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Home NRC Library Document Collections Events, Reports Associated with Part 21 Reports 1996

Part 21 Report - 1996-150

 
 


ACCESSION #: 9601050092



                              Public Service

                              Electric and Gas

                              Company



E. C. Simpson                 Public Service Electric and Gas Company

                              P.O. Box 236, Hancocks Bridge, NJ 08038

Senior Vice President -       609-339-1700

Nuclear Engineering

                                   DEC 28 1995

                                   LR-N95244



United States Nuclear Regulatory Commission

Document Control Desk

Washington, DC 20555



Gentlemen:



10CFR21 INTERIM REPORT -

SCRAM DISCHARGE VOLUME DRAIN VALVE FAILURE

HOPE CREEK GENERATING STATION

FACILITY OPERATING LICENSE NO. NPF-57

DOCKET NO. 50-354



Pursuant to the notification requirements of 10CFR21.21(a)(2), Public

Service Electric & Gas Company (PSE&G) hereby provides the attached

interim report regarding failure of Scram Discharge Volume (SDV) drain

valve 1BFHV-F011.  This failure is considered potentially reportable in

accordance with 10CFR21.  However, further evaluation is required to

determine the root cause of this failure, and if this failure mechanism

constitutes a Deviation as defined in 10CFR21.3(e).  Therefore, a

determination whether the condition is reportable under 10CFR21 can not

be made at this time.  The attached provides a summary of the results of

the investigation completed to date, and actions planned to evaluate this

deficiency and determine reportability in accordance with 10CFR21.  The

final determination of reportability will be completed prior to restart

of Hope Creek from the current refueling outage presently scheduled for

February 6, 1996.



Please contact us should you have any questions regarding this submittal.



                                   Sincerely,



Attachment



                                                            DEC 28 1995

Document Control Desk               2

LR-N95244



c    Mr. T. T. Martin, Administrator - Region I

     U. S. Nuclear Regulatory Commission

     475 Allendale Road

     King of Prussia, PA 19406



     Mr. D. Jaffe, Licensing Project Manager - Hope Creek

     U. S. Nuclear Regulatory Commission

     One White Flint North

     11555 Rockville Pike

     Mail Stop 14E21

     Rockville, MD 20852



     Mr. R. Summers (X24)

     Senior Resident Inspector



     Mr. K. Tosch, Manager, IV

     Bureau of Nuclear Engineering

     33 Arctic Parkway

     CN 415

     Trenton, NJ 08625



LR-N95244

                               ATTACHMENT



10CFR21 INTERIM REPORT -

SCRAM DISCHARGE VOLUME DRAIN VALVE FAILURE

HOPE CREEK GENERATING STATION

FACILITY OPERATING LICENSE NO. NPF-57

DOCKET NO. 50-354



I.   BACKGROUND



Scram Discharge Volume (SDV) Drain Valves (1BFHV-F011 & F181) are

redundant air operated valves installed in series that are normally open

to keep the SDV drained, and are automatically closed following a reactor

scram.  The SDV drain valves are 2 inch 2500 lb. globe valves that were

manufactured by Hammel Dahl which is now owned and serviced by Neles

Jamesbury.  These valves are designed such that in the event of a single

failure, isolation of the SDV drain line is ensured to prevent the loss

of reactor coolant inventory.  Should failure of both SDV drain valves

occur, this could result in a flow path from the reactor pressure vessel

through the SDV.



While performing the monthly surveillance test in accordance with

Technical Specification 4.1.3.1.1 for SDV drain valve 1BFHV-F011 on

September 9, 1995, the monitoring instrumentation did not actuate to

indicate that the valve was fully closed.  Further investigation

determined the measured valve travel was 7/8 inch instead of the expected

1-1/8 inch travel.  When the valve was stroked a second time, it was

observed that the spring tension on the actuator was completely relaxed

when the valve was in the closed position.  This prevented the valve from

going to the fully closed position.  It was concluded at that time that

the cause of the incomplete closure was due to the spring adjuster on the

valve stem backing off the spring, possibly due to vibration.  The spring

adjuster was tightened to provide positive valve closure.  The valve was

then retested and declared operable within the required Technical

Specification allowed outage time of 24 hours.



II.  EVALUATION



An evaluation of possible causes of the failure has been performed.  The

evaluation included (1) a review of plant documentation including

incident reports/problem reports, work orders and drawings, (2) a review

of vendor documentation including drawings and engineering data, and (3)

discussions with site personnel and valve engineering personnel.



It was initially identified that the cause of the failure of SDV drain

valve 1BFHV-F011 was the result of the spring adjuster



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LR-N95244

                               ATTACHMENT



backing off the spring.  Further evaluation identified three (3) possible

failure mechanisms including changes in the spring adjuster setting

during normal operation which could result in loss of spring compression.

Loss of spring compression could result in the valve sticking open due to

hydraulic forces present when the valve is required to close following a

reactor scram.  The following is a discussion of the three (3) possible

failure mechanisms:



Spring Mis-adjustment -



Following actuator disassembly (such as for diaphragm replacement), reset

of the spring adjuster is required.  Following completion of some

maintenance activities such as replacement of valve packing, resetting of

the spring adjuster may be performed.  If the adjustment is not performed

in accordance with the vendor's instruction, the adjustment may result in

the spring being nearly or completely unloaded with the valve in the

closed position.



