United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 93-44: Operational Challenges During a Dual-Unit Transient

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

                                 June 15, 1993


NRC INFORMATION NOTICE 93-44:  OPERATIONAL CHALLENGES DURING A DUAL-UNIT 
                               TRANSIENT


Addressees

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

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to inform addressees of an event during which an atypical shift
staffing level and lack of familiarity with the tasks to be performed in that
shift configuration affected the ability of the control room operating shift
to respond to the event.  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 December 31, 1992, a dual-unit reactor trip initiated by an electrical
fault in the switchyard occurred at the Sequoyah Nuclear Plant.  Units 1 and 2
at Sequoyah share a common control room.  At the time of the event the control
room reactor operator staffing was the minimum allowed by the plant Technical
Specifications (TS); shift staffing consisted of five licensed senior
operators (the shift operations supervisor, one assistant shift operations
supervisor for each unit, the shift technical advisor, and an additional
senior operator) and three reactor operators - two assigned to Unit 1 and one
assigned to Unit 2.  The NRC inspection team investigating the event concluded
that the Unit 2 response to the event, with one reactor operator, was hampered
by lack of adherence to procedures, operator errors, and an unnecessary
cooldown of the reactor coolant system (RCS) after the reactor trip.  The 
Unit 1 response to the same event, with two reactor operators, was normal.

Discussion

An NRC inspection team reviewed the effects of the Unit 2 staffing level
during the event with regard to the crew's ability to stabilize the unit after
the reactor trip occurred.  The inspection team concluded that the Unit 2
staffing level delayed the recovery of plant systems, contributed to erroneous
decisions made by the assistant shift operations supervisor (ASOS), and 



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                                                            IN 93-44
                                                            June 15, 1993
                                                            Page 2 of 3


overburdened and challenged the crew's ability to perform tasks in the manner
in which it was trained.  Control room simulator training scenarios had not
been conducted using only one reactor operator.

Although the normal shift staffing and training consisted of two 
reactor operators for each unit, licensee operational staffing practices
resulted in the frequent use of one reactor operator for one of the units. 
The licensee used this reduced staffing configuration 12 times in 
December 1992.  In this configuration, with the dual-unit transient, the
single reactor operator performed all of the recovery evolutions for the unit
as directed by the ASOS in charge of the unit. 

Because of delays caused by the one reactor operator performing primary and
secondary system recovery evolutions, as required by the applicable recovery
procedures, an RCS cooldown resulted.  This was a direct result of the crew
not adequately controlling auxiliary feedwater after the reactor trip.  The
atypical staffing level also contributed to problems involving the decision of
the assistant shift operations supervisor to use the normal-batch borate
process in response to the cooldown rather than the emergency borate process
as required by the emergency procedure.  The decision not to use the emergency
borate process was made, in part, because of the reluctance of the assistant
shift operations supervisor to commit the one reactor operator to the
emergency borate process, which restricts the operator's attention to
monitoring only that activity.

As a corrective action to prevent recurrence, the licensee implemented revised 
administrative controls to ensure that the control room staffing will be
maintained at two reactor operators for each operating unit.  The need for
additional training at minimum staffing levels is being evaluated by the
licensee.

Related Generic Communications

1.    IN 85-80, "Timely Declaration of an Emergency Class, Implementation of
      an Emergency Plan, and Emergency Notifications," dated October 15, 1985

2.    IN 91-77, "Shift Staffing at Nuclear Power Plants," dated November 26,
      1991
.

                                                            IN 93-44
                                                            June 15, 1993
                                                            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 Office of
Nuclear Reactor Regulation (NRR) project manager.


                                       ORIGINAL SIGNED BY


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

Technical contacts:  S. M. Shaeffer, RII
                     (615) 842-8001

                     D. R. Desaulniers, NRR
                     (301) 504-1043

Attachment:  
List of Recently Issued NRC Information Notices

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