ML20045G491
| ML20045G491 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 06/03/1993 |
| From: | Richardson J Office of Nuclear Reactor Regulation |
| To: | Collins S NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| Shared Package | |
| ML20045G485 | List: |
| References | |
| GL-89-10, NUDOCS 9307140037 | |
| Download: ML20045G491 (4) | |
Text
4 ATTACHMENT j ucg s
4 UNITED STATES
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MEMORANDUM FOR:
Samuel J. Collins, Director M 03 S Division of Reactor Safety Region IV FROM:
James E. Richardson, Director Division of Engineering Office of Nuclear Reactor Regulation
SUBJECT:
OVERSTRESSING OF MOTOR-0PERATED VALVES AT SOUTH TEXAS By memorandum dated April 30, 1993, I forwarded guidance prepared jointly by NRR and the regions for the performance of inspections of motor-operated valve (MOV) programs developed in response to Generic Letter (GL) 89-10, " Safety-Related Motor-Operated Valve Testing and Surveillance."
In the enclosure to that memorandum, the staff stated that, where an MOV is overthrusted or overtorqued, the MOV should be considered to be degraded and an operability evaluation performed as described in Generic Letter 91-18.
With regard to particular MOVs at South Texas, your staff has requested assistance in determining the extent of overstress that may be allowed before an M0V should be considered inoperable.
In Section 6.2.2.1 of NP-6660-0, " Application Guide for Motor-Operated Valves in Nuclear Power Plants," the Electric Power Research Institute (EPRI) stated that Limitorque motor actuators are designed to survive a one-time torque overload of two times the maximum torque rating and a thrust overload of two and one-half times the thrust rating.
EPRI stated that the actuator might not withstand an event where this " survivable" torque or thrust is exceeded.
In Maintenance Update 92-1, Limitorque stated that it considers its SMB actuators to be capable of withstanding this one-time allowable overload without loss of l
actuator qualification.
If a licensee finds that an actuator has been overloaded greater than two times the torque rating or two and one-half times the thrust rating, Limitorque recommends that the actuator be inspected.for damage to determine if the actuator is suitable for further service.
Limitorque also stated in its maintenance update that, if the torque ratings are exceeded, increased wear (and not gear failure) is the usual result but that overtorquing may result in cracks in the gearing.
If it is found that excessive torque has been applied, limitorque stated that the gearing and, in particular, the worm, should be visually inspected for excess wear and cracks.
Limitorque has qualified its actuators for a one-time allowable overload of two times the torque rating and two and one-half times the thrust rating.
l Although minor overload is primarily a wear problem, NRR concludes that the i
South Texas licensee should have declared the MOVs inoperable when they were found to have been overstressed beyond 200% of the torque rating or 250% of r
the thrust rating.
Following internal actuator inspection, the licensee may have returned the MOVs to service if adverse wear or cracks were not found.
The licensee could also have prepared a justification for interim operation until the next available outage that would have allowed internal inspection.
A KO O
Samuel J. Collins 2
If you have any questions on this information, please contact me at 301-504-2722, or James A. Norberg, Chief, Mechanical Engineering Branch, at 301-504-3288.
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Jales E*.
icnarason, Director Di'rision of Engineering Office of Nuclear Reactor Regulation cc:
M. Wayne Hodges Albert F. Gibson Thomas 0. Martin Kenneth E. Perkins, Jr.
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05/24/93 15:58 5129728298 OG2 The Light comapany8 "'I"**** #'"l**'
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H.u. son Light:ng & Power May 18, 1993-ST-HL-AE-4453 File No.:
G02.04 10CFR2.201 Director, Office of Enforcement U.
S.
Nuclear Regulatory Commission Attention Document control Desk Washington, DC 20555 South Texas Project Units 1 and 2 l
Docket Nos. STN 50-498; STN 50-499 Reply to Notice of Violation for InsDection FeDert 93-08; Enforcement Action 93-047 l
Houston Lighting & Power Company (HL&P) has reviewed the l
Notice of Violation and submits the attached reply to Violation II, i
the violation not assessed a civil penalty.
HL&P's replies to violationu I.A.
and I.D.,
violations that were assessed a civil j
penalty, are being submitted to the NRC in a separate letter.
HL&P denies that the violation occurred.
Details of the j
denial are provided in the Attachment to this letter.
If you have any questions, please contact C.
A.
Ayala at l
(512) 972-8628 or me at (512) 972-7138.
L.
Rosen s
Vice President, Nuclear Engineering DNB/sr
Attachment:
Reply to Notice of Violation, Violation II It\\93 111.002 Project Manager on Behalf e.f the Participants in she south Texa. Propet gy l lN U
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ST-HL-AE-4453 File No. : G02.04-Page 2 c:
Regional Administra.c
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- V Rufus S.
