Low level radioactive liquid discharges have been carried out in the Loire
river since 1963. Since then, the number of power plants located on the Loire
river and its tributaries has been steadily increasing to reach, in the year
2000, 14 reactors operating on 5 different sites. The question arose to evaluate
to what extent the addition of several nuclear power plants on the same river
system could increase the concentrations in radionuclides in the environment
and affect the dose to the public. To address this issue, EDF initiated in 1998
the “Loire river and estuary radioecology” program with the focus on assessing
possible accumulation of radionuclide in river bottom sediments or on river shores.
The following radionuclides were considered because of their importance in power
plant liquid discharges: tritium, 14C, 58Co, 60Co,
134Cs, 137Cs, 54Mn, 124Sb, and 131I. Radionuclide concentrations
in the dissolved, particulate and sedimentary forms were evaluated using the CRESCENDO model.
The development and validation of this model required a multi-step process. The first step was
to design a 350-km long 1D hydraulic and water transport based on currently available
tools and data. Next, daily tritium concentrations measured in Angers, at the downstream
limit of the river, were compared with computed values. The following step was to
calibrate the sediment transport model. Areas where fine particles settled (dams and river
shores) were monitored to improve our understanding of sediment dynamics. Then equations
representing radionuclide exchange between water and particles were derived from
laboratory experiments and included in the model. After each step the computed values
were compared to measure data sets to ensure the model adequately described the
processes involved. In the final step, the CALVADOS model was used to calculate
dose to the public at different locations along the Loire river.