IR 05000309/1988004

Insp Rept 50-309/88-04 on 880229-0304.Major Areas Inspected: Corrective Actions from IE Bulletin 85-003 That Addressed Improper Limit Switch & Torque Switch Settings in motor- Operated Valves,Including Engineering & Maint Activities

ML20154C814
Person / Time
Site:	Maine Yankee
Issue date:	04/19/1988
From:	Anderson C, Thomas Koshy NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
To:
Shared Package
ML20154C813	List: IR 05000309/1988004 ML20154C810
References
50-309-88-04, 50-309-88-4, IEB-85-003, IEB-85-3, NUDOCS 8805180328
Download: ML20154C814 (14)

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V.S. NUCLEAR REGULATORY COMMISSION

REGION I

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Report N /88-04 Docket N License No. DPR-36 Licensee: Maine Yankee Atomic Power Company, Edison Drive, Augusta, Maine 04336 Facility Name: Maine Yankee Atomic Power Station Inspection At: Augusta and Wiscasset, Maine Inspection Conducted: February 29 to March 4, 1988 Inspectors: / O T. Koshy, d Reactor Engineer date Approved by: C L C. J gAnderson, Chief, Plant Systems Section

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'date Inspection Summary: Inspection on February 29 to March 4, 1988

[ Inspection Report Number 50-293/88-04)

Areas Inspected: Special announced inspection to review the corrective actions that resulted from IE Bulletin 85-03 that addressed improper limit switch and torque switch settings in motor operated valves. This inspection reviewed the engineering and maintenance activities to assure the operational readiness of the motor operated valves. A previous reported licensee concern regarding contractor recommendations for torque switch settings was also reviewe Results: The licensee has addressed all the significant aspects of the bulletin. The corrective actions were properly coordinated by engineering with maintenance and operation One item remained unresolved at the end of inspection. This deals with the impact of valve seat wear and maintenance of limit switch setpoint for valves that are closed purely on limit. This is addressed in Section l

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8805180328 890511 PDR ADOCK 05000309 O DCD

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1.0 Persons Contacted Maine Yankee Atomic Power Company (MY)

• Boucher, Electrical Maintenance E. T. Boulette, Plant Manager L. A. Lawson, QA Section Head R. Lawton, Manager, Operations Support B. Lord, Sr. Operations Support Engineer

• J. Mathieson, Plant Superintendent '

• S. Morrison, Lead Maintenance Engineer , U.S. Nuclear Regulatory Commission (NRC)

R. Freudenberger, Resident Inspector C. Holden, Senior Resident Inspector

• Not present at the exit meeting 2.0 Purpose  !

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The purpose of this inspection was to review the licensee actions taken in response to IE Bulletin 85-03, Motor Operated Valve (MOV) common mode failures during plant transients due to improper switch settings and to j review a licensee identified concern regarding contractor recommendations '

for motor operated valve torque switch setting !

3.0 Background

On June 9, 1985, the Davis-Besse Plant experienced a complete loss of main I and auxiliary feedwater which was caused, in part, by MOV failures. This l event resulted in IE Bulletin 85-03 that promulgated NRC requirements to assure the operational readiness of MOVs in the high pressure coolant injection / core spray and emergency feedwater systems. The bulletin specified that licensees take the following action (a) Review and document the design basis for the operation of each valve, including the maximum differential pressure expected during the normal and abnormal operatio (b) Using the above data, establish the correct switch settings for torque, torque bypass, position limit and overload for each valve and perform the modifications as neede l l (c) Individual valves will be demonstrated to be operable by testing the l valve at the maximum differential pressure based on the performance I requirements. In the absence of differential pressure testing, a justification should be provide l s ,

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(d) Prepare and revise procedures to ensure that correct switch settings are determined and maintained throughout the life of the plan (e) Submit a schedule to accomplish the above program including a final l submittal with the results of (b) through (d).

