IR 05000454/1990011
| ML20034B550 | |
| Person / Time | |
|---|---|
| Site: | Byron  |
| Issue date: | 04/16/1990 |
| From: | Danielson D, James Smith NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | |
| Shared Package | |
| ML20034B542 | List: |
| References | |
| 50-454-90-11, 50-455-90-10, GL-89-10, IEB-85-003, IEB-85-3, NUDOCS 9004270333 | |
| Download: ML20034B550 (12) | |
Text
F
.
.
!
.
.
.
.
U. S. NUCLEAR REGULATORY COMMISSION REGION 111 Report Nos.: 50-454/90011(DRS);50-455/90010(ORS)
00cket Hos.: 50-454; 50-455 License Nos.: NPF-37; NPf-66 Licensee: Commonwealth Edison Company Post Office Box 767 Chicago, IL 60690
. Facility Name:
Byron Nuclear Power Station - Units 1 and 2 Inspection At: Byron, IL 61010-9750 Inspection Conducted: March 26-30, 1990 Inspector:
.
I 4-/g.-94 f
. F. Smith
'
Date Approved By: eITJ7-Lb,s(tt. (#
&/10 D. H. Danielson, Chief Date 11aterials and Processes Section Inspection Summary Inspection on March 26-30. 1990 (Report Nos. 50-454/90011(0RS); 50-455/90010(0RS))
Areas Inspected: Routine announced safety inspection of inservice testing UST) of valves with emphasis on setting and testing switches on motor operatedvalves(MOVs). Areas inspected included responses to IE Bulletin (IEB)
85-03andinitialworkwithGenericLetter(GL)89-10.
Result _s_:_
Within the areas inspected, no violations were identified. When a technical omission concerning MOV switch setting was identified by the inspector, corrective action was promptly initiated by the licensee's staff.
As a result of this inspection, the following conclusions were drawn:
The licensee has properly implemented the action required by IEB 85-03.
- The licensee is progressing toward implementation of GL 89-10 in an acceptable manner.
'
Personnel associated with the testing of MOVs and setting of switches appear to be competent and well trained.
- The licensee has demonstrated a strength in staff competence; however, this strength may mask a potential weakness in procedures because they are not being written in the same detail as would be required for less experienced personnel.
l
9004270333 900416 DR ADOCK 0000
f
^
.
.
.
,
..
>
DETAILS
!
1.
Persons Contacted I
Coninonwealth Edison Company (Ceco)
-
- R. Pleniewicz, Station Manager
- S. Barrett, Radiation Protection Supervisor
- D. Berg, Nuclear Safety
- R. Branson, MOV Coordinator
'!
- R. Campbell, MOV Coordinator
- E. Falb, Master Electrician
- R. Flahive, Technical Staff Supervisor
- T. Higgins, Assistant Superintendent. Operations
- W. Pirnot, Operating Experience Administrator
- T. Schuster, Nuclear Licensing Administration
- G. Schwartz, Production Superintendent
- D. St. Clair, Assistant Superintendent, Work Planning
- D. Winchester, Nuclear Quality Program Superintendent
>
- D. Wozniak, Project Manager
- E. Zittle, Regulatory Assurance Staf f U. S. Nuclear Regulatory Commission (U. S. NRC)
,
- W. Kropp, Senior Resident inspector
- R. Sutphin, Resident Inspector
- Denotes those present at the exit interview on March 30, 1990.
2.
Licensee Action on IE Bulletins (73756)
'
(Closed)IEBulletin 85-03 (454/85003-BB; 455/85003-BB): Motor Operated Valve (MOV) Common Mode Failure During Plant Transients Due to improper i
Switch Settings, n.
Limitorque Operated, Rising Stem, G6te and' Globe Valve Switch Setting
.
Evaluation
IE Bulletin (IEB) 85-03 concerns the proper setting of switches controlling the operations of MOVs.
Item b. of the bulletin requires that correct switch settings be established; Item c. requires differential pressure testing areferably, or other justification to demonstrate operability with tie settings from item b.
IEB 85-03 has been superseded by Generic Letter (GL) 89-10 and subsequently, the bulletin requirements will be encompassed by the actions taken to address GL 89-10; however, inspection of the licensee's IED 85-03 MOV program was conducted to ensure that the
!
licensee had, in fact, addressed the bulletin adequately.
l f
.
(-
-
.
