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.