United States Nuclear Regulatory Commission - Protecting People and the Environment

IE Circular No. 78-19, Manual Override (Bypass) of Safety Actuation Signals


CR78019 

                                        December 28, 1978 

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

FROM:               Harold D. Thornburg, Director, Division of Reactor  
                    Construction Inspection, IE 

SUBJECT:            IE CIRCULAR NO. 78-19, MANUAL OVERRIDE (BYPASS) OF 
                    SAFETY ACTUATION SIGNALS 

The subject document is transmitted for issuance on December 29, 1978. The 
Circular should be issued to all power reactor facilities with a 
construction permit. This matter has been conveyed to all power reactor 
facilities with an operating license via a generic letter from the NRR 
Operating Reactor Branches. Also enclosed is a draft copy of the transmittal 
letter. 


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

Enclosures: 
1.  IE Circular No. 78-19 
2.  Draft Transmittal Letter 

CONTACT:  W. R. Rutherford, IE 
          49-27551 
.

(Draft letter to all power reactor facilities with a construction permit) 

                                                      IE Circular No. 78-19 
Addressee: 

The enclosed Circular 78-19 is forwarded to you for information. If there 
are any questions related to your understanding of the requested actions, 
please contact this office. 

                                        Sincerely, 


                                        Signature 
                                        (Regional Director) 

Enclosures: 
1.  IE Circular No. 78-19 
2.  List of IE Circulars 
      Issued in 1978 
.

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

                            December 29, 1978 

                                                     IE Circular No. 78-19 

MANUAL OVERRIDE (BYPASS) OF SAFETY SYSTEM ACTUATION SIGNALS 

Description of Circumstances: 

A review of several recent events has raised questions about safety system 
circuit designs which incorporate manual override (bypass) features. The two
events described below directly relate to the practice of containment 
purging during normal plant operation by manually overriding containment 
isolation signals. In these instances the automatic isolation function of 
the purge system containment isolation valves was unintentionally made 
inoperable, and this condition was neither continuously indicated in the 
control room nor known to the plant operators. 

During a review of operating procedures on July 25, 1978, the Northeast 
Nuclear Energy Company discovered that since May 1, 1978, intermittent 
containment purge operations had been conducted at Millstone Unit No. 2 with
the safety actuation isolation signals to both inlet and outlet redundant 
containment isolation valves (48 inch butterfly valves) in the purge inlet 
and outlet penetrations manually overridden and inoperable. The isolation 
signals which are required to automatically close the purge valves for 
containment integrity were manually overridden to allow purging of 
containment with a high radiation signal present. The manual override 
circuitry designed by the plant's architect/engineer defeated not only the 
high radiation signal but also all other isolation signals to these valves. 
To manually override a safety actuation signal, the operator cycles the 
valve control switch to the closed position and then to the open position. 
This action energized a relay which blocked the safety signal and allowed 
manual operation independent of any safety actuation signal. This circuitry 
was designed to permit reopening these valves after an accident to allow 
manual operation of certain safety equipment. 

On September 8, 1978, the Public Service Electric and Gas Company advised 
the staff that, as a matter of routine, Salem Unit No. 1 has been venting 
the containment through the containment ventilation system valves to reduce 
pressure. In certain instances this venting has occurred with the 
containment high particulate radiation monitor isolation signal to the purge 
and pressure-vacuum relief valves overridden. Override of 

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IE Circular No. 78-19                                      December 29, 1978

the containment isolation signal was accomplished by resetting the train A 
and B reset buttons. Under these circumstances, six valves in the 
containment vent and purge systems could be opened with a high particulate 
isolation signal present. This override was performed after verifying that 
the actual containment particulate levels were acceptable for venting. The 
licensee, after further investigation of this practice, determined that the 
reset of the particulate alarm also bypasses the containment isolation 
signal to the purge valves and that the purge valves would not have 
automatically closed in the event of an emergency core cooling system (ECCS) 
safety injection signal. 

These events and information gained from recent licensing actions have 
raised a generic concern relative to potential design deficiencies that 
could permit manually defeating a protection function. Since all plants with 
construction permits must meet the requirements of IEEE 279, we recommend 
that you review the design of all safety actuation signal circuits which 
incorporate a manual override feature to ensure that overriding of one 
safety actuation signal does not also cause the bypass of any other safety 
actuation signal, that sufficient physical features are provided to 
facilitate adequate administrative controls, and that the use of each such 
manual override is annunciated at the system level for every system 
impacted. 

Compliance with Federal Regulation 50.55a(h) requirements will be verified 
by NRC through the licensing review process and during regular onsite 
inspections for plants with construction permits. NRC's requirements 
relative to this matter have been conveyed to all operating plant licensee's 
via a generic letter. 

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. 

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