Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
SSINS No.: 6835
IN 83-75
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C., 20555
November 3, 1983
Information Notice No. 83-75: IMPROPER CONTROL ROD MANIPULATION
Addressees:
All nuclear power reactors holding an operating license (OL) or construction
permit (CP).
Purpose:
This information notice is provided as a notification to licensees of
improper control rod manipulations. The improper manipulations were used
because of inadequate communications from and controls by plant management.
It is expected that recipients will review the information for applicability
to their facilities.
Description of Circumstances:
On March 10, 1983, Unit One at Quad Cities Station was being shut down in
preparation for a weekend maintenance outage. The operators were inserting
rods using what they thought was an approved "fast shutdown sequence"
provided by the station nuclear engineers. They were actually using a rod
worth minimizer (RWM) computer printout that had been attached to the
approved sequence. The RWM computer printout listed the rod groups to be
inserted in reverse order of the actual sequence required.
As the shutdown continued the operators attempted to activate the RWM
according to the normal unit shutdown procedure. The RWM immediately
produced a rod block and indicated that rod insertion errors had occurred.
After discussing the situation with the shift supervisor, it was decided
that the RWM should be declared inoperable and bypassed.
The shutdown continued with the shift supervisor acting as the independent
rod verifier using the RWM computer printout as the assumed correct
sequence. At approximately 10% power, the turbine generator was tripped and
the reactor was manually scrammed as part of the normal shutdown. On the
following morning, March 11, 1983, plant management discovered that the
control rods had been inserted in reverse order using the RWM computer
printout.
On July 14, 1983, Hatch Unit 2 was operating at about 25% power, following a
startup after a refueling outage, when condenser vacuum began to decrease.
It was apparent to the plant operators that there was a problem with the
steam jet air ejector and reactor power would have to be decreased to start
a mechanical vacuum pump to prevent the loss of a reactor feed pump and a
reactor
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IN 83-75
November 3, 1983
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scram. The operators began to insert rods using the approved rod sequence,
but because of the low worth of the control rods in this portion of the
sequence, the power was not being decreased at the desired rate. At this
time a decision was made by licensed operators and the shift technical
advisor to insert rods using the Rod Out Notch Override Switch in the
emergency in position and by individually scramming rods from the scram test
panel. The operators did not have any approved procedure for this type of
shutdown and defeated the rod sequence control system (RSCS) and the RWM.
When the mechanical vacuum pump was put into service at a reduced power
level and the vacuum had stabilized, an operator found a control rod in an
out-of-sequence position, The operator then manually scrammed the unit
following a plant procedure concerning out-of-sequence control rods.
Discussion:
The events, described above did not result in fuel damage, but affected the
plants' ability in a rod drop accident. The control rod sequence, the RWM,
and the RSCS are all used to mitigate the consequences of a control rod drop
accident. The misuse of these protective features could result in fuel
damage. Plant managers should train and properly communicate to their
operators the importance of these protective features and the adherence to
approved rod sequence procedures.
No written response to this notice is required. If you have any questions
regarding this matter, please contact the Regional Administrator of the
appropriate NRC Regional Office, or this office.
Edward L. Jordan Director
Division of Emergency Preparedness
and Engineering Response, IE
Technical Contact: Paul R. Farron, IE
(301) 492-4766
Attachment:
List of Recently Issued IE Information Notices
.
