Argonne National Laboratory Reports (2024)

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13
Ongoing experiments at SRL with very small additions of Cr, Al, Si,
Fe, and Mo (either separately or in combination) to uranium have produced
interesting results.34 Most of these alloys were quenched from 725*C,
then irradiated to 9000 and 13000 MWd/t at various temperatures ranging
from 200 to 600*C. Swelling rates of 3-4%/at. % burnup were found for alloys
containing 800-1150 ppm Al + Si at temperatures below the swelling threshold
of 350 C. Alloys containing the above Al + Si concentrations were further
improved br the addition of 250-350 ppm Fe, 200 ppm Cr, and 1000 ppm Mo.
An alloy containing 800 ppm Al, 350 ppm Si, 350 ppm Fe, and 1000 ppm Mo was
found to be stable to approximately 425*C.
The early irradiations of U3Si fuel material produced mixed re-
sults.30 Extruded samples irradiated to 0.17 at. % burnup by Westinghouse-
Atomic Power Division were found to have increased in both length and dia-
meter. Several samples were bowed and all exhibited cracks, blisters and
bands. However, in tests performed by ANL, both cast and extruded samples
exhibited good irradiation stability. In recent experiments at AECL, U3Si
and aluminum-modified U3Si showed excellent irradiation perfor-
mance.36'37 Diameter increases for Zi.rcaloy-clad U3Si in the form of annular
fuel rods were less than 1% after 10,000 MWd/t and about 1.2% after 19,000
MWd/t at a maximum temperature of about 500-600*C. With the addition of 1.5
and 2.4 wt. % aluminum, diameter increases were reduced slightly and, as
noted earlier, the corrosion resistance of the alloy fuel was improved.
Despite its poor thermal conductivity, U0, performs well since it can
be operated at steady-state central temperatures broaching its melting
point.38 U02 was used as the fuel material for 'his country's first proto-
type power reactors - the Shippingport pressurized water reactor (PWR) and
the Vallecitos boiling water reactor (BWR) - which were built in the late
1950s. However, metal fuels were utilized in the early experimental reactors
(the Ship Thermal Reactor developed by ANL, Westinghouse, and the Naval
Reactors Division - USAEC; and the Experimental Boiling Water Reactor de-
veloped by ANL).39 The shift to oxide fuel occurred because the behavior of
metal alloy fuels was found to be inadequate.38
The reference fuel for both the PWR and the BWR is still U02 in the
form of pellets of "93% theoretical density. Satisfactory performance has
been obtained at burnups of over 40,000 MWd/t.40,41 This led to the con-
sideration of oxide fuel for liquid metal-cooled fast breeder reactors and
to the development of an information data base on oxide fuels for this appli-
cation.42 A similar document is available for light water reactor oxide-fuel
behavior.43 U02 fuel rods which contain %5% enriched uranium have also been
used in the PULSTAR reactors.
More recently, the French have utilized U02 wafers (caramels) in a
compartmentalized Zircaloy cladding arrangement for plate-type reactors.44
The plates have performed well to a maximum burnup of 30,000 MWd/t. The
French design is similar in concept to that employed in the second core of
Shippingport, which utilized U02-Zr02 as fuel and U02 in the blanket. As
part of the development of the U02 plates for the blanket, Westinghouse per-
formed high-temperature irradiations to burnups as high as 1.40,000 MWd/t
 

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