United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 92-47: Intentional Bypassing of Automatic Actuation of Plant Protective Features

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

                              June 29, 1992


NRC INFORMATION NOTICE 92-47:  INTENTIONAL BYPASSING OF AUTOMATIC
                               ACTUATION OF PLANT PROTECTIVE FEATURES


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 alert licensees to the importance of having formal criteria and
training regarding limitations on bypassing plant protective features. 
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 8, 1991, the Florida Power Corporation's Crystal River Nuclear
Station, Unit 3, experienced a slow loss of reactor coolant system (RCS)
pressure at 10 percent power during startup, because a pressurizer spray
valve failed in a partially open position.  The operators did not promptly
determine the cause of the pressure decrease, in part, because they were
misled by an erroneous spray valve closed position indication.  Believing
the pressure decrease to result from an increasing steam demand, the
operators subsequently withdrew control rods several times in an attempt
to maintain RCS temperature as steam flow was increased in preparation for
loading the generator.  However, the RCS pressure continued to decrease,
and the reactor tripped on low pressure.  Approximately 2 minutes later,
the "ES A and B Not Bypassed" alarms annunciated.  These alarms indicate
that the high pressure injection (HPI) system and other engineered
safeguards (ES) functions are not blocked, although they may be blocked
during normal plant cooldown.  Approximately 1 minute later, a control
room operator inappropriately actuated the ES bypass switches for the A
and B HPI system.  Approximately 6 minutes later, when a sufficient number
of actuation logic bistables tripped to actuate the system if it had not
been bypassed, the Acting Operations Superintendent questioned the Shift
Supervisor about the advisability of bypassing the ES, and the ES was then
unbypassed at which time the high pressure injection and other systems
activated.  Operators then established manual control of the high


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pressure injection system to maintain RCS pressure above 1500 psig.  The
operators did not determine the cause of the decrease in RCS pressure
until after the spray line isolation valve was closed about an hour later.

Discussion

One of the significant lessons of the Three Mile Island, Unit 2, (TMI-2)
accident was that the core damage resulted from operators manually
terminating safety injection based on an inaccurate diagnosis of plant
conditions.  In 1979, the NRC issued a series of Bulletins requesting
licensees to review operating procedures and training to ensure that
operators do not override automatic ESF actuation without carefully
reviewing plant conditions.  After the accident at TMI-2, licensees made
many enhancements to emergency operating procedures to improve the
operator's control of safety functions and engineered safety features.

At Crystal River, the licensee's staff lacked formal guidance delineating
limitations on bypassing the automatic actuation of engineered safeguards
functions.  This lack of guidance may have contributed to having high
pressure injection bypassed with the plant in a degraded condition for
approximately  6 minutes without understanding the cause of the decrease
in RCS pressure.  One of the licensee's corrective actions was to develop
administrative guidance on when it is appropriate to bypass the automatic
actuation of engineered safeguards functions.  This guidance has been 
incorporated into plant procedures.

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


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

Technical contact:  Thomas Koshy, NRR
                    (301) 504-1176

Attachment:  List of Recently Issued NRC Information Notices


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