Hyogo officials are blocking the release of data from a simulation run last year predicting what would happen to surrounding prefectures in the event of a meltdown crisis at one of Fukui Prefecture's four atomic plants.

Citizens' groups said Tuesday they were told by Hyogo officials earlier this month that the data would be released before May along with data from a new simulation the prefecture is conducting.

The backtrack on the data release has raised concerns that the prefecture is trying to downplay the possibility of a worst-case scenario for disaster planning purposes.