ML16342A670
| ML16342A670 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 01/29/1999 |
| From: | Steven Bloom NRC (Affiliation Not Assigned) |
| To: | Rueger G PACIFIC GAS & ELECTRIC CO. |
| References | |
| TAC-M98283, TAC-M98284, NUDOCS 9902050259 | |
| Download: ML16342A670 (10) | |
Text
Mr. Gregory M. Rueger Senior Vice President and General Manager Pacific Gas and Electric Company Diablo Canyon Nuclear Power Plant P.O. Box 3 Avila Beach California 93242 I
SUBJECT:
REQUEST FOR ADDITIONALINFORMATION-PROPOSED W*STEAM GENERATOR TUBE REPAIR CRITERIA (TAC NOS. M98283 AND M98284)
Dear Mr. Rueger By letter dated March 10, 1997, as supplemented by letters dated May 20, 1997, March 13, 1998, August 28, 1998 and October 22, 1998, Pacific Gas and Electric Company (PG&E) submitted Revision 1 of Westinghouse Electric Corporation (Westinghouse) technical reports of WCAP-14797 (proprietary) and WCAP-14798 (non-proprietary), "Generic W", Tube Plugging Criteria for 51 Series Steam Generator Tubesheet Region,WEXTEX Expansions."
These reports are to be used as the bases for License Amendment Request 97-04, to modify the steam generator tube plugging criteria in Technical Specification (TS) 3.4.5 and the allowable operational leakage limit in TS 3.4.6.2.
The NRC has reviewed your submittal and has identified the need for additional information in order to determine the acceptability of your request.
The enclosure describes the spe'cific information requested by the NRC.
This request was discussed with Mr. Terry Grebel of your staff on January 27, 1999.
A mutually agreeable target date of February 15, 1999, for your response was established.
If circumstances result in the need to revise the target date, please call me at the earliest opportunity. Ifyou have any questions regarding this matter, please contact me at (301) 415-1313.
9902050259 9'3iOi29
P Sincerely, Original Signed By Steven D. Bloom, Project Manager Project Directorate'IV-2 Division of Reactor Projects III/IV Office of Nuclear Reactor Regulation Docket Nos. 50-275 and 50-323
Enclosure:
Request for Additional Information cc w/encl:
See next page DOCUMENT NAME: DC98283R.WPD DISTRIBUTION
- Docket i
PUBLIC PDIV-2 Reading E. Adensam W. Bateman S. Bloom OGC ACRS K. Brockman L. Smith, RIV E. Peyton P. Rush OFC NAME DATE PDI
/PM S
lo 1/2 /99 P DIV-2/LA EPe on 1/cW/99 OFFICIAL RECORD COPY (3400~~>
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Mr. Gregory M. Rueger january 29, 1999 cc: w/encl:
NRC Resident Inspector Diablo Canyon Nuclear Power Plant do U.S. Nuclear Regulatory Commission P. O. Box 369 Avila Beach, California 93424 Dr. Richard Ferguson, Energy Chair Sierra Club California 1100 11th Street, Suite 311 Sacramento, California 95814 Ms. Nancy Culver San Luis Obispo Mothers for Peace P. O. Box 164 Pismo Beach, California 93448 Chairman San Luis Obispo County Board of Supervisors Room 370 County Government Center San Luis Obispo, California 93408 Regional Administrator, Region IV U.S. Nuclear Regulatory Commission Harris Tower 8 Pavillion 611 Ryan Plaza Drive, Suite 400 Arlington, Texas 76011-8064 Christopher J. Warne, Esq.
Pacific Gas 8 Electric Company Post Office Box 7442 San Francisco, California 94120 Mr. David H. Oatley, Vice President Diablo Canyon Operations and Plant Manager Diablo Canyon Nuclear Power Plant P.O. Box 3 Avila Beach, California 93424 Telegram-Tribune ATTN: Managing Editor 1321 Johnson Avenue P.O. Box 112 San Luis Obispo, California 93406 Mr. Truman Burns Mr. Robert Kinosian California Public Utilities Commission 505 Van Ness, Room 4102 San Francisco, California 94102 Mr. Steve Hsu Radiologic Health Branch State Department of Health Services Post Office Box 942732 Sacramento, California 94232 Diablo Canyon Independent Safety Committee ATTN: Robert R. Wellington, Esq.
Legal Counsel 857 Cass Street, Suite D Monterey, California 93940
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RE UEST FOR ADDITIONALINFORMATION PACIFIC GAS AND ELECTRIC COMPANY DIABLOCANYON POWER PLANT UNITS 1 AND 2 DOCKET NOS. 50-275 AND 50-323 1.
