Civil Engineering Reference
In-Depth Information
with regard to measures already undertaken, or about measures that become
required in addition (e.g. resettlement), and also about the stepwise cancellation
of existing measures. The transitional phase can last from days to several weeks.
The long-term post-accident phase can last up to several years or even decades.
It is characterized by a long-term contamination and an associated low but long-
lasting radiation exposure of people that can be regarded as an existing exposure
situation in the sense of ICRP 103 and ICRP 111 [
3
]. The question is then how
individual, social and economic life can be shaped in the affected areas. This
requires a culture of treating radiation protection issues that needs to be communi-
cated with the affected population and economic agents, and the further optimiza-
tion of measures has to be realized in a social consensus. In most cases, medical
surveillance of the population in the contaminated areas is also necessary.
20.3.3 Off-Site Radiation Protection Measures and Their
Initiation
Measures for avoiding or reducing radiation doses can take effect only on antici-
pated doses; once a dose has been received it cannot be undone. This means that the
doses underlying the decisions about future measures can only come from prog-
nostic assessments, including extrapolations from existing contamination patterns
and exposure histories; they cannot be measured in advance.
At present, a given measure is initiated when the estimated value of a dose
quantity, calculated with rules specific for the measure, exceeds a given limit (the
“intervention level”) or is within a given limiting interval, respectively, also
specific for the measure. There are significant international differences in the
rules for determining the dose quantity, i.e. in the exposure pathways and time
periods to be taken into account, and whether the “projected dose” or the “avertable
dose” shall be used. But even if the same concept is in operation, the dose limits
may differ between different countries.
Since a couple of years, the International Commission on Radiological Protec-
tion has developed a new concept and published it in ICRP-103 which implies that
the individual dose in the population, expected from all exposure pathways—food
ingestion included and typically integrated over 1 year—should not exceed a given
dose level, the so called reference level. Strategies of countermeasures have to be
defined and optimized in the planning stage to assure that in an acute event this
reference level will not be exceeded. The advantages and disadvantages of this
concept and the practical implementation are currently being debated both on
national and international levels.
The next two chapters outline the measures which can be taken for avoiding or
mitigating off-site radiation exposure of the population in the early and late phases
of an accident.
