Scope of Bioassay Program - doe-std-1136-20040111

DOE-STD-1136-2004

Guide of Good Practices for Occupational Radiological Protection in Uranium Facilities

have been classified as class Y have shown a more rapid clearance from the lung than for other class Y

compounds, i.e., having a 100-day effective half- life in the lung compared to the class Y compounds that

have a 500-day effective half-life. This may be due to the existence of mixtures having more than one

physicochemical form (ICRP 1988b; Fisher et al. 1990). A report (Forrest and Barber 1993) on class "Q"

material has behavior similar to that of special class Y. Class Q material was found to consist of 8- m size

particles (instead of the 1-m size assumed under ICRP Publication 30 methodology and to consist of two

parts: 90% class W material with a 120-day effective half- life in the lung and 10% class Y material with a

500-day effective half- life in the lung. It should be cautioned that even if specia l class Y or class Q

material is suspected, the relative transportability of the material should be determined and documented

before establishing action levels (ANSI/HPS 1995). As uranium ages in a residual, loose contamination

form, such as might be found in old duct work, glove boxes, or other such components, it can be expected

to undergo slow oxidation to a more insoluble form. Thus, class Y forms of uranium may be reasonable

assumptions of what to expect during many decommissioning operations.

For depleted uranium to present a chemical toxic hazard from inhalation, the depleted uranium

would have to be subdivided into soluble particles that can be inhaled, transported into the lungs, and

transferred to the blood for transport to the kidneys. Depleted uranium metal is not readily subdivided

into small, respirable particles. However, depleted uranium metal can slowly oxidize under ambient

environmental conditions (corrosion), resulting in formation of small particles. The rate of oxidation will

vary with the amount of water vapor present and the temperature. The oxidation rate will, in turn,

influence the solubility of the material inhaled.

Following an accidental release from a nuclear reactor, fission and activation products may be

present in fragments of irradiated fuel, of which the matrix is predominately uranium oxide (Devell

1988; Begichev et al. 1989; Toivonen et al. 1992). Studies of the in vitro dissolution of particles released

from the Chernobyl accident, seven out of ten of which consisted mainly of uranium (Cuddihy et al. 1989),

were consistent in assigning all the gamma-emitting radionuclides to class W (ICRP 1996).

Particle size is an important consideration for inhalation exposures. The normal practice for an aerosol

is to identify the activity median aerodynamic diameter (AMAD) and its associated particle -size

distribution. Particle sizes of 10 m or less are considered respirable. For compliance with 10 CFR 835, the

common practice is to assume a 1-m particle size for dosimetry purposes unless actual particle size

information is available. Particle size data are most readily obtainable for chronic exposure situations.

Unless representative air sampling is performed in the immediate proximity of a worker during abnormal

working conditions, the practical likelihood of obtaining good particle -size information is slim.

5.3 SCOPE OF BIOASSAY PROGRAM

For classes D and W uranium compounds, the monitoring programs need to be designed to maintain

exposures, including those from single acute intakes, below levels that will cause transient kidney damage

due to the heavy metal toxicity of uranium. Typically, urine sampling is the preferred method of

monitoring for classes D and W uranium. For class Y natural uranium and all classes of highly enriched

uranium, radiological considerations are more limiting. In addition, local factors concerning the diversity

of chemical forms of uranium must be taken into account when designing a bioassay monitoring program.

For these materials, a combination of direct and indirect monitoring may be required.

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