ML20248M252
| ML20248M252 | |
| Person / Time | |
|---|---|
| Site: | Kewaunee  |
| Issue date: | 06/09/1998 |
| From: | Long W NRC (Affiliation Not Assigned) |
| To: | Marchi M WISCONSIN PUBLIC SERVICE CORP. |
| References | |
| TAC-MA0193, TAC-MA193, NUDOCS 9806150200 | |
| Download: ML20248M252 (9) | |
Text
j June 9, 1998 Mr. M. L. Marchi Site Vice President - Kewaunee Plant Wisconsin Public Service Corporation P.O. Box 19002 Green Bay, WI 54307-9002
SUBJECT:
. COMPLETION OF STAFF REVIEW OF KNPP CYCLE 22 STEAM GENERATOR INSPECTION 90 DAY REPORT (TAC No. MA0193)
I
Dear Mr. Marchi:
On September 3,1997, you submitted "Kewaunee Cycle 22 Alternate Repair Criteria 90 Day l
Report." The staff has reviewed the report. An assessment is enclosed for your information.
1 If you have any questions regarding this review, please contact me at (301) 415-3026.
Sincerely,
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Original signed by:
William O. Long, Sr. Project Manager Project Directorate IH.3 Division of Reactor Projects !!!/lV Office of Nuclear Reactor Regulation Docket No. 50-331
Enclosure:
As stated cc w/ encl: See next page DISTRIBUTION:
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June 9, 1998
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Mr. M. L. Marchi Site Vice President - Kewaunee Plant Wisconsin Public Service Corporation P.O. Box 19002 Green Bay, WI 5430'7-9002 Sc6 JECT: COMPLETION OF STAFF REVIEW OF KNPP CYCLE 22 STEAM GENERATOR INSPECTION 90 DAY REPORT (TAC No. MA0193)
Dear Mr. Marchi:
On September 3,1997, you submitted "Kewaunee Cycle 22 Alternate Repair Criteria 90 Day Report." The staff has reviewed the report. An assessment is enclosed for your information.
If you have any questions regarding this rea'iew, please contact me at (301) 415-3026.
Sincerely, l
I Original signed by:
William O. Long, Sr. Project Manager Project Directorate 111-3 Division of Reactor Projects ill/IV Office of Nuclear Reactor Regulation Docket No. 50-331
Enclosure:
As stated cc w/ encl: See next page i
DISTRIBUTION:
t Docket File A. Keim i
PUBLIC.
ACRS PD3-3 Reading MModes -
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G. Grant, lll DOCUMENT NAME: G:\\KEWAUNEE\\ CYCLE 22.LTR OFFICE PD33:PM E
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NAME WLong V EBarnhill Qfy RBellamyID
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OFFICIAL RECORD COPY I
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UNITED STATES s
g NUCLEAR REGULATORY COMMISSION 2
WASHINGTON, D.C. 30666 4001
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June 9, 1998 Mr. M. L Marchi Site Vice President - Kewaunee Plant Wisconsin Public Service Corporation P.O. Box 19002 Green Bay, WI 54307-9002
SUBJECT:
COMPLETION OF STAFF REVIEW OF KNPP CYCLE 22 STEAM GENERATOR INSPECTION 90 DAY REPORT (TAC No. MA0193)
Dear Mr. Marchi:
On September 3,1997, you submitted "Kewaunee Cycle 22 Alternate Repair Criteria 90 Day Report." The staff has reviewed the report. An assessment is enclosed for your information.
If you have any questions regarding this review, please contact me at (301) 415-3026.