.
-
.
.
..
Below is a list of the switches involved and concerns for their
.
"
proper setting, typical setting approaches that he,ve been taken in the industry, and either the resolution adopted at Byron or an identification of the need for additional information or other action. The switches are:
Thermal overload relay
- Open torque switch
- Close torque switch
Geared limit switch
- Open limit
- Open indication
- Open torque switch bypass
- Close limit
- Close indication
- Close torque switch bypass-(1) Thermal Overload Relay Discussion: Thermal overloads are sometimes used to protect motor winding insulation from breakdown. Devices used consist ofheatersatthemotorcontrolcenter(MCC)whichtrip_aheat sensitive relay, the contacts of which either interru to the contactor closure coil (which stops the motor)pt current or initiate an overload alarm, or both. Where thermal overload relays stop operator motor rotation on tripping, the heaters must either be sized to prevent inadvertently stopping the motor, or bypassed when motor operation is important to safety.
Site Specifics: Thermal overload switches used on MOVs~at-Dyron are not bypassed during normal operations. However, the thermal overload devices are sized in accordance with Station NuclearEngineeringDepartment(SNED)DesignGuide#26,which is the CECO Corporate Guide. That guide provides for selection of a thernel overload which will carry locked rotor current for the muimum time possible before tripping to protect the motor. The configuration is consistent with the information presented in Regulatory Guide 1.106, " Thermal Overload protection for Electric Motors cr Motor Operated Valves," and is
.
.
. _.
-. _ -
-
,
.
,
i
acceptable. The licensee indicated that the advantages of the more conservative configuration of bypassing the thermal overloads during normal operation were recognized and that
conversion to this method will be considered in the near future.
-
(2) Open Torque Switch (TS)
Discussion:
This switch is normally used as a mechanical fuse
to limit the mechanical thrust applied to a valve or operator
,
when stroking the valve in the open direction.
It generally provides no normal control function and.is a backup for some other failure that may require its need.
If the switch is
.
used, it must be set properly to enable the valve operator to
!
apply adequate thrust on the valve stem to operate the valve
'
againstthelimitingdifferentialpressure(dp).
Site Specific: The open-torque switches used at Byron are bypassed for 20% or more of the valve stroke.to assure that the
-
disk will pull out of the seat with the unrestricted thrust of the operator. At the end of the open stroke, the torque switch provides only a backup function to stop the stroke and to prevent damage in the event of a failure of the normal control i
switch.
During the period when the torque switch is operational, it l
must be set to accommodate the loads imposed on the valve by i
the high 3ressure and high flow of.the system. Thrusts required
,
to meet t1ese requirements were provided by the MOV vendor and testing was conducted by the licensee using the Valve Operation TestandEvaluationSystem(VOTES)equipmenttoensurethatthe valve achieved the desired results. The NRC inspector reviewed a sample of test data and confirmed that the valves met the desired thrust in accordance with the approved program.
(3) Close Torque Switch Discussion: The close torque switch is normally used to stop motor rotation on the completion of valve travel in the close direction. The limiting requirement for closure is at the end of travel when the thrust requirements are highest. The thrust at torque switch trip should equal the most limiting closure
,
"
thrust requirement including the thrust needed to overcome the
,
dp across the valve.
Site Specifics: Most valves covered by IEB 85-03 close with the
,
torque switch interrupting travel when a specified seating
.
torque has been applied.
This is the conventional configuration and is considered acceptable. Some valves close without the use i
of the torque switch at the advice of the valve manufacturer.
l However, the initial setting of the limit switch for these
-
r
.
l L
_ __
.
.
.
..
valves is derived from seating the valve under control of the torque switch. This, too, is an acceptable configuration.
Additional discussion of this subject appears in the description of the close limit switch.
(4) Open Limit Switch Discussion: This switch provides the control function of determining the upper limit of valve stem travel in the open direction and stops motor rotation by opening the circuit to the associated motor contactor coil. The setting of this switch mest provide an adequete valve stroke but, normally, must prevent backseating. Deliberate backseatint using the power of the motor-operator, or motor inertia, can and has caused valve stem shearing, stem thread twisting, and valve bonnet metal working until stem scoring and packing blowout occur. Hence, it is important to set the open limit switch away from the backseat and with enough margin to allow for motor contactor dropout time and inertia.
