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 [[:05003411]] OR [[:Fort Saint Vrain]] OR [[:Shoreham]] OR [[:Satsop]] OR [[:Trojan]] OR [[:Atlantic Nuclear Power Plant]] OR [[:Crane]] </code>.
pilot valves. 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 are not NRC requirements; therefore, no specific action or written
response is required.
Description of Circumstances
On February 18-19, 1995, while LaSalle County Station, Unit 2, was entering
into a refueling outage, the control room was unable to close two outboard
MSIVs. The MSIVs at LaSalle use Ralph A. Hiller electrically operated
pneumatic actuators.
The actuator has a pneumatic control assembly, which was
designed to use an Automatic Switch Company (ASCO) Model NP8323 solenoid- operated valve (SOV) as the pilot valve to control the opening and closing of
the MSIVs. The ASCO NP8323 SOV (see Figure 1) is a dual-coil, 3-way solenoid
valve, which is commonly used in both foreign and domestic MSIV applications.
The testing interval for the MSIVs that failed had been extended to 118 days
from the usual period of 92 days.
On June 11,
1995, LaSalle Unit 1 experienced a similar failure in that one of
the outboard MSIVs failed its 30-day surveillance test. Two internal parts of
the SOV (the core and the plugnut) stuck together for approximately
15 seconds.
Discussion
Commonwealth Edison (ComEd), the licensee for LaSalle County Station, initiated an investigation and determined that the ASCO solenoid valves had
failed to oper:a: because the core (item 9 in Figure 1) and the plugnut
(item 8) had stuLk together. The root cause of the sticking of the two pieces
appeared to be the presence of a lubricant (Nyogel 775A) and a thread sealant
(Loctite PST 550 or Neolube 100), which had formed an adhesive film between
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5, and 9 covering inspections at LaSalle between February and July 1995, and
99900369/95-01 which provides details of an NRC vendor inspection at ASCO on
March 13-14, 1995).
Neither ComEd, ASCO, General Electric (GE), nor the NRC inspectors were able
to conclusively determine how the lubricant or thread sealant got on the core
and the plugnut. The thread sealant cures only under anaerobic conditions.
If the thread sealant was improperly installed on any of the connecting pipe
fittings, or not allowed to cure for 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> before air was blown through the
pneumatic actuator, some of the uncured thread sealant could migrate through
the system. Additionally, on the basis of NRC staff observations of the ASCO
assembly techniques and discussions with ASCO personnel, it was concluded that
the ASCO NP8323 assembly and testing methods could have allowed inadvertently
applied lubricant (Nyogel 775A) to be transferred to the core and/or plugnut
during fabrication or operational testing activities.
Extensive testing was performed by both ComEd and ASCO in an attempt to
determine the root cause of the sticking SOVs. ComEd concluded that the
Nyogel 775A lubricant used during assembly at the factory was applied in
sufficient quantity to deposit a film on the core and plugnut interface.
Although the Nyogel 775A alone would not cause the SOV to stick, the licensee
believes that the Nyogel film acted as a collection point for microscopic
amounts of uncured thread sealant that migrated through the pneumatic
actuators, and over time enough thread sealant accumulated to cause the SOVs
to stick. The licensee noted that all three of the installed valves that
failed were found to have Nyogel present at the core and plugnut interface.
GE and ASCO determined from their testing that Nyogel 775A lubricant would not
develop sufficient adhesive force between the core and the plugnut to cause
them to stick. However, their testing showed that uncured thread sealant
applied to the core and plugnut interface could cause the core and the plugnut
to stick together and prevent operation of the SOV.
Long-term corrective measures taken by LaSalle personnel included better
control of the use of thread sealant and the replacement of ASCO NP8323 solenoid valves with valves made by a different manufacturer (Valcor).
Experience Feedback Report, Solenoid-Operated Valve Problems at U.S.
Reactors," to distribute NUREG-1275, Volume 6, to the industry. This document
contained the NRC staff analysis of recent experience with SOVs at U.S. light- water reactors (primarily 1984-1989). Appendix D to NUREG-1275, Volume 6, listed NRC generic communications on SOYs. Five of the information notices
listed discuss the sticking of solenoids as a result of contamination of valve
internals from maintenance activity by the licensee or manufacturer assembly.
IN 95-53 December 1, 1995 This information notice requires no specific action or written response.
If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below or the appropriate Office of
