Calculation method by Particle-In-Cell model for atmospheric diffusion of radioactive cloud released instantaneously, (1)

A computer code PUFF-20 was developed for simulating atmospheric diffusion of radioactive cloud from a nuclear plant on an emergency. A physical model used in the code is a Particle-In-Cell (PIC) model and it's efficiency for atmospheric diffusion has been verified by some computer codes, for example ADPIC (by Laurence Livermore Lab.) and field experiment. In the present study, computer code PUFF-20 has two main assumption that the cloud is released instantaneously and the variation of meteorology in time is given by single-tower data because of the lack of effective method for presenting regional variation. This first report shows about PIC method, Program of PUFF-20, verification of PUFF-20 method by comparison with theoretical formula and two examples applied to real field. (author)