Exchange Reactions

DOE-HDBK-1132-99

standpoint, however, experience has shown that, regardless of the tritiated

compound that enters into the reaction, an HTO (i.e., a tritiated water vapor)

component can be expected to come out. Presumably, this is due to catalytic

effects and/or exchange effects that derive from the outward migration of the

tritiated species through molecular layers of water vapor that are bound to the

surface of the material.

Exchange Reactions . Driven primarily by isotope effects, exchange reactions

involving tritium can be expected to occur at a relatively rapid pace. Moreover,

the speed at which reactions of this type can occur can be further enhanced by

the addition of energy from radioactive decay. For tritium, therefore, reactions

similar to the following can be expected, and they can be expected to reach

equilibrium in time frames that range from seconds to hours:

CH4 + 2T2 W! CT4 + 2H2 ,

(5)

2H2O + T2 W 2HTO + H2 .

and

(6)

Equation (5) describes the preferential form of tritium as it exists in nature in

the earth' upper atmosphere. Equation (6) describes the preferential form of

tritium as it exists in nature in the earth' lower atmosphere (i.e., in a terrestrial

environment).

Equation (6) is particularly important because it describes the formation of

tritiated water vapor (i.e., HTO) without the involvement of free oxygen (i.e.,

with no O2). A comparable reaction that would involve free oxygen would take

the form of a classic inorganic chemical reaction, such as

H2 + T2 + O2 6 2HTO .

(7)

I-94