ML13302A296
| ML13302A296 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 11/08/1991 |
| From: | Rosenblum R Southern California Edison Co |
| To: | Martin J NRC/IE, NRC/RGN-V |
| Shared Package | |
| ML13302A297 | List: |
| References | |
| NUDOCS 9111260009 | |
| Download: ML13302A296 (9) | |
Text
ACCELERATED DISTRIBUTION DEMONSTRATION SYSTEM REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)
ACCESSION NBR:9111260009 DOC.DATE: 91/11/08 NOTARIZED: NO DOCKET #
FACIL:50-362 San Onofre Nuclear Station, Unit 3, Southern Californ 05000362 AUTH.NAME AUTHOR AFFILIATION ROSENBLUM,R.M.
Southern California Edison Co.
RECIP.NAME RECIPIENT AFFILIATION Region 5-(Post 820201)
R
SUBJECT:
Requests extension of temporary waiver of compliance from requirements of TS Limiting Conditions for Operation 3.0.3 &
3.4.1.1 re reactor coolant pump flywheel insp until next refueling outage scheduled to begin on 920118.
D DISTRIBUTION CODE: IE01D COPIES RECEIVED:LTR ENCL SIZE:
S TITLE: General (50 Dkt)-Insp Rept/Notice of Violation Response NOTES:
S &ee, A
RECIPIENT COPIES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL D
PD5 PD 1
1 KOKAJKO,L.
1 1
INTERNAL: ACRS 2
2 AEOD 1
1 D
AEOD/DEIIB 1
1 AEOD/DSP/TPAB 1
1 DEDRO 1
1 NRR HARBUCK,C.
1 1
S NRR MORISSEAU,D 1
1 NRR/DLPQ/LHFBPT 1
1 NRR/DLPQ/LPEB10 1
1 NRR/DOEA/OEAB 1
1 NRR/DREP/PEPB9H 1
1 NRR/DST/DIR 8E2 1
1 NRR/PMAS/ILRB12 1
1 NUDOCS-ABSTRACT 1
1 OE DI' 1
1 OGC/HDS3 1
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F1 1
RGN5 FILE 01 1
1 EXTERNAL: EG&G/BRYCE,J.H.
1 1
NRC PDR 1
1 NSIC 1
1 R
D S
A D
D NOTE TO ALL "RIDS" RECIPIENTS:
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TOTAL NUMBER OF COPIES REQUIRED: LTTR 24 ENCL 24
Southem California Edison Company 23 PARKER STREET 2
A 8: 5b IRVINE, CALIFORNIA 92718 November 8, 1991 R. M. ROSENBLUM TELEPHONE MANAGER OF (714) 454-4505 NUCLEAR REGULATORY AFFAIRS U. S. Nuclear Regulatory Commission Attention:. J. B. Martin, Regional Administrator NRC Region V 1450 Maria Lane, Suite 210 Walnut Creek, CA 94596-5368
Subject:
Docket No. 50-362 Request for Extension of Temporary Waiver of Compliance Reactor Coolant Pump Flywheel Inspection San Onofre Nuclear Generating Station, Unit 3
References:
- 1.
Regulatory Guide 1.14, "Reactor Coolant Pump Flywheel Integrity," Revision 1, August 1975
- 2.
October 30, 1991 letter from R. P. Zimmerman (NRC) to R. W. Krieger (SCE),
Subject:
Extension of the Temporary Waiver of Compliance from San Onofre Unit 1 Technical Specification 4.7 and San Onofre Unit 3 Technical Specification 4.4.9, Inservice Inspection of Reactor Coolant Pump Flywheels
- 3.
October 26, 1991 letter from R. W. Krieger (SCE) to John B. Martin (NRC),
Subject:
Request for Temporary Waiver of Compliance, Reactor Coolant Pump Flywheel Inspection, San Onofre Nuclear Generating Station, Units 1 and 3 This letter requests an extension to the Temporary Waiver of Compliance from the requirements of Technical Specification (TS)
Limiting Conditions for Operation (LCO) 3.0.3 and 3.4.1.1 for San Onofre Unit 3 until the next San Onofre Unit 3 refueling outage, currently scheduled for January 18, 1992. Approval of the current temporary waiver for Unit 3 was granted until December 1, 1991 by Reference 2. As discussed below, our extensive evaluation of this issue indicates that continued operation until the next scheduled refueling outage has no adverse safety significance. This letter also requests one change to the compensatory actions presently in effect as discussed in paragraph C below.
1 00 1
Document Control Desk
-2 This temporary waiver extension is requested to be effective until the next Unit 3 refueling outage, which is scheduled to begin on January 18, 1992, but no later than January 31, 1992.
Although the outage is scheduled for January 18, the additional time to January 31 allows for small unforeseeable changes to this schedule as well as sufficient time to reach an Operating Mode when the RCPs are no longer required to be Operable.
A.
Requirements for Which the Temporary Waiver is Requested TS 3.4.9 "Reactor Coolant System -
Structural Integrity,"
establishes the structural integrity requirements of ASME Code Class 1, 2, and 3 components. Associated TS Surveillance Requirement 4.4.9 establishes the Regulatory Guide 1.14, Revision 1, August 1975, Regulatory Position C.4.b, RCP motor flywheel inspection requirements.
