The Challenge of High-level Radioactive
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.
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
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.