Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
October 25, 1990
Information Notice No. 90-66: INCOMPLETE DRAINING AND DRYING OF
SHIPPING CASKS
Addressees:
All holders of operating licenses for nuclear power reactors and all
registered users of NRC approved waste shipping packages.
Purpose:
This information notice is intended to alert addressees to a possible safety
problem resulting from incomplete draining and drying of shipping casks. 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 May 9, 1990, a Chem-Nuclear System (CNSI) operator opened a Transnuclear,
TN-RAM shipping cask (USA/9233/B(U)) containing approximately 16,000 curies
of waste-irradiated hardware (sheared control rod blades and local power
range monitors) at the Low-Level Radioactive Waste Disposal Site operated by
CNSI at Barnwell, South Carolina. The irradiated hardware was to be placed
in the Class C waste trench. When the CNSI operator opened the shipping
cask, approximately 75 gallons of water, having a near contact dose rate of
5 mr/hr, spilled from the cask, contaminating the off-loading equipment and
the surrounding ground area. CNSI personnel immediately closed the cask,
removed it from the trench area, and placed it in a secure parking area
within the burial site. Subsequently, when the cask was completely
dewatered at the waste facility, an additional 121 gallons of contaminated
water was removed from the cask. The total volume of water found in this
event was approximately 40 percent of the total cask volume.
Discussion:
The shipment originated at Millstone Nuclear Power Station, Unit 1. The
irradiated hardware was in a waste liner which was stored in the spent fuel
pool. The waste liner and cask were to be drained and dried before
shipment.
The main cause of this event was an inadequate procedure used for draining
and drying the cask and liner. This procedure failed to incorporate any
method for quantifying the amount of water drained from the cask.
Additionally, this procedure failed to specify an accurate reference value
for the pressure of the
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IN 90-66
October 25, 1990
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cask cavity with which to conduct the "dryness verification" test. The
procedure specified that the test be conducted at any pressure above a
"minimum" pressure of 10 mbar, while the safety analysis report (SAR) called
for the test to be conducted at a pressure of 10 mbar (+2, -0 mbar). As a
result, the test was actually conducted at 27 mbar, which was the vapor
pressure for water at the ambient temperature. Because the pressure in the
cask cavity was not sufficiently below the vapor pressure of water, the test
results were incorrectly interpreted, which allowed water to remain
undetected in the cask.
Since this event the license holder has corrected these deficiencies in the
test procedure. The revised test procedure requires that the water drained
from the cask be quantified and compared to the volume of the container and
that the dryness test be consistent with the SAR by specifying that the
dryness test be performed at 10 mbar (+2, -0 mbar).
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 NRC project
manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts: George H. Gardes, NMSS
(301) 492-0495
Joseph T. Furia, RI
(215) 337-5373
Attachment: List of Recently Issued NRC Information Notices
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