From Kyodo News English (4/18/2011):
The Nuclear Safety Commission of Japan has released only two computer-simulated estimates of radioactive substance dispersal since the nuclear accident at the Fukushima Daiichi power plant, although more than 2,000 of them were made, sources familiar with the matter said Monday.
The estimates were made using the Nuclear Safety Technology Center's networked computer system known as SPEEDI, or system sor prediction of environmental emergency dose information, developed and operated with a budget of about 12.8 billion yen.
The government commission released the two estimates on March 23 and April 11, including accumulated exposure to a radiation dose of more than 1 millisievert even outside a radius of 30 kilometers from the Fukushima plant that was crippled by the March 11 earthquake and tsunami.
The same news in Kyodo Japanese gives a bit more details:
The Nuclear Safety Technology Center in Tokyo, who runs SPEEDI, says it has been running the simulations taking into consideration the wind directions, rain, and amount of radioactive materials released. The Center has been making the 3-hour dispersion predictions ever since the accident happened. There are over 2,000 dispersion simulation charts drawn up so far.
The reason why the Nuclear Safety Commission hasn't disclosed the simulation results is that there's not enough data on the amount of radioactive materials released. "Simulations are different from the actual dispersions, and that would lead to misunderstanding," says the Commission. However, some of the simulation charts were similar to the actual dispersions.
風向、降雨といった気象や放射性物質の放出量など、さまざまな 仮定の条件に基づいた試算を繰り返している。ほかにも事故直後から１時間ごとに、その時点で放射性物質が１ベクレル放出されたと仮定して３時間後の拡散を 予測。これまでに作成した拡散試算図は、２千枚以上になるという。
Shoot these people. They are more keen on covering their behind and staying in good grace with their benefactor the government than warning their fellow citizens.