Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
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.
8608130575
.
IN 86-69
August 18, 1986
Page 2 of 2
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
