United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 88-92: Potential for Spent Fuel Pool Draindown

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

                                November 22, 1988


Information Notice No. 88-92:  POTENTIAL FOR SPENT FUEL POOL DRAINDOWN 

Addressees: 

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

Purpose: 

This information notice is being provided to alert addressees to potential 
problems resulting from the failure of the fuel transfer canal door seal.  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 2, 1988, with Surry Unit 1 in cold shutdown, the licensee was pre-
paring to test the fuel transfer system (see attached figure) before fuel 
off-load.  The transfer canal door was in place and the single door seal was 
inflated.  The fuel transfer canal was dry.  The fuel transfer tube was open, 
the blind flange was removed on the containment side, and the gate valve was 
open on the spent fuel pool side.  The refueling cavity seal was not in place.
An accidental pinhole puncture of the single air supply line to the transfer 
canal door pneumatic seal was promptly detected and the air leak quickly 
stopped before it could lead to a loss of seal integrity. 

Discussion: 

A review of this event by the licensee showed that, given the configuration of 
the transfer canal, the transfer tube, and the refueling cavity existing at 
the time of the event, an inadvertent draindown of the spent fuel pool could 
occur to a height of only 13" above the top of the fuel assemblies (see 
attached figure).  This postulated draindown assumes no operator action and a 
loss of instrument air or pneumatic seal failure.  Increased radiation levels 
in the spent fuel pool building would have limited stay time in the building 
and impeded recovery.  The licensee estimated that the dose rate, based on the 
spent fuel inventory at the time of the event, could have reached 50 R/hour on 
the operating deck.  The licensee also calculated that with the refueling 
cavity seal assembly in place, the spent fuel pool could only draindown to 14 
feet above the top of the fuel assemblies.  



8811160470
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                                                            Page 2 of 3 


If newly discharged fuel had been placed in the spent fuel pool, a postulated 
draindown of the spent fuel pool could have led to even higher radiation 
levels in the spent fuel pool building than the radiation levels postulated by 
the licensee.  If a seal failed and spent fuel pool water were lost while a 
fuel assembly was lifted, fuel could be uncovered and fuel cladding could 
fail. 

The licensee is considering several actions based on the review of this event.
The short-term actions include: (1) revising procedures to require that the 
refueling cavity seal assembly be installed before opening the transfer tube 
gate valve for dry testing the fuel transfer system, (2) reviewing and up-
grading a procedure for the loss of spent fuel pool inventory, (3) upgrading 
the material of the plastic air hose in which the pinhole occurred, and (4) 
providing an emergency escape system for personnel in the transfer canal.  The
long-term actions include: (1) evaluating the canal door and seal design in-
cluding the need for a backup air supply, a low air pressure alarm, and a 
backup seal, (2) evaluating other pneumatic seals used at Surry, (3) 
developing a procedure for installing, inspecting, and testing the seals in 
accordance with the manufacturer's recommendations, (4) revising procedures to 
ensure the transfer tube blind flange is installed whenever the transfer canal 
is drained for maintenance on the transfer tube gate valve, and (5) reviewing 
further the procedures for loss of spent fuel pool and refueling cavity water 
level, after the short-term modifications to these procedures. 

In 1981, a related event occurred at Arkansas Nuclear One, Unit 2.  At the end 
of a refueling outage with the transfer canal door closed and the door seal 
inflated, the transfer canal was drained in preparation for performing 
maintenance on the fuel upender.   Concurrent maintenance on the air system 
resulted in a loss of air pressure to the seal, and water leaked from the 
spent fuel pool into the fuel upender pit.  The transfer gate valve was closed 
and acted as a barrier to the flow.  The leakage stopped when the water levels 
equalized.  The spent fuel pool level had decreased by 7 feet.  If the seal 
had leaked while the maintenance on the upender was in progress with the fuel 
transfer tube gate valve open and the fuel transfer tube blind flange removed, 
the spent fuel pool could have drained down to a level just above the top of 
the fuel assemblies. 

Pneumatic seals are also used in the refueling cavity seal assembly.  In many 
cases, the failure modes of the refueling cavity seals (IE Bulletin 84-03, 
"Refueling Cavity Water Seal" and Information Notice 84-93, "Potential for 
Loss of Water From the Refueling Cavity") apply to the spent fuel pool gate 
seals. 

These events show that a door equipped with a single seal and/or a single air 
supply is subject to complete loss of function from a single failure.  There-
fore, the seal must be properly installed, and the seal and air supply system 
must be carefully maintained.  The scenarios discussed also point out the need 
for carefully coordinating such activities as maintenance and testing to avoid 
undesirable interactions between systems which could result in fuel uncovery, 
personnel injury, and personnel contamination.
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                                                            November 22, 1988 
                                                            Page 3 of 3 


No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact the technical 
contact listed below or the Regional Administrator of the appropriate regional 
office. 




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

Technical Contact:  Daniele Oudinot, NRR 
                    (301) 492-1174 
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                                                            IN 88-92 
                                                            November 22, 1988 
                                                            Page 1 of 1

                             LIST OF RECENTLY ISSUED
                             NRC INFORMATION NOTICES
_____________________________________________________________________________
Information                                  Date of 
Notice No._____Subject_______________________Issuance_______Issued to________

88-91          Improper Administration       11/22/88       All holders of OLs
               and Control of                               or CPs for nuclear
               Psychological Tests                          power reactors and
                                                            all fuel cycle 
                                                            facility licensees
                                                            who possess, use, 
                                                            import, export, or
                                                            transport formula 
                                                            quantities of 
                                                            strategic special 
                                                            nuclear material. 

88-90          Unauthorized Removal of       11/22/88       All NRC licensees 
               Industrial Nuclear Gauges                    authorized to 
                                                            possess, use, 
                                                            manufacture, or 
                                                            distribute 
                                                            industrial nuclear
                                                            gauges. 

88-89          Degradation of Kapton         11/21/88       All holders of OLs
               Electrical Insulation                        or CPs for nuclear
                                                            power reactors. 

88-88          Degradation of Westinghouse   11/16/88       All holders of OLs
               ARD Relays                                   or CPs for nuclear
                                                            power reactors. 

88-87          Pump Wear and Foreign         11/16/88       All holders of OLs
               Objects in Plant Piping                      or CPs for nuclear
               Systems                                      power reactors. 

86-106,        Feedwater Line Break          11/10/88       All holders of OLs
Supp. 3                                                     or CPs for nuclear
                                                            power reactors. 

88-86          Operating with Multiple       10/21/88       All holders of OLs
               Grounds in Direct Current                    or CPs for nuclear
               Distribution Systems                         power reactors. 

88-85          Broken Retaining Block        10/14/88       All holders of OLs
               Studs on Anchor Darling                      or CPs for nuclear
               Check Valves                                 power reactors. 
_____________________________________________________________________________
OL = Operating License
CP = Construction Permit
Page Last Reviewed/Updated Tuesday, November 12, 2013