Item (a) is currently under review by the NRC office of Nuclear Reactor Regulation, NR The scope of this inspection was to review items (b)

through(d). ,

The licensee utilized the services of MOVATS to establish the torque switch settings. These torque switches are set based on the required

, thrust to operate the valve. MOVATS provided these data from a proprietary data base of test data. These data are important as they assure the capability of the valves to perform their safety related function during normal and abnormal operation. At the time of this inspection, the licensee had completed valve testing and was in the process of developing a final response to the NR .0 Maine Yankee response to IE Bulletin 85-03 4.1 _ Status of Commitments In a letter dated June 4,1986 Ref: 2 Attachment-1, the licensee '

completed the documentation of maximum differential pressure expected across a MOV during normal and abnormal operatio In the same letter, the licensee committed to establish the correct switch settings by January 1, 1987. This commitment was met on December 22, 1986 and is documented in Ref. 3 Attachment 1.

The commitment for demonstrating the operability of the valves was .

July 1, 1987. This was accomplished by May 20, 1987, the recent j outage. The procedure to maintain the limit and torque switches was ;

completed by March 19, 1987, the commitment date was September 1, 1987. '

Maine Yankee has identified a few minor items to be completed within i 60 days after the next refueling outage. These relate to the thrust calculations and the resulting adjustments to the torque switche .2 Affected Valves The Motor operated valves identified for Maine Yankee IEB 85-03 {

consideration are listed in table l 4 '

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4.3 Switch Settings Item (b) of the bulletin requires that the correct switch settings for torque, torque bypass, position limit and overload for each valve be establishe These items are addressed below:

Open Torque Switch & Open Bypass Limit Switch This switch is normally used as a mechanical fuse to limit the mechanical thrust applied to the valve in the open direction. It generally provides no control function and is a protection device for some other valve related failure that may cause its need. This switch is usually bypassed during the initial valve unseating, which is the most challenging portion of the open stroke. Failure to set this switch to the required value or not bypassing this switch in the initial opening stroke, can cause valve failur The licensee does not torque seat the valve in the opening directio This has proven to be a good practice for valve performance. The licensee has elected to set the open torque switch to the maximum possible setting based on the limitations of the assembly. This is a conservative approach to have the highest confidence to open the valve even during an abnormal operation. As the valve is not backseated, the valve is not subjected to any undue strai The licensee has set the open bypass limit switch at approximately 10*i of the valve travel beyond the valve coming off the seat. This setting is sufficient to prevent the actuation of the opening torque switch in the initial spike of the opening torque switc This is an acceptable configuratio Close Torque Switch The close torque switch is used to stop the motor rotation on the completion of valve travel in the close direction. Since this switch provides a normal control function and is exercised on every closure stroke, this switch setting needs more careful consideration than for the open torque switch. The limiting requirement of the close torque switch is at the end of the closure stroke when the thrust requirements are the highest. The thrust at torque switch trip should equal the most limiting closure thrust requirement including the thrust needed to overcome the differential pressure across the valv Diff2rential pressure testing using process system pumps with appropriate data gathering and diagnostic evaluation is the positive means of assuring the adequacy of the torque switch set point. Other approaches based on similarity and analysis may also be acceptable with sufficient basi ,.- .-

Main Yankee has performed differential pressure testing for valves HSI-M-41 and HSI-M-42 using the services of MOVATS. The setpoints in these cases were developed based on the thrust required to operate the valve at the design condition plus 15 percent margin. The licensca collected the calculated thrust values from Limitorque, the manufacturer, and from MOVATS for all valves and has utilized the most conservative values with a suitable margin to set the torque switche For the valves that were not differential pressure tested, the MOVATs data base for similar and identical valve test data was used. M0 VATS has collected a substantial amount of valve test data for several types of valves. When there is sufficient data for a particular valve type, MOVATS calculates the thrust requirements statistically based on the available data points. This calculation is based on an equation developed using the 'best-fit' line drawn through the test data points. This equation is used to predict the additional thrust required to be overcome by the valve when subjected to the differential pressur To this value the normal running load thrust is added to obtain the required total thrust needed from the motor which is translated into the torque switch setpoin During the process of developing the thrust values MOVATS supplied l the following data to Maine Yankee for two identical valve l l

Document l Thrust Values for Valves (in LBS)

l Dated l CH - M - 1 1 CH - M - 87 l Open i Close j Open l Close IMin./ Ma Min./ Ma I letter Ref. 5 l l l l June 26, 1987 l 337 l 261 l l letter Ref 4 l l l l 337 l 261 June 17, 1987 l l l l l Tetter Ref. 6 l l 2252/2440 l l 12252/2440 September 23, 1987 l l l l l letter Ref. 7 l l l l l 3,956*

January 26 l l l l l

• Includes running thrust of 1705 lb .

