ML13330B460
| ML13330B460 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 01/20/1989 |
| From: | Nandy F SOUTHERN CALIFORNIA EDISON CO. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| NUDOCS 8901240094 | |
| Download: ML13330B460 (6) | |
Text
Southern California Edison Company P. 0.
BOX 800 2244 WALNUT GROVE AVENUE ROSEMEAD, CALIFORNIA 91770 F. R. NANDY TELEPHONE MANAGER OF NUCLEAR LICENSING January 20, 1989 (818) 302-1896 U. S. Nuclear Regulatory Commission Attention:
Document Control Desk Washington, D.C. 20555 Gentlemen:
Subject:
Docket No. 50-206 Steam Generator Tube Inspection San Onofre Nuclear Generating Station Unit 1 This letter provides as an Enclosure the response to the NRC questions transmitted by letter dated December 19, 1988. Since the discovery that certain sleeves were missing expansions and hard rolls during a steam generator leak test in February 1988, an extensive effort was conducted to identify and document the condition of every sleeve installed in the Unit 1 steam generators. Those sleeves not meeting the required acceptance criteria have been removed from service. Information regarding this issue was also provided in LER 88-018 submitted to the NRC on January 11, 1989.
A formal report documenting this effort in detail is being prepared and will be provided to you in early February, 1989. We are also available to meet with you to provide any additional clarification you may require.
If you have any questions regarding this information, please let me know.
Very truly yours, Enclosure cc: C. M. Trammell, NRR Project Manager, San Onofre Unit 1
- 3. B. Martin, Regional Administrator, NRC Region V F. R. Huey, NRC Senior Resident Inspector, San Onofre Units 1, 2 and 3 8--'901240094 890120 DR ADOCK 05000206 PDC
Response to Request For Additional Information San Onofre Unit 1 Docket No. 50-206 January 1989 Southern California Edison Company Rosemead, California
Response to Request For Additional Information
REFERENCES:
(a) Letter, Charles M. Trammell, NRC, to Kenneth P. Baskin, SCE; subject: Steam Generator Tube Inspections,; dated:
December 19, 1988.
(b) Letter, K. P. Baskin, SCE to D. M. Crutchfield, NRC; subject:
Steam Generator Inspection Report; dated: September 12, 1982.
(c) "Technical Evaluation Report for Hybrid Sleeve", Westinghouse Electric Corporation Report No. NS-MFSE-81-054 dated March 1981, Proprietary Version, Submitted by Letter, K. P. Baskin, SCE, to D. M. Crutchfield, NRC; subject: Steam Generator Repair Program; dated March 5, 1981.
The purpose of this enclosure is to provide the information necessary for the NRC to continue the review of the Unit 1 steam generator tube inspections.
Answers to the six questions identified in reference (a) are provided below.
- 1. Question: What is the primary-to-secondary leak rate history of San Onofre Unit 1? Why was the problem of leakage caused by deficiently hard rolled sleeves not identified before Cycle 9?
Answer: After startup from the 1981 tube repair (sleeving) outage, primary-to-secondary leakage was observed and a steam generator leak test was performed in 1982 in conjunction with the Cycle 8 midcycle outage Technical Specification eddy current examination as reported in reference (b).
The leak test was conducted by pressurizing the secondary side of the steam generator with water at approximately 800 psig and observing leakage on the primary side. Three sleeves in "C" steam generator exhibited minor leakage (one to two drops per minute) and although this leakage was within the acceptable amount for a leak limiting sleeve, all three sleeved tubes were plugged. The results of the eddy current testing (ECT) conducted on these sleeves indicated no abnormalities.
Limited primary-to-secondary leakage occurred again during Cycle 8 operation (approximately 1 gpd) and although a leak test was planned, it could not be conducted as scheduled during the Cycle 9 refueling outage due to repairs required on the feedwater system. It was determined that the leakage was consistent with the allowable leakage design margins for leak limiting sleeves and the technical specification limits.
The next opportunity to conduct a steam generator leak test was during the Cycle 9 midcycle outage in February 1988. It was during this leak test that the problem of deficiently hard rolled sleeves was identified. A total of 19 leaking sleeves were identified of which six were identified as deficiently hard rolled sleeves. Based on leaking sleeved tubes identified to date, there is no direct correlation between deficiently hard rolled sleeves and sleeve leakage.
-1
Since completion of the steam generator tube repair in 1981, all primary-to-secondary leaks have been within Technical Specification allowable limits and have not required an unscheduled plant outage.
- 2. Question: When is the next steam generator eddy current inspection planned? What is the extent of the planned inspection?
