[cdn-nucl-l] Kyoto U. team developing subcritical nuclear reactor

["Adam McLean" <adam.mclean@utoronto.ca>]

Posted in the Daily Yomiuri online on June 9, 2003 and at:
http://www.yomiuri.co.jp/newse/20030607wo72.htm
Local criticality dependent on operation of an external proton accelerator.

Adam

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Kyoto U. team developing subcritical nuclear reactor 

Yomiuri Shimbun 

Researchers at Kyoto University are developing a nuclear power reactor that
does not require criticality to produce energy, thereby drastically reducing
the risk of accidents, The Yomiuri Shimbun learned Friday. 

Elementary particles, which create nuclear fission and, in turn, energy,
will be fed into the core of the reactor. 

The reactor will be able to accommodate a variety of fuels. If natural
uranium is used, the usual enrichment process, which discharges depleted
uranium and other waste, is omitted altogether. 

This groundbreaking method of power generation is the subject of studies
worldwide. 

Kyoto University's Research Reactor Institute in Kumatoricho, Osaka
Prefecture, will work with six universities, including Osaka University and
Tohoku University, the High Energy Accelerator Research Organization and
private firms to develop a working reactor. 

They will begin by developing an elementary particle accelerator of about 12
meters in diameter and installing it in a laboratory. The machine will be
able to accelerate protons up to 80 million kph, turning them into beams.
The beams will be aimed at heavy metals inside the core of an existing
reactor named Kyoto University Critical Assembly (KUCA), generating a large
number of neutrons to create nuclear fission. 

The energy output from such a reaction is 60 to 100 times greater than the
energy input of the beams themselves. 

Work on the accelerator will begin this fiscal year, and experiments will
begin in fiscal 2005 after it has been connected to KUCA. 

In conventional lightwater reactors, uranium, an essential element for
nuclear fission, is concentrated into the reactor core to create
criticality, which leads naturally to nuclear fission. 

The chain reaction is artificially controlled by rods that absorb unwanted
neutrons. 

A subcritical reactor of the kind being developed, however, would not
contain enough uranium to naturally bring about nuclear fission. 

No reaction is possible, therefore, unless the beams are directed at the
core of the reactor, making the process much safer than that used in
lightwater reactors. There is no need to maintain a chain reaction in such
reactors, so natural uranium and thorium deposits can be used as fuel. Also,
by aiming neutrons against a mixture of fuel and nuclear waste, which
remains highly radioactive for tens of thousands of years, the method could
be used to alter the makeup of nuclear waste so that it remains radioactive
for a much shorter period. 

Researchers in the United States, France, Russia, South Korea and other
countries are looking into the feasibility of such a reactor.