Scott i
Nuclear Regula,o'.y :en. '. ssion Associate General Counsel 611 Ryan Plaza Orie F.Its 100 Houston Lighting & Power Company Arlington, TX 76r. -
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Box 61R67 Houstan, TX 7720s Project Manager U.S.
Nuclear Regulatory C a ke'
- v ion Institute of Nuclear Power Washington, DC 20555 operations - Records Center 1100 Circle 75 Parkway, #1500 J.
I. Tapia Atlanta, GA 30339-3064 Senior Resident Inspector c/o U.
S.
Nuclear Regulatory Dr. Joseph M.
IIendrie Comminnion 50 Dallport Lane P.
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Box 910 Bellport, NY 13713 Bay City, TX 77414 D. K. Lacker J.
R.
Newman, Esquire Durs'u of. Radiation Control Newman & Holtzinger, P.C.,
STE 1000 T6. 44 ' Department of Health 1615 L Street, N.W.
Ilta West 49th Street Washington, DC 20036 Austin, TX 78756-3189 D. E.-Ward /T.
M.
Puckett U.S.
Nuclear Regulatory Comm.
Cent.ral Power.snd Light Company Attn; Document Control Desk P.
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Box 2121 Washington, D.C.
20555 Corpus Christi, TX 78403 J.
C. Lanier/M.
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Lee City of Austin Electric Utility Department 721 Barton Springs Road Austin, TX 78704 K. J. Fiedler/M. T. liardt City Public Service P.
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Box 1771 San Antonio, TX 78296
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ST-ML-AE-4453 Page 1 of 2 Reply to Notice of Violation. Violation II I
I.
Statement of Violation II:
10 CFR 50, Appendix B, criterion XVI, states, in part, that measures shall be established to assure that conditions adverse to quality are promptly identified and corrected.
5 Contrary to the above, on February 2,
1993, the licensee i
determined that five STP Unit 1 Renidual Heat Removal suction isolation motor-operated valves had incurred torque loadings of up to 253% of the actuator qualified limit for up to 50
.l~
cycles, a condition adverse to quality, but failed to identify the full scope of the deficiency and take adequate corrective action.
specifically, the licensee concluded that the valves were operable based on valve internal inspections conducted during the previous outage, which recorded " excessive" wear on the worm gear (a component vulnerable to the effects of high torque).
The licensee developed no justification or basis consistent with the recommendations of the actuator vendor or information published by or for the users of motor-operated valves in the nuclear power industry for the continued application of torque values in excess of the qualified limit.
This is a Severity Level IV violation (Supplement I).
11.
Houston Liahting & Power Position:
HL&P denies that the cited violation occurred.
Specifically, HL&P contends that the Residual Heat Removal (RMR) suction i
isolation motor-operated valves (MOVs) were correctly determined operable and that the basis and justification for the operability determination was adequate.
In retrospect, HL&P admits that, although adequate, the basis i
of the operability determination could have been more fully, and more clearly documented.
In the future, MOV operability r
determinations will be guided by the use of a recently developed MOV Operability Checklist.
The use of this l
checklist should assure that the basis and justification of subsequent operability determinations are consistent and t
clearly documented.
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ST-HL-AE-4453 Page 2 of 2 Reniv to Notice of Violation, Violation II III.
Reasol_for Donial:
HL&P maintains that the operability determination performed on February 2,
1993 was correct and adequate because of the following:
1.
The MOVs operated successfully in the overtorqued condition since the Spring 1990 refueling outage (1RE02).
A minimal number of cycles were anticipated prior to the next outage (1RE05), when the MOVs were scheduled to be reworked.
2.
The MOV actuators were disassembled and inspected during the Fall 1992 fourth refueling outage (1RE04).
Although wear was noted, the wear was determined not to require immediate corrective action.
3.
The MOVs had been demonstrated to have acceptable thrust by Motor Operated valve Actuator Test system (MovATs) testing at the end of 1RE04.
The acceptable thrust values showed that the MOVs would have performed their intended safety function.
4.
Operability of the MOVs is not directly affected by overtorquing the actuator.
Overtorque could cause accelerated wear of the mechanical components in the actuator.
Accelerated wear could reduce the " life" of the actuator, but the accelerated wear does not necessarily render the MOV inoperable.
HL&P believes that the above listed information, when considered collectively, provided adequate basis and justification to support the determination on February 2, 1993, that the Unit 1 RHR MOVs were operable.
IV.
Additional Information:
The overtorque conditions on the Unit 1 RHR MOVs have been corrected.
The review of the Unit 2 RHR MOV test packages identified one MOV with a slight overtorque condition, which has also been corrected, tests.....ooz
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