By Richard Martin
Friday, September 04, 2015
For years nuclear scientists have talked about a revival
of molten salt reactors, which are powered by a liquid fuel rather than solid
fuel rods, that will help spark the long-awaited “nuclear renaissance.” Recent
developments indicate that this alternative nuclear power technology is finally
making gradual progress toward commercialization.
A consortium of research institutes and universities
working under the aegis of the European Commission, including the Technology
University of Delft (TU Delft), in the Netherlands, France’s National Center
for Scientific Research, and the Commission’s Joint Research Center, in
Brussels, in August embarked on a four-year research program designed to
demonstrate the safety benefits of molten salt reactors. Called “Safety
Assessment of the Molten Salt Fast Reactor,” or Samofar, the effort will lead
to the building of a prototype reactor in the early 2020s if all goes as
planned.
First built and tested in the 1960s, at Oak Ridge
National Laboratory, molten salt reactors would be the first genuinely new
technology for nuclear power generation to reach the market in the last three
decades. Producing zero carbon, they use a radioactive solution that blends
nuclear fuel with a liquid salt. They can run on uranium, but are also ideally
suited for thorium, an alternative nuclear fuel that is cleaner, safer, and
more abundant than uranium.
Molten salt reactors also offer inherent safety
advantages: because the fuel is liquid, it expands when heated, thus slowing
the rate of nuclear reactions and making the reactor self-governing. And they’re built like bathtubs, with a drain
in the bottom that’s blocked by a “freeze plug.” If anything goes wrong, the
freeze plug melts and the reactor core drains into a shielded underground
container. They can operate as producers of thermal power or as “burner”
reactors that consume nuclear waste from conventional reactors.
Essentially, molten salt reactors could solve the two
problems that have bedeviled the nuclear power industry: safety and waste.
While the advantages of molten salt reactors have been
understood for some time, they remain at the R&D stage because, in the
post-Fukushima era of low-price natural gas, it’s hard to convince investors to
fund any alternative nuclear technology. In the United States it can take a
decade or more, and hundreds of millions of dollars, just to bring new a
reactor design to the Nuclear Regulatory Commission for a license application.
Samofar is focused on fast reactors, which are more
efficient than conventional light-water reactors and can breed fissile elements
from nuclear waste. The researchers will build experimental laboratory
facilities—not, at least for the next few years, an actual working reactor—to
test the geometry of the freeze plug, the coatings of vessel and pipe
materials, the behavior of the liquid fuel during circulation and draining, and
other key safety metrics.
The project represents “the first step towards large
scale validation and demonstration of the technology,” says Jan-Leen Kloosterman,
a professor of nuclear physics at TU Delft and the lead researcher on Samofar.
“Hopefully the results will also lead to much more commitment from the large
nuclear industry.”
Getting that commitment remains an uphill struggle, but a
report funded by the United Kingdom government and released recently by Energy
Process Developments, a London-based research firm, reviews technologies from
six potential molten salt reactor developers—Flibe Energy, Moltex Energy,
ThorCon Power, Seaborg Technologies, Terrestrial Energy, and Transatomic
Power—and finds encouraging signals for molten salt reactors over the next 10
years (see “Experiments Start on a Meltdown-Proof Nuclear Reactor”). After a
decade of work, the companies “are ready now with proposals for the next step
to implementation, namely engineering design to prepare the safety case and to
proceed to design and build.”
The most advanced program for liquid-fuel, thorium-based
reactors is in China, where the Shanghai Institute of Applied Physics reportedly
plans to build a prototype in the next few years. The Shanghai program is a collaboration with
Oak Ridge National Laboratory, where molten salt nuclear technology was born.
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