SREL Reprint #1839
SENSITIVITY ANALYSIS OF ECOSYS-87: AN
EMPHASIS ON THE INGESTION PATHWAY AS A
FUNCTION OF RADIONUCLIDE AND TYPE OF
DEPOSITION
T. G. Hinton
Abstract-A sensitivity analysis of parameters associated with the ingestion
pathway was conducted for the computer model ECOSYS-87. The model is
currently being used extensively throughout Europe for accident consequence
analysis following a nuclear release. Individual parameter perturbation was used
to develop sensitivity indices. The sensitivity indices identified parameters whose
uncertainties had a large impact on model results. The relative ranking of the
sensitive parameters depended on the radionuclide (137Cs, 90Sr, 131I, or 239Pu),
whether dose 1 y or 50 y postaccident was being considered, and whether the
deposition event was dry or mixed. The most influential parameter for 239Pu was
resuspension. Parameters to which human dose was sensitive following exposure
to 137Cs, 90Sr, and 131I, were as follows: yield (biomass) of vegetation, transfer
of radionuclides from plants to animals, deposition velocity, changes in
radionuclide concentrations due to food processing, livestock feeding rates, and
weathering of radionuclides from plant surfaces. The ranking of 131I's parameters
was governed by its 8-d physical half-life. Parameters that affected the initial
deposition, parameters that could rapidly affect the transfer of 131I from the biota
to humans, or parameters that allowed 131I to decay prior to consumption were
important. Important parameters specific to 90Sr and 131Cs included transfer of
radionuclides from soil to plant, leaching from the plant rooting zone, and
resuspension. Parameters associated with the movement of radionuclides within
the soil were not as important for 137Cs as they were for 90Sr. With the
exception of the deposition velocity, if a parameter proved to be sensitive for dry
deposition, it was as sensitive, or even more so, for a mixed deposition event.
Extending the model end point from 1 y to 50 y postaccident also caused a shift
in the relative ranking of sensitive parameters for 137Cs and 90Sr. Parameters
that were not important for any of the radionuclides considered under this
scenario were those related to timing and length of crop harvest, transfer of
radionuclides from leaf surfaces to edible portions of plants, rate at which
radionuclide concentrations in plants decrease due to growth dilution, and time
for animals to reach marketable size.
Key words: environmental transport; ingestion; 137Cs; 90Sr
SREL Reprint #1839
Hinton, T.G. 1993. Sensitivity analysis of ecosys-87: an emphasis on the ingestion pathway as a function of a radionuclide and type of disposition. Health Physics 66:513-531.
