ST-HL-AE-2385, Final Part 21 & Deficiency Rept Re Actuator Motor shaft-to- Pinion Keys Which Sheared Due to Incorrect or Defective Matl.Initially Reported on 870917

Final Part 21 & Deficiency Rept Re Actuator Motor shaft-to- Pinion Keys Which Sheared Due to Incorrect or Defective Matl.Initially Reported on 870917

ML20235Y990
Person / Time
Site:	South Texas
Issue date:	10/15/1987
From:	Goldberg J HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
REF-PT21-87, REF-PT21-87-180-000 PT21-87-180, PT21-87-180-000, ST-HL-AE-2385, NUDOCS 8710200555
Download: ML20235Y990 (2)

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i October 15, 1987 ST-HL-AE-2385 File No.: G12.402, G2.2 10CFR50.55(e)

U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555 South Texas Project Units 1 and 2 Docket Nos. STN 50-498, STN 50-499 Final Report Concerning Actuator Motor Shaft-to-Pinion Keys On September 17, 1987, HL&P notified your office, pursuant to 10CFR50.55(e), of an item concerning actuator motor shaft-to-pinion keys which sheared due to incorrect or defective material. Attached as our Final Report is a copy of our previously submitted Licensee Event Report on this item.

HL&P has determined that this item is reportable pursuant to 10CFR50.55(e) ,

(Unit 2 only) and 10CFR21.

If you should have any questions on this matter, please contact Mr.

J. S. Phelps at (512) 972-7071. 1 J. H. Goldberg '

Group Vice Presi ent, Nuclear h l JSP/hg y 05::-

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Attachment:

Final Report Concerning (Licensee Event e i Report) Actuator Motor Shaft-to-Pinion Keys >$

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.c-U1 8710200555 071015 PDR ADOCK 05000499 S PDR L4/NRC/mt I

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' Regional Administrator, Region IV -

Nuclear Regulatory Commission

.611 Ryan Plaza: Drive, Suite 1000 Arlington, TX 76011 N. Prasad Kadambi, Project Manager U.S. Nuclear Regulatory Commission 7920 Norfolk Avenue Bethesda, MD 20814 Dan R. Carpenter Senior Resident' Inspector / Operations e/o U.S. Nuclear Regulatory Commission P.O. Box 910 l Bay _ City, TX 77414 l l

Claudo E. Johnson i Senior Resident Inspector / Construction c/o U.S. Nuclear Regulatory Commission P.O. Box 910-Bay City, TX 77414 J.R. Newman, Esquire Newman & Holtzinger, P.C.

1615 L Street, N.W.

-Washington, DC 20036 R.L. Range /R.P. Verret Central Power & Light Company P. O. Box 2121 Corpus-Christi, TX 78403 M.B. Lee /J .E. Malaski City of Austin P.O. Box 1088 Austin, TX 78767-8814 R.J. Costello/M.T. Hardt City Public Service Board ,

P.O. Box 1771 i San Antonio, TX 78296 I Revised 10/15/87 l'

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On August 17, 1987 at approximately 1735 hours0.0201 days <br />0.482 hours <br />0.00287 weeks <br />6.601675e-4 months <br /> a normal Essential Cooling ,

WLter (ECW) System startup was being performed when the ECW pump 1B tripped I after having been started for approximately ten (10) seconds. Immediate investigation indicated that the motor operated discharge valve did not fully ,

open due to a sheared actuator motor shaft-to-pinion key. The actuator is a  !

Limitorque SMB-0-25 motor operator. During April of 1987 a similar key l failure occurred in the C train ECW discharge valve motor operator.

Metallurgical analysis indicated that ECW valve keys failed as a result of the key materials not being consistent with the material specified by Limitorque.

The project judged that other valve operators of this type were suspect and an evaluation has been performed of other Limitorque actuator models used in safety related applications at South Texas. The keys have been replaced in each SMB-0-25 motor operator in Unit 1 (a total of twelve operators). i s .

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DESCRIPTION OF OCCURRENCE:

I On August 17, 1987 at approximately 1735 hours0.0201 days <br />0.482 hours <br />0.00287 weeks <br />6.601675e-4 months <br />, prior to the receipt of the l Operating License NPF-71'for the South Texas Project (STP) Unit 1,'a normal Essential Cooling Water (ECW) system startup was being performed when the ECW IB pump tripped after having been running for approximately ten (10) seconds. )

The ECW pumps are designed to trip automatically if the pump discharge valve /

does not fully open within a set time delay. The ECW system consists of.three identical independent -safety traitis that provide the. ultimate heat sink for normal plant operating loads as well as essential loads in the event of an accident.

