Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
May 1, 1989
Information Notice No. 89-43: PERMANENT DEFORMATION OF TORQUE SWITCH
HELICAL SPRINGS IN LIMITORQUE SMA-TYPE
MOTOR OPERATORS
Addressees:
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose:
This information notice is being provided to alert addressees to potential
problems resulting from permanent deformation of the torque switch helical
springs in Limitorque SMA-type motor operators. It is expected that re-
cipients 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:
Problems with the helical springs were discovered during a series of dynamic
tests that were conducted with a motor-operated wedge-gate valve from the
decommissioned Shippingport Atomic Power Station (Shippingport). The valve
was installed in a portion of the piping system that had been modified to
simulate the stiffness of a typical United States piping system. The valve
was 30 years old and had its original Limitorque SMA-type motor operator.
One of the main objectives of these tests was to determine the operating
capability of the valve when subjected to simultaneous internal hydraulic
and seismic loadings. This was typically accomplished by operating the
valve to achieve maximum hydraulic loading during maximum seismic loading.
During testing, an operability problem with the valve motor operator occurred.
Disassembly and inspection of the motor operator revealed that the torque
switch helical spring had a free length of 3.99 inches. Review of the
Shippingport records for the valve indicated that the torque switch spring
had not been changed while the valve had been in service at Shippingport.
Limitorque's records indicated that the original free length of the spring
was 4.46 inches. Thus, the spring had developed a permanent deformation
of 0.47 inches during the motor operator's 30-year life. Since the spring
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May 1, 1989
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had been installed in a space 4.06 inches in length, a gap of approximately
0.07 inch had existed during the tests. This gap appears to indicate that
there was no preload on the helical spring during the tests.
The torque switch helical spring from a second Shippingport valve with a
Limitorque SMA-type motor operator was also found to have a permanent defor-
mation. For this second spring, the original free length was 3.84 inches;
the current free length was 3.74 inches; and it was installed in a space 3.37
inches in length. However, even though this spring was subjected to a preload
and there was no gap, the amount of preload was less than expected because of
the permanent deformation.
Discussion:
Permanent deformation of the torque spring without compensating for it will
reduce the torque required to open the torque switch. The switch setting
that is selected corresponds to the closing torque that the motor operator
is to deliver. If the permanent deformation of the spring sufficiently
reduces this closing torque, it may cause the motor operator to stop before
the valve is fully seated. In an extreme case, the motor operator may stop
with the valve partially open.
The design of the SMA-type motor operator is such that the torque switch
helical spring is in its most compressed condition when the valve is closed.
Thus, a normally closed valve is more likely to experience permanent
deformation of the helical torque spring. A review of the Shippingport
records indicated that both of these valves had been used as normally closed
valves at Shippingport. Thus, normally closed, safety-related valves with
Limitorque SMA-type motor operators may not accomplish their intended
safety-related function because the original torque switch setting may result
in lower output torque caused by the permanent deformation of their torque
switch helical springs.
No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact one of the techni-
cal contacts 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 Contacts: Gerald H. Weidenhamer, RES
(301) 492-3839
Richard J. Kiessel, NRR
(301) 492-1154
Attachment: List of Recently Issued NRC Information Notices
.. Attachment
IN 89-43
May 1, 1989
Page 1 of 1
LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
_____________________________________________________________________________
Information Date of
Notice No._____Subject_______________________Issuance_______Issued to________
88-97, Potentially Substandard 4/28/89 All holders of OLs
Supp. 1 Valve Replacement Parts or CPs for nuclear
power reactors.
89-42 Failure of Rosemount 4/21/89 All holders of OLs
Models 1153 and 1154 or CPs for nuclear
Transmitters power reactors.
89-41 Operator Response to 4/20/89 All holders of OLs
Pressurization of Low- or CPs for nuclear
Pressure Interfacing power reactors.
Systems
88-75, Disabling of Diesel 4/17/89 All holders of OLs
Supplement 1 Generator Output Circuit or CPs for nuclear
Breakers by Anti-Pump power reactors.
Circuitry
89-40 Unsatisfactory Operator Test 4/14/89 All holders of OLs
Results and Their Effect on or CPs for nuclear
the Requalification Program power reactors.
89-39 List of Parties Excluded 4/5/89 All holders of OLs
from Federal Procurement or CPs for nuclear
or Non-Procurement Programs power reactors.
89-38 Atmospheric Dump Valve 4/5/89 All holders of OLs
Failures at Palo Verde or CPs for nuclear
Units 1, 2, and 3 power reactors.
89-37 Proposed Amendments to 4/4/89 All U.S. NRC
40 CFR Part 61, Air licensees.
Emission Standards
for Radionuclides
89-36 Excessive Temperatures 4/4/89 All holders of OLs
in Emergency Core Cooling or CPs for nuclear
System Piping Located power reactors.
Outside Containment
_____________________________________________________________________________
OL = Operating License
CP = Construction Permit
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