MANAGEMENT OF RADIOACTIVE WASTES 633
are recorded in the nearest approximation we have
to a perpetual repository of archives—a government
department. Beyond that we can only rely on folk
memory. After all, farmers in Europe have been
ploughing around Neolithic tumuli and prehistoric
roads for thousands of years for no good reason
known to them, except that it was accepted to be the
right thing to do.
b) Dilution and dispersion is the traditional method
that men have always used for dealing with their
wastes. Until recently it seemed to work fairly well
unless populations became very concentrated, but
it is now becoming clear that there are so many
people that the system is showing signs of break-
ing down. It depends upon the capacity of the
environment to dilute or detoxify the wastes to a
level that is innocuous to man and to organisms of
interest to man. We are still a very long way from
contaminating our environment with radioactivity
to a point where radiation effects are observable,
even in close proximity to nuclear enterprises, but
we must maintain vigilance to ensure that slow
and subtle changes do not occur which escape our
notice until it is too late.Safety in discharge to the environment depends
upon three factors—(1) Dispersion by such means
as atmospheric dilution, mixing into big bodies of
water, or spreading through large volumes of soil.
(2) Fixation of radionuclides on soil minerals and
organic detritus. (3) Decay of radionuclides, dis-
persed or fixed, before they are able to affect man.
The principle of dispersion has one logical trap
into which regulatory bodies have sometimes
fallen. In some countries the discharge of liquid
and gaseous wastes is limited by the concentra-
tion in the effluent pipe or the concentration at the
stack mouth. This is based upon the assumption
that if the concentration is limited to the maxi-
mum permissible value, all will be well. However,
the “dilution capacity” of a river is a function of
the number of Curies per day put into the river,
divided by the daily flow of water. If an operator
wishes to dispose of double the amount of waste,
and he is limited only by the concentration in the
effluent pipe, he need simply double the amount
of water flowing in the pipe. But the downstream
effect will be a doubling in the concentration,
unless he has doubled the flow in the river.FIGURE 3 Pouring a concrete monolith. Steel drums filled with waste, solidified by mixing with cement, were stacked on
concrete slabs surrounded with forms. The forms were filled with concrete. The monoliths were about 2 m below ground level.C013_001_r03.indd 633C013_001_r03.indd 633 11/18/2005 10:38:19 AM11/18/2005 10:38:19 AM