Power Line
The Federation of Electric Power Companies of Japan Vol.4
May 1999

The Challenge of High-level Radioactive Waste Disposal

NUCLEAR POWER IS USED to generate electricity through the fission of uranium fuel. Spent fuel contains "unburnt" uranium as well as plutonium, which is generated as a by-product of the fission process. These elements are extracted by "reprocessing," thereby enabling them to be used again. The object of reprocessing, a crucial component of the entire process known as the "nuclear fuel cycle," is to make more efficient use of uranium as an energy source.

A serious problem must be overcome, however, which is how best to dispose of the radioactive waste generated by the nuclear fuel cycle. High-level radioactive waste is the liquid by-product generated when spent fuel is chemically treated in the reprocessing operation.

Flow of High-level Radioactive Waste

Vitrified Waste

The high-level radioactive waste produced through the reprocessing is mixed with glass and melted at high temperatures, then poured into a highly resistant steel container, or canister, and allowed to solidify. The process, known as vitrification, is the preferred method to solidify the waste because glass is highly stable, both structurally and chemically.

To date, 168 containers of vitrified waste have been returned from France to Japan and stored in Japan Nuclear Fuel Limited's (JNFL) Vitrified Waste Storage Center. Another 62 containers of vitrified waste have been similarly stored in the Japan Nuclear Cycle Development Institute's (JNC) Tokai Vitrification Facility (TVF).

Continued reprocessing both in Japan and abroad will call for the storage of increasing numbers of vitrified waste containers. The number of containers that would be required to house the spent fuel produced by the nuclear power generation process as of the end of September 1998 has been estimated at approximately 12,600.

Vitrified waste retains a high degree of heat as a result of its radioactivity. Over the 30- to 50-year period that the waste is stored, however, its radioactivity and heat gradually decrease. Still, since it contains radioactive materials with a longer half-life (the period of time necessary to reduce radioactivity by half), the wastes must be disposed of safely so as not to pose a threat to either human beings or the natural environment.