2022 ,
15 , 7804
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3. Radiotoxicity and Retention Times of Disposal 3.1. Radiotoxicity The ingestion hazard (
H p ) of a radioactive material is defined as the volume of drink-
ing water in which the initial material containing contaminants at concentrations
C i must
be diluted to obtain the water being contaminated at permitted contamination levels
PL i ,
and shows the maximum possible volume of contaminated drinking water when the con-
taminants are completely dissolved in it [20]. The index of radiotoxicity
I p is then defined
by the equation:
= ∑
(
)
,
(1)
where
C i is the initial concentration of
i -th radionuclide in the nuclear waste,
λ i is the ra-
dionuclide decay constant, and
t is time. The radiotoxicity index gives the necessary dilu-
tion ratio to obtain drinking water by diluting the contaminated solution with clean water.
Dilution of contaminants is the simplest disposal route; however, it can only be used when
the total amount of contaminants is limited and low. The environment naturally contains
contaminants although in most cases at lower concentrations compared to man-made
sources. Often the relative radiotoxicity index (
RTI ), also termed relative radiotoxicity, is
used, which is defined as the ratio of waste radiotoxicity to the natural ore radiotoxicity
[21]:
=
(
)
(
)
(2)
The
RTI of nuclear waste diminishes with time due to radioactive decay. Figure 5
demonstrates the declining
RTI of SNF and HLW as a function of time.
