses in the roll. Describe the steps that are being taken to monitor and mitigate future degradation in the rerolled region of the tubes.
- 8.
Describe installation procedures for reroll installation.
- 9.
Experiences with leaking rerolled joints at other PWRs have led licensees to apply a reroll acceptance criterion based on the degree of tube expansion in field rolled joints.
Provide acceptance criteria for reroll during the installation phase and during future inservice inspections.
- 10.
The rerolling process introduces compressive loads into repaired tubes. Discuss the maximum number of rerolls that can be applied to a single tube. Consider the combined effects from postulated accident loads (e.g., loss-of-coolant accident) in the assessment.
- 11.
The qualification test program described in BAW2303P, Revision 2, assumed that the upper tubesheet crevice is free of significant deposits. Operating experience with rerolled tubes in other PWRs indicates that crevice deposits may be a significant contributor to a reduction in the leakage integrity of rerolled tubes. Discuss the basis for the assumption in the qualification testing regarding the presence of tubesheet crevice deposits. Include a discussion of any actual inspection results of pulled tubes and/or upper tubesheet crevice areas.
- 12.
The topical report addresses the potential reduction in tubesheet joint structural integrity due to tubesheet bore dilation resulting from bowing effects. However, no discussion is provided to address a reduced resistance to leakage from similar effects. Provide the basis for concluding that the bounding per tube leakage value determined in the topical report applies to rerolled tubes with dilated tubesheet bores.
- 13.
In accordance with the staff's approach to risk informed regulation, changes in licensing bases are to be accompanied by an assessment of the associated potential for changes in risk. In view of your proposed changes to the design basis, (i.e., reroll of the tubes),
address the implications for tube integrity under severe accident conditions.
Specifically, address the effect due to defects left in service.
-5 C. Questions Related to Inspection Findings The rerolling repair process is proposed to return to service a number of tubes with degradation initiating from the inside diameter (ID) of the tubes. With the one unusual exception, no other licensees with OTSGs have identified such degradation in their OTSG tubing. Given the significant number of degraded tubes that were identified in the current refueling outage and the potential implications for the leakage integrity of the tubes, the staff requests the following information:
- 1.
Discuss the root cause for the development of ID-initiated degradation in the "B' OTSG tubes.
- 2.
Provide details of an operational assessment that considers this mode of steam generator tube degradation.
- 3.
Discuss the potential for the development of similar degradation in other components constructed with alloy 600 materials in the reactor coolant system (e.g., CRDM nozzles).