ML13330B484
| ML13330B484 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 03/03/1989 |
| From: | Trammell C Office of Nuclear Reactor Regulation |
| To: | Baskin K Southern California Edison Co |
| References | |
| TAC-71853 NUDOCS 8903130192 | |
| Download: ML13330B484 (6) | |
Text
March 3, 1989 Docket No.:
50-206 DISTRIBUTION, lDocket File
/.Lpnk NRC & LPDRs L. Lois CTramiell (2) GHsii Mr. Kenneth P. Baskin MVirgilio KWichman Vice President JLee RHermann Southern California Edison Company OGC-WF LMarsh 2244 Walnut Grove Avenue PD5 Plant File CYCheng Post Office Box 800 Edordan JRichardson Rosemead, California 91770 BGrimes LShao ACRS(1O)
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Dear Mr. Baskin:
DSellers TCollins MHum PTKuo
SUBJECT:
REACTOR VESSEL THERMAL SHIELD (TAC NO 71853)
Re:
San Onofre Nuclear Generating Station, Unit No. 1 In reviewing the information presented to us at our meeting on January 27,1989, together with your application for amendment dated February 17, 1989 regarding the condition of the reactor vessel thermal shield, the staff has identified a7 number of concerns regarding your plan to defer repair until the next refueling outage. These concerns are contained in the enclosure to this letter. We request that you address these concerns at a further meeting with us in Rockville as soon as possible.
The reporting and/or recordkeeping requirements contained in this letter affect fewer than ten respondents; therefore, 0MB clearance is not required under Pub. L.96-511.
Please contact us if you should have any questions regarding this request.
Sincerely,
/ s/
Charles M. Trammell, Senior Project Manager Project Directorate V Division of Reactor Projects
- III, IV31 V and Special Projects
Enclosure:
Concerns Re:
Thermal Shield d fid cc: w/e stclosure:
See next page
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IR UNITED STATES a-NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 March 3, 1989 Docket No.:
50-206 Mr. Kenneth P. Baskin Vice President Southern California Edison Company 2244 Walnut Grove Avenue Post Office Box 800 Rosemead, California 91770
Dear Mr. Baskin:
SUBJECT:
REACTOR VESSEL THERMAL SHIELD (TAC NO 71853)
Re:
San Onofre Nuclear Generating Station, Unit No. 1 In reviewing the information presented to us at our meeting on January 27, 1989, together with your application for amendment dated February 17, 1989 regarding the condition of the reactor vessel thermal shield, thestaff has identified a number of concerns regarding your plan to defer repair until the next refueling outage. These concerns are contained in the enclosure to this letter. We request that you address these concerns at a further meeting with us in Rockville as soon as possible.
The reporting and/or recordkeeping requirements contained in this letter affect fewer than ten respondents; therefore, OMB clearance is not required under Pub. L.96-511.
Please contact us if you should have any questions regarding this request.
Sincerely, Charles M. Trammell, Senior Project Manager Project Directorate V Division of Reactor Projects - III, IV, V and Special Projects
Enclosure:
Concerns Re: Thermal Shield cc: w/enclosure:
See next page
.Fir. Kenneth P. Baskin San Onofre Nuclear Generating Southern California Edison Company Station, Unit No. 1 cc Charles R. Kocher, Assistant Mr. Jack McGurk, Acting Chief General Counsel Radiological Health Branch James Beoletto, Esquire State Department of health Southern California Edison Company Services Post Office Box 800 714 P Street, Office Bldg. 8 Rosemead, California 91770 Sacramento, California 95814 David R. Pigott Mr. Hans Kaspar, Executive Director Orrick, Herrington & Sutcliffe Marine Review Committee, Inc.
600 Montgomery Street 531 Encinitas Boulevard, Suite 105 San Francisco, California 94111 Encinitas, California 92024 Mr. Robert G. Lacy Manager, Nuclear San Diego Gas & Electric Company P. 0. Box 1831 San Diego, California 92112 Resident Inspector/San Onofre NPS U.S. NRC P. 0. Box 4329 San Clemente, California 92672 Mayor City of San Clemente San Clemente, California 92672 Chairman Board of Supervisors County of San Diego 1600 Pacific Highway Room 335 San Diego, California 92101 Director Energy Facilities Siting Division Energy Resources Conservation &
Development Commission 1516 - 9th Street Sacramento, California 95814 Regional Administrator, Region V U.S. Nuclear Regulatory Commission 1450 Maria Lane, Suite 210 Walnut Creek, California 94596
ENCLOSURE CONCERNS REGARDING THERMAL SHIELD AT SONGS 1 OVERALL o
The overall concerns are that the thermal shield may (a) vibrate and cause damage to the core barrel, (2) create sizable and numerous loose parts, (c) obstruct flow and cause flow maldistribution, or (d) cause fuel failure due to deformation of the core barrel from thermal shield dis location. The licensee has not analyzed transient or accident conditions with the thermal shield in either its current configuration or with progressively more damage.