Change in spring Adjuster Setting Due to Normal Operation -



The existing valve design does not include a locking device to maintain

the spring adjuster in its set position.  Vibration or normal cycling of

the valve may result in the spring adjuster backing out from its original

set position.  This failure mechanism could also be a result of spring

mis-adjustment as discussed above if the spring is nearly or completely

unloaded with the valve in the closed position.  The design relies on

frictional loads between the threads in the actuator stem and spring

adjuster to prevent movement of the spring adjuster.



Spring Relaxation -



The stresses of the actuator spring are greatest in the normally open

position.  If the stresses at this position exceed the yield point due to

mis-adjustment, a defective spring or a design deficiency, compression

set may occur which would reduce the compression in the closed position.

If the compression set changes over time, the spring compression may

reduce sufficiently to keep the valve from fully closing.



III.  DISCUSSION



Evaluation has determined that the three possible failure mechanisms

discussed above could affect the SDV drain valves 1BFHV-F011 and 1BFHV-

F181, and SDV vent valves 1BFHV-F010 and 1BFHV-F180.



                               Page 2 of 5



LR-N95244

                               ATTACHMENT



A review of operating experience for the SDV drain valves was performed

to determine if evidence exists to directly support the failure

mechanisms proposed above.  A review of monthly and quarterly

surveillance test results was performed.  In general, the SDV drain

valves have tested satisfactorily, and no failures were identified

related to incomplete valve closure.  The five second time delay between

the closure of the inboard and outboard drain valves sometimes requires

readjustment.  Readjustment typically consists of slightly changing the

regulated air pressure so that the time needed to bleed down the air is

changed.



Some maintenance has been performed on valve 1BFHV-F011 that would

require reset of the spring adjuster from initial receipt from the

manufacturer.  In 1989, the diaphragm was replaced which required spring

removal.  In 1991, the actuator was rebuilt which required spring

readjustment.  As of the date of the failure, no work activities on the

valve were identified since 1991 that would have reset the spring

adjuster.  In addition, no preventive maintenance requirements were

identified by the vendor for the valves to ensure proper spring

adjustment is maintained.



A failure of 2500-lb Hammel Dahl SDV vent and drain valves was reported

to the NRC (see NRC Information Notice 86-82, Revision 1).  These

failures were attributed to the manual handwheel not being positioned in

the neutral position which resulted in the deformation and disengagement

of the coupling between the actuator stem and valve stem when the valve

was operated.  This failure does not appear to be a possible cause for

loss of spring compression.



This model actuator and other similar models are not provided with

locking devices.  The design relies on frictional loads between the

threads in the actuator stem and spring adjuster to prevent movement of

the spring adjuster.  The valve is normally open which is when the spring

is under its maximum compression.  The frictional loads resisting

loosening are also maintained during this period.  Neles-Jamesbury does

not use a locking device on any spring adjuster for the actuator model in

question, or the new actuator model that has replaced it.



Neles-Jamesbury has indicated that valve/actuator combinations of this

configuration have never been reported to have lost spring compression

either by the adjuster becoming loose or spring relaxation.  Seismic

qualification testing on a similar 2 inch valve with a frame yoke

actuator has been performed.  The results showed that the valve was

operating acceptably after the vibration test.  Although not specifically

identified for



                               Page 3 of 5



LR-N95244

                               ATTACHMENT



inspection, no indication was given that the stem adjuster loosened

during the test.



Industry operating experience indicates that helical springs in

compression over an extended period of time can develop some relaxation

or compression set (See NRC Information Notice 89-43).  Based on the

vendor information for this model valve, a compression set of 0.3 inches

(with a nominal free spring length of 9 inches) is sufficient to unload

the spring in the closed position.



IV.  SUMMARY AND CORRECTIVE ACTIONS



Both SDV drain valves 1BFHV-F011 and 1BFHV-F181 and the SDV vent valves

1BFHV-F010 and 1BFHV-F180 are susceptible to each of the three possible

failure mechanisms.  The identified failure could have resulted from a

deficiency in the design of the valve and actuator including the spring,

or due to lack of proper valve maintenance requirements.  However,

insufficient information is presently available to determine the specific

root cause of the failure, and if this failure mechanism constitutes a

Deviation as defined in 10CFR21.3(e).  Therefore, a determination whether

the condition is reportable under 10CFR21 can not be made at this time.



Further investigation is ongoing to identify the root cause and necessary

corrective actions, and determine reportability.  This investigation will

consist of the following:



(1)  measuring valve stroke versus air pressure for each of the four

affected SDV drain and vent valves both with and without stem packing

loads applied,



(2)  removing the spring from valve 1BFHV-F011, and measuring the

physical dimensions, spring rate and selected material properties, and



(3)  confirming that the spring and spring adjuster design are adequate

to maintain spring compression for valve closure.



Items 1 through 3 above will be completed prior to restart of Hope Creek

from the current refueling outage presently scheduled for February 6,

1996.  The results of Items 1 through 3 will be used to complete the root

cause determination, and the evaluation to determine if this condition is

reportable under 10CFR21.  The final determination of reportability will

be completed prior to restart.



                               Page 4 of 5



LR-N95244

                               ATTACHMENT



To prevent the spring adjuster from backing off the spring resulting in

loss of spring compression, PSE&G will also install a locking device for

the spring adjuster on the SDV vent and drain valves.  This modification

will also be completed prior to restart.



                               Page 5 of 5



*** END OF DOCUMENT ***

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