ML20136D653
| ML20136D653 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 03/07/1997 |
| From: | Wetzel B NRC (Affiliation Not Assigned) |
| To: | Richard Anderson NORTHERN STATES POWER CO. |
| References | |
| TAC-M96654, TAC-M96655, NUDOCS 9703120439 | |
| Download: ML20136D653 (6) | |
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i March 7, 1997 Mr. Roger 0. Anderson, Director Licensing and Management Issues Northern States Power Company 4
414 Nicollet Mall Minneapolis, Minnesota 55401
SUBJECT:
EVALUATION OF NSP RESPONSE TO NRC' STAFF REQUEST FOR ADDITIONAL i
INFORMATION (RAI) 0F FEBRUARY 13, 1997, REGARDING APPLICATION 0F F* AND EF* STEAM GENERATOR TUBE REPAIR CRITERIA:
4 i
PRAIRIE ISLAND NUCLEAR GENERATING PLANT UNITS 1 AND 2 i
< (TAC NOS. M96654 AND M96655)
Dear Mr. Anderson:
The Nuclear Regulatory Commission staff has reviewed your February 19, 1997, i
response to the subject RAI concerning the use of F* and EF* repair criteria in evaluating steam generator tube leak test and eddy current examination results obtained~during the current Unit 2 outage, including tubes previously repaired using the F* tube repair criteria. The staff's review focused on
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verifying that ~the structural and leakage integrity of Unit 2 steam generator tubes repaired by the rerolling process was consistent with the assumptions i
and conclusions in the~F* assessment. As. discussed in the enclosed.
evaluation, the staff concludes from its review of your RAI response that the assessment of leakage through F* tubes at Prairie Island, Unit 2, is consistent with the original assessment provided with the Unit 2 F* license amendment (License Amendment No. 111, dated May 15,1995). The information provided in your RAI response adequately addresses the staff's questions and concerns regarding leakage through F* tubes. Accordingly, the staff no longer considers these matters a Unit 2 startup issue.
The staff will continue to review your February 19, 1997, submittal in connection with its ongoing review of your technical specification amendment request dated September 24, 1996, " Incorporation of Elevated F* Steam Generator Tube Repair Criteria," as supplemented by your submittals dated October 17, 1996, January 3, January 20, and February 3, 1997.
If you have any questions, please contact me at (301) 415-1355.
Sincerely, d by Kevin Connaughton
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for Beth A. Wetzel, Project Manager Project Directorate III-1 Division of Reactor Projects - III/IV I
Office of Nuclear Reactor Regulation
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Docket Nos. 50-282 and 50-306 DISTRIBUTION:-
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Enclosure:
As stated Docket File :
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i Mr. Roger 0. Anderson, Director Licensing and Management Issues i
Northern States Power Company 414 Nicollet Mall Minneapolis, Minnesota 55401 l
SUBJECT:
EVALUATION OF NSP RESPONSE TO NRC STAFF REQUEST FOR ADDITIONAL i
INFORMATION (RAI) 0F FEBRUARY 13, 1997, REGARDING APPLICATION 1
0F F* AND EF* STEAM GENERATOR TUBE REPAIR CRITERIA:
PRAIRIE ISLAND NUCLEAR GENERATING PLANT UNITS 1 AND 2 l
(TAC NOS. M96654 AND M96655) l
Dear Mr. Anderson:
The Nuclear Regulatory Commission staff has reviewed your February 19, 1997, j
response to the subject RAI concerning the use of F* and EF* repair criteria in evaluating steam generator tube leak test and eddy current examination i
results obtained during the current Unit 2 outage, including tubes previously repaired using the F* tube repair criteria. The staff's review focused on i
verifying that the structural and leakage integrity of Unit 2 steam generator tubes repaired by the rerolling process was consistent with the assumptions i
and conclusions in the F* assessment. As discussed in the enclosed safety evaluation, the staff concludes from its review of your RAI response that the assessment of leakage through F* tubes at Prairie Island, Unit 2, is i
consistent with the original assessment provided with the Unit 2 F* license i
amendment (License Amendment No. Ill, dated May 15,1995). The information provided in your RAI response adequately addresses the staff's questions and concerns regarding leakage through F* tubes. Accordingly, the staff no longer considers these matters a Unit 2 startup issue.
i The staff will continue to review your February 19, 1997, submittal in connection with its ongoing review of your technical specification amendment request dated September 24, 1966, " Incorporation of Elevated F* Steam Generator Tube Repair Criteria," as supplemented by your submittals dated October 17, 1996, January 3, January 20, and FebrJary 3, 1997.
l If you have any questions, please contact me at (301) 415-1355.
