Special Tritium Compounds cont'd

DOE-HDBK-1184-2004

Because it decays by emission of low energy beta particles that cannot penetrate human

skin, tritium is not typically considered a significant external radiation exposure hazard.

However, inhalation, ingestion or skin absorption of tritium can result in internal radiation

doses. Because tritium, in its prevalent oxide form, behaves chemically identically to

water, it undergoes fairly rapid uptake by, and elimination from, the human body. These

biological processes make tritium oxide relatively easy to detect in bodily excretions

(primarily urine) at very low levels, simplifying the radiobioassay, dose assessment, and

exposure control processes.

DOE has provided a significant amount of information applicable to basic tritium processes

and properties in DOE-HDBK-1079-94 (DOE 1994), Primer on Tritium Safe Handling

Practices , and DOE-HDBK-1129-99 (DOE 1999e), Tritium Handling and Safe Storage.

1.3 Special Tritium Compounds

The detection and control of tritium are complicated when it is produced, used, and stored

in some chemical and physical forms. Hydrogen atoms tend to migrate through surfaces

with which they come into contact, and form chemical bonds with the host material. The

hydrogen atoms may be released at a later time (commonly referred to as "outgassing").

While this property of hydrogen atoms may complicate measures implemented to contain

tritium, it has been well characterized, and appropriate materials can be specified to

minimize adverse effects. This property can also be used to practical advantage, as

hydrogen atoms (including tritium) can be diffused through other materials, particularly

metals, such as uranium, and stored within the matrix for subsequent extraction and use.

Tritium atoms may also diffuse into, and form chemical bonds with, organic materials with

which they come into contact. The most common of these host materials are lubricating

oils, solvents, and plastics.

The term "special tritium compound" (STC) is used to describe these compounds of tritium

with host metals and organic materials.

The diffusion of tritium atoms into host metals and organic materials can complicate efforts

to detect, and quantify levels of, tritium contamination in the workplace, environment, and

individuals. These complications generally fall into three categories:

Detection Once the tritium atom has migrated into the matrix of the host material,

some fraction of its emissions may not be able to escape that matrix.

Physical and Chemical Behavior If a tritiated material exists in a particulate state, or

is subjected to any forces (e.g., heat, abrasion, cutting) that reduce it into a particulate

state, the tritiated particles will behave physically and chemically like the host material

particles, not like hydrogen. Therefore, the characteristics that are important variables

in the internal dose assessment process (e.g., particle size, solubility, disassociation,

inter-compartment transport, etc.) differ from those of tritium in elemental or oxide form.

Emitted Radiation Although only a small percentage of the beta particles emitted by

the decaying tritium atoms may be detected, they may interact with surrounding host

material atoms, resulting in emission of bremsstrahlung radiation and internal

bremsstrahlung from the nucleus.