MATERIALS COMPATIBILITY OF SNAP FUEL COMPONENTS DURING SHIPMENT IN 9975 PACKAGING Page: 6 of 15
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P. R. Vormelker WSRC-STI-2006-00140 Rev. 1
November, 2006 Page 2 of 10
ceramic coating contains primarily oxides of aluminum, silicon, titanium, manganese, and
barium with smaller amounts of sodium, lithium, and potassium.(4-5) This ceramic coating was
generally applied in three firings (~1010 C) during which a small quantity of samarium oxide
(Sm203) was included in the last two firings.(4-5) Depletion of the samarium oxide (a burnable
poison) is intended to provide more than one year of stable reactor operation without complex
mechanical control rods. The ceramic coating also acts as a barrier to hydrogen leakage from the
fuel during irradiation. The fuel element was then backfilled with helium prior to final weld
closure of a Hastelloy N end cap to individual tubes.
The SNAP fuel rods destined for this shipment were never installed in the SNAP 10FS-3 reactor
for power generation and thus, the calculated decay heat is approximately 0.0023 Watts versus
the 9975 SARP limit of 19 Watts (6). The temperature of the SNAP fuel is expected to be
equilivalent to ambient conditions due to extremely low decay heat release. The fuel rods are
expected to be dry and stable with no intentional moisture in the loaded convenience can except
that from the loading environment at LANL.
3.0 POTENTIAL FOR CORROSION/DEGRADATION
Since there are three unique metals that will be contained within the SNAP convenience can, the
potential for electrochemical interaction between these metals can be detrimental in the right
environment. The actual fuel, UZrHx, is protected by the chromized Hastelloy N tube and a
ceramic coating and is expected to be stable at ambient conditions. The only plausible
environment detrimental to the fuel is water, although it is not expected during final packaging of
the fuel. The last material that could have possible interaction with the three metals is the PVC
tape used to secure the two convenience cans together. The potential of each material's response
in a water environment is considered by the following discussion.
3.1 304 Stainless Steel
The convenience can is constructed of 304 stainless steel which is expected to be resistant to
corrosion in freshwater or condensation as long as chloride levels are below 250 ppm.(7)
3.2 Hastelloy N With Chromized Diffusion Coating
The outside cladding on the fuel is Hastelloy N, an alloy that was originally developed by the
Oak Ridge National Laboratory as a container material for high temperature (>700 C) molten
fluoride salts. The SNAP fuel was designed to be used in a liquid sodium-potassium eutectic
alloy at 650 0C with a lifetime of greater than one year. The chromized surface layer on the
Hastelloy N material was used to improve its resistance to internal oxidation due to the high
fusing temperatures of the ceramic coating. Hastelloy N (without the high chromium surface
content) is similar to Hastelloy C-276 and C-22 in corrosion and high temperature oxidation
The corrosion rate in seawater for Hastelloy N was measured as 0.0001 mil per year.(9) This
corrosion rate is extremely low and should be further reduced with additional chrome content on
the surface. Low corrosion rates in seawater with significant chloride content is a positive
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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/m1/6/: accessed April 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.