Information Notice No. 86-29: Effects of Changing Valve Motor-Operator Switch Settings

                                                            SSINS No: 6835 
                                                            IN 86-29       

                                UNITED STATES
                           WASHINGTON, DC 20555

                               April 25, 1986

                                   SWITCH SETTINGS 


All nuclear power reactor facilities holding an operating license (OL) or a 
construction permit (CP) 


This notice is provided to alert recipients to potential significant safety 
effects of changing valve motor-operator switch settings as part of a 
program to meet the requirements of Inspection and Enforcement Bulletin 
(IEB) 85-03, "Motor-Operated Valve Common Mode Failures During Plant 
Transients Due to Improper Switch Settings" Changes to switch settings can 
effect valve position indication and signals such as "permissives" to other 
equipment It is expected that recipients will review the information for 
applicability to their facilities However, suggestions contained in this 
notice do not constitute NRC requirements; therefore, no specific action or 
written response is required 

The information herein is being provided as an early notification of a 
possibly significant matter that is still under consideration by the NRC 
staff If NRC evaluation so indicates, licensees will be kept informed of 
further developments 

Description of Circumstances: 

On January 23, 1986 the Southern California Edison Company notified NRC 
[licensee event report (LER) 85-036] that it had exceeded the cooldown rate 
limitation of its Technical Specifications at Unit 3 of the San Onofre 
Nuclear Generating Station on December 24, 1985 The licensee failed to 
fully followup on the effect of changing the valve motor-operator torque 
bypass switch setting as a part of the program to meet the requirements of 
IEB 85-03 

The plant had entered Mode 3 on December 18, 1985 following their first 
refueling outage The plant entered Mode 4 on December 22, 1985 to perform 
maintenance on a reactor coolant pump Cooldown continued, and on December 
24, 1985 the shutdown cooling system (SDCS) was aligned for warmup At the 
time of alignment, the SDCS heat exchangers were thought to be bypassed and 
isolated, as indicated by observation of the isolation valve position in the
control room When SDCS flow was aligned, an initial increase in the reactor


                                                             IN 86-29      
                                                             April 25, 1986 
                                                             Page 2 of 3   

system (RCS) cooldown rate was expected; however, RCS temperature was found 
to decrease at a rate which was considerably greater than expected and which
exceeded the technical specification limitations When the plant operators 
recognized the excessive cooldown rate, they attempted to reduce the rate of
RCS temperature decrease by throttling the SDCS loop injection valves to 
reduce the SDCS flow rate As part of this process, the control room 
switches for the SDCS heat exchanger isolation valves were depressed and 
held in the closed position to confirm the existing control room indication 
that these valves were indeed in the closed position The RCS cooldown rate 
was immediately noted to decrease, thereby indicating SDCS flow had, until 
then, been permitted to pass through the SDCS heat exchangers, contrary to 
the control room indication With the SDCS heat exchanger isolation valves 
truly closed, the RCS cooldown ate was adjusted and maintained within the 
limitations of the Technical Specifications 

Another limiting condition of the plant's Technical Specifications requires 
that two independent emergency core cooling system (ECCS) subsystems be 
operarable in Modes 1, 2, and 3 with the pressurizer pressure greater than 
or equal to 400 psia) The valve alignment to assure this condition is 
verified twice a day by observation of the control room position 
indications Subsequent investigation indicated that both of the SDCS heat 
exchanger isolation valves could have been as much as 16 percent open while 
the control room indication of their position showed closed 

The valve motor-operator, torque bypass switches on the SDCS heat exchanger 
isolation valves had been adjusted because of concerns raised in IEB 85-03 
The motor operators on these valves are protected from overload by torque 
switches It was determined that the torque bypass switch had to be 
precisely set such that the increased torque required to initially open 
valves against high differential pressure would not result in deenergizing 
the motor operator However, due to the design of the valve control 
circuitry, the torque bypass switch and the valve position indicating limit 
switch are on the same position indicating rotor Therefore, when the 
position of the rotor was changed to extend the range of the torque bypass 
switch, it also affected the closed position indication 

The valves involved are throttle, or "jog", valves and are operated by 
holding the control switch in the direction of valve travel until the 
desired position is reached Both maintenance and operations personnel were 
aware of the premature fully closed indication which resulted from the 
recent adjustment to the torque bypass switches on the valve motor 
operators They planned on compensating for this condition by holding the 
valve control switch in the close position for a brief period of time after 
the "closed" indication was observed However, the exact time to hold the 
switch was not specified in the procedures, and apparently, when the valves 
were operated on December 18, 1985, for the surveillance test, they were not 
fully closed Subsequent observation of the valve operation by operations 
personnel determined that it was necessary to hold the valve switch in the 
closed position for at least 15 seconds after the "closed" indication was 
observed in the control room This information is being incorporated into 
the appropriate operating procedures 

                                                             IN 86-29      
                                                             April 25, 1986 
                                                             Page 3 of 3   


This LER points up the importance of fully understanding the effects of 
changing any of the valve motor-operator switch settings Even though the 
plant operations personnel were aware of the premature valve "closed" 
signal, they did not fully appreciate how early this signal was being 
produced; hence the operator did not hold the close switch for a long enough 
time when they performed the initial valve verification as they entered Mode 

This problem occurred on a throttle valve that did not have a "seal-in" 
feature Valves that do have the "seal-in" feature should continue to torque
closed regardless of the setting of the close position limit switch, and 
thus should not experience this particular problem 

However, whether or not the valve has the "seal-in" feature, the changing of
the valve motor-operator switch settings could have effects on other aspects
of plant operation, because of the limited number of position rotors 
available in the typical valve motor operator For instance, frequently the 
valve closed signal is used as a "permissive" signal to other pieces of 
equipment Thus, increasing the torque bypass switch setting could result in
the premature starting of some other plant operation--an action which may 
not have been fully analyzed with respect to its safety implications 

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 Contact:  Richard J Kiessel, IE
                    (301) 492-8119

List of Recently Issued IE Information Notices


Page Last Reviewed/Updated Friday, May 22, 2015