Developing Event Scenarios - doe-std-1128-98

DOE-STD-1128-98

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

performed.

(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.

9-5