1 j.
Sincerely, l
Beth A. Wetzel, Project Manager l
Project Directorate III-l Division of Reactor Projects - III/IV Office of Nuclear Reactor Regulation Docket Nos. 50-282 and 50- a6 i
DISTRIBUTION:
Enclosure:
As stated Docket File JMJacobson, DRP, RIII i
PUBLIC JStrosnider cc w/ enc 1: See next page PD3-1 R/F THarris (TLH3)
JRoe ACRS 6./[a EAdensam (EGAl) OGC i
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DOCUMENT NAME: G:\\WPDOCS\\ PRAIRIE \\PI96654.SE1
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NANE KConnaughton BWetzel:sp CJamerso &Y#$4hef JHannon i
NAME 03/ /97 03/
/97 03/ 7 /97[j 03/ 1/97 03/
/97 0FFICIAL RECORD CDPY
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NUCLEAR REGULATORY COMMISSION I
2 WASHINGTON, D.C. 30006-4001
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March 7, 1997 l
Mr. Roger 0. Anderson, Director i
Licensing and Management Issues l
Northern States Power Company 414 Nicollet Mall j
Minneapolis, Minnesota 55401 l
SUBJECT:
EVALUATION OF NSP RESPONSE TO NRC STAFF REQUEST FOR ADDITIONAL i
INFORMATION (RAI) 0F FEBRUARY 13, 1997, REGARDING APPLICATION i
0F F* AND EF* STEAM GENERATOR TUBE REPAIR CRITERIA:
PRAIRIE ISLAND NUCLEAR GENERATING PLANT UNITS 1 AND 2 (TAC NOS. M96654 AND M96655)
Dear Mr. Anderson:
The Nuclear Regulatory Cosmiission staff has reviewed your February 19, 1997, l
response to the subject RAI concerning the use of F* and EF* repair criteria i
in evaluating steam generator tube leak test and eddy current examination i
results obtained during the current Unit 2 outage, including tubes previously I
repaired using the F* tube repair criteria. The staff's review focused on j
verifying that the structural and leakage integrity of Unit 2 steam generator tubes repaired by the rerolling process was consistent with the assumptions i
and conclusions in the F* assessment. As discussed in thg enclosed i
evaluation, the staff concludes from its review of your RAI response that the i
assessment of leakage through F* tubes at Prairie Island, Unit 2, is j
consistent with the original assessment provided with the Unit 2 F* license amendment (License Amendment No. 111, dated May 15,1995). The information 4
provided in your RAI response adequately addresses the staff's questions and concerns regarding leakage through F* tubes. Accordingly, the staff no longer considers these matters a Unit 2 startup issue.
The staff will continue to review your February 19, 1997, submittal in i
connection with its ongoing review of your technical specification amendment request dated September 24,1996, " Incorporation of Elevated F* Steam l
Generator Tube Repair Criteria," as supplemented by your submittals dated j
October 17, 1996,.lanuary 3, January 20, and February 3, 1997.
i If you have any questions, please contact me at (301) 415-1355.
Sincerely, Beth A. Wetzel, Project Manager i
Project Directorate III-I i
Division of Reactor Projects - III/IV
)
Office of Nuclear Reactor Regulation j
Docket Nos. 50-282 and 50-306
Enclosure:
As stated f
j cc w/ enc 1: See next page
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Mr. Roger 0. Anderson, Director Prairie Island Nuclear Generating Northern States Power Company Plant cc:
J. E. Silberg, Esquire Tribal Council Shaw, Pittman, Potts and Trowbridge Prairie Island Indian Cosmiunity 2300 N Street, N. W.
-ATTN: Environmental Department Washington DC 20037 5636 Sturgeon. Lake Road Welch, Minnesota 55089 Plant Manager Prairie Island Nuclear Generating Plant Northern States Power Company 1717 Wakonade Drive East Welch, Minnesota 55089 Adonis A. Nebiett Assistant Attorney General Office of the Attorney General 455 Minnesota Street Suite 900 St. Paul, Minnesota 55101-2127 U.S. Nuclear Regulatory Comission Resident Inspector's Office 1719 Wakonade Drive East Welch, Minnesota 55089-9642 Regional Administrator, Region III U.S. Nuclear Regulatory Commission 801 Warrenville Road Lisle, Illinois 60532-4351 Mr. Jeff Cole, Auditor /Treasttrer Goodhue County Courthouse Box 408 Red Wing, Minnesota 55066-0408 Kris Sanda, Comissioner Department of Public Service 121 Seventh Place East Suite 200 St. Paul, Minnesota 55101-2145 Site Licensing Prairie Island Nuclear Generating Plant Northern States Power Company 1717 Wakonade Drive East Welch, Minnesota 55089 m a im
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UNITED STATES
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NUCLEAR REGULATORY COMMISSION a
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wasmMGTON, D.C. sese64em Evaluation of NSP Response to NRC Staff Request for Additional Information of February 13, 1997 l
The licensee for Prairie Island Unit 2 recently reported to the NRC that tubes i
previously repaired by the F* repair criteria were observed with secondary-to-primary leakage during hydrostatic testing of the unit steam
- 17. A total of ten tubes in SG 21 generators (SG) at the end-of-Cycle (E0C) be either slowly dripping or damp i,
and two tubes in SG 22 were determined to l
from the testing. The leak path was a>parently through the hardroll repair joint and out degraded areas in the tu>e existing below the F* distance. At i
the end of the previous operating cycle, the licensee measured the i
primary-to-secondary bakage in SG 21 to be on the order of 2 to 4 gallons per day.
