United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 91-04: Reactor Scram Following Control Rod Withdrawal Associated with Low Power Turbine Testing

                               UNITED STATES
                       NUCLEAR REGULATORY COMMISSION
                   OFFICE OF NUCLEAR REACTOR REGULATION
                          WASHINGTON, D.C.  20555

                             January 28, 1991


Information Notice No. 91-04:  REACTOR SCRAM FOLLOWING CONTROL ROD 
                                   WITHDRAWAL ASSOCIATED WITH LOW POWER 
                                   TURBINE TESTING 

Addressees: 

All holders of operating licenses or construction permits for nuclear power 
reactors. 

Purpose: 

This information notice is provided to alert licensees to an event 
involving a reactor scram at low power following control rod withdrawal 
during a turbine test at the Commonwealth Edison Company's Quad Cities 
Station. 

This event demonstrates the need for careful planning, increased awareness, 
training, proper review and use of procedures, and good communications when 
a plant is placed in a non-typical mode of operation because of special 
testing or other unusual conditions.  It is expected that recipients will 
review the information for applicability to their facilities and consider 
actions, as appropriate, to avoid similar problems.  However, suggestions 
contained in this information notice do not constitute NRC requirements; 
therefore, no specific action or written response is required. 

Description of Circumstances: 

On October 27, 1990, Quad Cities, Unit 2, scrammed on a hi-hi intermediate 
range scram signal, when the operator withdrew rods to increase reactor 
pressure without recognizing the need to follow the normal procedures for 
re-establishing reactor criticality.  The operator focused on controlling 
reactor pressure and did not adequately monitor reactivity.  

In preparation for performing a turbine torsional test with the reactor at 
low power and with the plant not supplying the grid, reactor power and 
pressure were reduced to close the turbine bypass valves and thereby allow 
the electro-hydraulic control (EHC) oil pumps to be secured and test 
equipment to be connected.  The procedure specified that reactor power and 
pressure be increased after the temporary alterations were made.  However, 
the licensee provided no special training for performing the turbine 
torsional test and the plant staff was unaware that the plant conditions 
required by the test were difficult to maintain.  In addition, the 
licensee's procedures were not sufficiently comprehensive to ensure stable 
plant operation during installation or removal of the test equipment. 



9101230299 
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                                                           IN 91-04 
                                                           January 28, 1991
                                                           Page 2 of 3 


The Shift 1 crew inserted control rods to decrease reactor power and 
pressure to permit installation of the test equipment.  At the end of Shift 
1, the crew reported to the Shift 2 nuclear station operator (NSO) that 
they had experienced high rod notch worth (i.e., large reactivity changes 
with relatively small amounts of rod movement) during these manipulations.  
However, the information was not recorded in the Unit 2 log book.  During 
Shift 2, the testing was not performed because of problems in controlling 
the turbine acceleration rate.  The information on high rod notch worth 
that was received by Shift 2 was not relayed to Shift 3.

Shortly after the start of Shift 3, the testing was aborted, and the shift 
engineer (SE) told the shift control room engineer (SCRE) to return to 
power operation.  The SCRE instructed the Unit 2 NSO to decrease reactor 
pressure to approximately 800 psig to ensure that the turbine bypass valves 
would be closed and to permit the securing of the EHC system and the 
removing of the test equipment.  The SCRE then became preoccupied with 
other activities such as reinerting the drywell and did not supervise the 
NSO's actions.  The NSO failed to use the procedure for going from power to 
hot standby.  The NSO monitored pressure as he inserted rods, but failed to 
stop when the reactor power dropped below the point of adding heat and went 
subcritical.  When all bypass valves were closed and reactor pressure was 
approximately 805 psig and decreasing, the NSO attempted to withdraw 
control rods to stabilize pressure, but was prevented because of a rod 
block caused by a low count rate on the source range monitor (SRM).  After 
clearing the rod block by inserting the SRMs and as the NSO began 
withdrawal of control rods, the reactor became supercritical and scrammed 
on hi-hi intermediate range flux.  A complete discussion of this event may 
be found in the Public Document Room in a memorandum dated December 28, 
1990, from Jack E. Rosenthal, Division of Safety Programs, Office for 
Analysis and Evaluation of Operational Data, to Thomas M. Novak, SUBJECT:  
HUMAN FACTORS STUDY REPORT - QUAD CITIES 2 (10/27/90). 

Discussion: 

The safety significance of this event is that the plant was placed in a 
non-typical mode of operation without adequate planning, awareness, 
training, review and use of procedures, and communications.  Factors that 
contributed to the event included the following:  

1.  Lack of awareness by the plant staff that the reactor conditions 
    required for the torsional test were difficult to maintain, 

2.  Insufficient comprehension of written procedures regarding reactivity 
    control, 

3.  Lack of specific training for the performance of the torsional test and 
    for achieving and maintaining the reactor conditions required, 

4.  Failure to communicate valuable information from previous shifts, and 

5.  Lack of adequate supervision of the nuclear operator. 

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                                                           IN 91-04 
                                                           January 28, 1991
                                                           Page 3 of 3 


This information notice requires no specific action or written response.  
If you have any questions about the information in this notice, please 
contact one of the technical contacts listed below or the appropriate NRR 
project manager. 




                             Charles E. Rossi, Director 
                             Division of Operational Events Assessment 
                             Office of Nuclear Reactor Regulation 


Technical Contacts:  E. Trager, AEOD
                     (301) 492-4496

                     B. Kaufer, AEOD
                     (301) 492-4544


Attachment:  List of Recently Issued NRC Information Notices
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