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Nakayama, Hiromasa; Takemi, Tetsuya*; Nagai, Haruyasu
no journal, ,
The Gaussian plume model is widely used for regulatory purposes due to its simplicity and low cost. The traditional Gaussian model is effective for a flat or nearly flat terrain but has limited applicability for densely built-up urban areas. However, urban surface geometries are highly inhomogeneous and covered with low- and high-rise buildings. Therefore, important issues remain in appropriately determining the representative wind speed and dispersion parameters within urban canopy. In this study, first we carried out LESs of plume dispersion in various urban areas and investigated canopy wind speed, lateral and vertical plume spreads. Then, we estimated the representative canopy wind speed and plume spreads by sensitive analysis based on the LES data. Our objective is to evaluate the urban-type Gaussian plume model using those representative parameters estimated by sensitive analysis.
Nagai, Haruyasu; Tsuzuki, Katsunori; Kobayashi, Takuya; Terada, Hiroaki
no journal, ,
The Fukushima Dai-ichi Nuclear Power Plant accident caused the month-long discharge of radioactive materials into the environment. Also, substantial amount of contaminated water remains undisposed within the site, and the environmental impact in case of leakage is grate concern. To cope with these problems, computer simulations on the dispersion of radioactive materials in the environment are useful. Japan Atomic Energy Agency are trying to apply a coupling simulation of atmospheric, terrestrial, and oceanic models on the radioactive material transport in the environment. This coupling simulation is necessary to predict the discharge and transport of radioactive materials deposited on the ground to rivers and ocean. It is also effective to predict the transport of tritium in contaminated water that has two-way exchange between the atmosphere and land/sea surface. The method and preliminary results of coupling simulations will be presented.
Katata, Genki; Chino, Masamichi; Ota, Masakazu; Nagai, Haruyasu; Terada, Hiroaki; Kajino, Mizuo*
no journal, ,
We estimated a detailed time trend of atmospheric releases during the accident by coupling additionally obtained monitoring data of air dose rate near the plant, parameters for the reactor events, and atmospheric dispersion simulation by WSPEEDI-II. The modified WSPEEDI-II using the newly estimated source term well reproduced local and regional patterns of air dose rate and surface deposition obtained by airborne observations. The results suggested that the major release occurred in the following periods during March 2011: afternoon on the 12th, midnight on the 14th, morning and night on the 15th, and morning on the 16th. Our dispersion simulations revealed that the highest radioactive contamination areas were created from 15th to 16th by complicated interactions among rainfall, plume movements, and phase properties and release rates.