IE Circular No. 79-07, Unexpected Speed Increase of Reactor Recirculation MG Set Resulted in Reactor Power Increase


                              April 30, 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, Office of Inspection and 


     The subject circular is transmitted for issuance no later than the 
close of business on May 2, 1979. The circular should be issued to all 
holders of BWR Operating Licenses or Construction Permits. Also enclosed is 
a draft copy of the transmittal letter. 

                                        Norman C. Moseley, Director 
                                        Division of Reactor Operations 
                                        Office of Inspection and Enforcement

1.   Draft Transmittal Letter
2.   IE Circular No. 79-07

CONTACT:  C. J. DeBevec, IE 

(Draft transmittal letter for IE Circular 79-07, to each holder of a BWR 
Operating License or Construction Permit.) 

                                                      IE Circular No. 79-07 


The enclosed IE Circular No. 79-07, is forwarded to you for information. No 
written response is required. Should you have any questions related to your 
understanding of this matter, please contact this office. 


                                        (Regional Director) 

IE Circular No. 79-07

                              UNITED STATES 
                          WASHINGTON, D. C. 20555 

                                May 2, 1979 

                                                      IE Circular No. 79-07 


Description of Circumstances: 

On November 24, 1978, an unexpected rapid speed increase was experienced on 
the `B' Reactor Recirculation MG set (RRMG) at the Cooper Nuclear Station. 
Prior to the event, the RRMG set had been inadvertently tripped during the 
performance of routine maintenance. Upon restart, the MG set would not 
respond to a speed increase signal. Licensee personnel commenced trouble 
shooting this problem in accordance with the instructions in the 
manufacturer's technical manual. 

One step of these instructions suggested removing the fuse from the Bailey 
scoop tube actuator circuit (a blown fuse would de-energize the actuator and
not permit the scoop tube to move). When the terminal panel cover was 
removed, licensee personnel noted two fuses instead of one as shown on the 
vendor drawings. When licensee personnel removed the second fuse to verify 
fuse integrity, a rapid speed increase of the MG set occurred. This increase
was terminated by replacement of the fuse or tripping of the MG set by the 
control room operator (both actions took place almost simultaneously). 

The input signal to the scoop tube actuator is received from the speed 
controller via a function generator. This signal is a scoop tube position 
demand signal. As the actuator drives the scoop tube in or out of the fluid 
coupler, a position followup signal is generated to null the input signal 
and stop scoop tube motion at the required position. The vendor's drawings 
of the scoop tube actuator circuit showed only one fuse in the circuit. The 
licensee contacted the vendor regarding the second fuse and was informed 
that this fuse had been added as a change in the initial circuit design to 
provide protection for certain electronic components in this circuit. This 
additional fuse is located in the position followup circuit. Removal or loss 
of the fuse would result in a loss of the nulling signal and would cause the 
scoop tube to drive to the maximum speed position. 

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IE Circular No. 79-07                                          May 2, 1979 

The licensee examined the circuit for the 'a' RRMG set scoop tube actuator 
and discovered that it contained only the single fuse as indicated on the 
vendor's drawings. 

At the time of the speed increase, the reactor was operating at 27 percent 
power. The speed increase on the RRMG set caused power to increase rapidly 
to 75 percent until terminated by the manual trip of the RRMg set. The short
term reactivity increase corresponded to a reactor period of less than 5 

A check of reactor parameters after this event verified that no core limits 
were exceeded. The FSAR contains an analysis of a similar transient which is
failure of a speed controller causing one RRMG set to drive to the maximum 
speed condition. This analyzed transient starts from a 100 percent power rod
pattern, whereas the observed transient commenced from a lower power rod 
pattern. Therefore, this observed transient falls within the bounds of the 
FSAR analysis. 

As part of the corrective action for the event, the licensee has placed a 
warning sign on the control panel cover to remind technicians of the effect 
of removing the second fuse. 

Recommended Actions for Licensee's Consideration: 

All holders of operating licenses for BWR plants employing variable speed 
Reactor Recirculation Motor Generator sets should be aware of the potential 
for occurrences of the type indicated above. It is recommended that this 
area be reviewed at your facility in the following respects: 

1.   A review of the scoop tube actuator circuit should be conducted to 
     verify that the circuit diagram indicates the actual number of fuses 

2.   Where the actual circuit configuration contains the second fuse (in the
     scoop tube position follow-up circuit) a warning statement describing 
     the consequences of its removal when the unit is operating should be 
     incorporated into the troubleshooting guides. A permanent label to the 
     same effect should be placed on the control panel cover which houses 
     the fuse. In addition, operating personnel and maintenance technicians 
     should be apprised of the effect of removing the fuse from the circuit.

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IE Circular No. 79-07                                          May 2, 1979 

3.   Review procedural controls for troubleshooting systems and components 
     that have the potential to affect significant plant parameters such as 
     power level, water level pressure, etc. Ensure that when a vendor's 
     technical manual is being used in lieu of a detailed procedure, all 
     personnel are sensitive to differences between the actual equipment and
     the manual description. When discrepancies are identified, resolution 
     should be obtained before proceeding. 

This circular is being forwarded to all holders of BWR construction permits 
for information. 

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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