Materials Compatibility Issues

DOE-HDBK-1132-99

available tritium begins to dissolve into the actual surface of the bulk material.

As the local saturation sites in the actual surface of the bulk material begin to

fill, the tritium dissolved in the surface begins to diffuse into the body of the

bulk material; at that point, the behavior of the tritium in the body of the bulk

material becomes totally dependent on the material in question.

Materials Compatibility Issues. Elemental hydrogen, regardless of its form

(H2, D2, T2, and all combinations thereof), can be expected to dissolve to some

extent in virtually all materials. For simple solubility reactions, such as

2H@Material ,

H2 + Material

(4a)

Hy + Material v xHy@Material ,

(4b)

H + Material

H @Material ,

and

(4c)

basic compatibility issues should be considered. As a general rule, the

solubility of tritium in pure metals and/or ceramics should have a minimal effect,

at normal room temperatures and pressures, except for the possibility of

hydrogen embrittlement. For alloyed metals, such as stainless steel, similar

considerations apply, again, at normal room temperatures and pressures. For

alloyed metals, however, additional consideration must be given to the possible

leaching of impurities from the alloyed metal, even at normal room

temperatures and pressures. [In LP-50 containment vessels, for example, the

formation of relatively large amounts of tritiated methane (i.e., up to

0.75 percent mole percent of CT4) has been noted after containers of high-

purity tritium have been left undisturbed for several years. The formation of the

tritiated methane, in this case, has long been attributed to the leaching of

carbon from the body of the stainless steel containment vessel.]

Pressure Considerations . Under increased pressures (e.g., from a few tens

to several hundred atmospheres), however, the general rules no longer apply

for, in addition to the possibility of hydrogen embrittlement and possible

leaching effects, helium embrittlement is also possible. Helium embrittlement

I-102