The Study Of Typical Airborne Radionuclide Dispersion And Radiation Dose In Fukushima Nuclear Accident

A9.0earthquake which epicenter was located in the seabed about130km east from the Sendai Port of Japan Honshu Island was occurred onMarch11,2011.This earthquake triggered a huge tsunami, and then caused aserious damage of the Fukushima Daiichi nuclear power plant unit as well asthe massive leak of radioactive substance. The accident has aroused awidespread concern of the public and researchers for emergency responseand radiation safety once again.ARTM, AERMOD and CALPUFF atmospheric dispersion models wereevaluated by the statistical method of Model Validation Kit. The resultsshowed that the three models are basically able to achieve the recommendedmodel standards. ARTM and CALPUFF model have a underestimate trendover the distance up to3km, while AERMOD model has an overestimatetrend. CALPUFF model had a relative superiority on simulation andprediction in the simulation area more than50km.In this paper, CALPUFF atmospheric dispersion model was used tosimulate the air and deposition concentration distribution of radionuclide¹³¹Iduring30days after the accident. The simulation area is a160km×160kmregion which center is located in the Fukushima Daiichi nuclear power plant.And an equivalent attenuation method was used to calculate the results ofradioactive decay correction. The peak air concentration during the accidentwas6.70×10⁶Bq/m³, and the peak ground deposition concentration was1.81×10⁵Bq/m². Northwest of the source of was the most polluted landdirection. The critical population, path and organ were determined and the thyroidradiation doses of the public within the study area were calculated throughsystem analysis method which simplified the ecosystem of the study area andused a series of differential kinetic equations to describe the ecologicaltransfer mechanism of the nuclide. The settlements who were of the biggestthyroid equivalent dose are located in Kazurao northwest of the source.In the early stage of Fukushima nuclear accident，a plant-wide poweroutage was happened and the extent of the core damage was unknown. In thiscase the source term cannot be obtained through the core operatingparameters and the damage extent. The hybrid genetic algorithm was coupledwith puff diffusion model to conduct a preliminary exploration of nuclearaccident source term back-calculation, realizing a rapid estimation of therelease rate, location and height. The comparison results showed that GeneticAlgorithm-Nelder Mead method not only combined the advantages ofGenetic Algorithm and Nelder Mead method, but also compensated theshortcomings of the two algorithms. The exactly matching inverse value, thewide versatility and the less cost made the hybrid genetic algorithm can beused for rapid estimation of the nuclear accident source term.