o The lack of UT increases uncertainty regarding the number and state of the damaged bolts and pins and the structural integrity of the core barrel.
o Many bolts and pins of the support blocks are already degraded and the rate of further degradation is based on engineering judgment rather than on facts.
o In view of uncertainty regarding the bolts of the support blocks there is a possibility that as a result of vibration of the thermal shield the support blocks may slip out from their positions. In the worst case the thermal shield could drop to the bottom of the reactor vessel.
The neutron monitoring system proposed is too vague. It cannot be con cluded from the available information that further degradation would be detected.
o The licensee did not provide sufficient information regarding seismic evaluation to enable the staff to formulate a meaningful opinion. More specific information regarding methodology used in computing impact loads and the techniques used for computing seismic loads at various locations would be required.
o The Westinghouse letter of February 12, 1988 to the licensee discusses three possible and progressively worse scenarios. Given the lack of definitive data on the current condition of the bolts and pins, and the relatively qualitative monitoring system, the staff is not convinced that the continued operation of SONGS-1 can be justified without repair.
SPECIFICS
- 1. Bolt Fatique Evaluation Concerns associated with the key assumptions for the bolt fatigue analysis include:
- a. Why was loss of bolt preload from radiation-assisted relaxation not considered?
ENCLOSURE CONTINUED
-2
- b. Why was a Section.III fatigue analysis not performed?
- c. Justify use of failure curves in lieu of lower bound (or "design") curves for fatigue analysis.
- d. Explain the basis for use of a strain concentration factor in the context of established procedures for CUF calculation.
- e. NB-3232.3(c) recommends use of a fatigue strength reduction value of not less than 4.0. Justify use of a smaller value.
- 2. During the 1988 refueling outage, a limited visual inspection was per formed based on the available access.
By using a different camera system or removing more fuel assemblies, could (a) additional surfaces of the components be inspected or (b) additional access be provided to the lower thermal shield support blocks, the limiter keys, or the core barrel radial support keys.
- 3. Core Barrel To Lower Support Weld.
Was this core barrel weld inspected during the 1988 refueling outage?
If so, extent of examinations?
- 4. Will one cycle of operation with the "Worst Credible Degraded Case" cause or increase the probability of fatigue cracking of the core barrel to lower support weld?
- 5. The licensee proposes to operate until the potential damage becomes an economic burden.
Describe the plausible additional damage to the thermal shield, core barrel or reactor vessel that the licensee is prepared to accept and repair after shutdown. Estimate the additional radiation exposure to repair personnel as a result of this plausible additional damage.
- 6. When did bolt and pin degradation occur?
- 7. What preload is currently assumed in bolts?
- 8. Assuming all bolts and pins in support blocks are failed what is the effect of this on thermal shield liftoff during a LOCA?
- 9. The following comments are related to the proposed thermal shield monitoring program for the SONGS-1 plant, presented to the staff on Friday January 27, 1989.
A neutron noise based internal vibration monitoring program was suggested. For such a surveillance program to be effective long-term baseline data is required and the detectability limits established.
8 0
ENCLOSURE CONTINUED
-3 The staff believes that neither is feasible for the SONGS-1 thermal shield.
Baseline To establish a baseline data base for the thermal shield:
(a) the thermal shield must have the proper preload on the supports to yield interpretable data, otherwise (b) it needs data collection from extended period of time.
Neither of these conditions is satisfied in the proposal.
Detectability Limits Such limits to be established require:
(a) an adequate data base and (b) parametric studies of the anticipated vibration mode.
Neither of these conditions is satisfied in the proposal.
Therefore, the staff does not believe that a thermal shield monitoring program based on exccre measurement of neutron noise can be established for SONGS-1 under the present conditions.
- 10. Describe the design of the repair that would be performed on the thermal shield components considering the known damage.