Following the explosion at the Chernobyl nuclear power plant, about 800
shallow trenches were dug to bury radioactive waste in the exclusion
zone. However, these trenches were built in permeable aeolian sand and
do not prevent the migration of radionuclides in the superficial
aquifer. Trench T22 allows us to explore general research problems such
as the uncertainty linked to the volume and the activity of radioactive
waste, and to the water quality in groundwater downstream the trench.
Previous estimations of the trench inventory assume that the correlation
between specific activity measured in soil samples and in situ count
rate is linear. Geostatistical simulations are used to analyze this
correlation and its sensitivity to the activity spatial variability and
to its surrounding environment. If the correlation can be considered as
linear, the study of field measurements undertaken in 2015 demonstrates
that it is better to apply cokriging to estimate the activity by the
count rate rather than transforming the count rate data.
The inventory of 137Cs calculated for 1999 is then compared to a
previous estimation. The trench boundaries are interpolated using the
results of ground penetrating radar profiles and gamma logging carried
on boreholes drilled into the trench. The new estimation is completed by
geostatistical simulations and enables us to quantify the uncertainty
of 137Cs trench inventory.
Finally, the effect of the source term spatial variability is explored
with the 90Sr migration modeling. The previous 90Sr transport model did
not take into account the water table fluctuations which may cause some
discrepancies between model predictions and field observations. They are
thus reproduced in a 2D non saturated model. A sensitivity analysis on
the flow and transport parameters as well as the source term variability
is undertaken.