If a Fukushima-style nuclear disaster were to occur in Fukui Prefecture, 26 percent of the surface of Lake Biwa in Shiga Prefecture would receive radioactive fallout exceeding the country’s threshold allowable for drinking water, Shiga officials speculated Tuesday.

The prefecture’s forecast, disclosed the same day, assumed the fallout of radioactive iodine would be the same as what occurred when the Fukushima No. 1 plant suffered three meltdowns in March 2011.

Last November, Shiga officials announced estimates that a nuclear disaster in Fukui might cause radioactive fallout exceeding safe levels to cover up to 21.7 percent of Lake Biwa’s surface.

The forecast this time has been prepared based on meteorological conditions that would likely affect the lake, including wind patterns and the amount of rainfall observed in Shiga Prefecture from fiscal 2010 to 2012. Meteorological data together with estimates of particulate and gaseous iodine, calculated in the same proportion, were used to precisely forecast the possible radiation effect on Lake Biwa.

The findings said if a nuclear disaster at the Mihama nuclear plant in Fukui occurs under weather conditions similar to those observed on Aug. 20, 2011, with rainfall and wind coming from the north, the top 5 meters of water may be affected most.

The top 5 meters of water in the lake are used as the intake source for water supply for domestic, industrial and other uses.

The results of recent research showed that a larger surface area of Lake Biwa may be affected.

Shiga said a regional disaster prevention plan will be created based on results of the research, which have been compiled into a final report.

The previous research was based on data from the Fukushima No. 1 plant, where the level of concentration of gaseous iodine was higher than particulate iodine.

Previously announced results of the research were also based on precipitation estimates under atmospheric conditions similar to those of Oct. 30, 2010, when there was rainfall and a northerly wind.

“If there is a high concentration of particles, (the lake) will be more vulnerable to being contaminated (with radioactive fallout) brought with rainfall,” prefectural officials said.

Shiga had previously announced that a disaster involving a Fukui nuclear plant might contaminate up to 18 percent of the lake with radioactive cesium.