TOKYO, Dec. 13 (Kyodo) — Japan's nuclear regulatory authority said Thursday it found errors in its radiation spread projections in the event of a severe accident for all the country's nuclear power plants after thoroughly reviewing its previous already mistake-plagued results.

The Nuclear Regulation Authority examined the data in detail to ensure there would be no more mistakes in the projections as local governments are expected to use the information to craft plans to prepare for nuclear disasters.

The NRA said there were significant changes in diagrams for how radiation could spread after accidents at Kyushu Electric Power Co.'s Genkai and Sendai plants and Hokkaido Electric Power Co.'s Tomari complex compared with the previously revised projections released on Oct. 29.

The three projections had to be revised either because weather data provided by the plant operator was wrong in the first place, or because provided data was incorrectly processed by the Japan Nuclear Energy Safety Organization, which was tasked to create the projections.

The process of creating the projections for the remaining 14 plants across the country, including the disaster-hit Fukushima Daiichi complex, also contained errors or was mishandled in some way or other, although this did not result in drastic changes in the projection trend, according to the NRA's secretariat.

The simulation showed the distances at which doses could reach 100 millisieverts a week after severe accidents like the one at the Fukushima Daiichi complex last year. At that dose level, evacuation is recommended by the International Atomic Energy Agency.

Among the 17 plants, the latest projection showed that the most distant point where radiation could spread is 40.1 kilometers east from Tokyo Electric Power Co.'s Kashiwazaki-Kariwa plant in Niigata Prefecture, in the city of Nagaoka.

In the earlier projection, the NRA had said the most distant point would be 40.2 km east in Nagaoka.