ML13304A385
| ML13304A385 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 12/29/1988 |
| From: | Medford M SOUTHERN CALIFORNIA EDISON CO. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| Shared Package | |
| ML13304A386 | List: |
| References | |
| TAC-71174, TAC-71175, NUDOCS 8901030228 | |
| Download: ML13304A385 (5) | |
Text
ACCELERATED DISTRIBUTION DEMONSTRATION SYSVTEM REGULORY INFORMATION DISTRIBUT&
SYSTEM (RIDS)
ACCESSION NBR:8901030228 DOC.DATE: 88/12/29 NOTARIZED: NO DOCKET #
FACIL:50-361 San Onofre Nuclear Station, Unit 2, Southern Californ 05000361 AUTH.NAME AUTHOR AFFILIATION MEDFORD,M.O.
Southern California Edison Co.
RECIP.NAME RECIPIENT AFFILIATION Document Control Branch (Document Control D sk)
SUBJECT:
Forwards final rept on "Exam,Testing, & Evaluation of R
Irradiated Pressure Vessel Surveillance Specimens.
I DISTRIBUTION CODE: A047D COPIES RECEIVED:LTR I ENCL
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SIZE:24-$
TITLE: OR Submittal: Inservice Inspection/Testing/Relief from ASME Code D
NOTES:
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ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD5 LA 1
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Southern California Edison Company P. 0. BOX 800 2244 WALNUT GROVE AVENUE ROSEMEAD, CALIFORNIA 91770 M.O.MEDFORD TELEPHONE MANAGER OF (818) 302-1749 NUCLEAR REGULATORY AFFAIRS December 29, 1988 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555 Gentlemen:
Subject:
Docket Nos. 50-361 and 50-362 Surveillance Capsule Test Report San Onofre Nuclear Generating Station Units 2 and 3
References:
- 1. SCE (M. 0. Medford) to NRC (Document Control Desk) letter dated September 20, 1988
- 2. SCE (Kenneth P. Baskin) to NRC (Document Control Desk) letter dated November 7, 1988
- 3. NRC (D. E. Hickman) to SCE (Kenneth P. Baskin) letter dated November 30, 1988 - Request for additional information (TAC Nos. 71174 and 71175)
By letter dated September 20, 1988 (Reference 1), SCE informed the NRC that the Unit 2 surveillance capsule materials test report required by Technical Specification Surveillance Requirement 4.4.8 would be submitted by December 31, 1988. Consistent with this commitment, the purpose of this letter is to transmit the subject report to the NRC. This report, entitled "Examination, Testing and Evaluation of Irradiated Pressure Vessel Surveillance Specimens from the San Onofre Nuclear Generating Station Unit 2," is provided as Enclosure I to this letter.
Besides satisfying a Technical Specification surveillance requirement, this report is of special interest to proposed Technical Specification Change (PCN) 278. The test results and conclusions provided in this report verify (within expected tolerances) the various calculational values that SCE utilized in formulation of updated pressure-temperature curves that were submitted to the NRC as PCN-278 (Reference 2).
Specifically, the report indicates (1) an acceptable decrease in the Charpy upper shelf energy and (2) the actual "measured" neutron fluence at the reactor vessel wall was within expected values.
(Note that "measured" fast neutron fluence is a derived quantity obtained by neutron activation analysis.)
The test results from the first surveillance capsule, removed from San Onofre Unit 2 on September 20, 1987, have indicated a "measured" neutron fluence at the reactor vessel wall that is 40% higher than the neutron fluence used by SCE in preparation of the updated P-T curves submitted with PCN-278.
<890 1030228 881229, 1 PR ADOCK 050 U
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Document Control Desk December 29, 1988 The surveillance capsule "measured" fluence, though higher than expected, is not unreasonable. It is generally accepted that flux values determined through neutron transport analysis have a tolerance of +/- 40%. Sources of this discrepancy include calculation bias errors (e.g., fast neutron cross-section uncertainties, transport calculation approximations, etc.), and random errors (e.g., reactor vessel ovality, reactor vessel off center from the core axis, etc.). It is believed the latter is the predominant reason for the unexpected measured fluence value (e.g., a 1/4 inch reduction in moderator provides for an approximate 40% increase in fluence) and that the measured fluence results are indicative of an "as-design" vessel dimensional tolerance effect localized near the particular capsule of interest.
