- A nuclear reactor that can meet the energy needs of developing
countries without the risk that they will use the by-products to make weapons
is being developed by the US Department of Energy.
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- The aim is to create a sealed reactor that can be delivered
to a site, left to generate power for up to 30 years, and retrieved when
its fuel is spent. The developers claim that no one would be able to remove
the fissile material from the reactor because its core would be inside
a tamper-proof cask protected by a thicket of alarms.
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- Known as the small, sealed, transportable, autonomous
reactor (SSTAR), the machine will generate power without needing refuelling
or maintenance, says Craig Smith of the DoE's Lawrence Livermore National
Laboratory in California.
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- Conventional reactors pose a threat of proliferation
because they have to be periodically recharged with fuel, which later has
to be removed. Both steps offer operators the chance to divert fissile
material to weapons programmes as is thought to have happened in North
Korea and Iran.
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- Electricity grid
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- Another reason to provide a small reactor is that conventional
nuclear stations generate around a gigawatt of electricity, and that is
overkill for plants in developing countries without an extensive electricity
grid to distribute it.
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- In an SSTAR the nuclear fuel, liquid lead coolant and
a steam generator will be sealed inside the housing, along with steam pipes
ready to be hooked up to an external generator turbine.
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- A version producing 100 megawatts would be 15 metres
tall, three metres in diameter and weigh 500 tonnes. A 10-megawatt version
is likely to weigh less than 200 tonnes.
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- The US will deliver the sealed unit by ship and truck
and install it. When the fuel runs out it will collect the old reactor
for recycling or disposal. The DoE hopes to have a prototype by 2015.
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- For this to happen, it will have to overcome many technical
challenges. In conventional reactors, the nuclear chain reaction depletes
the fissile isotopes in the fuel rods, which is why they have to be replaced
every few years.
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- Extended life
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- To sustain power generation for 30 years, the sealed
reactor will have to be engineered to act as a breeder, using some of the
neutrons to convert non-fissile isotopes such as uranium-238 into fissile
plutonium-239.
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- To further extend the reactor's life, the cylindrical
core will be engineered to sustain fission only when surrounded by a metal
cylinder that reflects neutrons back into the fuel.
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- This mirror will start at one end of the core, and over
the course of the reactor's lifetime move slowly along to the opposite
end, consuming the fuel as it goes. Engineering long-term reliability into
such a system will be a major task.
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- Automated controls will monitor the sealed reactor, Smith
says, adjusting its electrical output and shutting it down if faults or
tampering are detected. Alerts will be sent over secure satellite radio
channels to the DoE or to an international agency overseeing the reactors.
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- The project faces strong political obstacles. Michael
Levi of the Brookings Institution, a think tank in Washington DC, questions
whether developing countries will be prepared to leave the keys to their
electricity supply in the hands of the US.
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- He also doubts that SSTAR will be as proliferation-proof
as the DoE hopes. While the design makes it hard for countries hosting
the reactors to cheat without getting caught, "what happens if they
don't care about what we think?" he asks. It would then be possible
to break into the reactor and reprocess the plutonium-rich fuel to make
weapons, he says.
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