Sincerely, A 0. 2 William O. Long, Sr. Project Manager Project Directorate 111-3 Division of Reactor Projects lil/IV Of3ce of Nuclear Reactor Regulation Docket No. 50-331
Enclosure:
As stated cc w/ encl: See next page
i a
M. L. Marchi Wisconsin Public Service Corporation Kewaunee Nuclear Power Plant ec:
Foley & Lardner ATTN: Bradley D. Jackson One South Pinckney Street P.O. Box 1497 Madison, WI 53701-1497 Chairman Town of Carlton l
Route 1 Kewaunee,WI 54216 Harold Reckelberg,, Chairman Kewaunee County I.loard Kewaunee County Courthouse Kewaunee,WI 54216 Attorney General i
114 East, State Capitol l
Madison, WI 53702 l
U.S. Nuclear Regulatory Commission Resident inspectors Office.
Route #1, Box 999 Kewaunee, WI 54216-9511 1
Regional Administrator - Region lli i
U.S. Nuclear Regulatory Commission 801 Warrenville Road Lisle, IL 60532-4531 James D. Loock, Chief Engineer Public Service Commission of Wisconsin P. O. Box 7854 Madison, WI 53707-7854 l
l
,L REVIEW BY THE OFFICE OF NUCLEAR REACTOR REGULATION I
OF THE STEAM GENERATOR 90 DAY REPORT SUBMITTED BY WISCONSIN PUBLIC SERVICE CORPORATION KEWAUNEE NUCLEAR POWER PLANT DOCKET NO. 50-305 l
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1.0 INTRODUCTION
1 By letter dated September 3,1997, Wisconsin Public Service Corporation submitted for staff review reports entitled "Kewaunee Cycle 22 Altemate Repair Criteria 90 Day Report," and
" Examination of Kewaunee Cold Leg Steam Generator Tube R15C28." These reports were j
submitted in accordance with Generic Letter (GL) 95-05 as a result of implementing the l
- voltage-based altemate repair criteria in the Kewaunee Nuclear Power Plant technical specifications.
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' GL 95-05, " Voltage-Based Repair Criteria for Westinghouse Steam Generator Tubes Affected by Outside Diameter Stress Corrosion Cracking," allows steam generator tubes having outside diameter stress corrosion cracking (ODSCC) that is predominately axially oriented and confined 4
l within the tube support plates to remain in service on the basis of, in part, bobbin coil voltage l
response. GL 95-05 specifies that inspection results and associated tube integrity analyses should be submitted within 90 days of each plant restart following a steam generator tube inspection. The report should include, at a minimum, calculations on voltage distribution,
. postulated tube leakage, and tube burst probability under normal and accident conditions.
2.0 GENERAL PLANT DESCRIPTION Kewaunee Nuclear Power Plant of the Wisconsin Public Service Corporation has been in operation since March 1974. The Kewaunee plant has two Westinghouse Model 51 steam generators. The tubes are 7/8 inch diameter and were fabricated from mill annealed alloy 600 l
material. The steam generators have drilled hole carbon steel tube support plates.
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On September 11,1996, the staff approved a permanent change to the licensee's technical j
specifications which implemented a steam generator voltage-based attemate repair criteria in l
i accordance with GL 95-05. The licensee had previously implemented similar criteria on an interim basis during cycle 21.
I 3.0 STAFF ASSESSMENT 3.1 Inspection Scope and Results in accordance with the attemate repair criteria (ARC) guidance provided in Generic Letter 95-05, the end of cycle (EOC)-21 inspection of the Kewaunee SGs consisted of a complete,100%
eddy current bobbin probe, full length examination of the tube bundles in both SGs. The rotating pancake coil (RPC) was used to inspect bobbin indications with amplitudes greater than 2 volts at the tube support plate intersections. The licensee detected a total of 968 indications Enclosure
at tube support plate intersections during EOC-21. Of those,102 indications were removed from service, of which only four indications did not meet the 2-volt repair criteria (the remaining indications were removed from service due to tube repairs for causes other than ODSCC at the tube support plates). The remaining 866 indications were retumed to service for 7ycle 22. In addition,23 indications from deplugged tubes were recovered and returned to service. This resulted in a total of 889 indications retumed to service for cycle 22.
l Based on the number of tubes retumed to service with bobbin coil indications, Steam Generator B is considered to be the limiting steam generator for cycle 22 operation. As discussed in Section 3.2.3 of this assessment, this conclusion is supported by the calculated estimate of accident tube leakage.
