Safety_Series_041_1975 - gnssn - International Atomic Energy ...

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122 APPENDIX IV
maximum degree of radiological exposure is trivial at this stage,
equivalent to a m ere 0.07% of the derived working lim it, it marks
an important step in environmental measurements. A sim ilar series
of calculations can be carried out for contamination of beach material,
for which the only important nuclides are caesium-137 and -134.
The maximum conceivable exposure by this route is even less than
by consumption of fish and shrimps, at 0.02% of the derived working
limit.
(C) Exposure not measurable by any method
Dilution of discharges from some sites is so large compared
with the quantities of radioactivity involved that it can be predicted
with confidence that no environmental material will be measurably
contaminated. Although there may be little or no scientific need to
carry out any environmental monitoring, a limited program me is
generally undertaken, at least in the early period of operation of a
site, prim arily to allay public fears. Ultimately, the program m es
can be contracted, and if this situation of no measurable contamination
persists after the station has reached operational equilibrium, it
will be possible to dispense with monitoring altogether, leaving any
occasional checks to the operator.
A good example of this type of site is provided by the nuclear
power station at Dungeness, Kent. Radiological exposure is not
measurable by any method, direct or indirect, but monitoring is
still designed on the critical path model which provides the only
meaningful and scientific basis for expressing results. Detectable
contamination is not necessary before potential critical routes can
be identified. Two groups of the public would be important in this
way — fishermen and bait-diggers — and the monitoring program me
is designed to cover their habits. Plaice and whelks are sampled
at approximately quarterly intervals subject to seasonal availability,
and a simple total beta assay is sufficient to show that no artificial
radioactivity is present. Occasionally, samples are analysed by
gam m a-spectrom etry to confirm that no radionuclides are being
m issed by the m ore simple beta analysis. Bait-digging for lugworm
is a regular occupation on the beaches to the east of the
power station and the potential critical effect would be external
gamma radiation exposure resulting from adsorption of radioactivity
on to the fine sand in this area. To cover this pathway gamma d oserate
measurements are made at selected points from half a m ile to
four m iles from the discharge point. Measurements have so far