ML13336A102
| ML13336A102 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 07/27/1988 |
| From: | Trammell C Office of Nuclear Reactor Regulation |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| TAC-68439 NUDOCS 8808170309 | |
| Download: ML13336A102 (10) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 July 27, 1988 Docket No.:
50-206 FACILITY:
SAN ONOFRE NUCLEAR GENERATING STATION, UNIT NO. 1 LICENSEE:
SOUTHERN CALIFORNIA EDISON COMPANY (SCE)
SUBJECT:
SUMMARY
OF MEETING HELD ON JULY 11, 1988 RE: EMERGENCY DIESEL-GENERATOR INSPECTIONS On July 11, 1988, the NRC staff met with representatives of Southern California Edison to discuss its application dated June 22, 1988 to uprate the emergency diesel generators from 4500 KW (+/-5%) to 5250 KW (+/-5%). Attendees at the meeting are shown in Enclosure 1. Photographs and stress diagrams of Shoreham piston skirts presented at the meeting are contained in Enclosure 2.
The meeting was requested by SCE in response to the staff request that main crankshaft journals no.-8 through 12 be inspected on both units before startup. Journals no. 8-12 are the most highly stressed; in order of decreasing stress: 9, 10, 8, 11, 12.
The DGs at San Onofre Unit 1 are V-20 DSRV engines made by TDI (now Imo Delaval Inc.). Three other such V-20 engines exist, not in nuclear service.
Fatigue cracking at the oil holes on the main journals has occurred in the past and has been repaired by both drilling the hole larger to remove the crack and polishing. The crankshaft experiences high stresses for a few cycles both during startup and shut down when the crankshaft speed sees three harmonics
("critical speeds") which cause increased stress. Stresses at steady-state loads up to 6000 KW are acceptable provided crankshaft inspections are conducted.
SCE explained the crankshaft limited-life analysis as follows:
as long as cracks are less than 18 mils deep, the crankshaft is acceptable for loads up to 6000 KW provided inspections are conducted at refueling outages to assure there are no cracks.
The crankshafts were last inspected in January 1986 and no cracks were found. Since that time, DG No. 1 has had 150 starts; DG No. 2 has had 120 starts. None of these were the "slow" starts of greater than 24 seconds called for in the safety evaluation for these engines issued to SCE on January 28, 1987.
8808170309 880727 PDR ADOCK 05000206 PNU DVOI0
-2 Most of these starts were in the 10-15 second time frame; a few were about 5 seconds. Total number of starts on DG No. 1 is about 900; DOG No. 2 is about 550.
Prior inspections in 1984 revealed cracking on DG No. 1 at journals No. 9 and 10; DG No. 2 also had a crack at journal no. 9.
SCE explained that to inspect journals no. 8-12 would require 2 1/2 weeks for both engines and would be unnecessary because journals no. 9 and 10 (the most highly stressed both by analyses and the prior finding of fatigue cracks) would be expected to crack first. SCE said that it would be inconceivable to have cracks on, say, no. 8 and not on no. 9 and 10. Therefore, SCE proposed to inspect journals no. 9 and 10 on both engines prior to plant startup. SCE noted that a much more comprehensive inspection will be conducted in about three months when the plant enters a refueling outage.
SCE also would also conduct slow starts (greater than 24 sec.) for all surveillance tests except for the one fast start required by Technical Specifications once per 18 months. Conducting slow starts would require temporary bypassing of the engine fail-to-start trip. For the next refueling outage,.SCE would modify the engines to provide for automatic slow starts, which must be done manually now.
As for the piston skirts, Shoreham found cracks where the crown is bolted to the skirt. FaAA found the cause to be fatigue cracks due to the existence of a point of high stress. The cracks propagate into a larger region and arrest and do not lead to failure. The piston skirts at San Onofre Unit 1 are designated type AF and are the Shoreham type although the firing pressure at Shoreham (8750 KW) is considerably higher than San Onofre 1.(4500 KW).
25%
of the piston skirts were inspected in 1984 and the rest were inspected in 1986. Some cracks were found and four piston skirts were changed to type AE which does not have the cracking problem found on the AF skirts.
At the conclusion ofthe meeting, the staff concluded that a crankshaft inspection of journals no. 8 and 9 on DG no. 1 and journals no. 9 and 10 on DG no. 2 should be conducted prior to restart and that increasing the load rating temporarily to 5250 KW would be acceptable subject to the following:
- 1. Journals no. 8-12 should be inspected at the next refueling outage and thereafter until the longer-term issue of crankshaft cracking is resolved.
