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Feature
Thorium Molten Salt Reactors:
Are they the solution?
In this article, we will examine how Thorium Molten
Salt Reactors work, their safety, efficiency, waste
management, proliferation concerns, and their current
status. Finally, we will look at their suitability
for ships.
Principle of operation exhausted as fuel (with no enrichment
Thorium is abundant in the Earth’s crust necessary). Because of this, thorium
– it is as abundant as lead. Molten Salt provides 200 times more energy than
Reactors (MSRs) work by having the fuel, uranium. Furthermore, thorium reactors
in this case thorium, dissolved in a high- can be refuelled with additional thorium
temperature (600 to 800°C) liquid, while online, with no downtime, and thus
together with salts that liquify at these can continue to operate for many years.
high temperatures. This liquid has the The reaction cannot become uncon-
viscosity of water, namely, it is not thick, trollable. MSRs are inherently safe,
and therefore it can be easily handled by or so-called “walk-away safe”. They do
pumps. The liquid acts both as the fuel not operate under pressure; thus, an
and the cooling medium of the reactor. explosion is not possible. Due to the
Thorium found in the earth is thorium- high temperatures, heat transfer is bet-
232 and is slightly radioactive but not ter and more efficient. There is a risk
Opinions expressed by fissile, meaning it does not split to cre- that the reactor will cool down if some-
Panos Zachariadis, ate nuclear energy. However, it is fer- thing goes wrong, but this will only
Technical Director of Atlantic Bulk tile to do so. When it is hit by neutrons, freeze the molten salt liquid, poten-
Carriers Management Ltd.
it absorbs one neutron, transforming into tially damaging some pumps and heat
thorium-233. Thorium-233 decays fast exchangers. However, this danger is to
to protactinium-233 and after 27 days the equipment, not to people. In the
to uranium-233. Note here that conven- unlikely event of extremely high tem-
tional reactors use rods of uranium-235, peratures, a plug melts, and the liquid
not uranium-233. Uranium-233 is fis- salt is collected by gravity into a sump
sile; thus, once hit by neutrons, it splits, tank, where it freezes.
releasing huge amounts of energy and
more neutrons. The new neutrons hit Waste
more thorium, and the cycle continues. The waste from thorium reactors is radi-
oactive for 300 years, rather than the
Safety and efficiency 200,000 to 300,000 years of conven-
In standard nuclear reactors, only 1% tional reactors using U-235. However,
of the mined uranium is used. The rest the waste includes aggressive liquids,
is discarded as spent nuclear waste. which may not be suitable for geological
Standard reactors must shut down every repositories. The quantity of the waste,
2 years to replace the fuel rods. In tho- however, is only 1% of that from stand-
rium reactors, all the thorium is used and ard reactors.
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