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Information Notice No. 93-01: Accuracy of Motor-Operated Valve Diagnostic Equipment Manufactured by Liberty Technologies
UNITED STATES NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION WASHINGTON, D.C. 20555 January 4, 1993 NRC INFORMATION NOTICE 93-01: ACCURACY OF MOTOR-OPERATED VALVE DIAGNOSTIC EQUIPMENT MANUFACTURED BY LIBERTY TECHNOLOGIES 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 (IN) to alert addressees to new information on the accuracy of motor- operated valve (MOV) diagnostic equipment manufactured by Liberty Technologies when used to estimate the thrust delivered by a motor actuator in opening or closing its valve. 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. Background Most licensees rely on MOV diagnostic equipment to provide information on the thrust delivered by the motor actuator in opening or closing its valve. The various types of MOV diagnostic equipment estimate valve stem thrust using different parameters, such as displacement of the spring pack or strain in the stem, mounting bolts, or yoke. Liberty Technologies has developed MOV diagnostic equipment, referred to as the Valve Operation Test and Evaluation System (VOTES), that estimates the thrust needed to open or close a valve based on strain of the valve yoke. The VOTES equipment derives thrust from yoke strain that has been calibrated to stem thrust using measured diametral strain of the valve stem and nominal engineering material properties. Many licensees make decisions regarding the operability of safety-related MOVs that are based on diagnostic equipment thrust readings. Therefore, the use of MOV diagnostic equipment can have a significant effect on the safe operation of a nuclear power plant. Description of Circumstances On October 2, 1992, Liberty Technologies notified the NRC, in accordance with Part 21 of the Title 10 of the Code of Federal Regulations, that it had determined that two new factors can affect the thrust values obtained with its 9212280087. IN 93-01 January 4, 1993 Page 2 of 3 equipment. Those factors involve (1) the possible use of improper stem material constants and (2) the failure to account for a torque effect when the VOTES equipment is calibrated by measuring strain in the threaded portion of the valve stem. In its October 2 submittal, Liberty Technologies states that the factors mainly cause the thrust estimated by its equipment to be less than the actual thrust. Therefore, the factors will primarily relate to the potential for the maximum allowable thrust limits of MOVs to be exceeded. In its October report, Liberty Technologies provided information on performing manual calculations to address these factors and stated that its new software, Version 2.3, assists in performing corrections to the thrust data. During an inspection of the MOV program at the LaSalle Nuclear Power Station in November 1992 (NRC Inspection Report 50-373/92-023 dated December 16, 1992), the NRC found that the licensee had performed the manual corrections of thrust data from MOV tests in accordance with guidance provided by Liberty Technologies to address the stem material and torque effect issues. In certain instances, the licensee determined that the VOTES equipment had underestimated by as much as 40 percent the thrust delivered by the motor actuator in opening and closing its valve. This underestimation of actual thrust by the VOTES equipment raised questions regarding the effect of higher thrust on the MOV assembly and the operation of the motor under degraded voltage conditions for several MOVs. Related Generic Communications The NRC has issued other generic communications on the accuracy of MOV diagnostic equipment and thrust limits. Most recently, (1) On March 27, 1992, the NRC issued IN 92-23, "Results of Validation Test- ing of Motor-Operated Valve Diagnostic Equipment," to alert licensees to information regarding the accuracy of MOV diagnostic equipment manufactured by ITI-MOVATS and ASEA-Brown Boveri Impell. (2) On December 17, 1992, the NRC issued IN 92-83, "Thrust Limits for Limitorque Actuators and Potential Overstressing of Motor-Operated Valves," to alert licensees to concerns identified in two programs used by licensees to increase thrust limits of Limitorque actuators. . IN 93-01 January 4, 1993 Page 3 of 3 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: Thomas G. Scarbrough, NRR (301) 504-2794 Attachment: List of Recently Issued NRC Information Notices .
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