By Kiyoshi Takenaka
TOKYO (Reuters) - In the Japanese city of Ohtawara, more than 100 km (62 miles) southwest of the crippled Fukushima nuclear plant, 400 tones of radioactive ash have piled up at a garbage incineration plant, which will run out of protected storage space in two weeks.
Further south, the city of Kashiwa has been forced to temporarily shut a high-tech incinerator because its advanced technology that minimizes the amount of ash produced has the side-effect of boosting the concentration of radiation.
Ohtawara and Kashiwa are just two of a growing number of municipalities across northern Japan that face similar problems after the Fukushima Daiichi atomic power plant, devastated by a huge March quake and tsunami, began spewing radiation into the atmosphere in the world's worst nuclear accident in 25 years.
Although the government aims to bring the Fukushima crisis under control by December, researchers say that problems arising from the radiation, scattered over mountains, rivers and residential areas, are set to persist for years.
"Residents say they are worried about their children's health and grandchildren's health. Faced with such pleas, we just cannot make a move," an Ohtawara city official said, explaining why the ash has not be taken to a nearby city dump.
Ohtawara has already cut the frequency of garbage collection by half to hold down the generation of radioactive ash, by-product of burning contaminated leaves and branches.
Nonetheless, fresh bags of radioactive ash will have to be left in empty outdoor space at the incineration facility with no proper shelter around them, the official said.
Radiation levels of most of the ash in question are below 8,000 becquerels per kilogram, low enough to be buried in dumping grounds, according to government guidelines.
But people living nearby remain worried.
"If you think about residents' feelings, it is quite natural. Some people just don't want to have it near them no matter how low radiation levels are," said Baku Nishio, co-director of Citizens' Nuclear Information Center, an anti-nuclear civic group.
"It is up to the government to set up storage facilities, but naturally, finding the place can be a real challenge."
A draft plan by the Environment Ministry calls for the government to take responsibility for disposing of ash and sludge with radiation levels above 8,000 becquerels/kg, but a ministry official said nothing concrete has been decided.
Following hydrogen explosions at the Fukushima plant in March, rainfall has brought radiation down to the earth's surface.
Part of the radioactive caesium, which can cause internal radiation exposure for an extended period, found its way into sewage systems and, through the purification process, was concentrated in sludge as well as the ash that is produced by burning sludge.
In northern Japan, stored-up radioactive ash and dehydrated sludge from the sewage treatment process alone totaled 52,000 tones in mid-September, up 63 percent from levels at the end of July, data from the Transport Ministry showed.
The volume is still growing by about 360 tones a day.
The growing piles of radioactive ash are also causing financial headaches for local governments.
Nagareyama city, next to Kashiwa, has set aside about 250 million yen ($3.2 million) in three of its four extra budgets so far this year for temporary storage and related projects.
Researchers say the problem is here to stay, although the government aims to declare a big step forward in dealing with the nuclear disaster by bringing the Fukushima plant to "cold shutdown" by year-end, a month ahead of the original schedule.
A "cold shutdown" is the term used to describe the reactor condition where water used to cool fuel rods remains below 100 degrees Celsius and radiation leakage is under control.
"I doubt the problem will go away in a year or two. It takes 30 years for caesium 137 to decay by half. Each time it rains, caesium deposited in mountains will be washed down to where people live," Kobe University professor Tomoya Yamauchi said.
($1 = 77.365 Japanese Yen)
(Editing by Linda Sieg and Yoko Nishikawa)