Site specifics: The open limit switches were set to open at 7% to 10% prior to the valve hitting the backseat. VOTES equipment and manual verification was used at Byron to ensure that no uncontrolled backseating occurred. The NRC inspector reviewed test data and current switch setting procedures.
Valves in the bulletin program were confirmed to be adjusted to prevent backseating.
(5) Open Indication (Limit Switch)
Discussion: Open indication is usually identified by a red light that goes out only when the valve is fully closed.
Sometimes the same rotor is used for both the open indication and the open torque switch bypass. This may cause problems because of conflicting requirements for the two functions. In setting the switch for ideal position indication, there is no adequate bypass of the torque switch to assure valve operability; conversely, changing the switch to satisfy the bypass requirements can result in false valve position indication.
Site Specifics:
At Byron, limit switches are of the four rotor type. The use of the four rotor switch climinates problems that can arise from the conflicting requirements noted above. The open indication switch operates shortly after valve unseating.
This configuration provides accurate indication of valve-position.
No problems were noted with this configuration.
a
.
4.
.
.
k (6) Open Torque Switch Bypass Discussion: When an open torque switch is used, the bypass switch is required to function during the initial portion of the opt.n stroke 50 that the torque switch will not prematurely stop valve stem travel due to the high torque conditions required for initial stem movement. There is no clear answer on where to set the bypass; but, if the valve disk (not the stem) has moved between 10% and 20% of its total travel distance away from the seat when the bypass opens, this has been accepted as adequate.
Site Specifics: The open torque switch bypass at Byron is set at 20-30%'6T 31sk travel in the open direction. The torque switch is operational for the remainder of the stroke. There are norn311y no high loads to challenge the torque switch in the remainder of the stroke, so it remains in the circuit primarily to backup the open limit switch in case of failure.
(7) Close Limit Discussion: The close limit switch is not often used on rising stem valves. When it is utilized, it is usually related to a special application and takes the place of the close torque switch by opening the motor circuit at the end of valve closure.
Site Specifics: Most NVs at Dyron operate in the conventional torque switch closure mde, and this is an acceptable configuration. However, some valves have their paint of closure determined by the close limit switch. The licensee indicated that the valves controlled in this manner were set up this way at the recommendation of the valve manufacturer. Settings are made relative to stem nut deflection or spring pack compression in accordance with the recommendations of the manufacturer.
Both methods are related to torque and thrust. Thrust values-are confirmed by VOTES testing and the MOV switch settings are corrected to ensure that thrusts developed are within the acceptable winoow.
The licensee indicated that experience with this method showed fewer long term problems than were observed with closure on torque switches. This appears to be an acceptable configuration.
(8) Closed Indication i
Discussion:
Closed indication is usually identified by the-
'
presence of a green light that goes out only when the valve is-fully open. This function is usually derived from the same rotor as the open limit switch, and while concern exists for the setting of the open limit, no problem has been identified with the
corresponding closed indication light switch.
,
I
.
i
.
.
~
Site Specifics: There was no concern for this switch setting based on discussions with the licensee.
Byron has set the l
switch based on the open limit switch requirements (7% to 10%
i from the backseat).
(9) Close Torque Switch Bypass
Discussion: This close torque switch bypass acts in the same i
manner as the open torque switch bypass; however, contrary to its counterpart function, it normally bypasses the torque switch l
during the lightest duty portion of the stroke.
If utilized, it
should be set to operate during the initial part of the stroke.
Site Specif_ics: The close torque switch bypass switch is activated by the same limit switch rotor as the open indication.
It bypasses the_close torque switch on initiation of the stroke, then permits the torque switch to be operational for the remainder of the stroke through the seating of the disk.
Procedures at Byron address the setting of these switches and there were no problems noted with this configuration.
b.
Testing of Motor Operated Valves The NRC inspector witnessed the performance of Surveillance No.
2BHS XLT-2, Unit 2, "Limitorque Valve Operator Diagnostic Test on B02CC-9473h-LOS." The testing of the 150#, 16" Velan Gate Valve with Limitorque SMB operator on the CC PP discharge header cross tie was performed using the " Valve Operation Test and Evaluation System" (VOTES) in accordance with procedure 2BHS XLT-2, Revision 2, dated Decenber 3,1989.
