Sensitivity analysis of ECOSYS-87: an emphasis on the ingestion pathway as a function of radionuclide and type of deposition.
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 137Cs 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.
Hinton
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Paul Scherrer Institute, Villigen, Switzerland.
D000059:Accidents; D000328:Adult; D002588:Cesium Radioisotopes; D003198:Computer Simulation; D005060:Europe; D005507:Food Contamination, Radioactive; D006801:Humans; D007457:Iodine Radioisotopes; D009688:Nuclear Reactors; D011005:Plutonium; D013326:Strontium Radioisotopes
D002588:Cesium Radioisotopes; D007457:Iodine Radioisotopes; D013326:Strontium Radioisotopes; D011005:Plutonium