ML003678700

Industry Recommended Steam Generator Tube Pull Program

ML003678700
Person / Time
Issue date:	01/28/2000
From:	Strosnider J Division of Engineering
To:	Modeen D Nuclear Energy Institute
andersen J
References
TAC MA7180
Download: ML003678700 (6)

Text

January 28, 2000 David J. Modeen, Director Engineering, Nuclear Generation Division Nuclear Energy Institute 1776 I Street, NW., Suite 400 Washington, DC 20006-3708

SUBJECT:

INDUSTRY RECOMMENDED STEAM GENERATOR TUBE PULL PROGRAM

Dear Mr. Modeen:

By letter dated September 22, 1999, you submitted Addendum 3 to the Steam Generator Degradation Specific Management Database, as well as the associated correlations for use by the industry in alternate repair criteria applications, for NRC review and approval. As part of that letter, you also included an industry recommended program for steam generator tube pulls in support of the voltage-based alternate repair criteria.

In your letter you state that the pulled tube database supporting the voltage-based repair limits has been significantly increased since the issuance of Generic Letter (GL) 95-05, Voltage-Based Repair Criteria for Westinghouse Steam Generator Tubes Affected by Outside Diameter Stress Corrosion Cracking, dated August 3, 1995. Therefore, you stated, it is appropriate to update the requirements for pulling steam generator tubes in support of the alternate repair criteria.

As stated in GL 95-05, one of the purposes of the tube removal program is to provide additional data to enhance the conditional leak rate, burst pressure, and probability of leakage correlations. In your recommended program, a licensee could delay tube removal by one outage if no pullable tube indications are found that would satisfy the industry target indications.

Therefore, the maximum interval between tube removals would be four operating cycles. You also recommend that if the requirement to pull a tube specimen coincides with the plants last scheduled outage before steam generator replacement, the requirement for a tube pull be waived. The staff finds this change acceptable except for the situation where tube pull specimens have not been obtained either during the plant steam generator inspection outage that implements the voltage-based repair criteria or during an inspection outage preceding initial application of these criteria.

With regard to the examination and testing portion of the program, the staff does not agree with your proposal that for small indications, leak tests do not need to be performed if the field and post-pull non-destructive testing data clearly show crack depths not greater than 85%. The NRC staffs complete review of the proposed tube pull program, including the above mentioned positions, are contained in the attached table.

David J. Modeen After reviewing the staffs comments, please contact Jim Andersen of my staff (301 415-1437) in order that we may discuss them further. If you find the staffs comments acceptable, please provide the revised steam generator tube pull program for NRC review.

Sincerely,

/ra/

Jack R. Strosnider, Director Division of Engineering Office of Nuclear Reactor Regulation

Attachment:

As stated

David J. Modeen After reviewing the staffs comments, please contact Jim Andersen of my staff (301 415-1437) in order that we may discuss them further. If you find the staffs comments acceptable, please provide the revised steam generator tube pull program for NRC review.

Sincerely, Jack R. Strosnider, Director Division of Engineering Office of Nuclear Reactor Regulation DISTRIBUTION: EMCB RF File Center JTsao SCoffin PMilano EMurphy

'2&80(171$0(*?(0&%?$1'(56(1?78%(38//5(63216(:3' INDICATE IN BOX: C=COPY W/O ATTACHMENT/ENCLOSURE, E=COPY W/ATT/ENCL, N=NO COPY OFFICE EMCB:DE EMCB:DE EMCB:DE DE:NRR NAME JAndersen:JWA EJSullivan:EJS WHBateman:WHB JRStrosnider:JRS DATE 01 / 12 /2000 01 / 12 /2000 01 / 18/2000 01/ 28 /2000 OFFICIAL RECORD COPY

STAFF COMMENTS ON INDUSTRY PROPOSED STEAM GENERATOR TUBE PULL PROGRAM Generic Letter 95-05 Guidance Industry Proposal NRC Staff Comments Number and Frequency of Tube Pulls Two pulled tube specimens with an objective of retrieving as Same as GL 95-05 with the following addition: The staff finds this many intersections as is practical (a minimum of four change acceptable.

intersections) should be obtained for each plant either However, if no pullable tube indications are found in this during the plant SG inspection outage that implements the inspection that would satisfy the industry database target voltage-based repair criteria or during an inspection outage indications, the tube removal may be delayed (utility option) preceding initial application of these criteria. to the next planned inspection with the goal of obtaining indications satisfying the database target. The tube pulls may not be delayed more than one planned outage following implementation of the repair criteria.

Additional tube pulls with an objective of retrieving as many Same as GL 95-05 except for the timing, the industry The staff finds this intersections as is practical (minimum of two intersections) proposal is three operating cycles following the previous tube change acceptable.

should be obtained at the refueling outage following pull. In addition, the industry proposal would add:

accumulation of 34 EFPMs of operation or at a maximum interval of three refueling outages, whichever is shorter, However, if no pullable tube indications are found in this following the previous tube pull. inspection that would satisfy the industry database target indications, the tube removal may be delayed (utility option) to the next planned inspection with the goal of obtaining indications satisfying the database target. The tube pulls may not be delayed more than one planned outage following the required time for an additional pulled tube specimen.

