MATERIALS COMPATIBILITY OF SNAP FUEL COMPONENTS DURING SHIPMENT IN 9975 PACKAGING Page: 8 of 15
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P. R. Vormelker WSRC-STI-2006-00140 Rev. 1
November, 2006 Page 4 of 10
3.6. Potential for Water in the Convenience Can
If SNAP fuel is loaded into the convenience can in an exterior or non-air conditioned
environment (temperature = 27 C, 50 % RH, 15 C dew point*), the air inside the can will
contain saturated moisture with a density of 12.83 g/m3.(16) When the outer shell is cooled to
it's dew point temperature at some point during shipping, the saturated air inside the convenience
can (assume air tight) may condense. The amount of free space inside the double convenience
can is estimated to be 34% without consideration for the aluminum foil volume. Using a value
of 222 in3 for the interior volume of the two convenience cans and multiplied by 34% to
represent the unused volume of 75.5 in3, The amount of condensed moisture can be found by
multiplying saturated moisture density (12.83 g/m3) by 75.5 in3 (1.23 x 10-3 m3) to obtain a
value of 0.016 grams of water.
When Rice (17) used pure nickel foil exposed to various humidity levels, moisture was absorbed
on the nickel surface and oxidation occurred. At the 30% RH level, nickel oxidizes and gains
weight at 0.011 pg/cm2hr . Assuming the following reaction (1) with 30% RH air:
(1) Ni + H20 - NiO + H2
For each mole of water, one mole of NiO is formed. Using 1 cm2 surface area and a time of one
hour, 1.1 e-8 g of NiO is created. One SNAP fuel rod has a calculated surface area of 51.3 in2
(331 cm2). Using 8760 hours/yr. and the oxidation rate of 0.011 pg/cm2hr, the amount of NiO is
calculated at 0.032 grams of NiO. This amounts to 4.3 e-2 % moles of NiO. This is a very small
amount considering this value is for pure nickel. Chromized Hastelloy N is expected to oxidize
at an even lower rate, if at all in a low moisture environment. Thus, any water within the
convenience can from condensation is not considered a corrosion risk for the Hastelloy N fuel
rods, 304 stainless steel convenience can, and aluminum foil filler material for the one year
3.7 Thermal Expansion Risk
Since there is a tight fit, height wise, between the 13.19 in. tall fuel rods and the inside height of
the double convenience can (13.22 in.), the risk of thermal expansion should be considered.
Since the thermal expansion coefficient of 304 stainless steel is approximately 50% greater than
that of Hastelloy N per Table 2, the convenience can is expected to grow more than the SNAP
fuel should temperatures exceed ambient conditions. Thermal expansion measurements for
alpha uranium (18) and zirconium hydrides (19) in Table 2 are below that for Hastelloy N except
for the highest value for alpha uranium. The thermal expansion values for alpha uranium were
based on varying fabrication techniques and may not represent the correct values for SNAP fuel
elements. Thus, interference conditions are not expected based on original dimensions.
However, the actual fuel rod dimensions should be measured to confirm if any changes have
occurred during storage since their original fabrication date.
Various scenarios were reviewed for potential instances of corrosion and degradation. In order
for corrosion to occur, water must be present. Although water is not specifically mentioned in
* Weather conditions Albuquerque area, August 31, 2006, National Weather Service
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Vormelker, P. MATERIALS COMPATIBILITY OF SNAP FUEL COMPONENTS DURING SHIPMENT IN 9975 PACKAGING, report, November 14, 2006; [Aiken, South Carolina]. (https://digital.library.unt.edu/ark:/67531/metadc880009/m1/8/: accessed April 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.