Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
SSINS No.: 6835
IN 87-13
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, D.C. 20555
February 24, 1987
Information Notice No. 87-13: POTENTIAL FOR HIGH RADIATION FIELDS
FOLLOWING LOSS OF WATER FROM FUEL POOL
Addressees:
All holders of a nuclear power reactor operating license (OL) or a
construction permit (CP) except Fort St. Vrain.
Purpose:
This information notice is to alert addressees of the potential for high
radiation fields following the inadvertent loss of water from the spent fuel
pool or transfer canal. Recipients are expected to review the information
for applicability to their facilities and consider actions, if appropriate,
to preclude similar problems occurring at their facilities. 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 December 2 and 3, 1986, the Hatch nuclear power plant lost 141,000
gallons of water from the spent fuel pool because of a leak from pneumatic
seals in the transfer canal, between Units l and 2. The redundant pneumatic
seals leaked because of a single failure. A valve in the single air supply
line to the seal was mistakenly closed. Although water level dropped about 5
feet and low level alarms in the spent fuel pool worked, the leak was not
specifically identified for several hours because a leak detection device
was valved out and none of the seals were instrumented to alarm on loss of
air pressure.
Analysis by the licensee after the event has shown that, if water had been
completely lost from the transfer canal, radiation fields would be high
enough that remedial measures may be difficult. High radiation fields would
be present because irradiated control blades are stored on short hanger rods
clipped over the side of the spent fuel pool. A control blade's roller
bearing is typically made of cobalt-rich stellite which, when activated, has
radiation levels of 8,000 to 10,000 R/hr on contact. Some of the control
blades would be completely uncovered if the water level dropped to the
bottom of the transfer canal. This drop in water level would result in
general area radiation levels of about 100 R/hr at the edge of the spent
fuel pool and 1 R/hr 6 feet from the edge of the pool. About 2 feet of water
would remain over the top of the spent fuel at the minimum level resulting
from draining via the transfer canal; so, there was no likelihood of fuel
damage because of fuel uncovery.
8702190620
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IN 87-13
February 24, 1987
Page 2 of 2
Discussion:
The potential for this general type of event was discussed in IE Information
Notice No. 84-93, "Potential for Loss of Water from the Refueling Cavity,"
issued on December 14, 1984 and IE Bulletin No. 84-03, "Refueling Cavity
Water Seal," issued on August 24, 1984. The transfer canal between the Hatch
units is an unusual design that illustrates yet another way a single failure
resulted in substantial loss of water from the spent fuel pool.
Although recipients of IN 84-93 and IEB 84-03 may have evaluated the
potential uncovering of spent fuel, recipients may not have fully evaluated
the potential for high radiation fields because of the potential uncovering
of short hangers or other short fixtures holding irradiated material such as
used control rods or neutron detectors.
Since the event, concern has been raised about the design of the leak
detection system for the seals. The leak detection system consists of a
level switch that is piped between the first and second pneumatic seals to
detect water leakage that gets past the first seal. The NRC is currently
evaluating this design to determine whether water would flow past the leak
detector if all seals failed and thus fail to detect the leak.
As corrective measures, the licensee has separated the air supply to the
transfer canal seals and the air supply to the inner and outer gates between
the transfer canal and the spent fuel pools and is studying other changes to
assure greater reliability. The licensee also is shipping the used control
rods in the spent fuel pool off the site.
No specific action or written response is required by this information
notice. If you have questions about this matter, please contact the Regional
Administrator of the appropriate NRC regional office or this office.
Edward L. Jordan Director
Division of Emergency Preparedness
and Engineering Response
Office of Inspection and Enforcement
Technical Contact: Eric Weiss, IE
(301) 492-9005
Floyd Cantrell, Region II
(404) 331-5534
Attachment: List of Recently Issued IE Information Notices
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