An.immediate investigation revealed that the motor. operated discharge valve had not fully opened in the required time. Adelitionally, the valve could not be closed by operation of the control room handswitch. Maintenance personnel disassembled the operator and found that the motor pinion gear had twisted out of position on the motor shaft. The key which mechanically connects the motor shaf t to the actuator pinion gear was found to be split longitudinally into two pieces.- The' pinion gear. setscrew had scored the motor shaft and no longer ,

held the pinion gear in place. '

The failed valve actuator'is a Limitorque SMB-0 vbich delivers 25 foot-pounds of starting torque (SMB-0-25). The motor operator is mounted on a Hills-McCanna (Rockwell) 30" butterfly valve. The torque switches for the valve operator are jumpered out by design; however, the limit switches are

. flinctional . The limit switches were confirmed to have been set such that the switches actuated to avoid excessive force on the valve seats.

During April of 1987, a similar key failure had occurred in the C train ECW discharge valve motor operator. .At that time, a review ~by Limitorque and the

. project' concluded that this was an isolated defective key failure and the key

-was replaced with a key from the corresponding Unit 2 valve operator.

The' broken key from the ECW 1B valve was sent to a metallurgical laboratory for analysis. The preliminary results, which were obtained on August 26, 1987, indicated that the key failure did not appear to be the result of

, fatigue. Additionally, it was determined that the material was not consistent

. with AISI 1018 requirements which Limitorque had recently identified as the l appropriate key material. The keys in the operators provided to STP were not described in detail in the STP purchase documents or in Limitorque Instruction Panuals.'

As a precaution, all three ECW disc'harge valves were placed in their safety (open) position and the three ECW trains were started. This was done to prevent potential key failure from impacting continued availability of th'e ECW trains. ,

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, On' August 28, 1997 after review of the final metallurgical report which was

. 'obtained:st approximately 1430, the project determined that other valve operators of this type (SMB-0-25), as well as those with larger motors with Limitorque. supplied keys, should be considered suspect. The affected safety-related, valves with suspect keys were placed in the " safe" position.

Inspection and replacement of. keys in each SMB-0-25 motor operator was initiated. .This included the t!ree ECW discharge. valves and three valve motor

-operators in each of the three Component Cooling Water (CCW) trains (a total of twelve SMB-0-25. operators).

The NRC was' notified of a reportable condition pursuant to 10CFR50.72(b)(2)(iii) at 1748 hours0.0202 days <br />0.486 hours <br />0.00289 weeks <br />6.65114e-4 months <br /> on August' 28, 1987. ,

Limitorque Corporation personnel performed a Motor Operated Valve (MOV) field

-diagnostic test on September 3, and 4,1987 on a sample of the valves in question and determined that the MOV loads were well within design limits.

Limitorque indicated that the key failures were not the result of excessive torque iciads in the operator gearing.

Inspection of'the three keys withdrawn from the ECW valves in late August identified one additional split. key (the setscrew had been holding the pinion i

gear in. place) ar.d two which showed deformation characteristic of the.

initiation of a similar failure. These keys were also metallurgically analyzed,'and this analysis again, showed that the key material was either defective or not AISI 1018 material. Two of the keys exhibited a thermal-history that typically lowers the strength and hardness of low carbon steel.

hased -on, the valve diagnostic test results and akstallurgical analysis, it' was hnoludedthattheultimatecauseofthefailureswasimproperordefective Xtyy material. When this conclusion was established the project determined nat the condition was reportable pursuant to 10CFR21 and notified the NRC accordingly on September 17, 1987.

C&LSE OF OCCURRENCE:

The results of the metallurgical analyses on trie failed key from the ECW 1B

. valve, the replacement key (obtained from a Unit 2 valve) and the keys from the other two ECW valve actuators indicated that they were either defective or were not AISI 1018 material (the required key material identified by

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.Limitorque).

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The commonality (i.e. keys of the same size and material) between SB-0-25 and SMB-0-25 Model Limitorque actuators was apparently overlooked during previous investigations of sheared key problems. In 1983 Westinghouse identified _a potential substantial safety hazard related to sheared pinion keys in Limitorque Model SD-0-25 motor operators. Keys in the Westinghouse supplied SB-0-25 actuators were replaced by Westinghouse prior to shipment to STP.

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, 7, ANALYSIS OF EVENT: '

F Defective and. incorrect key baterial'in the pump discharge. valve:of each train l --

, of tho'ECW system'couldjhave prevented the fulfillment of the safety function:

l of the' system which is_to provide the ultimate heat sink in accident.

