United States Nuclear Regulatory Commission - Protecting People and the Environment

IE Circular 77-13, Reactor Safety Signals Negated During Testing


                            September 22, 1977 

MEMORANDUM FOR:     B. H. Grier, Director, Region I 
                    J. P. O'Reilly, Director, Region II 
                    J. G. Keppler, Director, Region III 
                    E. M. Howard, Director, Region IV 
                    R. H. Engelken, Director, Region V 

FROM:               H. D. Thornburg, Director, Division of Reactor  
                    Operations Inspection, IE 

                    DURING TESTING 

The subject document is transmitted for issuance on September 22, 1977. The 
Circular should be issued to all holders of Reactor Operating Licenses and 
Construction Permits. Also enclosed is a draft copy of the transmittal 

                                        Harold D. Thornburg, Director 
                                        Division of Reactor Operations  
                                        Office of Inspection and 

1. Circular 77-13 
2. Draft Transmittal Letter 

CONTACT:  V. D Thomas, IE 

Transmittal letter for Circular 77-13, to each holder of an NRC Operating 
License and Construction Permit. 


The enclosed Circular 77-13, is forwarded to you for information. If there 
are any questions related to your understanding of the suggested actions, 
please contact this office. 

                                        (Regional Director) 

IE Circular 77-13 

                                                 IE Circular 77-13 
                                                 Date: September 22, 1977 
                                                 Page 1 of 3 


On July 12, 1977, the Commonwealth Edison Company reported that while 
conducting a surveillance test at Zion Unit 2, test signals were 
simultaneously injected into several sensors which affected both protection 
and control systems. Injection of these test signals resulted in: (1) the 
loss of instrument indications for the affected protection and control 
systems, (2) the loss of automatic control capability for the affected 
control systems, and (3) the loss of automatic protection capability for the
affected protection systems. 

At the time of the event, the unit was in a hot shutdown condition and 
preparations for start-up were underway. Station management decided to 
perform a surveillance test of the reactor protection logic circuitry. A 
combination of test procedure inadequacies and the failure to follow 
prescribed administrative controls related to instrumentation testing led to
the insertion of test signals which replaced the actual signals from three 
pressurizer water level sensors, three water level sensors in each of the 
four steam generators, four pressurizer pressure sensors and three flow 
sensors in each of the primary coolant loops. The test signals had been 
inserted for approximately 40 minutes when, due to unexpected indications of
the main coolant pump seal flow rate and other anomalous indications, the 
operator requested that the test signals be removed. When the test signals 
were removed, it was observed that the pressurizer water level had dropped 
below the range of indication. 

The drop in pressurizer water level resulted from the pressurizer water 
level test signal being slightly higher than the automatic pressurizer level
control set point. In response to this condition the changing pump flow was 
automatically reduced to the minimum pump flow rate, which was maintained 
until the test signals were removed. During this forty minute period the 
letdown flow remained constant. Consequently, the rate at which coolant was 
being removed from the primary coolant system was approximately 75 gpm 
greater than the rate at which coolant was being returned to the system. 
Approximately 5300 gallons of water was required to bring the pressurizer 
water level back to its original level of twenty-two percent. 

                                                 IE Circular 77-13 
                                                 Date: September 22, 1977 
                                                 Page 2 of 3 

As mentioned above, operator action, in response to other available 
instrumention indications terminated the event. Subsequent investigation by 
the licensee revealed that no damage to plant equipment was sustained during
or after the event. 

This incident represents an example of an event which resulted from a series
of errors involving lax management control and improper attention of plant 
personnel to established procedures. 

All holders of operating licenses should be aware of the potential for 
adverse operational events which can occur during performance of particular 
surveillance tests. For example, if an excessive number of safety sensors 
are disabled simultaneously as was the case in this event, automatic action 
may not occur as intended. Care must be taken to assure that test signals do 
not negate automatic initiation of protection systems. It is recommended 
that the following considerations be incorporated in your reviews of this 

1.   Facility procedures should specifically identify the limitations and 
     restrictions which are required for each mode of operation during which
     testing or surveillance activities may be conducted such that required 
     safety protection systems will remain operable in accordance with the 
     facility Technical Specifications. 

2.   In order to provide additional assurance that required safety related 
     capabilities of plant systems are not defeated during testing or 
     surveillance activities, training programs for operations and craft 
     personnel should include sufficient information to assure an indepth 
     understanding of system functions, system interactions, and Technical 
     Specification requirements. 

3.   Management controls should be strengthened as necessary to assure 
     adherence to administrative procedures involving reviews, approvals, 
     and communication between, plant supervision, operators and craft 
     personnel performing testing and surveillance activities. Such controls 
     should consider the "man-machine" interfaces, and should assure that 
     the human component of this pair is not overburdened. 

                                                 IE Circular 77-13  
                                                 Date: September 22, 1977 
                                                 Page 3 of 3 

No written response to this Circular is required. If you require additional 
information regarding this matter, contact the Director of the appropriate 
NRC Regional Office. IE inspectors will review this matter with licensees 
during future inspections. 

List of IE Circulars: 
  Issued in 1977 

Page Last Reviewed/Updated Tuesday, September 01, 2015