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The references 4 and 5 addressed above did not indicate that the thrust values were based on limited test data. References 6 and 7 ;

indicated a substantial change in the closing thrust values. A concern was raised that the earlier data could have led to a non-conservative setting of the valves. The licensee set the torque switch to a conservative value, Presently the close torque switch is set for 10,500 lbs for CH-M-87 and 3,900 lbs for CH-M-1. This is substantially above the required calculated torque of 1,965 lbss the sum of maximum running thrust and the thrust needed to overcome the maximum differential pressure across the valv Close Torque Switch Bypass The close torque switch bypass acts in the same manner as open torque [

switch bypass; however, contrary to its counter part function, it ,

normally bypasses the torque switch during the lightest duty portion ~

of the stroke, the beginning of the closin0 stroke. The use of this ,

switch is not critical; however if utilized it should be set to l operate during the initial part of the strok Maine Yankee has adjusted this switch for 4 rotor valves to 95%, such ,

that the torque switch will not see the initial hammer blow in the '

opening stroke. For two rotor valves, this switch is set as per the bypass function needed for the open limit switch. No deficiencies were identifie ,

Open Limit Switch

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This switch provides the control function for determining the upper j limit of the valve stem travel in the open direction and stops the

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motor rotation by opening the circuit. The setting of this switch

must assure adequate valve opening and should prevent back seatin '

Valve backseats are normally to provide a seal that is redundant to

, the valve packing in order to allow valve packing replacement without the need to drain down the process system. Using the motor power to

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' backseat can and has caused valve stem shearing and stem thread twisting. Therefore it is important to set the open limit switch away from the back seat with enough margin to allow for motor

deenergization and inerti Maine Yankee has set the open limit switch such that the valve does not back seat by inertia. No problem was identified with this

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Close Limit Switch This switch is usually used with the close torque switch in series for over torque protection. For high speed operators, where torque switches cannot react in sufficient time, the close limit switch deenergizes the motor and the remaining inertia forces seat the valve,

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Maine Yankee has set this switch such that the valve seats closed or when valve position indicates closed. This setpoint is approximately within one percent of being on the seat. For two rotor limit switches,.

the closed limit switch will be set such that the valve does not sea This is because a cam operates the torque bypass functio See section 4.5 for an unresolved item on the setting of this switc Open Indicatio_n This signal is taken from close rotor limit switch actuation set very close to the end of valve closure. The same rotor is used for open torque switch bypass switch. The setting of the point where the rotor turns to actuate the switch has conflicting requirements. In the setting for ideal position indication, there is not adequate bypass of the torque switch to assure valve operability; conversely changes to satisfy the bypass requirement have resulted in false valve position indicatio Maine Yankee has elected to give precedence to the valve operability and set the limit switch based on toroue switch bypass. The operators are made aware of the fact that the valve movements continues a few seconds longer than what is indicated by the light. The inspector had no further question Close Indication The signal to indicate valve closed is usually taken from the open rotor actuation. This rotor turns 90 degrees at the end of the open i

stroke to indicate the closed position, The open rotor is usually set such that the valve does not back seat. There are no problems identified in the setting of this switch.

Maine Yankee has set this switch based on the open limit switch requirements, which is to prevent the back seating of the valv This configuration indicates the deenergization of the motor, When t

the light indication changes, the only movement left is the inertia of the valve. The inspector had no further questions.

l Thermal Overload Relay

Thermal overloads are used to protect motor winding insulation from breakdow Devices used appear to uniformly consist of heaters at the motor control center which trip a heat sensitive relay, the contacts of which either interrupt current to the contractor closure

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coil (which stops the motor) or initiate an overicad alarm, or bot l Where thermal overload relays stop operator motor rotation on tripping, l l

' the heaters must either be sized to prevent inadvertently stopping the motor or bypassed when motor operation is important to safet They should be sized to protect the motor windings from thertral damage. Regulatory Guide 1.106, thermal overload protection for electric motors on motor operated valves provices guide lines on the design criteria for thermal overload _ . _.- . _ _ _ . _