The test was performed on schedule and without incident. The resulting data were analyzed for compliance with established criteria and found to be acceptable. The VOTES provides a computer generated record of the test which may be recorded on a floppy disk and reproduced in its entirety for later reference. The data provided is similar to that provided by other systems in the areas of motor current and switch operation, but provides a different thrust pattern for opening and closing because the signal is derived from a strain gauge mounted on the valve yoke. The signal is indicative of the yoke strain, which is, in turn, related to the stem load and the thrust.
This system provides a continuous stem load from full negative to full positive readings, without the " Dead Zone" near zero thrust, typical of methods which derive their signal from spring pack compression. As with other MOV analysis methods, hard copies of all data may be obtained from the disks.
c.
Administrative Control of MOV Testing and Surveillance The NRC inspector confirmed that administrative controls were in place to cover the maintenance operations which affect the settings I
.
.
.
.
,
of switches in MOVs. The inspector reviewed selected portions of these documents for general content and for compliance with the requirements (,f IES 85-03 and GL 89-10. This review covered the documents listed below.
- Limitorque Valve Operator Inspection," 1 BHS EQ-27, Revision 1,
dated September 3, 1988.
"Limitorque Valve Operator Signature," 1 BHS XLT-1, Revision 0,
dated r bruary 3,1987.
e
"Limitorque Valve Operator Diagnostic Test," 1 BHS XLT-2,
Revision 2, dated December 3, 1989.
"Limitorque Valve Operator Rotary Geared Limit Switch
Maintenance," BHP 4200-37, Revision 5, dated October 25, 1989.
"Limitorque Valve Operator Torque Switch Maintenance," BHP 4200-39,
Revision 7, dated January 3,1989.
"Limitorque Valve Operator Electrical Checkout," BHP 4200-41,
Revision 5, dated January 7, 1988.
" Preventive Maintenance for Motor Operators for Valves," BHP 4200-69,
Revision 1, dated December 21, 1988.
"Limitorque Valve Operator Motor Replacement," BHP 4200-103, Revision 2, dated May 19, 1989.
" Thermal Overload Relay Testing," 1BHS OL-1, Revision 1. December -
1990.
No violations or deviations were noted.
The NRC inspector also reviewed " Guidelines for Motor Operated Valve (MOV) Testing, Maintenance, and Evaluation," N0D-MA.1, Revision 1, dated March 31, 1989. Although the inspector had several comments concerning this document, they are not included in the report because the guidelines are a corporate document rather than a plant procedure.
Because of this, the guidelines are not under the exclusive control of the Byron Station. The comments were forwarded to the appropriate organization for information, d,
Position Indicating Light Test Procedure 1BVS 0.5-2.MS.3, Revision 3, " Main Steam System Valve Indication Test Limits," Revision 3, dated October 7, 1987, was reviewed to determine measures taken to ensure that valve stroke times taken from the control room accurately reflected the actual
r
.
.
,
i
-
.
.
,
valve stroke time. The concern in this case was that the position
,
indicating lights were on switches that were actuated at positions I
remote from the extremes of travel. Stroke timing through the use of such lights would be optimistic in that it could indicate the stroke
.
time of 75% or less of the full stroke travel. Additionally, the portion of the stroke most likely to be truncated is that during which the disk is being seated or unseated. Unfortunately, these periods j
are the ones in which disk travel is most likely to be retarded.
The procedure reviewed avoids this problem by performing the position indication test with observers at both the control room and at the r
MOV. The stroke time was taken in the conventional manner (switch-to-light) at the control room. At the valve, the actual stroke time was taken.
That is, the time between initiation and i
termination of stem motion. The procedure requires a comparison of
the two results. Valves with stroke times up to 5 seconds are
,
allowed a difference of 120% (or up to one second).
Valves with
'
stroke times five seconds or longer are allowed i one second. This correlation is considered adequate for all practical purposes, e.
MOV Stroke Initiation Criteria Stroke time is normally measured as the time between the actuation of the MOV switch and the operation of light that indicates the end-of the stroke. For the purpose intended, this is adequate, recognized and accepted.
However, this is a unique application.. Extrapolation of these start and stop criteria to other tests is not always practical nor advantageous.
There are several alternate ways in which to measure the stroke of the valve. Each offers some advantage in testing. Stroke measurement methods include the following:
Timing the period between 6ctuation and release of the MOV
Timing of the duration of MOV current flow.
Counting the number of handwheel turns between open and closed.
- Timing from hammer blow to motor current termination.