Regulatory Guide 1.14 requires that at approximately 3 year intervals, during the refueling or maintenance shutdown coinciding with the Inservice Inspection schedule, an in-place ultrasonic volumetric examination of the areas of higher stress concentration at the bore and keyway be performed.
As stated.in Reference 3, on October 24, 1991, at approximately 1700, it was identified that the flywheel inspections for the Unit 3 RCPs were last performed in February 1987. Because the time since the last inspection exceeded 3 years, the surveillance interval as defined by TS 4.4.9 and Regulatory Guide 1.14 was considered to have been exceeded, and TS 3.0.3 was considered to be applicable. In addition, TS 3.4.1.1 requires that in Modes 1 and 2 both reactor coolant loops and both RCPs in-each loop shall be in operation. Within one hour, the plant must be placed in Mode 3 if fewer than 4 RCPs are in operation. The structural integrity of the flywheel affects the operation of the RCP; therefore, the Action requirement of TS 3.4.1.1.
was also considered to apply.
In summary, this letter requests an extension of the temporary waiver of compliance from the Action requirements of TS 3.0.3 and 3.4.1.1 until the next Unit 3 refueling outage, which is currently scheduled to begin on January 18, 1992, but no later than January 31, 1992, to avoid an unnecessary shutdown of Unit 3.
Document Control Desk
-3 B.
Circumstances Surrounding the Situation Extension of the existing waiver is requested to preclude an unnecessary reactor shutdown to inspect the RCP flywheels because the existing temporary waiver of compliance expires on December 1, 1991.
A shutdown of Unit 3 to inspect the RCP flywheels would have the following impacts:
- 1) increased personnel doses, 2) additional replacement energy costs, and 3.) an unnecessary increase in plant risk associated with.an unwarranted shutdown and restart of the unit.
C.
Compensatory Actions Necessary The flywheel inspection is intended to allow a means to detect the initiation and potential propagation of flaws (cracks) in areas of high stress concentration at the bore and keyway region such that catastrophic failure of the flywheel will be avoided. The primary objective of avoiding catastrophic flywheel failure is prevention of missile generation damage to critical reactor coolant piping and components. Although initiation of a crack and subsequent propagation to catastrophic failure of the flywheel is considered extremely remote as discussed below, if an undetected flaw were to exist, it is possible that crack growth would manifest itself in flywheel imbalance and resultant changes in motor/pump vibration signatures. As, such, the following compensatory actions will be in effect for the duration of the waiver.
- 1.
Baseline vibration data for each pump has been established based upon the vibration history during the past six months.
If the amplitude of the vibration increases to 3 mils or greater above the established baseline, an engineering evaluation of the condition will be initiated and the NRC Resident Inspectors will be notified within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. If the vibration increases to 6 mils or greater above the established baseline, shutdown of Unit 3 will be initiated in accordance with the ACTION requirements of TS 3.0.3 to an operating mode which permits the affected RCP to be secured. The vibration levels will be monitored once per shift.
Document Control Desk
-4
- 2.
This request for extension of the waiver also requests a change to one of the compensatory actions presently in effect as follows. Each RCP is provided with 2 vibration probes (only 1 probe is presently functional for RCPs P003 and P004.).
If none of the vibration probes are operable for any pump, such that vibration data cannot be obtained, we will restore vibration monitoring or obtain NRC agreement to alternate monitoring within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
If we are unable to restore vibration monitoring or obtain NRC agreement to alternate monitoring within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, shutdown of the unit will be initiated in accordance with the ACTION requirements of TS 3.0.3 to an operating mode which permits the affected RCP to be secured.
- 3.
The Unit 3 RCPs have been verified to be operating within the manufacturer's recommended tolerances for pump vibration.
D.
Evaluation of the Safety Significance of the Request.
An evaluation of San Onofre Units 2 and 3 RCP flywheel inspection data, a survey of industry experience related to RCP flywheel inspections, and a fracture mechanics evaluation have recently been completed. The additional pump operating days until the Unit 3 refueling outage has also been compared to the pump operating days since the last Unit 3 flywheel inspection. All of this information supports an extension of the temporary waiver until the next Unit 3 refueling outage as follows:
- 1.
San Onofre Units 2 and 3 RCP.Flywheel Inspection Data A review of the past flywheel inspection data for both Unit 2 and Unit 3 has identified no unsatisfactory indications.
Flywheel inspections on the four Unit 2 RCPs have just been satisfactorily completed with no recordable indications. These results provide additional confidence in the acceptability of the Unit 3 RCP flywheels.
- 2.
Industry Experience Surveys of industry experience related to RCP flywheel failures have identified no reportable indications from inservice inspections of reactor coolant pump motor flywheels and no recorded flywheel failures. This review included discussions with the Unit 3 reactor
Document Control Desk
-5 supplier, RCP supplier, inservice inspection representatives at many plants, and a review of the Nuclear Plant Reliability Data System data base.
