Safety_Series_041_1975 - gnssn - International Atomic Energy ...

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120 APPENDIX IV
TABLE XXX. RADIOACTIVITY IN FISH IN LAKE TRAWSFYNYDD,
1967-68
S p ecies
1 3 4 _ Cs
R ad ioactiv ity
(p C i/g (w et))
137Cs
Trout 0 .7 5 .9
Perch 1 .8 17
W eighted m ean 1. 0 8 .7
The maximum consumption rate has been estimated at 100 g/d
from habits surveys, which have in addition formed the basis for
identifying the critical group and other important factors. Unlike
a marine or estuarine site, there is little possibility of an external
dose-rate problem ; farmland is not periodically flooded in such a
way that significant contamination of working areas could occur.
Concentrations of caesium radionuclides in fish in 1967-1968 are
shown in Table XXX. No attempt has been made to identify an
average rate for the critical group since it is relatively small,
and this estimate of 2.5% of the derived working lim it is therefore
an overestimate of that which the average member has received.
(B) Exposure assessable only by sampling indicator m aterials
The value of critical materials is m ost readily appreciated
during the early years of operation of a site. Discharge rates tend
to build up slowly, and the laboratory is currently surveying several
sites where it appears that, though potentially critical m aterials are
not measurably contaminated at present, this may not remain so
indefinitely. In these circum stances the most useful and econom ic
development of effort consists of adding an indicator material to
the sampling program me whilst maintaining a small survey of
potentially critical m aterials, and analysing the indicator material
for specific radionuclides known to be present in the waste d ischarged.
Part of the monitoring scheme is common to sites in
category (C) in that, in the early period of operation of a site, the
local public may naturally be somewhat anxious, and a limited
program me is needed to reassure them.