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Designs that are being used at this time to eliminate the threat of inadvertent motor trips include: (1) removing the heaters or relay contacts fro.n use; (2) using the relay contacts for alana only; (3)

bypassing the relay contacts during all operating modes except when a valve is being exercised for testing; (4) bypassing the relay-contacts only during the presence 1of an automatic safety actuation signal; and, (5) oversizing the thermal overload The Maine Yankee design utilizes the thermal overloads during normal and accident operation. Maine Yankee uses the following criteria in sizing the thermal overload . When carrying locked rotor cur ent, the thermal overload relay should actuate in a time within the motor's limiting time for carrying locked rotor curren . When carrying a current equal to nameplate full load current times the service factor, the motor should not trip in a time period less than twice the MOV stroking tim This approach adequately supports the operation of the valve during normal and abnormal operation. The inspector reviewed licensee calculation MYC-979, MOV Thermal overload heater calculation dated August 26, 1987 that covers all the bulletin valves. The inspector verified the field installed thermal overloads for HSI-M-4 and 4 The installation agreed with the required ratings established in the calculation. The inspector had no further question \

4.4 Demonstration of Operability This involves demonstrating the valve to be operable by testing the 1 valve under maximum differential pressure after changing the individual valve settings as appropriate based on the design base In the absence of testing wit' full differential pressure across the valve, a justification is to te provided. The use of M0 VATS data base to set the torque switches for a particulac type is considered as an acceptable approach to exclude differential pressure testing, provided this type of valve has sufficient test data to establish similarit However, a suitable test is needed to establish that the desired force is available at the seat for ciosur Maine Yankee has utilized the MOVATS equipment for demonstrating the operability of the valve Even though all valves were tested using the MOVATS equipment, only two valves, HSI-M-41 HSI-M-42, were tested with differential pressure across the valv For the remaining valves, the licensee used the predicted value from MOVATs' data base. The tests done at the desired setpoint confirmed that sufficient thrust is available for the operation of the valve The inspector verified the test and design records and confirmed that the torque developed at the seat exceeds the calculated requirements for valves HSI-M-11

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g and HSI-M-1 In certain cases, the licensee has elected to set the torque switches much higher than the required values. This is an acceptable approach since the valve operation is better assured and i that the licensee has given adequate consideration for equipment fatigue and structural limitations due to operation. The as-found '

and as-left values of torque switch settings and the total thrust developed were transmitted to the NRC in Ref: 1 Attachment-1. The inspector had no further' question .5 Maintenance-Procedures The bulletin requires that licensees prepare or revise procedures to ensure that correct switch settings are maintained through>>ut the life of the plant and also to ensure that applicable industry recom- i mendations are considered in the preparation of the procedur The inspector reviewed the procedures listed in attachment 2. The licensee had revised these procedures for mair.taining the limit and torque switch settings. The specific instruct'ons on installirg and :

setting limit and torque switches did incorporate the industry '

recommendations. As the plant was operating at full power, access to these valves was limited. However, the limitorque compartment for two valves HSI-M-54 and HSI-M-55 was opened up for inspectio The I torque and limit switch cnntacts appeared to be clean and free from corrosion and pitting. The inspector verified the control wiring to l be in conformance to the stated licensee criteria communicated to NRC l in Ref: 1 in Attachment 1. The licensee technicians were knowledge- )

able in the manual operation of the valve j l

The inspector observed a minor discrepancy on the close torque switch set poin The observed value was 3.0 whereas the required value was 4.0. The licensee took prompt measures to determine the potential cause of this anomaly. All the valves that were tested with the MOVATS equipment had documented evidence (test data) to support the adequacy of the torque switch set point. Eight of these valves were reworked. The licensee inspected all of these valves. The observed values of the set points were within the achievable values of the- 1 setting device except for SIA-M-54. The close torque switch was set l at 3 instead of 4, the required setpoint. The licer.see thoroughly !

examined this problem and found out that the spring pack assembly of the MOV has become soft. It cannot be set at the desired setpoint with the existing spring pack. The licensee plans to replace this spring pack and set the torque switch at the desired setpoint. The softening and hardening of the limitorque spring pack is a newly observed problem using the present day diagnostic equiprant. This phenomena can be identified during diagnostic checks. However, there is not enough industry experience to predict this type of proble .

