The economy ministry estimates that about 30 percent of the Japanese archipelago is suitable on scientific grounds for the final disposal of high-level radioactive waste for at least 100,000 years.

It released a “scientific characteristics map” July 28 that indicates areas regarded as favorable from the standpoints of geological conditions and transportation.

If any municipalities show interest in offering land for the long-term disposal, the Ministry of Economy, Trade and Industry (METI) plans to request that they allow detailed surveys to go ahead.

“The release of this map is an important step to realize final disposal (of high-level radioactive waste). It is the first step on the long road,” economy minister Hiroshige Seko said in a news conference held after a Cabinet meeting on July 28.

High-level radioactive waste is generated from spent fuel produced at nuclear power plants. The spent fuel has to be mixed with glass and vitrified before it is buried more than 300 meters underground.

Storage conditions will have to endure for at least 100,000 years until radioactivity falls to levels that will not impact the land surface, even if the glass and containers melt in several tens of thousands of years.

Thus, the ministry is interested in areas where changes in the groundwater and soil conditions are minimal.

The map does not pinpoint potential nuclear waste repository sites, but classifies the Japanese archipelago into four color-coded categories based on factors such as active faults, volcanoes and soil conditions that are already in the public domain.

Areas deemed unfavorable from the standpoint of underground stability and other factors are depicted in orange. Areas that fall into this category include those that lie within a radius of 15 kilometers from volcanoes or are located close to active faults.

Areas with reserves of oil, natural gas, coal and other minerals that could be drilled in the future are shown in silver.

Areas deemed suitable as final disposal sites are shown in green, and if they lie within 20 km of the coastline they are shown in dark green to signify that they are also favorable from the standpoint of transportation by ship.

Municipalities with dark green areas number about 900, more than half of all municipalities in Japan. Some of the 900 municipalities are located in Tokyo and Kanagawa, Aichi and Osaka prefectures that have sprawling cities.

From autumn this year, the economy ministry plans to hold discussions with municipalities that include dark green areas to explain about the necessity of pinning down final disposal sites and the risks of storage over tens of thousands of years.

It hopes to narrow down the candidate sites in about 20 years.

The Nuclear Waste Management Organization of Japan (NUMO) began asking municipalities from 2002 about offering themselves as candidate sites for surveys. At that time, Toyo in Kochi Prefecture applied for the survey. Later, however, it withdrew the application because of opposition from local residents.