Civil Engineering Reference
In-Depth Information
a short period of time, in particular in winter, or on the long-term the inadvertent
ingestion of contaminated soil during the grazing period. The processes leading to a
contamination of plants in general have already been described, but for forage
plants, other plants are relevant (such as grass) or other parts of plants (such as
entire corn plants, not only the cobs). Again, the time of accident is very important,
on the one hand with respect to the forage plants, and on the other hand, because
feeding practices may vary with the season (such as grazing on pasture in summer
and keeping the animals indoors on stored feed in winter).
All processes described so far do not only depend on the time of an accident, but
also on the food item itself and the type of radionuclides causing the contamination,
and on regional climatic and soil conditions and agricultural practices.
Before culinary use, vegetable products for human consumption are washed or
peeled (salad, vegetables, herbs, potatoes) and, possibly, converted into a secondary
form of product (such as flour from grain) or stored (potatoes, flour, frozen
vegetables, herbs). Animal food stuffs also get stored, usually for at least a couple
of days prior to consumption, or are converted into secondary products with longer
shelf life (e.g. cheese from milk). During storage there is radioactive decay, and the
food processing can also influence the contamination levels; therefore, the contam-
ination of a product ready for consumption in general differs from that of the raw
initial animal or plant product.
The modeling of terrestrial ingestion pathways may pursue two aims:
1. Estimating the aggregate activity intake of humans resulting from the consump-
tion of specific food items or a representative food basket
2. Estimating the time-dependent contamination in food and feed stuffs as a
function of the time of accident
On the whole, models for estimating the aggregate activity supply are less
sophisticated. They mainly provide factors for manual calculations that are appli-
cable for stationary or quasi-stationary conditions (e.g. in normal operation of
nuclear power plants), or for rough estimates of the activity intake following
accidental releases; here, usually two sets of factors are provided, one each for
assumed accidents during and outside the vegetation period. Ingestion models of
this type are included for example in the RESRAD Family of Codes (
http://web.
ead.anl.gov/resrad/home2/resrad.cfm
)
and in the American WASH-1400 Risk
Study [
14
].
Knowledge of the contamination of food and feed stuffs as a function of the time
after an accident is required for detailed planning and preparation of agricultural
measures as well as for the analysis of the possible effectiveness of the measures.
Models developed for such purposes must take into account the dynamic processes
described in this chapter. Dynamic approaches decompose the food chain into
transport-related components, or “compartments,” and describe the seasonal devel-
opment stage of plants and animals at the time of the accident analytically or by
datasets. The transport between the compartments, and their development over
time, is calculated on the basis of transfer factors derived from measurements,
and biological half-lives. The German model ECOSYS [
7
] is an example of a
