Scope of Bioassay Program

DOE-STD-1128-98

Guide of Good Practices for Occupational Radiological Protection in Plutonium Facilities

in DOE facilities. Isotopically pure forms of radionuclides can also be encountered. Table 5.5

demonstrates the impact of aging on the activity composition of two mixtures. The composition of

plutonium in the facility can significantly affect the design and capabilities of an internal dosimetry

program. As part of the program technical basis, the plutonium mixtures need to be determined. In

addition, determinations should be made at the time of identified incidents of potential intake.

Methods for such determination may include radiochemical analysis or chemistry followed by mass

spectrometry.

The physical-chemical form of plutonium also affects the internal hazard posed. Oxides of

plutonium tend to exhibit inhalation class Y behavior, whereas other compounds such as nitrates are

assigned class W by the ICRP. However, as noted in Section 2.4.1, extremes have been observed

with regard to both highly soluble and highly insoluble forms, leading to the good practice of

performing dissolution rate (i.e., solubility) tests on standard materials in a facility.

As plutonium 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 plutonium may be reasonable assumptions of what to

expect during many decommissioning operations.

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

aerosol is to identify the activity median aerodynamic diameter and its associated particle-size

distribution. Particle sizes of 10 m or less are considered respirable. The common practice is to

assume a 1-m particle size for dosimetry purposes because actual particle size information is

usually lacking. 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

The relatively low annual limit on intake of plutonium renders its radiation hazard substantially

more restrictive than its industrial hygiene or chemical toxicity hazard. Thus, internal radiation

dose or intake monitoring is the appropriate focus of bioassay monitoring.

5-9