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Just as Japan’s prototype fast reactor went critical earlier this month,
the government announced it may use the plant to burn up plutonium rather
than ‘breed’ it.

Japan’s long-term energy policy is based on plutonium and depends in
large part on fast breeder reactors, which can produce more plutonium than
they use for fuel. But Yasutaka Moriguchi, director of the nuclear fuel
division at the Science and Technology Agency, says the government announcement
is not a sign of waning enthusiasm for plutonium.

The reactor, named Monju, went critical on 5 April. About 100 demonstrators,
including Buddhist monks, protested outside the plant, which is some 300
kilometres west of Tokyo. Akira Izumi, deputy head of Monju, said the start-up
went ‘extremely well’.

But Moriguchi has introduced a note of caution over the project. ‘In
the first stage, perhaps until the year 2000 or beyond, we would like to
breed plutonium at Monju,’ he says. ‘After that, we don’t need so much plutonium,
so we’ll just burn it.’ Moriguchi denied that this move represented any
weakening of commitment to a plutonium-based energy cycle. ‘We are now reviewing
the long-term programme of nuclear energy. So we do not yet have a formal
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But critics say that Japan feels uncomfortable at being the only country
looking to plutonium for its energy. Earlier this year the Japanese government
postponed the successor to Monju, a commercial prototype (This Week, 29
January). Other countries have already abandoned fast breeders. Last month,
Britain shut down its prototype fast breeder reactor at Dounreay, and France
says it will turn its commercial-scale fast reactor, Superphenix, into
a plutonium incinerator.

The core of a fast breeder reactor is surrounded by a ‘blanket’ of
uranium-238, which cannot support fission. Neutrons from the core bombard
this uranium, turning it into plutonium, which is fissile. This is later
extracted and used as fuel in the core. To change a reactor from a breeder
into a burner, the blanket is simply left off.

Moriguchi says the plutonium that Monju produces initially will be stored
for use in the prototype commercial fast breeder. And whatever is finally
decided, Japan will still take back plutonium from the spent nuclear fuel
it has sent to Europe for reprocessing. That will still be needed for research
and development, Moriguchi says.