Consequently, the maximum interval between tube removals is four operating cycles to provide a periodic confirmation of crack morphology.

Or participate in an industry sponsored tube pull program Industry has proposed a tube pull program which is the N/A endorsed by the NRC that meets the objectives (1) to subject of this letter.

confirm the degradation mechanism for plants utilizing the GL for the first time, (2) to continue monitoring the ODSCC mechanism over time, (3) to enhance the burst pressure, probability of leakage, and conditional leak rate correlations, and (4) to assess inspection capability.

Generic Letter 95-05 Guidance Industry Proposal NRC Staff Comments Number and Frequency of Tube Pulls (cont.)

If the above time requirements for a pulled tube specimen The staff finds this coincide with the plants last scheduled outage before SG change acceptable, replacement, the requirement for a tube pull is waived. except for the situation where tube pull specimens have not been obtained either during the plant SG inspection outage that implements the voltage-based repair criteria or during an inspection outage preceding initial application of these criteria.

If indications with unanticipated voltage levels substantially The staff finds this higher than the structural limit (for example, >10 volts) from change acceptable.

the burst correlation are found in an inspection, the indication should be considered for removal and destructive examination if the test results are likely to determine whether or not condition monitoring or operational assessment results would satisfy acceptance limits.

Selection Criteria Should be an emphasis on removing tube intersections with The following would replace the current criteria: The staff finds this large voltage indications. change acceptable.

The primary emphasis for selecting an intersection for removal should be an indication that satisfies the target indication voltages of Table 8-3, Summary of Current Number and Target Number for Pulled Tube Intersections with Leakage. If the target voltage range cannot be satisfied, the emphasis should be on intersections with large voltage indications.

Generic Letter 95-05 Guidance Industry Proposal NRC Staff Comments Selection Criteria (cont.)

Where possible, the removed tube intersections should No change. N/A cover a range of voltages, including intersections with no detectable degradation.

As a minimum, selected intersections should ensure that the The following would replace the current criteria: The staff finds this total data set include a representative number of change acceptable.

intersections with RPC signatures indicative of a single For selection between indications of comparable voltage dominant crack as compared to intersections with RPC levels, the preference for removal should be intersections signatures indicative of two or more dominant cracks about with RPC (or equivalent probe) signatures of a single the circumference. dominant crack as compared to intersections with RPC signatures indicative of two or more dominant cracks about the circumference.

Examination and Testing Removed tube intersections should be subjected to leak and The following would be added: The generic letter burst tests under simulated MSLB conditions to confirm that guidance should the failure mode is axial and to permit enhancement of the For small indications (<1.5 volt for 3/4" tubing and 2.5 volt for continue to be followed.

supporting data sets for the burst pressure and leakage 7/8" tubing), leak tests do not need to be performed if the field NRC analysis shows correlations. The systems for future test should and post-pull NDE data clearly show crack depths not greater that a 0.25 inch crack, accommodate, and permit the measurement of, as high a than 85%. These indications may be included in the 95% through wall, can leak rate as is practical, including leak rates that may be in probability of leakage correlation as non-leakers if the pop through and leak the upper tail of the leak rate distribution for a given voltage. destructive examination results show maximum crack depths under MSLB conditions.

Leak rate data should be collected at temperature for the # 95%. In addition, it is unclear differential pressure loadings associated with the maximum whether the 85%

postulated MSLB. When it is not practical to perform hot number allows for eddy temperature leak tests, room temperature leak rate testing current uncertainties.

may be performed as an alternate. Burst testing may be performed at room temperature. The burst and leak rate correlations and/or data should be normalized to reflect the appropriate pressure and temperature assumptions for a postulated MSLB.

Generic Letter 95-05 Guidance Industry Proposal NRC Staff Comments Examination and Testing (cont.)

Subsequent to burst testing, the intersections should be The following would be added at the *: The staff finds this destructively examined to confirm that the degradation change acceptable.

morphology is consistent with the assumed morphology for For uncorroded ligaments, the following information should ODSCC at the tube-to-TSP intersections. The destructive be reported: location within the elevation of the overall examinations should include techniques such as macrocrack; angular orientation (approximate degrees) metallography and scanning electron microscope (SEM) relative to the primary direction of the macrocrack; and size of fractography as necessary to characterize the degradation the ligament such as uncorroded ligament area.

morphology (e.g., axial ODSCC, circumferential ODSCC, IGA involvement, cellular IGA, and combinations thereof) and to characterize the largest crack networks with regard to their orientation, length, depth, and ligaments.* The purpose of these examinations is to verify that the degradation morphology is consistent with the assumptions made in Section 1.a of this attachment. This includes demonstrating that the dominant degradation mechanism affecting the tube burst and leakage properties is axially oriented, ODSCC.