Information Notice No. 92-73: Removal of a Fuel Element from a Research Reactor Core While Critical

                                 UNITED STATES
                         NUCLEAR REGULATORY COMMISSION
                            WASHINGTON, D.C.  20555

                               November 4, 1992

                               REACTOR CORE WHILE CRITICAL


All holders of operating licenses or construction permits for nuclear power


The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert licensees to a recent event in which licensed operators at a
research reactor inadvertently removed a fuel element from a reactor core that
was critical.  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 are not NRC requirements; therefore, no specific action or written
response is required.

Description of Circumstances

On June 8, 1992, at the University of Michigan's (the licensee's) Ford
research nuclear reactor facility the Assistant Reactor Manager for Operations
(ARM) and two other senior reactor operators (SROs) were conducting tests to
measure changes in core reactivity.  In each test, the operators would perform
the following:  move the fuel, bring the reactor to low power, collect data,
and shut down the reactor.  After collecting data following the third fuel
movement, and with the reactor still critical at low power (8 kW), the ARM
directed the two SROs to move the fuel a fourth time.  The SRO acting as the
control room operator then informed the ARM that the 2-hour control room log
readings were due.  The ARM then gave the SROs instructions on what to do
while he obtained the log readings.  The ARM subsequently told the NRC that he
instructed the SROs to prepare for the fourth move; however, the SROs believed
that they had clear direction to move fuel.  The SROs then began moving the
fuel.  While one SRO monitored the test, the other latched a fuel element with
the fuel handling tool, and then removed the fuel element.  The research
reactor immediately went subcritical and the control rod's servo-mechanism
switched out of automatic control.  At that time, another SRO not directly
involved in the fuel movement, but recognizing what had happened, entered the
control room and manually inserted the shim rods and control rod.  The
equipment performed as designed and the reactor remained in a safe condition. 


                                                            IN 92-73
                                                            November 4, 1992
                                                            Page 2 of 3


As discussed in NRC's Augmented Inspection Team (AIT) Report No. 50-002/92001,
dated July 9, 1992, and associated correspondence, several factors led to this
1.    There was frequent informal turnover of control room responsibilities
      between the ARM and the control room operator during the fuel movements. 
      Who was to have overall control of the reactor between the third and
      fourth fuel movements was not clearly established.
2.    The ARM and the other two SROs moving the fuel did not communicate well.
      For example, both SROs believed that they had clear instructions to move
      the fuel, while the ARM believed that he only instructed them to prepare
      to move fuel.  An intercom system between the control room and the fuel
      handling bridge was not used until the fuel element was being moved.
3.    Relying on their experience and the routine nature of the fuel moves,
      the SROs did not use or review the procedures that applied to moving
      fuel either before or during the actions to move the fuel.

4.    An excessive work load may have contributed to the event.  For example,
      the NRC inspectors found that, after correcting a previous problem with
      the control and shim rod magnets, the SRO's had only four hours during
      their normal shift schedule to complete the planned fuel moves.  This
      was said to create a rushed atmosphere for the test activities.

In moving the fuel element while the reactor was critical, the two SROs
handling the fuel indicated that they did not clearly know the condition of
the reactor when they removed the fuel element.  The ARM did not maintain
adequate control over the entire test activity.  The distraction of completing
the control room log contributed to poor communications with the other SROs.

The licensee has modified its procedures and will install illuminated
indicators on the rod drive housing located on the bridge.  The indicators
will be illuminated only when the rods are fully inserted.  These changes to
the procedures and equipment will give more positive communication, enable
operators to better control fuel changes, and visually indicate the status of
the control rods.  

This event is an example where licensed operators at a research reactor became
so involved in tasks that they failed to maintain adequate control of the
reactor.  The operators did not maintain current knowledge of the condition of
the reactor and therefore were not cognizant of the effect that their actions
would have on that condition.


                                                            IN 92-73
                                                            November 4, 1992
                                                            Page 3 of 3

This information notice requires no specific action or written response.  If
you have any questions about this matter, please contact the technical contact
listed below or the appropriate Nuclear Reactor Regulation (NRR) project

                                   ORIGINAL SIGNED BY

                                Brian K. Grimes, Director
                                Division of Operating Reactor Support
                                Office of Nuclear Reactor Regulation

Technical contact:  Charles Cox, RIII
                    (708) 790-5298

Project Manager:    Theodore S. Michaels, NRR
                    (301) 504-1102

Attachment:  List of Recently Issued NRC Information Notices


Page Last Reviewed/Updated Friday, May 22, 2015