Category:NRC Information Notice[Table view]The following query condition could not be considered due to this wiki's restrictions on query size or depth: <code> [[:Beaver Valley]] OR [[:Millstone]] OR [[:Hatch]] OR [[:Monticello]] OR [[:Calvert Cliffs]] OR [[:Dresden]] OR [[:Davis Besse]] OR [[:Peach Bottom]] OR [[:Browns Ferry]] OR [[:Salem]] OR [[:Oconee]] OR [[:Mcguire]] OR [[:Nine Mile Point]] OR [[:Palisades]] OR [[:Palo Verde]] OR [[:Perry]] OR [[:Indian Point]] OR [[:Fermi]] OR [[:Kewaunee]] OR [[:Catawba]] OR [[:Harris]] OR [[:Wolf Creek]] OR [[:Saint Lucie]] OR [[:Point Beach]] OR [[:Oyster Creek]] OR [[:Watts Bar]] OR [[:Hope Creek]] OR [[:Grand Gulf]] OR [[:Cooper]] OR [[:Sequoyah]] OR [[:Byron]] OR [[:Pilgrim]] OR [[:Arkansas Nuclear]] OR [[:Braidwood]] OR [[:Susquehanna]] OR [[:Summer]] OR [[:Prairie Island]] OR [[:Columbia]] OR [[:Seabrook]] OR [[:Brunswick]] OR [[:Surry]] OR [[:Limerick]] OR [[:North Anna]] OR [[:Turkey Point]] OR [[:River Bend]] OR [[:Vermont Yankee]] OR [[:Crystal River]] OR [[:Haddam Neck]] OR [[:Ginna]] OR [[:Diablo Canyon]] OR [[:Callaway]] OR [[:Vogtle]] OR [[:Waterford]] OR [[:Duane Arnold]] OR [[:Farley]] OR [[:Robinson]] OR [[:Clinton]] OR [[:South Texas]] OR [[:San Onofre]] OR [[:Cook]] OR [[:Comanche Peak]] OR [[:Yankee Rowe]] OR [[:Maine Yankee]] OR [[:Quad Cities]] OR [[:Humboldt Bay]] OR [[:La Crosse]] OR [[:Big Rock Point]] OR [[:Rancho Seco]] OR [[:Zion]] OR [[:Midland]] OR [[:Bellefonte]] OR [[:Fort Calhoun]] OR [[:FitzPatrick]] OR [[:McGuire]] OR [[:LaSalle]] OR [[:05000000]] OR [[:Zimmer]] OR [[:Fort Saint Vrain]] OR [[:Shoreham]] OR [[:Satsop]] OR [[:Trojan]] OR [[:Atlantic Nuclear Power Plant]] OR [[:Crane]] </code>.
the isolation safety function for the containment/reactor creates the potential
for failure to limit the release of radioactivity during a reactor transient or
accident condition.
It is expected that recipients will review the information
for applicability to their facilities and consider actions, as appropriate, to
avoid similar problems. However, suggestions contained in this information
notice do not constitute NRC requirements; therefore, no specific action or
written response is required.
Description of Circumstances
Following an event at Dresden Unit 2 on December 24, 1987, in which the "1B" MSIV
failed to close when the air supply line pulled out of the manifold on the valve
operator, Commonwealth Edison Company (the licensee) designed a special test to
respond to a Region ITT concern regarding MSIV operability on the loss of motive
"air" pressure.
The test was designed to evaluate whether the MSIVs would close, as expected, on spring force alone.
On May 16, 1988, the licensee performed a spring closure test, which required
total isolation of the pneumatic supply to the MSIV actuators.
The Dresden
"air" or pneumatic system used to assist in MSIV closure is non-safety grade;
air is supplied to the outboard MSIVs and nitrogen is supplied to the inboard
MSIVs. Each of the inboard and outboard valves was tested and each failed to
fully close.
On May 17, 1988, continuing with the MSIV special test program. the licensee
performed a slow loss-of-air test that isolated supply nitrogen, but not the
accumulator from the valve actuator, thus allowing stored nitrogen in the ac- cumulator to assist in closing the MSIV. When the volume of gas under the
piston was vented, the valve again failed to fully close.
The same test was
perfcrmed with similar results on all outboard isolation valves.
At this point, all eight MSIVs were declared to be inoperable.
8807180101
IN 88-51 O'uly 21, 1988 The licensee developed a series of tests to evaluate possible root causes of
the problems observed regarding failure of the MSIVs to fully close.
Initially it was believed that the MSJV failures were caused by the
Automatic Valve Company (AVCO) 4-way solenoid valves moving to an intermediate
position, where they "hung up," thus preventing proper venting of the gas volume
from under the piston.
Subsequently the results of the MSIV root cause failure
tests showed that excessively tight MSIV chevron packing clamped the stem, pre- venting the valve from traveling freely to its closed position.
Details may be
found in Augmented Inspection Team Report No. 50-237/88013.
Discussion:
The MSIVs are 20-inch, air-spring-operated, balanced "Y."
configuration Crane
lobe valves.
Air or nitrcgen is supplied under the actuator piston to open
and to hold open the valve.
When the supply is interrupted or when the MSTV
main solenoid coils are de-energized, the accumulator air/nitrogen is routed
to the top of the actuator and air/nitrogen from the bottom is vented, thereby
assisting the spring in closing the MSIV. The action of the main solenoids
causes an AVCO 4-way valve to reposition and open the pathway to the actuator.
According to the Updated Safety Analysis Report, the valves are designed to
close with either pneumatic or spring action; thus, the coil springs located
around the shafts are used for closinq the valves in the event of pneumatic
supply- fa-iure.-
The Dresden Technical Specifications require quarterly functional testing to
evaluate MSIV closure with combined actuator air and spring forces even though
the pneumatic supplies are from non-safety grade sources. The most recent
testing demonstrated that the MSIVs would not close with spring forces alone
which is contrary to the plant's safety design basis.
During a slow loss-of- air/nitrogen test, the over-tightened valve packing clamped the valve stem, and the 4-way solenoid valve "hung up" in a manner such that air/nitrogen did
not assist in closing the MSIV. However, even with the loss of air-assisted
closure, the valves should have closed on spring force only.
It is because
of this that the root cause of failure was attributed to the over-tightened
chevron packing. Moreover, it was determined that post-maintenance testing
was inadequate to detect the overly tight valve stem packing condition.
This event indicates that MSIV testing may be inadequate to detect certain
deficiencies in design of the MSIV, its installation, or maintenance that
could affect its design function.
Excessive pressure on the gland rut may
be maintained without problems for some types of packing; however, for certain
self-setting-type chevron packing, such as that in use at Dresden Unit 2, the
excessive friction will inhibit stem movement.
Thus, the potential exists for
a situation in which the design-basis closure requirements are not met.
This event emphasizes the need to consider carefully the adequacy of surveil- lances in establishing the operability of MSIVs or other similar valves.
The
IN P2-51 July 21, 1988 MSIVs passed the typical surveillance test of spring closure assisted by the
pneumatic operator; however, on a slow depressurization, which is more typical
of a leak of the pneumatic system, the valves could potentially fail to close
if the packing is over-torqued.
No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the technical
contact listed below or the Regional Administrator of the appropriate regional
office.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact:
Carl S. Schulten, NRR
(301) 492-1192 Attachment: List of Recently Issued NRC Information Notices