3- . conditions. As such,lthis condition was reportable. pursuant'to 10CFE50.73(a)(2)(v)'and 10CFR50.73(a)(2)(vii). This: item was'also doterrined to be reportable pursuant to 10CFE21 due to the generic. implications of common.

>>a' ' mode failure of'SMB-0-25 key failures in each train of the ECW system. .. This

! . condition was also determined to be reportable pursuant to 10CFE50.55(e).on.

? STP Unit 2. i L-l The failure of pinion gear keys has occurred at STP on Model SMB-0-25

-actuators only.- Other Limitorque actuator model's used in safety-related ~l applications:were reviewed as part of this evaluation'. Larger Limitorque actuators with starting torques greater than or equal to 100 foot-pounds were

.previously inspected-(for an unrelated. construction phase concern) and

-certified AISI 4140 key' material was confirmed to have been installed.

.Limitorque actuator models other than SB-0-25 or SMB-0-25 with starting

' torques less than 100 foot-pounds were evaluated based on key. size' and applied operating stresses and were determined to be unaffected by this failure mode.

CORRECTIVE ACTION:

• The corrective actions taken and planned as a result of this event includes o The iteys for the three ECW valves have been replaced with keys of certified AISI.,1018 steel obtained from Sukor Products. The documentation of this

'7 work is not yet complete.

o The keys for the nine other SMB-0-25 actuators in the CCW system have also been replaced with certified AISI 1018 material.

+. .,

o A' sample of other Limitorque actuator models that have less than

'25 foot-pounds starting torque will be inspected by mid-November, 1987, as an additional precaution.

c' Key material 11:the twelve Unit 2 valves with SMB-0-25 actuators will be  !

replaced prior to fuel load of Unit ?.

ADDITIONAL INFORMATION:

There have been no previous failures of pinion keys in other Limitorque actuator models at STP. .

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.NL.LER87003 33....

, ATTACHMENT ST-IIL- AE-2 38 5 '

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September 26, 1987 ST-HL-AE-2368 File No.: G26, G12.402

,. 10CFR50.73 10CFR21 10CFR50.55(e)

U. S. Nuclear Regulatory Commission Attentions Document Control Desk Washington, DC 20555 South Texas Project Unit 1 & 2 Docket Nos. STN 50-498, STN 50-499 Licensee Event Report Regarding Actuator Motor Shaft-to-Pinion Keys Sheared Due to Incorrect and Defective Material Pursuant to 10CFR21, 10CFR50.73, and 10CFR50.55(e), Houston Lighting &

Power Company (HL&P) submits the attached Licensee Event Report (LER 87-003) regarding actuator motor shaft-to-pinion keys which sheared due to incorrect and defective material.

If you should have any questions on this matter, please contact Mr. C.A. Ayala at (512) 972-8628.

cd J' G. E. Vaughn Vice President l Nuclear Plant Operations i G"V/CAA/smq

Attachment:

Licensee Event Report Regarding Actilator Motor Shaf t-to-Pinion Keys Sheared Due to Incorrect and Defective Material.

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, Page 2 of*6 p ' i Houston Ug)1 ting, & Power Company - September 26, 1987 t ,

ST-HL-AE-2368' i

File No. G26, G12.402

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-Regional Administrator, Region IV H.B. Lee /J.E. Malaski 'l

- ' Nuclear. Regulatory Commission City of. Austin j 611-Ryan Plaza Drivei Suite 1000- P.O. Box 1088 . ,

' Arlington, TX .76011 Austin, TX' 78767-8814 N. Prasad Kadambi, Project Manager A. von Rosenberg/M.T. Hardt U.S. Nuclear'Regulat'ory Commission City Public Service Board 7920 Norfolk Avenue P.O. Box 1771 Bethesda,.KD 20814 San Antonio, TX 78296 i

Dan R. Carpenter Advisory Committee on Reactor Safeguards Senior Resident Inspector / Operations U.S. Nuclear Regulatory Commission c/o U.S. Nuclear Regulatory 1717 H Street Commission. Washington, DC 20555 P.O. Box 910:

Bay City, TX 77414 Claude E. Johnson Senior Resident Inspector / Construction c/o U.S. Nuclear Regulatory Commission P.O. Box 910 Bay City,zTX 77414= l M.D. Schwarz, Jr., Esquire Baker & Botts one Shell Plaza Houston, TX 77002 J.R.' Newman, Esquire-Newman & Holtzinger, P.C.

1615 L Street,'N.W.

Washington, DC 20036 R.L. Range /R.P. Verret Central Power & Light Company

.P.O.-Box 2121 Corpus Christi, TX 78403 d J

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