Plutonium facility decommissioning projects may present a different set of
challenges for worker protection. In particular it is likely that clean up of areas will
involve more plutonium that is not contained than is the case during normal
operations. In addition, the workers involved may be relatively transient as the
project progress through phases requiring different craft labor mixes. This being the
case, more frequent bioassay may be necessary to provide good assurance that dose
limits are not exceeded. As discussed in Section 5.3.1, it is likely that program
administrators will require a baseline measurement prior to the start of work and
another at the termination of work. However, if the worker moves between tasks, it
may be difficult to determine the source of an uptake without intermittent bioassay.
In such cases, the use of breathing zone air samplers may be appropriate.
Special Bioassay as Supplements to Routine Bioassay Programs
Special bioassay programs for workers with known or suspected acute inhalation
intakes of plutonium or other alpha-emitting radionuclides should include both urine
and fecal sampling. Special bioassay measurements should be initiated for each
employee in a contaminated work area when surface contamination is detected by
routine surveillance if it is possible that the contamination resulted in a CEDE of 100
mrem or greater. Excreta samples should not be collected where they may be
contaminated by external sources of plutonium. Ideally, total urine and feces should
be collected for about a week following intake. This permits a sensitive assessment of
potential intake and internal dose. Longer term special samples collected at various
times from a month to a year following intake can help to discriminate between
ingestion, class W inhalation, and class Y inhalation. See Section 5.9 for indicator
levels where special bioassay should be considered.
Long-term Follow-up Bioassay Programs
Following an intake a long-term follow-up bioassay program may be required for a
worker to compare the actual excreta or in vivo results with those projected by the
evaluation. This is important to verify the accuracy of intake and dose assessments.
The frequency and duration of a special program is dependent upon the projected
values; it is suggested that as long as a worker continues to have detectable bioassay
results, he or she should continue to be monitored. It is particularly important to have
good baseline data and projections for individuals who return to plutonium work. The
ability of a bioassay program to distinguish between an established, elevated baseline
and a new potential intake is important in the continued monitoring of workers once
an intake has occurred. Because of statistical fluctuations in low-level plutonium and
americium measurements, it can be very difficult to identify a new intake by routine
bioassay if a worker has an elevated baseline.