Simulation of Radioactive Tracer Transport Using Isorsm and Uncertainty Analyses

Abstract

Due to the massive earthquakes and tsunami on March 11th, 2011 in Eastern Japan, Fukushima Daiichi nuclear power plant was severely damaged and some reactors were exploded. Then radioactive particles were widely spread out. In this study, we modified the stable isotope module of RSM (IsoRSM, Yoshimura et al.) to enable to simulate the transport of the radioactive tracers, namely iodine 131 and cesium 137, by including the dry and wet deposition processes. The control experiment with 10km resolution and the emission estimated by Chino et al. (2011) showed reasonable temporal results for Toukatsu area (eastern part of Tokyo metropolis and western part of Chiba prefecture), i.e., on March 22th, the tracers from Fukushima was reached and precipitated in a significant amount as wet deposition. Thus, we conducted 4 experimental simulations to analyze the uncertainty due to different meteorological patterns and different parameters for wet and dry deposition and diffusion. Though the temporal patterns of deposition of radioactive particles were moderately similar each other in all experiments, we revealed that the deposition parameters and boundary conditions can cause the uncertainties largely in the distribution of deposition.

Dispersion characteristics of radioactive materials estimated by wind patterns

“…The wet deposition (washout process) is calculated as: where C is the atmospheric concentration of radioactive materials; α is the washout coefficient (0.5); and P and q are the water condensation and the water vapour at each atmospheric layer, respectively 30 .…”

Long-distance transport of radioactive plume by nocturnal local winds

“…where C is atmospheric concentration of radioactive materials, α is the washout coefficient (0.5), and P and q are the vertically integrated water condensation and the water vapour in the atmospheric column, respectively36.…”

Precipitation Redistribution Method for Regional Simulations of Radioactive Material Transport During the Fukushima Daiichi Nuclear Power Plant Accident

“…For the results reported herein, we used a version of IsoRSM in which aerosol forms of 131 I and 137 Cs and their deposition processes were implemented by Saya et al (). Yoshikane et al () showed that the radioactive material version of IsoRSM was reasonably skilled at simulating radioactive materials produced in the Fukushima accident.…”

“…The following equation developed by Saya et al () was applied as the wet deposition process. The wet deposition process can be separated into two types, rainout and wash out, depending on when materials are incorporated into precipitation.…”

“…In our previous study, a set of sensitivity tests for the parameters in dry and wet deposition processes, that is, dry depositional speed and washout coefficient, was conducted. It could be concluded from the results that the washout coefficient in the model formulation of the wet deposition process clearly impacted the wet deposition concentrations and their spatial and temporal distributions, whereas changes in that parameter in the dry deposition process did not influence the dry deposition as much as for wet deposition (Saya et al, ).…”