- 2. The piston skirts should be changed to type AE at the next refueling.
- 3. All surveillance starts should be slow starts (greater than 24 seconds) except one performed at 18 month intervals.
- 4. SCE should conduct confirmatory load testing of the six largest loads after startup and report the results to the NRC staff.
3 -
July 27, 1988
- 3. The Technical Specifications should be modified to provide for monthly load testing up to 5250 KW (+/-5%) but the load test should be conducted at 4500 KW for the majority of the running time.
The NRC staff explained that the above is not to be considered to be a final resolution of the crankshaft cracking problem. The NRC staff does not consider accelerated inspections to be an adequate long-term solution for a deficiency in design which makes these crankshafts prone to fatigue cracking.
original signed by Charles M. Trammell, Senior Project Manager Project Directorate V Division of Reactor Projects -
- III, IV, V and Special Projects
Enclosure:
- 1. Attendees
- 2. Photographs cc:
See next page DISTRIBUTION Docket File PDR LPDR PDV Reading GKnighton Project Manager OGC-WF EJordan BGrimes NRC Participants ACRS (10)
MRJohnson DKirsch Plant Service List (See next page)
Licensee R
V DRSP/DPDV M r mell:dr GWKnighton
/ 88 7 / /88 OFFICIAL RECORD COPY
Mr. 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 Mr. Dennis M. Smith, Chief Manager, Nuclear Radiological Programs Division San Diego Gas & Electric Company Governor's Office of Emergency Svcs.
P. 0. Box 1831 State of California San Diego, California 92112 2800 Meadowview Road Sacramento, California 95832 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
- 3. The Technical Specifications should be modified to provide for monthly load testing up to 5250 KW (+/-5%o) but the load test should be conducted at 4500 KW for the majority of the running time.
The NRC staff explained that the above is not to be considered to be a final resolution of the crankshaft cracking problem. The NRC staff does not consider accelerated inspections to be an adequate long-term solution for a deficiency in design which makes these crankshafts prone to fatigue cracking.
Charles M. Trammell, Senior Project Manager Project Directorate V Division of Reactor Projects -
- III, IV, V and Special Projects
Enclosure:
- 1. Attendees
- 2. Photographs cc:
See next-page
ENCLOSURE 1 ATTENDANCE LIST NRC/SCE MEETING July 11, 1988 NRC SCE C. Trammell D. Pilmer E. Murphy J. Rainsberry S. Saba J. Mangum J. Knight M. Hartzman SCE Consultant C. Berlinger P. Johnston -
FaAA F. Rosa
Stresses (psi)
-73300 to -70727
-70727 to -65581
-65581 to -60435
-60435 to -55289
-55289 to -50143
-50143 to -44997
-44997 to -39851
-39851 to -34705 Stud hole
-34705 to -29559
-29559 to -24413
-24413 to -19267
-19267 to -14121
-14121 to
-8975
-8975 to -3829 T
-3829 to -1256 Figure 4-9. AF piston skirt local model with stress contour of average element (a
) stresses for a skirt with a pressurized crown and no loading on the outer ring.
Stresses (psi)
-35100 to -33825
-33825 to -31275
-31275 to -28725
-28725 to -26175
-26175 to -23625
-23625 to -21075
-21075 to -18525
-18525 to -15975
-15975 to -13425
-13425 to -10875
-10875 to -8325
-8325 to
-5775
-5775 to -3225
-3225 to
-675
-675 to 600 Figre -8.AF ison kir glbalmoel"ithstrss onourof vergeelement (a
)I stresses for a skirt with a pressurized crown and no loadina on the outer ring.
Figure 2-3.
A crown-to-skirt attachment boss inside a piston skirt re moved from EDG #101.
The boss has been machined by spot-facing from 2 inches high down to the observed 1/4 inch.
The removed segment of ridge was subsequently broken open and is shown in Figures 2-8 and 2-9.
Figure 2-4.
A crown-to-skirt attachment boss from EDG #102.
The piston skirt has been tested with red dye penetrant and white developer.
A red linear indication is visible at the base of the vertical ridge that remained after spot-facing.
2-9 FeAA-84-2-14
Figure 2-1.
Photograph of an AF-type piston from the Shorehain Nuclear Power Station emergency diesel generator piston skirt (left) and crown (right).
Figure 2-2.
Interior of an AF-type piston skirt.
The white coating and red dye are from the dye penetrant examination.
Through holes for the crown studs and spot-faced boss are circled.
2-8 FaAA-84-2-14