POWER May 2017 - 9

design fits the country's needs, said that if all fares well during
its assessment period, it will recommend the design as the basis
for Indonesia's first commercial nuclear power plant.
ThorCon is a " straightforward " scale-up of an experimental
molten salt reactor at the Oak Ridge National Laboratory (ORNL)
in Tennessee, which operated between 1965 and 1969 (Figure
1). ORNL conceived the concept of " liquid fuel " as an alternative
to the water-cooled, zirconium-clad uranium oxide solid
fuel rods used in light water reactors. In a molten salt reactor,
thorium and uranium fluorides are dissolved in molten salt,
which, in ThorCon's case is a mix of fluorides of beryllium and
sodium heated between 560C and 700C. The fuel flows through
the reactor vessel-where it fissions and grows hotter-then
through a pump and heat exchanger to cool it.
Remarkably, ORNL's Molten Salt Reactor Experiment (MSRE)
was inspired by a campaign to build a nuclear-powered airplane
in the 1950s, because engineers saw promising results from the
design that used molten fluoride salt as fuel carrier and coolant
for an onboard carrier. But that project was scrapped in the
1960s, and molten salt reactor efforts have since transitioned
to power generation.
Benefits touted by the MSRE technology's proponents were
that it could make fuel as it operated-mitigating worries
about scarce uranium supplies-and that the circulating fuel
eliminated change outs of solid fuel and control rod mechanisms.
Another highlighted aspect was intrinsic safety: " Molten
salts expand as they heat up, " explained ORNL. " The expansion
causes some of the fuel to leave the core, shutting down the
reactor, so operator response is not required to turn the reactor
off. "
Like the experimental reactor, ThorCon is designed for installation
15 to 30 meters underground (Figure 2). " ThorCon has
three gas tight barriers between the fuelsalt and the atmosphere, "
said its developer. " The reactor operates at slight overpressure
so that in the event of a primary loop rupture, there is
no dispersal energy and also no phase change. The spilled fuel
merely flows to a drain tank where it is passively cooled. The
most troublesome fission products, including [strontium-90]
and [cesium-137], are chemically bound to the salt. They will
end up in the drain tank as well. "
ThorCon also noted that an entire plant can be manufactured
in blocks on a shipyard-like assembly line, claiming that
a single large reactor yard can churn out 100 1-GW ThorCons
per year. Manufacturing costs for building a 500-MW ThorConLand
power plant are about $1.2/W, it said. Generation costs
could hover around $0.024/kWh. Capital costs are low, it said,
because the reactor operates at 700C, enabling the use of supercritical
steam turbine generators, such as those installed at
modern coal plants.
The design also uses " few exotic materials. " While stainless
steel " suffices for most salt handling, " use of TZM and Hastelloy
alloys are limited. Also, the reactor doesn't need multiple, redundant,
engineered safety-grade control systems because the
design relies on physical principles and material properties to
prevent overheating, it said.
" Currently the designers foresee no technical reason why a
full-scale 250-MW prototype cannot be operating within four
years, " the company said. ThorCon anticipates prefission testing
to begin in 2018, and fission testing in 2020. " The intention
is to subject this prototype to all the conceivable potential
failure modes that the designers claim the plant can handle. As
soon as the prototype passes these tests, commercial production
can begin, " it said.
May 2017 | POWER
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Trends Suggest New Directions for
Global Hydropower
While hydropower installations worldwide fell slightly in 2016
to 31.5 GW compared to 33 GW in 2015, the sector marked a
colossal jump in pumped storage installations last year, the International
Hydropower Association (IHA) reported in a briefing
surveying key trends in hydropower released this March.
The organization pegged the hydropower installation decrease
3. Global total installed hydropower capacity (GW)
by country at the end of 2016, including pumped
storage. Courtesy: International Hydropower Association
www.powermag.com
9
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POWER May 2017

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