3.2 Evaluation of Probabilistic Methodologies for Estimating Conditional Probability of Burst and Total Leak Rate Under Postulated Steam Line Break Conditions Acceptable tube integrity at the conclusion of cycle 22 operation is demonstrated, in part, by a calculated conditional probability of tube burst for the limiting steam generator less than the reporting threshold indicated in GL 95-05 and an estimated accident-induced steam generator tube leak rate from ODSCC at tube support plate intersections below plant-specific limits.
Three distinct probabilistic calculations are necessary to determine these results. The following summarizes the staff's evaluation of the results reported on these calculations.
l 3.2.1 - Projected End-of-Cycle Voltage Distribution The licensee's 90-day report compared the as-found distribution of voltages determined from the EOC-21 refueling outage to those estimated from the predictions made following the prior outage inspections (EOC-20). Projections of the distributions of voltages made following the EOC-20 inspections estimated that the Kewaunee steam generators would contain approximately 1350 tube indications in the EOC-21 outage. Steam generator "B" was considered to be the limiting steam generator with respect to the overall number and voltage of indications projected. A comparison between the as-found distribution and the projected j
distribution of voltages indicates that the predictive methodology previously used to estimate l-the voltages of indications in subsequent outages yields conservative results. The maximum predicted indication voltage was estimated to be approximately 3 volts. However, the maximum voltage identified during the inspection was 2.3 volts. The maximum indication voltage identified in the "A" SG during EOC-21 was also less than the projected voltage. In addition, the number of indications identified in each steam generator was leu than that projected from the previous outage inspection results.
In order to obtain the most conservative results with respect to the growth rate distribution used
~in Monte Carlo simulation, the licensee utilized steam generator specific growth rate distributions obtained from operation in Cycles 20 and 21. GL 95-05 recommends that the more conservative growth distribution from the last two cycles be used for projecting EOC distributions for the next operating cycle. The licensee conservatively used Cycle 20 bobbin voltage growth rates for predicting EOC-22 conditions.
Enclosure
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During recent inspections in some plants with 7/8" SG tubes, relatively high growth rates were observed for indications in tubes deplugged and retumed to service at the beginning of their last operating cycle. The licensee monitored the growth rate of the tubes returned to service and compared it to the growth rates in previously ective tubes. The licensee did not observe any discernable difference between the growth rates for EOC-20 deplugged and Cycis 20 active tubes.. Therefore the licensee combined the Cycle 21 growth data for both sets of tubes.
According tc the Westinghouse ARC analysis presented in WCAP-14277 Revision 1, the licensee should use the larger of the composite growth rate for all SGs and the SG-specific growth rate should be used in projecting SLB leak rate and tube burst probability for individual SGs. Since the SG "A" growth rates are below the composite growth rate and SG "B" growth rates are higher than the composite growth rate, the composite growth rate should be applied to SG "A" and its own growth rate for SG "B". The licenseec conservatively applied the SG "B" specific growth rate to both steam generators in predicting EOC-22 conditions.
Using the inspection findings in the EOC-21 inspection, the !icensee calculated the projected EOC-22 voltage distribution for bobbin coil probe TSP indications. Based on the overall number of indications anticipated at the EOC-22, the "B" steam generetor is the limiting steam generator for the next cycle of operation. The staff independently verified the licensee's calculations by completing a Monte Carlo simulation to estimate the EOC-22 voltage.
distributions. The results of these calculations confirm that the predictive methodology used by the licensee to estimate the EOC voltage distributions is consisten: with the guidare provided in GL 95-05.
