{sup 14}C release from failed spent fuel containers Page: 1 of 5
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BNL-43768
14C RELEASE FROM FAILED SPENT FUEL CONTAINERSC. PESCATORE
Brookhaven National Laboratory
Building 830
Upton, New York 1373
(516) 282-2731ABSTRACT
Partially failed containers may provide a
meaningful barrier to the release of gaseous
radionuclides. A modeling approach is
outlined and sample calculations are
provided that show the effects on release
due to a limited perforation area, to
decreasing temperature, and to the partial
occlusion of the perforated area by
corrosion products.
INTRODUCTiCN
Under disposal conditions in the
unsaturated zone, the reference condition in
the United States, 14C can be released from
the spent fuel as soon as a container is
breached because of its presence in the
cladding waste.' The most important
mechanism for "C mobilization is its
-xidation, in air, into gaseous 1C02-12
From the latest version of the Yucca
Mountain Site Characterization Plan (SCP),3
the following prompt oxidation fractions, f,
of the total "C inventory within the spent
fuel can be deduced:f - 1% for
f - 0.2% for
f < 0.1% forT > 215*C
170 < T < 215*C
T < 170*CThese prompt oxidation fractions have to be
augmented further, by adding 2%, at least,
in order to reflect recent experimental data
under both oxidizing and "inert"
conditions.2
'Roughly 38% of the 14C in spent fuel resides
in the U02 pellets; 62% is associated with
the rest of the assembly materials (clad-
ding waste).BNL--43768
DE90 007833The most stringent criterion on waste
package (WP) performance promulgated by
the U.S. Nuclear Regulatory Commission
(NRC) applies when the WP is at its
hottest and stipulates that, for a period
of 300 to 1,000 years, the WP must provide
a "substantially complete containment" of
all the radionuclides that have been
disposed of.' Although "substantially
complete containment" is a term of law
rather than a term of science, it needs to
eventually be quantified, as 100% absence
of containers failure can never be
demonstrated. We assume, therefore, that
a certain number of containers is allowed
to fail provided that the 14C annual
release from the ensemble of spent fuel
containers is confined to 10-6 of the
total inventory of "C present in any
given year. This is a more restrictive
criterion than the analogous 10-5
criterion which applies after the
substantially complete containment period.
The SCP suggests that the 14C02 is
released instantly from the breached
container. Under this assumption,
exceedingly few containers (1 in 25,000
roughly) can fail per year even under the
10-6 criterion. It can be argued,
however, that prompt oxidation of 1"C into
14C02 should not necessarily result in
prompt release of all the oxidized
fraction out of the spent fuel containers
unless the average perforation area in the
container surface is large enough. In
other words, a small average perforation
area with respect to the total surface
area of the container could still
guarantee that the release is slow enough
to allow more reasonable container failure
rates. Our initial calculations s hrt
this point. MS TE
MISTIBQTC OF T~ :Ks 2CMENT IS UNLIMITED
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Pescatore, C. {sup 14}C release from failed spent fuel containers, article, February 1, 1990; Upton, New York. (https://digital.library.unt.edu/ark:/67531/metadc624174/m1/1/: accessed April 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.