By letter dated May 15, 1995, the NRC approved an amendment to the Prairie l.
Island Technical Specifications to allow the use of the F* repair criterion.
The licensee's as:;essment of potential steam generator tube leakage in the application for the amendment detemined that leakage through rerolled F*
tubes is possible due to the presence of corrosion products in the tubesheet i
crevice existing prior to rerolling. Based on the qualification testing of i
the rerolling procedure, the licensee determined that leakage was more likely to occur in tubes with hard-packed corrosion products and that hard-packed corrosion products would influence the torque trace generated during the i
i rerolling process.
In order to minimize the potential for bypass leakage around rerolled tube-to-tubesheet joints, the licensee committed to remove j
from service those tubes identified as having hard-packed crevices as determined by the reroll torque trace. Subsequent to the identification of the tubes that experience bypass leakage in the hydrostatic testing, the licensee reviewed the records for the installation of the reroll joints. No anomalies were identified from the installation process that would indicate i
the tubes would have the potential for leakage. Thus, monitoring the reroll torque trace does not ensure the identification of all F* tubes that have the potential for bypass leakage around a rerolled joint.
4 Although the licensee's F* amendment application concluded that bypass leakage is possible and would be minimal in instances where it occurs, by letter dated February 19, 1997, the licensee submitted results of additional work to j
evaluate tubes repaired by rerolling. The assessment included additional testing of rerolled tubes to attempt to better quantify leakage and to 2
identify a means to identify tubes potentially susceptible to leakage j
following installation of the hardrolled joint. An upper bound leakage was determined by com>1eting in-situ pressure testing of the tubes identified with moisture during tie hydrostatic testing. Based on the licensee's i
calculations, the anticipated leakage through all F* tubes repaired by ENCLOSURE j f 4
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rerolling is consistent with the original assessment that the F* 1eakage would be less than the assumed primary-to-secondary leakage in the accident analysis
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for offsite dose calculations.
l For the E0C 17 refueling outage, the licensee has modified the F* reroll 3
repair process to include additional inspection of the hardrolled joint to identify tubes that may have a higher potential for leakage, and an additional roll expansion will be added over the original hardroll.
The licensee will also perform a post-maintenance leak check with a secondary side pressure test. These added measures to the F* rerolling process should minimize the potential for bypass leakage through F* tubes.
l Sased on the infomation provided by the licensee in its letter dated j
February 19, 1997, the NRC has determined that the leakage identified through l
F* tubes at the EOC 17 is bounded by the original leakage integrity assessment.
I Although the identification of tubes that may be more susceptible to leakage via monitoring the reroll torque traces may not ensure that all reroll joints are leaktight, additional modifications to the reroll repair process j
implemented in the E0C 17 outage should improve the licensee's ability to repair or remove tubes with a higher potential for leakage from service.
3 These modifications should ensure that no tubes will leak in excess of the i
value detemined from the licensee's testing and assumed in the bounding calculations. These calculations are considered to be conservative since all j
tubes left in service with F* criteria were assumed to leak whereas experience j
indicates that only a small percentage of tubes leaked under the previous j
reroll process.
Based 'on the staff's review of the information provided in the licensee's 1
February 19, 1997, letter, the staff has concluded that the assessment of l
1eakage through F* tubes at Prairie Island Unit 2 with the reroll process as modified in the current refueling outage is consistent with the original i
assessment provided with the F* amendment authorized by License Amendment No. 111 dated Nay 15, 1995. NSP has satisfactorily addressed the i
NRC staff concerns regarding leakage through F* tubes and, therefore, this is no longer considered a restart issue.
Principal contributors:
T. Sullivan P. Rush Dated: 2/24/97 i
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