3.2.2 Conditional Probability of Tube Burst Due to the relatively low number of higher voltage indications both projected and identified during inspections at Kewaunee, the calculated conditional probability of tube burst is typically below the reporting threshold of 1x102 specified in GL 95-05. Fol!owing the EOC-20 refueling outage, the licensee estimated an EOC-21 burst probability for the limiting steam generator of 1.2x10d. Using the actual inspection results as the input into the calculation for tube burst, the licensee determined the as-found conditional burst probability following the most recent inspections to be 3.1x10-5 for the limiting SG. Therefore, the calculational methodology used to predict the EOC-21 conditional burst probabilities yielded conservative results over the previous cycle of operation.
Using the growth rate distributions determined for each steam generator, the licensee reported the projected EOC-22 conditional tube burst probabilities. The calculated probability of tube burst for steam generators "A" and "B" was determined to be 3.7x10-5 and 8.6x104, respectively.- The projected values are well below the GL reporting threshold, and therefore, the estimated tube burst probability due to ODSCC at tube support plates is well within acceptable L
. limits for Cycle 22 operation.
Enclosure
4-4 3.2.3 Steam Line Break Leak Rate Projection The staff eva!uated the steam line break leak rate reported by the licensee similar to the assessment of the conditional tube burst probabilities. For the limiting SG "B", the EOC-21 projected leak rate was previously estimated to be 2.2 gpm (at room temperature) versus an as-found estimate based on the inspection results obtained in the EOC-21 outage of 1.2 gpm (at room temperature). The licensee estimated the steam line break leak rate for the limiting SG "B" for EOC-22 to be 2.9 gpm (at room temperature) and for SG "A" to be 0.9 gpm. This value is much smaller than the Kewaunee steam'line break leak rate limit of 22.6 gpm (at room temperature). Therefore, the projected tube leakage integrity for ODSCC indications is well within the allowable limit established for Kewaunee.
3.3 Database for Tube Integrity Calculations in order to calculate the conditional tube burst probabilities and postulated steam line break primary-to-secondary leak rate the methodology approved for GL 95-05 requires the use of burst and leak rate data obtained from model boiler tubes and tubes removed from actual sts sm generators. The industry has developed correlations relating bobbin coil voltage and the measured leak rate, probability of burst, and burst pressure through testing of these tubes. The database used for the ARC correlations that were applied in the licensee's analysis were consistent with the NRC SE dated September 11,1996, supporting amendment No.126 for Kewaunee Nuclear Power Plant, which utilizes industry and NRC approved methodology for the inclusion of new data.
3.4 -
Tube Pull Results GL 95-05 requires periodic tube specimen removals to monitor the morphology of ODSCC degradation at tube support plate intersections and to obtain additional data for inclusion in the correlations relating bobbin coil voltage amplitude to tube bufst pressure, probability of Isakage, and leak rate. The removal of a single tube in the fall of 1996 satisfies the periodic degradation monitoring requirements specified in GL 95-05.
The licensee removed the first and second tube support plate crevice regions of cold leg tube
~ R15C28 from steam generator "B" at Kewaunee. The removed tube section was examined by nondestructive and destructive examination techniques. Shallow, but extensively distributed, OD-origin intergranular corrosion was found contained in the tube support plate crevice regions of the mill annealed Alloy 600 tubing. The staff has reviewed the destructive examination results of the pulled tube specimen and concluded that the ODSCC morphology exhibited in the tube is consistent with the criteria specified in GL 95-05.
4.0
SUMMARY
- The comparison of the projected EOC-21 results to that of the as-found EOC-21 results indicate that predictive methodologies are yielding acceptable results. In addition, the calculated EOC-21 condiGonal probability of burst and projected MSLB leak rate were less than GL 95-05 Enclosure i
.a
. criteria and site allowable leak rate limits, respectively. Lastly, the projected EOC-22 conditional probability of burst and projected MSLB leak rate were also less than GL 95-05 I
criteria and site allowable leak rate limits, respectively.
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i Enclosure 1