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HomeNRC LibraryDocument CollectionsGeneric CommunicationsInformation Notices1979

# Information Notice No. 79-29, Loss of Nonsafety-Related Reactor Coolant System Instrumentation During Operation

```
IN79029 

                            November 16, 1979 

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:               Norman C. Moseley, Director, Division of Reactor 
                      Operations Inspection, IE 

SUBJECT:            Information Notice No. 79-29, LOSS OF 
                    NONSAFETY-RELATED REACTOR COOLANT SYSTEM INSTRUMENTATION
                    DURING OPERATION 

The subject document is transmitted for issuance on November 16, 1979. The 
Information Notice should be issued to all power reactor facilities holding 
operating licenses and construction permits. 

Also enclosed is a draft copy of the transmittal letter. 


                                        Norman C. Moseley, Director 
                                        Division of Reactor Operations 
                                          Inspection 
                                        Office of Inspection and Enforcement 

Enclosure: 
1.   Draft Transmittal Letter 
2.   Information Notice No. 
       No. 79-29 

CONTACT:  H. W. Woods, IE 
          49-28180 
.

(Transmittal letter for Information Notice No. 79-29 to each holder of an 
NRC Operating License and Construction Permit.)  

                                            Information Notice No. 79-29 

Addressee: 

This Information Notice is provided as an early notification of a possibly 
significant matter. It is expected that recipients will distribute this 
Notice to their operating personnel and will review the information for 
possible applicability to their facilities. No specific action or response 
is requested at this time. However, we anticipate that further NRC 
evaluations will result in issuance of an IE Circular, Bulletin, or NRR 
Generic Letter in the near future which will recommend or request specific 
applicant or licensee actions. If you have questions regarding the matter, 
please contact the Director of the appropriate NRC Regional Office. 

                                        Sincerely, 


                                        Signature 
                                        (Regional Director) 

Enclosures: 
1.   Information Notice No. 
       No. 79-29 
2.   List of IE Information 
       Notices Recently Issued
.

                                                            SSINS No.:  6300
                                                            Accession No.: 
                                                            7910250490 
                              UNITED STATES 
                      NUCLEAR REGULATORY COMMISSION 
                   OFFICE OF INSPECTION AND ENFORCEMENT 
                          WASHINGTON, D.C. 20555 
                                     
                            November 16, 1979  

                                           Information Notice No. 79-29 

LOSS OF NONSAFETY-RELATED REACTOR COOLANT SYSTEM INSTRUMENTATION DURING 
OPERATION 

This notice contains information regarding a loss of reactor coolant system 
instrumentation as a consequence of a failure of a static transfer switch to
transfer to an alternate supply. 

At 3:15 p.m. on November 10 with Unit 3 of the Oconee Station at 100 percent
power, the main condensate pumps tripped, apparently as a result of a 
technician performing maintenance on the hotwell level control system. This 
led to reduced feedwater flow to the steam generators, which resulted in a 
high reactor coolant system (RCS) pressure reactor trip and simultaneous 
turbine trip at 3:16:57 p.m.  At 3:17:15 p.m., the inverter power supply, 
nonsafety-related, feeding all power to the integrated control system (ICS) 
tripped and failed to automatically transfer its loads from the DC power 
source to the regulated AC power source. The inverter had tripped due to 
blown fuses, resulting in loss of RCS indicators and recorders in the 
control room, except one wide range RCS pressure recorder. 

This condition existed for approximately three minutes, until an operator 
could reach the equipment room and switch the inverter manually to the 
regulated AC source. As a result of the power failure to the ICS, all valves
controlled by the system assumed their respective fail positions. This 
resulted in a cool down of the RCS to 1635 psi and 530 degrees F. The 
operator, expecting this condition, started all makeup pumps and opened the 
associated high pressure injection valves to the RCS which limited the rate 
of RCS pressure reduction and associated reduction in pressurizer level. At 
3:20:42 p.m., power was restored to the ICS and RCS conditions were 
restored. 

Although RCS cooldown limits were exceeded, the pressurizer and steam 
generators did not go dry, and at least 79 degrees F subcooling was 
maintained during this event. No engineered safety features actuation 
setpoints were reached, and, except for the components discussed above, no 
component malfunctions occurred. 

The licensee has installed a redundant electromechanical transfer switch 
between the loads and the regulated supply. This switch will actuate and 
power the loads from the regulated supply should the original static switch 
fail to transfer. 

Longer term resolution of the need or desirability to separate these 
instruments onto diverse electrical supplies or to provide redundant 
instrumentation display channels for operator use from essential power 
supplies are also under 
.

Information Notice No. 79-29                           November 16, 1979 
                                                            Page 2 of 2 

consideration. It is anticipated that further NRC evaluations will result in
issuance of an IE Circular, Bulletin, or NRR Generic letter in the near 
future which will recommend or request specific applicant or licensee 
actions. 

This Information Notice is provided to inform licensees of a possibly 
significant matter. It is expected that recipients will disseminate the 
information to all operational personnel working at their licensed 
facilities. If you have questions regarding this matter, please contact the 
Director of the appropriate NRC Regional Office. 

No written response to this Information Notice is required.
```

*Page Last Reviewed/Updated Friday, May 22, 2015*

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