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As a result of this bulletin, the testing and the trending of the test results at various licensees may provide better methods to detect and prevent this problem. Even though this phenomena influences

the operation of the valve, the margins built into the setpoint, provide a reasonable assurance of valve operability. The inspector had no further question Four of the valves that 'are cevered under the bulletin are closed using the limit switch. The valvas are'HSI-M-50, HSI-M-51, CS-M-91 and CS-M-92. When the closing of valve motion is terminated using a signal from the limit switch, the residual energy is only the moment of inertia, which drives the valve into full closure. It requires a precise setpoint for the limit switch such that there is sufficient inertial forces lef t in the equipment to seat the valve adequatel The licensee procedure 5-18-1 referenced in attachment 2 lacks specific instruction to precisely set this close limit switc Such precision is not needed for valves that are seated using the torque switch, as the torque switch takes over the control of the final stroke of the valve and the motor is stopped after sufficient torque is developed on the seat. There is no immediate concern on the present setting of ,

these valves because the MOVATS test records indicate a sufficient i thrust development on the seat. The licensee's management agreed to address this problem for long term maintenanc Another rel ~d concern on the same type of valve is the influence '

of wear or valve seat. The motor will get a signal to shut off ,

the limit sw .ch at a definite point during the closing stroke based l on the limit switch setpoint. If the valve seat suffers erosion or i any type of wear, the inertia force available af ter the motor shuts off may not be sufficient to seat the valve adequately. This is an unresolved item pending NRC review of the licensee action to precisely set the close limit switch and to assess the influence of seatwear on valve closure for valves that are closed using only the limit switch

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(50-309/88-04-01).

The licensee currently plans to buy M0 VATS test equipment for valve j maintenance. The proposed valve maintenance program is addressed in '

licensee letter Reference 1 in Attachment ,

i 4.6 Independent Calculations The inspector performed independent calculations to verify the technical adequacy of the licensee calculations on thermal overload sizing and protection. No deficiencies were identifie ... . .- . - ~

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l 5.0 Conclusions The licensee has addressed all the significant aspects of the bulleti The commitments communicated to NRC in the references (Attachment 1) were verified to be met. Engineering and maintenance have taken special training for addressing the concerns addressed in'the bulletin. Based on the review of the licensee activities, it was concluded that there is reasonable assurance that the valves covered under the bulletin can

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perform their safety-function during normal and abnormal operatio .0 Unresolved Items Unresolved items are matters for which more information is required in order to ascertain whether they are acceptable, violations, or deviation One unresolved item is discussed in section 4.5 of thii repor .0 Exit Interview ,

At the conclusion of the inspection on February 5,1988, the inspector met with the licensee representatives, denoted in section 1.0. The ,

inspector summarized the scope and findings of the inspection at that :

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l Attachment - 1 REFERENCES 1. Licensee letter from John B. Randazza to USNRC Region 1 to the attention of William T. Russell dated December 15, 198 . Licensee letter from John B. Randazza to USNRC Region 1 to the attention of Thomas E. Murley dated June 4,198 . Licensee letter from G. D. Whittier to USNRC Region 1 to the attention of Thomas Murley dated December 22, 198 . MOVATS Letter from Rod Eslinger to Bruce Lord, Maine Yankee dated June 17, 198 . MOVATS Letter from Rod Eslinger to Bruce Lord, Maine Yankee dated June 26, 198 . MOVATS Letter from Susan Morlan to Maine Yankee Atomic power company to the attention of Bruce Lord, dated September 23, 1987 l MOVATS speed letter from Rod Eslinger to Bruce Lord Maine Yankee Atomic Company dated January 26, 198 . - - _

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Attachment - 2 1. Procedures 5-18-1 Revision 5 Limitorque operator electrical checkout and adjustment 5-18-2 Revision 8 Limitorque operator removal and installation 5-18-4 Limitorque operator overaul (SM8000 and SMB00)

5-18-5 Revision 2 Limitorque operator overhaul (SMB 0 through SMB4)

3-5-99 Oraf t measurement of limitorque motor operator motor load Drawings 11550-FE-120 Revision 8 electrical wiring drawing 11550-FE-12E Revision 9 electrical wiring drawing 11550-ESK-6BN Revision 5 elementary diagram 480VMCC 11550-ESK-6BQ Revision 6 elementary diagram 480VMCC

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