Timing from beginning of stem motion to motor current termination.
- Timing from beginning of stem motion to end of stem motion.
Timing from initiation of disk travel to motor current termination.
_
l
,
!
,
.
.
'
In order to be able to set or test MOV switches, the basis for such setting must be defined. At Byron, the start of the stroke is taken
>
to be the initial motion of the disk. Although personnel who dealt I
with MOVs were aware of this information, it was not form 611y identified in their training nor in the document from which work i
would be performed.
It was identified in the corporate " Guideline i
for MOV Testing, Maintenance, and Evaluation," but this is not normally available at the job site. Thus, although stroke initiation criteria had been established and informally disseminated, it was not included in training nor readily available for reference. The licensee, when apprised of this, took imediate corrective action by generating Action Item Records 454-225-90-08400 and 454-225-90-08500 to add this information to both training and procedure BHS-XLT-1(MOVsignatures). No further action is considered necessary, f.
Maintenance of Switch Settings Both IEB 85-03 and GL 89-10 require that-correct switch settings be determined for important valves in the plant. They also require that these settings, once established, be maintained for the~ life of the plant. Although the licensee is currently reviewing the scope of work on MOV switch settings to make the initial settings of each valve comply with the requirements of GL 89-10, there is no plan to perform routine examination of these valves exclusively to confirm that these switch settings will t.ontinue to provide satisfactory results.
The proper initial setting of MOV switches does not ensure continued satisfactory operation of the MOV. There are a number of factors which can change the output of the operator at the original settings or change the thrust required to operate the valve..It is the responsibility of the licensee to anticipate these changes by monitoring the condition of the MOVs and to provide appropriate corrective actions to avoid problems with valve operability.
Among the problems which the licensee must preclude are the following:
(1) Spring pack deterioration; (2) Electrical contact deterioration; (3) Non-metallic material deterioration: weakening, swelling, shrinking, cracking, etc. from the hostile environment; (4) Hydraulic lock-up of spring pack; (5) Deterioration of grease in operator; (6) Loss or deterioration of stem lubrication;
.
-
..
... _..
_
_ _ _
.
.
.
(7) Oxidation of metals; (8) Deterioration of moving contact surfaces through friction and abrasion from foreign materials; (9) Loss of switch settings through loosening of set screws because of vibration, thermh1 cycling, or material dimensional changes; and (10) Mechanical damage to parts (such as bent steins or shafts)
increases the thrust to open or clost over that required for valves with undamaged parts.
One of the most valuable tools to provide finite guidance in the establishment of reasonable and practical inspection intervals is the development of a solid trending data base. Development of such a base is planned by the licensee, but it is not yet in operation.
At present, the retesting of switch effectiveness is mandated by the frequency of maintenance operations.
In accordance with IWV-3200 of-ASME Section XI, testing must always follow any operation which could affect the operation of the valve.
In turn, maintenance inspection frequency is controlled by NOD-MA.1 (which will soon be revised).
The current frequency may be adequate. However, if the periods between maintenance become excessive, consideration must be given to whether or not more frequent inspection would be appropriate for switch settings and required thrusts. The possibilities for error demand that a suitable effort be devoted to determining the maximum reasonable period that may be permitted between MOV tests, g.
MOV Training The licensee has provided a dedicated training facility with operable MOVs on which to train and test MOV workers. Training courses have been developed with identified content.
Both manual and_ written examinations are given to demonstrate the trainees proficiency.
Records are kept and disseminated to allow management personne1'to assign work to properly qualified workers, h.
Conclusion The licensee has addressed the significant aspects of the bulletin.
The commitments communicated to the NRC were verified to be met.
Based on the review of the licensee activities, it was concluded that there is reasonable assurance that the valves covered under the bulletin, and supplement 1 to the bulletin can perform their safety-function during normal and abnormal conditions (addressed within the scope of the bulletin). This item is considered closed.
. _ -...........
...
.
..
.
.
.
.
.....
.
.
...,
f
,
.
.
,,
f 3.
Exit Meeting The NRC inspector met with licensee representatives (denoted in Paragraph 1)onMarch 30, 1990 to discuss the scope and. findings of the inspection.
The inspector also discussed the likely informational content of the.
inspection report with regard to documents or processes reviewed by the inspector during the inspection. The licensee did not identify any such documents / processes as proprietary.
<
,
i