Information Notice No. 89-66: Qualification Life of Solenoid Valves
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
September 11, 1989
Information Notice No. 89-66: QUALIFICATION LIFE OF SOLENOID VALVES
Addressees:
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose:
This information notice is being provided to alert addressees to a potential
problem, resulting from a common-mode failure, that may affect the operability
of main steam line isolation valves or similarly designed components. The
problem relates to control solenoid valves whose elastomer discs (seats) are
exposed to temperatures higher than originally assumed in calculating their
qualified life and which may be presently in service beyond their actual
qualified service life. 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 a reactor trip in August 1989, the operators of Grand Gulf Unit 1
closed the main steam line isolation valves (MSIVs) manually. However, they
observed that one outboard MSIV did not close until more than 15 minutes after
a subsequent automatic closure set point (low vacuum) was reached. Upon
investigating the event, the licensee found a piece of the elastomer seat from
the solenoid valve used for control of that MSIV on an outlet screen. The
licensee concluded that the piece had been lodged in the solenoid valve
internals, thereby keeping the solenoid valve from venting control air and
hence keeping the MSIV from closing. It is believed that after the piece of
elastomer became dislodged from the internals, the MSIV closed.
Subsequent inspections by the licensee of all eight dual-coil solenoid valves
piloting the MSIVs disclosed that all eight solenoid valves had degraded
seats. Initial visual inspection did not reveal the degradations. However,
the degradations became apparent under microscopic examination. The EPDM
(ethylene propylene dimer) seats of all eight solenoid operated valves had
cracking. However, on six of them, the raised portion of the seat formed by
the annular
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. IN 89-66
September 11, 1989
Page 2 of 3
impression made in the seat by the exhaust port was missing. Thus, it appears
as if six of the eight solenoid valves had experienced similar sloughing of
material from the seat. This had been sufficient to prevent one of the
solenoid valves from operating properly, thereby preventing the MSIV from
operating properly.
The solenoid valves in question are dual-coil solenoid valves manufactured by
Automatic Switch Co. (ASCO Model NP8323). In 1985, the Grand Gulf licensee
calculated the qualified life of these valves with EPDM seats using
single-coil heatup data. The resultant qualified life was calculated at 5.9
years on inboard MSIVs. After the recent event, the licensee repeated the
qualification calculations using heatup data for dual-coil solenoids (which
became available in 1987) and estimated the life to be about 2.9 years. These
solenoid valves had been in service for about 4.5 years.
Recent qualification calculations by the Perry licensee for their solenoid
valves, which have operating conditions similar to those at Grand Gulf, found
that NP8323 solenoid valves with Viton seats on the inboard MSIVs have an
estimated service life of about two years. These solenoid operated valves are
routinely changed every refueling outage at Perry.
Discussion:
A number of operability problems have been associated with the dual-coil
solenoid valve Model NP8323 manufactured by ASCO. Information Notice No.
88-43, "Solenoid Valve Problems," dated June 23, 1988, identifies older
generic communications and describes potential common-mode failure mechanisms,
for example, contamination, thermal degradation of the elastomer, sticky
material, and deficient maintenance. ASCO issued a service bulletin dated May
23, 1989, which stated that rebuilding kits for the "NP" series valves were
being discontinued. ASCO has also recently indicated that it plans to phase
out the NP8323 solenoid valve and that two NP8320 nuclear qualified
single-coil solenoid operated valves connected in series may be an acceptable
substitute.
Since better and more recent temperature information is now available, it is
important to note that the calculated maximum service period data supplied
with solenoid valves used at both boiling water reactors and pressurized water
reactors may be based on temperatures at the elastomer seat that are too low.
Therefore, the calculated service life may be in error. Temperatures in the
vicinity of the elastomer seat are dependent upon the plant-specific ambient
temperatures, localized hot spot heat sources, and heat input from the
solenoid coils during the time the solenoids are energized. A temperature
rise of about 100 F above ambient temperature could be expected in the
vicinity of the seat with the dual solenoid coils energized. ASCO has
temperature profile data available for various solenoid valve designs. The
temperature profile data vary for different solenoid valves under different
operating conditions.
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September 11, 1989
Page 3 of 3
In a service bulletin dated April 12, 1988, ASCO stated that it had no
evidence of elastomer degradation when Viton was used. General Electric
Company issued SIL No. 481, dated February 14, 1989, which recommended that
the elastomer be changed from EPDM to Viton. Regardless of the material used,
the qualified life will be adversely affected by higher temperatures and may
be significantly less than the initially determined qualified life and
possibly even less than the actual operating time.
MSIVs are subject to different testing and surveillance requirements. Some
licensees test MSIVs for operability once each quarter and others may use
special slow-closing testing techniques such as that described in IN 88-43.
Regardless of the testing or frequency, the MSIVs may be susceptible to a
common mode of failure which could disable both MSIVs in a steam line. This
failure, in itself, would not cause a significant accident; however, should
the MSIV failures occur in conjunction with a steam line break, radioactivity
released to the public could result in doses in excess of the guidelines of
10 CFR Part 100.
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 NRR project
manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts: J. Carter, NRR
(301) 492-1194
H. Ornstein, AEOD
(301) 492-4439
Attachment: List of Recently Issued NRC Information Notices
. Attachment
IN 89-66
September 11, 1989
Page 1 of 1
LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
______________________________________________________________________________
Information Date of
Notice No._____Subject_______________________Issuance_______Issued to_________
88-46, Licensee Report of 9/11/89 All holders of OLs
Supp. 4 Defective Refurbished or CPs for nuclear
Circuit Breakers power reactors.
89-65 Potential for Stress 9/8/89 All holders of OLs
Corrosion Cracking in or CPs for PWRs.
Steam Generator Tube
Plugs Supplied by
Babcock and Wilcox
89-64 Electrical Bus Bar Failures 9/7/89 All holders of OLs
or CPs for nuclear
power reactors.
89-63 Possible Submergence of 9/5/89 All holders of OLs
Electrical Circuits Located or CPs for nuclear
Above the Flood Level Because power reactors.
of Water Intrusion and Lack
of Drainage
89-62 Malfunction of Borg-Warner 8/31/89 All holders of OLs
Pressure Seal Bonnet Check or CPs for nuclear
Valves Caused By Vertical power reactors.
Misalignment of Disk
89-61 Failure of Borg-Warner Gate 8/30/89 All holders of OLs
Valves to Close Against or CPs for nuclear
Differential Pressure power reactors.
88-48, Licensee Report of Defective 8/22/89 All holders of OLs
Supp. 2 Refurbished Valves or CPs for nuclear
power reactors.
89-60 Maintenance of Teletherapy 8/18/89 All NRC Medical
Units Teletherapy
Licensees.
89-59 Suppliers of Potentially 8/16/89 All holders of OLs
Misrepresented Fasteners or CPs for nuclear
power reactors.
______________________________________________________________________________
OL = Operating License
CP = Construction Permit
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