Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
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
. In 88-92
November 22, 1988
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.
. IN 88-92
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
. Attachment 2
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
