United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 92-25: Potential Weakness in Licensee Procedures for a Loss of the Refueling Cavity Water

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

                               March 31, 1992


NRC INFORMATION NOTICE 92-25:  POTENTIAL WEAKNESS IN LICENSEE PROCEDURES FOR 
                               A LOSS OF THE REFUELING CAVITY WATER 


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 addressees to a potential weakness in licensee procedures 
for loss of the refueling cavity water.  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 October 8, 1991, at the McGuire Nuclear Station, Unit 1, maintenance 
personnel failed to raise the reactor lower internals sufficiently while 
removing them from the reactor vessel.  As a result, the bottom of the 
internals was dragged across the reactor vessel flange face and caught the 
edge of the refueling cavity water seal.  Subsequent inspections disclosed 
minor damage to both the reactor vessel flange and the refueling cavity 
water seal.  If the internals had been even lower during the refueling 
activities, the impact of the internals on the cavity seal could have more 
severely damaged the seal, which could have led to the rapid drainage of the 
refueling cavity.  

In its response to NRC Bulletin 84-03, "Refueling Cavity Water Seal," the 
licensee indicated that if a large seal leak occurred, the refueling cavity 
could drain rapidly.  The procedures and makeup capability for refilling the 
refueling cavity would be insufficient to prevent drainage.  In anticipation 
of such an event, the licensee developed an abnormal procedure for safely 
storing a fuel assembly if one was positioned above the vessel flange level 
during a loss of the refueling cavity water.  However, the abnormal 
procedure did not address actions for repositioning the reactor lower 
internals, if such an event occurred while the internals were being moved.


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                                                            IN 92-25
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In response to this event, the licensee provided additional training for 
employees, implemented improvements to the procedures, and developed 
contingency plans for a loss of canal integrity while moving the reactor 
lower internals.  These contingency plans included the following actions:

�    reinsert the lower internals in the reactor vessel

�    close the equipment hatch concrete shield

�    evacuate the lower containment and annulus

�    clear nonessential personnel from the containment and the video control 
     station

�    implement management controls for infrequently performed tasks

Further details of the event may be found in NRC Inspection Report 
50-369/91-22. 

Discussion

This event and the results of NRC inspections have raised concerns regard-ing 
the adequacy of procedures for a loss of water in the refueling cavity.  At 
McGuire, the reactor lower internals, especially the neutron absorber 
panels, result in extreme radiation levels when exposed above water.  The 
licensee estimated that dose rates could reach 3,300 rem/hr at the operating 
deck and 450 rem/hr at the crane operator cab.  The licensee's procedure did 
not address the consequences of uncovered reactor lower internals and did 
not provide for timely actions and radiation protection contingencies 
appropriate to the circumstances.

It is important that licensees' procedures provide clear guidance to 
operating personnel when responding to the draining of the refueling cavity 
and the possible dose consequences from a fuel assembly or the reactor lower 
internals.  Draining of water from the refueling cavity could result from a 
number of events besides a seal failure.  These include the failure of a 
nozzle dam in a pressurized-water reactor (PWR) steam generator, inadvertent 
opening of a loop isolation valve on a PWR so equipped, loss of coolant 
through the decay heat removal system, failure of a plug in a boiling-water 
reactor (BWR) main steam line, and inadvertent opening of BWR safety valves.   

Related Generic Communications

NRC Bulletin 84-03, "Refueling Cavity Water Seal"

Information Notice 84-93, "Potential for Loss of Water from the Refueling 
Cavity" 

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                                                            IN 92-25
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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.




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


Technical contacts:  Peter K. Vandoorn, RII
                     (704) 875-1681

                     Lawrence L. Lawyer, RII
                     (404) 331-4700

                     Richard D. McWhorter, RII
                     (615) 842-8001     


Attachment:  List of Recently Issued NRC Information Notices  
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