Lessons learned from atmospheric modeling studies after the Fukushima nuclear accident: Ensemble simulations, data assimilation, elemental process modeling, and inverse modeling

Deposition and Dispersion of Radio‐Cesium Released Due to the Fukushima Nuclear Accident: Sensitivity to Meteorological Models and Physical Modules

“…In the current simulation, as mentioned earlier, all of the radio‐Cs nuclides were carried by sulfate aerosols, as inferred by Kaneyasu et al () and assumed by all simulations except for those of Adachi et al () and Kajino, Sekiyama, et al (). In terms of the physical parameters of Cs‐carrying sulfate during the emission (although sulfate is clearly “not” directly emitted from the reactor, it is assumed that the emitted Cs was mixed with environmental sulfate aerosols immediately after its emission from the reactor), we used a number‐equivalent geometric mean dry diameter of 102 nm, a geometric standard deviation of 1.6, a particle density of 1.83 g/cm 3 , and a hygroscopicity κ of 0.4 (see Adachi et al, ).…”

“…The unit activation fraction was assumed for all cloud types, including fog and stratiform and convective clouds. Although there existed other types of Cs‐bearing particles, found and named as Cs‐ball by Adachi et al (), which are totally different in size and hygroscopicity (super micron and nonhygroscopic) than sulfate particles (submicron and hygroscopic), the Cs‐ball was not considered in the current simulation, following almost all previous simulation studies, except those of Adachi et al () and Kajino, Sekiyama, et al (). The impact of Cs‐ball on dispersion and deposition will be presented and quantitatively discussed in our next paper.…”

“…Thanks to the substantial efforts to reveal the atmospheric behavior and budget of radio‐Cs by using field observations and numerical models, knowledge has been accumulated (Kajino, Sekiyama, et al, ; Mathieu et al, ). The major isotopes of radio‐Cs emitted to the air were 134 Cs and 137 Cs, with almost equal activity.…”

Deposition and Dispersion of Radio‐Cesium Released due to the Fukushima Nuclear Accident: 2. Sensitivity to Aerosol Microphysical Properties of Cs‐Bearing Microparticles (CsMPs)

“…The contaminated air mass traveled over Japan and the radionuclides were deposited into and contaminated terrestrial ecosystems; this phenomenon was discovered by field measurements (Igarashi et al., 2015; Ikehara et al., 2020; NRA [Nuclear Regulation Authority], 2012; Oura et al., 2015; Sanada et al. 2014, 2018; Torii et al., 2012; Tsuruta et al., 2014, 2017, 2018, 2019) and has been investigated by numerical simulations (Kajino et al., 2018, 2019a; Morino et al, 2011, 2013; Nakajima et al., 2017; Sekiyama & Iwasaki, 2018; Sekiyama & Kajino, 2020; Saya et al., 2018; Sekiyama et al, 2015, 2017; Terada et al., 2020). The radionuclides were transported and deposited over the ocean (Aoyama et al., 2016) and further to North America (Wetherbee et al., 2012) and Europe (Masson et al., 2011, 2013).…”

Relative Risk Assessment for Hypothetical Radioactivity Emission at a Snow Climate Site

“…The massive release of radioactivity in the atmosphere caused by the accident at the Fukushima Daiichi Nuclear Power Plant (NPP) in March 2011 has been evaluated in many publications. Owing to the difficulty of bottom-up estimates of the emission from the nuclear reaction inside the plant, an atmospheric dispersion-deposition model (ADM) combined with radioactivity monitoring data was used to assess the time-evolution of various radioactive materials emitted from the plant inversely (Kajino et al 2018). Since the preliminary estimation by Chino et al (2011), modeling studies have steadily updated the emission information with an accurate simulation of the surface deposition of radioactivity (Terada et al 2012;Saunier et al 2013;Winiarek et al 2014;Katata et al 2015; and a comprehensive review by Mathieu et al 2018).…”