Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
March 31, 1993
Information Notice No. 93-23: WESCHLER INSTRUMENTS MODEL 252
SWITCHBOARD METERS
Addressees
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to possible problems with Weschler Instruments
(Weschler) Model 252 commercial grade switchboard meters. 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 November 9, 1992, Weschler informed the NRC of sticking meter movements in
some Model 252 meters manufactured and supplied as commercial grade items.
Although Weschler reported having no evidence that meters manufactured
specifically for safety-related service are affected, Weschler was concerned
that affected commercial grade meters could have been dedicated for use in
nuclear safety-related applications.
Discussion
Weschler determined that some of the commercial grade meters returned for
repair or calibration were inaccurate and erratic. The vendor engineering
report attributed this problem to sticking of the meter movement because of an
off-center torsion spring. Weschler determined that this condition resulted
from a deviation in the dimensions associated with the torsion head screws
combined with several coincidental factors that included (1) degradation of
clip-to-torsion screw lubrication, (2) low initial force from the spring-
retaining clip or fatigue of the spring-retaining clip, (3) variations in the
alignment of the meter movement during initial assembly, and (4) the effect of
the summation of the dimensional tolerances in the assembly of the
subcomponents.
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IN 93-23
March 31, 1993
Page 2 of 2
To prevent this deficiency in future products, Weschler revised its production
inspection procedures to specifically require checking the dimensions in
question. Weschler also revised its nuclear quality assurance procedures to
require specific checks of torsion head screw dimensions, although the vendor
has not detected a problem with meters manufactured specifically for safety-
related applications.
Weschler could not determine whether or not any Model 252 switchboard meters
sold as commercial grade items through the various distributors had been
dedicated for use in nuclear safety-related applications. Therefore, Weschler
has not directly notified any licensees about this problem.
Weschler stated that the principal corrective action it has taken for affected
meters returned for repair and recalibration is to replace the faulty torsion
head screws because they can't be repaired. Upon request, Weschler will give
licensees information about the problem and the recommended corrective
measures.
This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
the technical contact listed below or the appropriate Office of Nuclear
Reactor Regulation (NRR) project manager.
ORIGINAL SIGNED BY
Brian K. Grimes, Director
Division of Operating Reactor Support
Office of Nuclear Reactor Regulation
Technical contact: S. V. Athavale, NRR
(301) 504-2974
Attachment:
List of Recently Issued NRC Information Notices
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