United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 86-93: IEB 85-03 Evaluation of Motor-Operators Identifies Improper Torque Switch Settings

                                                            SSINS No.:  6835
                                                            IN 86-93 

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT
                            WASHINGTON, DC 20555

                              November 3, 1986

Information Notice No. 86-93: IEB 85-03 EVALUATION OF MOTOR-OPERATORS 
                                 IDENTIFIES IMPROPER TORQUE SWITCH SETTINGS 

Addressees: 

All nuclear power reactor facilities holding an operating license or a 
construction permit. 

Purpose: 

This notice is provided to alert recipients of a potentially significant 
safety problem discovered while performing the evaluation requested by IE 
Bulletin 85-03, "Motor-Operated Valve Common Mode Failures During Plant 
Transients Due to improper Switch Settings,"(IEB 85-03). It is expect view 
the information for applicability to their facilities and consider actions, 
if appropriate, to preclude similar problems from occurring at their 
facilities. However, suggestions contained in this notice do not constitute 
NRC requirements; therefore, no specific action or written response is 
required. 

Description of Circumstances: 

As a result of followup on IEB 85-03, Duke Power Company (DPC) discovered 
problems with valves operated by Rotork valve actuators at McGuire Nuclear 
Station. Specifically, the problem involved valves for which the factory-set
torque switch settings had been previously changed at the plant site using a 
generic correlation between actuator torque output and torque switch 
setting. This could cause valve actuator motors to switch off before the 
valves complete their travel. Arbitrarily raising the torque switch setting 
to its maximum may result in damage to the valve and/or motor especially 
since thermal overload protection has been eliminated in many applications. 
Based upon this information, DPC has declared safety systems inoperable and 
shut down McGuire Units 1 and 2. 

Discussion: 

The vendor states that whenever the factory torque switch setting is changed
in the field, an individual calibration curve or a bench test is required to
accurately determine torque output. 


8610310306 
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                                                       IN 86-93 
                                                       November 3, 1986 
                                                       Page 2 of 3 

According to information recently provided by the vendor, torque switch 
settings of 1, 2, 3, 4, and 5, do not always correspond to rated torque 
output values between 40 and 100 percent as was used based on general 
information available several years ago. Tests and analytical evaluations by 
the licensee now confirm that the correlation used by the licensee was 
incorrect for some actuators. For example, evaluation of several valve 
actuator certificates for the same model revealed that the actual torque 
output with a switch setting of "1" varied through a range of 11 to 55 
percent of maximum actuator torque output. The review did not indicate a 
variation in maximum output at the number 5 setting. 

Analysis of two valves installed in the normal charging path, which would be
required to close during safety injection, indicated that they may not be 
able to do so under differential pressure conditions which could exist 
following a loss-of-coolant accident. Although the as-found switch setting 
agreed with the design setting determined by DPC,the application of output 
torque values being linear between 40 and 100 percent was not correct for 
all actuators. Preliminary data indicates that up to 41 nuclear units may 
have some Rotork valve actuators. It is not known whether or not these are 
used in safety related applications. 

The above example specifically deals with improper setting of the torque 
switches and illustrates the need for exercising extreme care in the setting
of motor-operator switches because all types of switches must be set 
properly to ensure that the valves will function properly when needed. In 
fact, the specific event that prompted the issuance of IEB 85-03 was caused 
by improperly set torque bypass switches. Improperly pet thermal overload 
switches recently (October 22, 1986) rendered the high-pressure coolant 
injection system inoperable at the Hope Creek Nuclear Station Unit 1. Both 
of these instances involved actuators manufactured by a company other than 
Rotork. 

In addition, care must be taken to insure that all of the ramifications of 
changes to any of the motor-operator switches are fully understood. For 
instance, Information Notice No. 86-29, "Effects of Changing Valve 
Motor-Operator Switch Settings, describes how the changing of the limit 
switches on certain motor-operated valves resulted in a control room 
indication that the valves were closed when, in fact, they were partially 
open. This led to an excessive cooldown rate in the reactor coolant system 
at San Onofre Nuclear Generating Station Unit 3. 

The information herein is being provided as an early notification of a 
possibly significant matter that is still under consideration by the NRC 
staff. Recipients should review the information for possible applicability 
to their facilities. If NRC evaluation so indicates, further licensee 
actions may be requested. 

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                                                       IN 86-93 
                                                       November 3, 1986 
                                                       Page 3 of 3 

No specific action or written response is required by this information 
notice. If you have any questions about this matter, please contact the 
Regional Administrator of the appropriate regional office.or this office. 


                                   Edward L. Jordan, Director 
                                   Division of Emergency Preparedness 
                                     and Engineering Response 
                                   Office of Inspection and Enforcement 

Technical Contacts:  George Schnebli, RII 
                     (404) 331-5582 

                     Richard J. Kiessel, IE 
                     (301) 492-8119 

Attachment:    List of Recently Issued IE Information Notices
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