Chapter 8 of WCAP 14797, Revision 1, states that a crack growth rate of 0.25 inches per EFPY is assumed for W*. This value was determined as the 95% cumulative probability value using data from three plants. The NRC notes that this value is inconsistent with the 95% cumulative probability value (0.28 inches) stated in Section 7.4. Discuss which value will be assumed in W'pplications.
Afixed, upper bound crack growth rate is used in the application of W*repair criteria.
However, crack growth rate data in WCAP 14797, Revision 1, may not be representative of crack growth rates for more mature PWSCC flaws that may remain in service for several cycles under W*. Discuss provisions in the proposed repair criteria for updating the assumed upper bound crack growth rates to address the potential for more rapid flaw progression in the future. Also discuss whether the use of a larger growth rate, ifapplicable, would be required.
The NDE uncertainty for measuring the distance between the bottom of the WEXTEX transition (BWT) and the crack tip was determined by combining the uncertainties from measuring the distance between the top of the tubesheet (TTS) and the BWT and the distance separating the TTS and the crack tip. The NDE measurement uncertainty assumed in the W*repair criteria for three rotating probe inspection coils (i.e., 0.115-inch, Plus Point, and 0.080-inch coils) was determined using the uncertainty in measuring the distance between the TTS and the BWTfor the 0.115-inch pancake coil.
Explain why the uncertainty in the measurement of this distance using the 0.115-inch diameter coil is applicable to the other rotating coils considered in the study.
Because of their design, Plus Point coils may have difficultyresolving crack inclination angles approaching 45'nd identifying the location of the bottom of the tubesheet expansion-transitions.
However, the staff notes that the analysis guidelines included as Appendix A in WCAP-14797 do not require data analysts to use alternate coils for locating the tips of the crack (for crack angles) and the expansion-transition.
Discuss the need to include restrictions on the use of Plus Point coils in the data analysis guidelines.
5.
Expansion-transitions in explosively expanded tubesheets tend to have more gradual changes in tube diameter over a given length of tube. This complicates the ability to accurately locate the position of the BWT. Describe the procedure that eddy current data analysts are to followto locate the BWT.
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6.
According to the submittal dated October 22, 1998, the licensee has committed to perform in-situ pressure testing of a number of tubes with expansion-transition flaws. It was stated that the tubes willbe pressurized to u,Po to assess their leakage integrity.
Willthe licensee in-situ pressure test tubes to ~Psu, that no longer satisfy the W'epair criteria regardless of whether the crack leaks at normal operating differential pressures' 7.
ln the submittal dated October 22, 1998, it was stated the BWTwould be redefined to be within 0.7 inches of the tube-to-tubesheet contact point when profiles such as Figure 2Q are identified.
Describe, in further detail, the criteria that willbe followed to redefine the BWT.
By "DCL-98-116, Forwards Response to NRC 980707 & 09 RAIs Re LAR to Convert Current [[TS" contains a listed "[" character as part of the property label and has therefore been classified as invalid.,2.0 & 3.0 to Improved Std TS|letter dated August 28, 1998]], the licensee submitted leak rate test data for the proposed W'team generator tube repair criteria. The staff's evaluation of this data has concluded that the measured leak rates are functionally dependent on the crevice length. For example, the figure below illustrates the dependence of the loss coefficient obtained from leak rate measurements on the crevice length. As seen in the data, different correlations are evident for the three general categorizations of the crevice length. This dependence, however, varies with each sample number (e.g., W4-018).
Based on information provided in WCAP-14797, Revision 1, the crevice leak rate model proposed forW'oes not account for this variable.
Discuss the root cause for the dependence of the measured leak rate on the specimen crevice length. Also, discuss whether the model willprovide accurate (or conservative) estimates of leakage from W*
tubes given that crevice lengths were not accounted for in the model relating the contact pressure to the loss coefficient.
1.00E +17 Crevice Length Effects Sample No. W4-018 1,00E +16 cc 100E+15 o
1.00E+14 Vaa 1.00E +13
%Short x Medium 4 Lon 1.00E+12 1.00E +11 1000 1500 2000 Contact Preslure 2500
0 9.
The proposed alternate tube repair criteria would allow tubes with cracks to remain in service. Although the flaws in these tubes would initiallybe confined below the tubesheet secondary face, they have the potential to grow into the freespan region (i.e.,
above the top of tubesheet).
As documented in NUREG-1570, "Risk Assessment of Severe Accident-Induced Steam Generator Tube Rupture, the staff is concerned with the potential consequences associated with freespan steam generator tube flaws. The NRC requests that the licensee provide an assessment demonstrating that an acceptable level of risk willbe maintained under postulated accident conditions for tubes returned to service using W'epair criteria. Alternatively, the licensee may consider modifying the proposed repair criteria to minimize the potential for developing freespan cracking in tubes returned to service using W*.
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