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Materials Compatibility Issues
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Design Considerations - index
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Organics cont'd - hdbk1132990120


DOE-HDBK-1132-99
tends to occur as a result of the dissolved tritium decaying within the body of
the material, the resultant migration of the helium-3 atoms to the grain
boundaries of the material, the localized agglomerations of the helium-3 atoms
at the grain boundaries, and the resultant high-pressure build-ups at these
localized agglomerations.
Temperature Considerations . Under increased temperature situations, the
matrix of solubility considerations becomes even more complicated because
virtually all solubility reactions are exponentially dependent on temperature. In
the case of diffusional flow through the walls of a containment vessel, for
example, it can be assumed that steady-state permeation will have been
reached when
Dt
2
L 0.45 ,
(10)
where D = the diffusion rate in cm  2/sec, t = the time in seconds, and L = the
thickness of the diffusion barrier. For type 316 stainless steel, the value for the
diffusion rate is
D = 4.7 10-3 e(-12,900/RT) ,
(10a)
and the corresponding value for R, in the appropriate units, is 1.987 cal/mole K.
With a nominal wall thickness of 0.125 inches (i.e., 0.318 cm), Equation (10)
indicates that it will take about 875 years to reach steady-state permeation, at a
temperature of 25EC. At 100EC, the time frame will be reduced to about 11
years, and at 500 EC, it only takes about 12 hours.
Organics . With the introduction of organic materials into any tritium handling
system, the matrix of solubility considerations becomes complicated to its
maximum extent because the simple solubility reactions, such as those shown
above as Equations (4a), (4b), and (4c), are no longer working by themselves.
With the availability of free tritium dissolved into the internal volume of the
organic material, the molecular surroundings of the organic material see a local
I-103


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