Isotopic mixture. Characterization of the isotopic mixture is important to the
accuracy of both dose calculations and contamination measurements. When the
inventory or quantity released is expressed as the total activity (Ci or Bq) of a
mixture of isotopes, the total often includes the 241Pu activity. Because 241Pu
decays almost exclusively by beta emission, it contributes little to the internal
dose from a mixture of Pu isotopes. Also, the fraction of 241Am (from decay of
241Pu) in plutonium can vary greatly, depending on the degree of irradiation and
the time since the plutonium was chemically separated from the reactor fuel.
Characterization of contamination from a plutonium mixture is often done by
detecting the low-energy photons emitted by 241Am, which requires knowledge
of the activity of 241Am compared to the other isotopes in the mixture.
(d) Developing Event Scenarios. The properties of the hazardous material do not
significantly affect the manner in which this step of the hazards assessment is
(e) Estimating Potential Event Consequences. For the scenarios developed in
the previous step, this step determines the area potentially affected, the need for
protective actions, and the time available to take those actions. The way these
consequences are determined depend on properties of the hazardous material.
For plutonium and its compounds, inhalation during plume passage is the most
important exposure process in the early phase of an emergency. After passage
of a plume, exposure to material deposited on the ground will dominate.
Therefore, the following features should be considered when selecting and
applying calculational models:
Inhalation pathway dose. For any realistic mixture of plutonium isotopes, the
great majority of the dose will be by the inhalation pathway. Therefore, the
model selected to estimate consequences of an atmospheric plutonium release
must be able to calculate the total effective dose equivalent (TEDE) to an
individual exposed by inhalation.