Answer: A standard Technical Specification steam generator tubing examination will be conducted during the Cycle 11 refueling outage or September, 1990, which ever occurs first. The inspection will be performed in "A" Steam Generator and the current plans are to inspect approximately 15% of all inservice tubes.
- 3. Question: What is the history of leaking sleeves and plugs? What surveillance and corrective actions are planned?
Answer: Since the completion of the steam generator tube repair in 1981, there have been a total of thirty-four (34) leaking sleeves and one leaking explosive plug. All but two of the leaking sleeves could be qualified as meeting the leak limiting criteria (210 drops per minute) described in reference (c).
SCE plans to monitor primary-to-secondary leakage in accordance with established procedures and conduct leak tests in conjunction with other steam generator work if there has been an indication of primary-to-secondary leakage.
- 4. Question: Describe the plans and schedule for the determination of the total number of deficient sleeves in the San Onofre Unit I steam generators.
Answer: All deficient sleeves in the San Onofre Unit I steam generators were identified and removed from service in December 1988. To identify these sleeves, the first step was to reevaluate the 1981 sleeve baseline eddy current data to establish those sleeves that may not have been properly rolled. This effort utilized the best available analysis techniques and equipment, the DDA-4, which was a significant improvement over the strip chart method used in 1981.
This effort was conservative because, although the analysis techniques and equipment used today are state-of-the-art, the data taken in 1981 is not as sensitive to the roll joint configuration as data taken today. The second step was to take those sleeves identified as not acceptable based on 1981 eddy current test data and retest them using the most sensitive technique. This technique used the MIZ-18 for data acquisition with absolute and differential frequencies of 600, 400, 100 and 50 KHz. The probe used was a standard, magnetically biased bobbin coil probe. The analysis was also done with the DDA-4. Any sleeve that did not exhibit the existence of an acceptable roll was identified and the tube was removed from service.
This involved the plugging of 156 tubes with sleeves that did not exhibit a hard roll and 12 tubes with leaking sleeves for a total of 168 tubes plugged.
- 5. Question: How has the inspection technique been qualified to ensure that all deficient sleeves are identified? Why is a new inspection using the best available current technology not justified, instead of the mere reexamination of previous inspection data?
Answer: As described in the answer to question 4, the 1981 Eddy current test (ECT) data, when analyzed with the DDA-4, was satisfactory in clearly identifying the presence of rolls in the majority of the sleeves installed at San Onofre. For these sleeves, the ECT signals are unambiguous and, therefore, a new inspection using "best available current technology" is not required to clarify the presence of rolls.
However, for those tubes which 1981 ECT data and DDA-4 analysis did not clearly indicate the presence of required rolls, current ECT technology was used to conduct additional evaluations.
In addition, in December 1988 a qualification of the eddy current testing/analysis techniques used in testing of sleeves for acceptance of sleeve upper hard roll joints was performed. This qualification was comprised of three sequential operations which are summarized below:
(1) SONGS 1 tube/sleeve joints were fabricated with the single variable in the process being varying documented roll conditions.
(2) Eddy current testing was performed on these joints in a manner to obtain data representative of that obtained during initial testing in 1981, and of that obtained in subsequent testing, including December 1988. This data was then analyzed in the same manner as discussed in the answer to Question 4.
(3) Each joint was pulled in tension on a tensile testing machine which recorded force and axial translation between the tube and sleeve.
This qualification showed that the eddy current data analysis techniques used in analyzing the 1981 initial test data and the best available current technology applied in December 1988 are both capable of distinguishing the presence of a hard roll.
The best available current technology provides better sensitivity and more information on both roll and expansion joint transitions, but the 1981 reevaluation techniques were proven to provide adequate sensitivity to detect the presence of hard rolls in the majority of the sleeves.
This indicated the appropriateness of reviewing previous eddy current testing data for all installed sleeves and testing with the best available current technology, those sleeves which were indicated to not be acceptable based on the review of previous data. Thus, the previous data, which provided less sensitivity to the presence of the roll, was used to identify those sleeves which required further testing with the best available current technology, for final disposition.
- 6. Question: In addition to missing sleeve expansions and hard rolls, what other deficiencies have been identified or are potentially present in installed sleeves?
Answer: Other than these missing expansions and hard rolls, no other deficiencies affecting sleeve performance have been identified. The only other potential deficiency is corrosion induced defects. To limit the potential impact of corrosion induced defects, the sleeves are included in the random sample of tubes to be inspected during a Technical Specification examination. Approximately ten percent of the various types of sleeves installed in the steam generator to be inspected are examined and there have been no corrosion induced defects identified.
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