MATERIALS COMPATIBILITY OF SNAP FUEL COMPONENTS DURING SHIPMENT IN 9975 PACKAGING Page: 7 of 15
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P. R. Vormelker WSRC-STI-2006-00140 Rev. 1
November, 2006 Page 3 of 10
indication that Hastelloy N's corrosion resistance to water would be very high. Thus, the fuel
cladding is expected to be very resistant to corrosion to any water/condensate in the convenience
3.3 Aluminum Foil
The current alloy used for Reynolds Wrap aluminum foil is 8111 (10) which is similar in
composition to the 1145 alloy but slightly different than the others shown in Table 1. In general,
these aluminum alloys are resistant to corrosion in water with pH levels of 6-9, conductivity
levels below 10 pS/cm, and with no halide ions.(11-13) Aluminum forms a protective air-
formed oxide which should protect itself for the 1 year shipping period.
Even though aluminum foil has the lowest melting point of the three metals used in the 9975 per
Table 2, the highest internal temperature expected during a fire condition is 525 C per the 9975
SARP.(6) Therefore, the aluminum foil will not melt during a fire condition. Aluminum's
higher thermal conductivity should not be a concern due to the low heat release of the SNAP
3.4 Galvanic Corrosion
While each of the above mentioned alloys is individually resistant to corrosion in water to
varying degrees; a potential for galvanic corrosion exists when they are in contact with each
other in the convenience can with some water content. According to the galvanic series in
Figure 4, aluminum alloys are the least noble of the alloys in contact with each other in the
convenience can. This means that in the presence of seawater, corrosion of aluminum foil will
probably occur. This will also occur in tap water. Since the fuel rods will be in point contact
with the convenience can, crevice corrosion may occur on the stainless steel can (assuming water
is present) at the point of contact. The surface area of the fuel is expected to be greater than that
of the can, thus increasing the potential for galvanic corrosion of the can in the presence of
water. Since water is precluded in the convenience can and containment vessel, galvanic and
crevice corrosion is not expected to occur.
3.5 PVC Tape
PVC (polyvinylchloride) tape is used to secure the two convenience cans together to confine the
SNAP fuel rods. At ambient temperatures the PVC tape is expected to remain in good condition
without interaction with the fuel or the convenience can. However, during previous elevated
temperature testing of 12 mil PVC film, charring and significant outgassing was experienced at
121 C (249 F).(14) Products of outgassing include chlorides, since significant levels are part of
the monomer used to produce PVC. Also, stress corrosion cracking was observed underneath
PVC pipe labels on 304 stainless steel cooling water piping in SRS reactors due to leaching of
chlorides from the label. Since temperatures above ambient are not expected in the convenience
can, tape outgassing is not expected. However, there is also a risk of stress corrosion cracking on
convenience can surfaces below the PVC tape if left on for long periods.(15) The use of non-
chloride based tape is suggested. However, corrosion of the convenience can does not
compromise the structural integrity of the stainless steel Primary Containment Vessel.
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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/m1/7/: accessed April 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.