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surfaces (see, for example, Ref. [37]), but comparatively little on decontaminating
large areas with a combination of techniques. In current consequence codes the
decontamination process is simply modelled with a decontamination factor (DF),
defined generally as the ratio of the contaminant existing before to that remaining
after decontamination. The DFs used in consequence analyses are typically in the
range of 2 to 10, with higher DF values being associated with higher decontamination
costs [38].
It is usual practice in consequence analysis codes to include intervention levels
for imposing or withdrawing food bans. Generally, these intervention levels are based
either on activity levels in food and drinking water or on maximum individual doses,
which should be incurred although in some codes they are based on the level of
ground contamination.
2.8. HEALTH EFFECTS
The exposure of individuals to ionizing radiation can lead to health effects
which are generally classified as either ‘deterministic’ or ‘stochastic’. Deterministic
effects result from exposure of the whole or part of the body to high doses of radiation.
Their severity is observed to increase with dose and there is usually a threshold
dose below which the effects are not induced. Stochastic effects of radiation include
increased incidence of cancer among the exposed population and of hereditary
disease in their descendants. For stochastic effects the probability of occurrence, but
not the severity, depends on the radiation dose. Effects observed in exposed individuals,
i.e. deterministic effects and cancers, are termed ‘somatic’ effects, while
those observed in their descendants are known as ‘hereditary’effects. Deterministic
effects and stochastic effects are often referred to as ‘early’effects and ‘late’effects,
respectively.
The methods currently used in consequence analysis for evaluating the various
health effects identified above are now briefly summarized.
2.8.1. Deterministic effects
Following Scott and Hahn [39], who developed a model of deterministic effects
for the NRC, it is now common practice to evaluate deterministic effects using a
‘hazard function’. In this approach, the probability or risk of an individual being
affected, r, is given by:
r = 1 - exp (-//) (1)
Generally, H, the cumulative hazard, is given by a two parameter Weibull function of
the form:
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