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Information Notice No. 93-23: Weschler Instruments Model 252 Switchboard Meters
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. 9303240274. 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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