The above findings do not represent a safety concern for the following reasons. As can be seen from Figures 6.7-3 and 6.7-4 of the enclosed report, measured Reference Temperature shifts for the surveillance material are still conservative with respect to predicted shifts using the methodology provided in Regulatory Guide 1.99, Rev. 2. Furthermore, the surveillance capsule fluence was achieved from exposure during Cycles 1-3. These cycles are representative of "out-in" fuel management loading patterns. Subsequent to the surveillance capsule removal (Cycle 4 and on), San Onofre Unit 2 went to a checkerboard fuel loading pattern in extending the operating cycle from 18 to 24 months. This represents a lower neutron leakage loading pattern than used in Cycles 1-3. The cycle 4 vessel wall neutron flux reduction was obtained from the 2 Group, 3-D nodal code Simulate-3 by comparing radial power distributions from Cycles 1-4. Results indicate a 30% fast flux (E > 1.0 MeV) reduction has occurred at the vessel I.D. surface due to the longer cycle and lower leakage fuel management. Furthermore, incore instrument neutrom flux measurements support these results. Therefore, it is expected when the second surveillance capsule is removed (Unit 3 at 5.6 EFPY), the "measured" accumulated fluence will be less than the trend indicated by the flux monitors from capsule #1.
While there will be no consequential long range effects from the higher than predicted surveillance capsule fluence, this measured fluence does affect the recently submitted PCN-278 (updated P-T limits).
Since the measured fluence data from the surveillance capsule were not available when the updated P-T,
curves were prepared, the P-T limits submitted to the NRC are 6 degrees F less conservative at 10 EFPY than if the analysis had been performed using the extrapolated "measured" fluence. This 6 degree F difference stems from an underpredicted Adjusted Reference Temperature associated with the predicted fluence being 70% of the "measured" fluence. Any potential safety concern can be resolved by shortening the period of applicability of the proposed updated P-T curves submittal, which in effect, would reduce the cumulative vessel wall exposure and corresponding Reference Temperature shifts to acceptable levels throughout the applicable operating period.
As submitted in PCN-278, the proposed P-T curves would be valid to 10 EFPY.
Based on this first surveillance capsule test results, it is requested that the applicability of the proposed P-T limits be adjusted to 8 EFPY. Revised pages for proposed technical specification change 278 that reflect P-T curve applicability to 8 EFPY are provided as Enclosure II to this letter.
Document Control Desk December 29, 1988 Considering the reduction in the fast flux seen at the vessel wall following Cycle 3, the limits determined for the updated RCS P-T curves as submitted in PCN-278 would be conservative for this duration. Additionally, the second surveillance material data point will be obtained when the 97 degree capsule is removed from Unit 3 at 5.6 EFPY (end of Cycle 5, projected for October 1991).
Following testing of this capsule, the P-T curves will be updated again using the surveillance data, at which time it is believed relief will be obtained by using the measured Reference Temperature shifts per Regulatory Guide 1.99, Rev. 2, Section 2.
Following receipt of SCE's letter of November 7, 1988 (Reference 2), the NRC requested (Reference 3) the reactor vessel wall neutron fluence at 10 EFPY and the piece number and heat number of the limiting material on which we based our calculations. The piece number is 215-03 and heat number is C-7595-1 as provided by FSAR Table 5.2-5 Sheet 6. The reactor vessel wall neutron fluence assumed at 10 EFPY is identified in calculation N-0220-019, "SONGS 2 RCS Pressure Temperature Curves for 10 EFPY" and is provided in Enclosure III to this letter. To further assist the NRC's review of PCN-278, calculation N-0220-020, "SONGS 2 and 3 Reactor Vessel Adjusted Reference Temperature for 10 EFPY and 32 EFPY" is also provided in Enclosure III to this letter. Both of these calculations use a fluence that is greater than that projected for 8 EFPY from surveillance capsule results and expected fuel management.
Accordingly, SCE has requested a reduction in the applicability of the proposed P-T curves to 8 EFPY.
The current P-T curves for San Onofre Unit 2 are scheduled to expire on March 20, 1989. Accordingly, it is requested that NRC review and approval be completed prior to this date to preclude unnecessary plant shutdown.
If you have any questions regarding this report or PCN-278, please contact me.
Very truly yours, Enclosure cc: 3. B. Martin, Regional Administrator, NRC Region V F. R. Huey, NRC Senior Resident Inspector, San Onofre Units 1, 2 and 3 J. H. Hickman, California Department of Health Services
ENCLOSURE I