United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 86-69: Spurious System Isolations Caused by Panalarm Model 86 Thermocouple Monitor

                                                          SSINS No.: 6835 
                                                            IN 86-69       

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT
                           WASHINGTON, D.C. 20555

                               August 18, 1986

Information Notice No. 86-69:   SPURIOUS SYSTEM ISOLATIONS CAUSED BY THE 
                                   PANALARM MODEL 86 THERMOCOUPLE MONITOR 

Addressees: 

All General Electric boiling water reactor facilities holding an operating 
license or a construction permit. 

Purpose: 

This notice is to alert recipients of a potentially significant problem 
involving isolations of various BWR systems caused by spurious trips of the 
Panalarm Model 86 thermocouple monitors, and of the actions taken by a 
licensee to mitigate the problem. It is expected that recipients will review
this information for applicability to their facilities and consider actions,
if appropriate, to preclude a similar problem 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: 

Licensee event reports (LERs) involving a spurious actuation of an isolation
system were recently compiled and evaluated in an NRC Office for Analysis 
and Evaluation of Operational Data Report (AEOD/E604, March 14, 1986). Of 
the 31 LERs studied from various facilities between January 1984 and 
November 1985, only 1 event involved a valid trip of the thermocouple 
monitor resulting from a high differential room temperature. Additional LERs 
related to spurious isolation have been reported since the AEOD compilation. 
To date the monitor trips have affected eight different plants and have 
caused spurious isolations of reactor core isolation cooling (RCIC), 
high-pressure coolant injection (HPCI), reactor water cleanup (RWCU), and 
main steam isolation valves. 

On January 14, 1985, General Electric issued a Service Information Letter 
(SIL No. 416) that provided recommended corrective actions for inadvertent 
isolations which occurred following loss and restoration of the ac power 
supply. In addition to the problem addressed by the GE SIL, three recurring 
problems have been identified from the LERs. The predominant source of the 
monitor trips were caused by the operation of the monitor's "READ/SET" 
switch. Trips also were attributed to electrical noise and nearby 
maintenance activities. The spurious actuations have not always been 
repeatable by testing. 




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Discussion: 

The Panalarm Model 86 thermocouple monitor has been manufactured or 
distributed by Ametek Panalarm Division, Scam Instrument Corporation, and 
Riley Panalarm Company. It consists of three major components: (1) a point 
module, which contains the appropriate thermocouple for each area monitored;
(2) an optional meter module, which permits reading the actual temperatures 
monitored; and (3) a thermocouple monitor, which amplifies the output of the
thermocouple. When the temperature being monitored, is in an alarm 
condition, the monitor can be set to close relay contacts and initiate 
further action such as isolations or provide annunciation. The actual 
monitoring function is performed continuously and is independent of the 
operation of any controls. The indication depends on the operation of a 
"READ/SET" switch which causes the outputs of each point module to be 
indicated by the respective meter module. As stated above, the transient 
caused by operation of this switch has been the most prevalent cause of the 
monitor trips. 

The Duane Arnold Energy Center, following spurious isolation events, has 
installed a 1-second time delay in the steam leak detection circuitry for 
the RWCU and is planning to install similar time delays in the HPCI and RCIC
circuits. The addition of a 1-second time delay appears to have been 
effective at eliminating spurious isolations while allowing an actual alarm 
condition to initiate isolation as designed. Duane Arnold Center verified 
that the addition of a 1-second time delay between the monitor and isolation
actuation would not cause any valve closure times to exceed the assumptions 
of the design basis and safety analysis of the various systems. The increase
in system reliability and reduction in challenges to the systems was 
considered by Duane Arnold Center to result in a greater margin of safety. 

GE has stated that additional information concerning increasing reliability 
of the thermocouple monitor will be issued in the near future via the SIL 
system. 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:  James Stewart, IE
                    (301) 492-9061

Attachment: List of Recently Issued IE Information Notices 
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