Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
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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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.
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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
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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.
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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.
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