Simulation of atmospheric dispersion of radionuclides using an Eulerian–Lagrangian modelling system

Abstract

In this paper we present an atmospheric dispersion scenario for a proposed nuclear power plant in Pakistan involving the hypothetical accidental release of radionuclides. For this, a concept involving a Lagrangian stochastic particle model (LSPM) coupled with an Eulerian regional atmospheric modelling system (RAMS) is used. The atmospheric turbulent dispersion of radionuclides (represented by non-buoyant particles/neutral traces) in the LSPM is modelled by applying non-homogeneous turbulence conditions. The mean wind velocities governed by the topography of the region and the surface fluxes of momentum and heat are calculated by the RAMS code. A moving least squares (MLS) technique is introduced to calculate the concentration of radionuclides at ground level. The numerically calculated vertical profiles of wind velocity and temperature are compared with observed data. The results obtained demonstrate that in regions of complex terrain it is not sufficient to model the atmospheric dispersion of particles using a straight-line Gaussian plume model, and that by utilising a Lagrangian stochastic particle model and regional atmospheric modelling system a much more realistic estimation of the dispersion in such a hypothetical scenario was ascertained. The particle dispersion results for a 12 h ground release show that a triangular area of about 400 km(2) situated in the north-west quadrant of release is under radiological threat. The particle distribution shows that the use of a Gaussian plume model (GPM) in such situations will yield quite misleading results.

Modeling and sensitivity analysis of transport and deposition of radionuclides from the Fukushima Daiichi accident

“…where r a is the aerodynamic resistance; r b is the quasilaminar layer (viscous sublayer) resistance; and r s is the surface resistance (describing the resistance of the surface to the uptake/absorption/adsorption of the gas). The parameterizations of these three resistances in our study follows Brandt et al (2002).…”

“…where u grav is the gravitational settling velocity. According to Brandt et al (2002), the gravitational settling velocity can be calculated from the Stokes equation (small particles in the atmosphere experience a creeping flow, Reynolds number 1, that appears to change in time due to the larger scale turbulent eddies):…”

“…Meteorological fields are however not the only source of uncertainty that can reduce the accuracy of transport and deposition simulations. Previous studies have also shown that different dry and wet deposition parameterizations can cause different deposition rates and accumulated amounts of radionuclides (see e.g., Brandt et al, 2002). In this study, several dry and wet deposition parameterizations are thus also added to the WRF-Chem model to test and intercompare their performances.…”

“…This review also points out that the partitioning between gaseous and particulate phases is crucial for capturing the ground deposition of radionuclides. Apart from the gas partitioning, the size distribution of particles is another important characteristic that has not been thoroughly studied, since some deposition schemes explicitly take the size distribution into account (Brandt et al, 2002).…”

Modeling and sensitivity analysis of transport and deposition of radionuclides from the Fukushima Dai-ichi accident

“…For this particular accident at Fukushima, the Community Multi-scale Air Quality (CMAQ) model (Morino et al, 2011), the Lagrangian transport models HYSPLIT and FLEXPART with meteorological conditions provided by the Weather Research and Forecasting (WRF) model (Srinivas et al, 2012), and the WRF-Chem tracer model which directly couples the simulation of the chemistry and meteorology (Huh et al, 2012(Huh et al, , 2013) have been used. These studies, together with many previous studies for other events, have identified a number of meteorological variables that can significantly influence the atmospheric transport and ground deposition of radionuclides, including wind and rainfall (Basit et al, 2008;Mathieu et al, 2012;Takemura et al, 2011;Ten Hoeve and Jacobson, 2012;Yamauchi, 2012). For example, the study of Morino et al (2011) has shown that during the period from 11 to 30 March 2011, the amounts of 131 I and 137 Cs transported across the eastern boundary (downwind) of their domain are 6.52 × 10 16 Bq and 4.58 × 10 15 Bq, respectively; while those across the western boundary (upwind) are only 1.49 × 10 12 Bq and 1.13 × 10 7 Bq, respectively.…”