Representatives from Westinghouse and ABB/Combustion Engineering (CE) have indicated that there have been no problems associated with any Babcock & Wilcox, Westinghouse, or ABB/CE plant RCP flywheel from any of the inservice inspections.
It is our understanding that this experience includes over 10 million RCP operating hours.
- 3.
Fracture Mechanics Evaluation A fracture mechanics evaluation has been completed which demonstrates that flywheel integrity is maintained under the severest loading combination.
Also, a flaw large enough to propagate to failure prior to the upcoming Unit 3 refueling outage would have been detected during the previous inspection of each RCP flywheel.
(This evaluation is provided as an Enclosure.)
The fracture mechanics model conservatively considered a crack size equal to the keyway depth plus twice the smallest detectable crack.
The evaluation considered.the following loadings:
- a.
Dynamic load due to overspeed
- b.
Interference fit stresses
- c.
Key loading due to shaft torque (it was conservatively assumed that the entire load acts on only one of the two axial keys)
- d.
Seismic (Design Basis Earthquake) loading
- e.
Vibration stresses (assuming overspeed conditions)
- f.
Pump seizure The total stress in the flywheel was based on the sum of the loads a through e above (pump seizure was evaluated separately).
The stress intensity factor for Mode I cracks (crack under tension), KI, was then calculated using the computer program PCCRACK. A safety factor of 4.7 was calculated based on the ratio KI/KIC, where KIC is the critical stress intensity for the flywheel material.
The unlikely event of pump seizure was also analyzed assuming a torque high enough to cause a shear failure in the curvic coupling. This case was shown to be enveloped by the overspeed condition described above.
Document Control Desk
-6 A crack growth of 0.005 inch was estimated based on 100 stop and start cycles since February 1, 1987 (there have been only 27 cycles since February 1, 1987).
Therefore, based on the above results, the likelihood of a flywheel failure during the requested waiver extension is considered extremely remote.
- 4.
RCP Starts and Operating Days The Unit 3 RCP flywheels have each accumulated 27 starts and approximately 1500 operating days (approximately 4.1 years) since the last inspection.
(Note: This value has been corrected from our October 26,'1991 letter.)
The additional time (approximately 49 days but no greater than 62 days) the pumps will be running as requested by this temporary waiver extension represents a small contribution to the total running time.
In summary, it is concluded that the flywheel integrity will be maintained for the duration of the temporary waiver extension based on the results of the recently completed:
fracture mechanics evaluation, the industry and San Onofre's experience related to flywheel structural integrity, and the compensatory measures described above.
E.
Justification of the Duration of the Waiver SCE is requesting that this tempofary waiver of compliance remain in effect until the upcoming Unit 3 refueling outage, which will extend the duration of this temporary waiver of compliance for Unit 3 by approximately 49 days, but-no longer than 62 days.
Flywheel inspections on the four.Unit 2 RCPs have just been satisfactorily completed with no recordable indications.
These results provide additional confidence in the acceptability of the Unit 3 RCP flywheels. As discussed above in Section D, the incremental addition of running time requested by this waiver extension does not significantly.
increase the likelihood of flywheel failure.
A fracture mechanics evaluation has been completed which demonstrates that a flaw large enough to propagate to failure prior to the upcoming Unit 3 refueling outage would have been detected during the previous inspection of each RCP flywheel.
Therefore,.the likelihood of a flywheel.
failure for the duration of the requested waiver extension is considered extremely remote.
Document Control Desk
-7 F.
Basis for No Significant Hazards Conclusion 10 CFR 50.92 defines that no significant hazards will occur if operation of the facility in accordance with the temporary waiver of compliance does not:
- 1.
Involve a significant increase in the probability or consequences of an accident previously evaluated; or
- 2.
Create the possibility of a new or different kind of accident from any accident previously evaluated; or 3..
Involve a significant reduction in a margin of safety.
As previously discussed, the likelihood of flywheel failure as a result of exceeding the inspection interval is extremely remote, therefore the consequences or probability of an accident previously evaluated will not be increased.
The possibility of a new or different kind of accident from any previously evaluated will not be created; nor does this involve a significant reduction in the margin of safety.
G.
Basis for No Irreversible Environmental Consequences It.has been determined that this temporary waiver of compliance involves no significant increase in the amounts, and no significant change in the types, of any effluent that may be released offsite and that there is no significant increase in individual or cumulative occupational radiation exposure. Accordingly, this extension to the existing temporary waiver of compliance meets the eligibility criteria for categorical exclusion set forth in 10 CFR Section 51.22(c)(9).
Pursuant to 10 CFR 51.22(b), no environmental impact statement or-environmental assessment need be prepared in connection with the granting of the temporary waiver of compliance.
The San Onofre Nuclear Generating Station Onsite Review Committee has reviewed and approved the actions discussed in this request to extend the temporary waiver of compliance.
Document Control Desk
-8 If you have any questions or comments, or if you would like additional information, please let me know.
Sincerely, Enclosure cc:
R. P. Zimmerman, USNRC, Region V C. W. Caldwell, USNRC Senior Resident Inspector George Kalman, USNRC Project Manager M. J. Virgilio, USNRC -