It’s been 30 years since America built a really new nuclear power plant, but we haven’t been idle over this time. A slew of new designs have emerged and, thanks to advances in computing capabilities and the understanding that smaller is better, many of these are ready to be built economically.
This is important. Over the last several years, there has been a growing consensus among climate scientists that nuclear energy is critical for mitigating the worst effects of global warming. States are shifting from Renewable Energy Mandates to technology neutral Clean Energy Standards that include nuclear energy.
So it is good that the development of new nuclear technologies is speeding along faster than most people think. Many new nuclear start-up companies have emerged in the United States, China and Canada, especially those designing small modular reactors (SMRs).
Importantly, all are walk-away-safe, which means the reactor just won’t melt down or otherwise cause any of the nightmares people think about when imagining the worse for nuclear power. It just shuts down and cools off.
Canadian Nuclear Laboratories announced SMR technology as a research priority and Canada now has a roadmap for them, and has vowed to build an SMR demonstration plant on their site by 2026.
China is also moving fast on its Linglong One 100 MW SMR with its first use to generate heat for a residential district, replacing coal-fired boilers.
While some SMR designs are based on the traditional light water reactor that uses slightly enriched uranium, others involve molten salt and other fuels such as thorium and thorium+uranium.
One such reactor is ThorCon, a fission reactor with a liquid molten salt fuel containing thorium+uranium. A full-scale 500 MW ThorCon prototype should be able to be built and operating within four years.
Molten salt reactors are not completely new. The United States successfully conducted a Molten Salt Reactor Experiment (MSRE) at Oak Ridge National Laboratory in the 1950s.
Irradiation tests on a mixture of lithium and thorium fluoride salts are under way at the High Flux Reactor at Petten in the Netherlands. Terrestrial Energy is also developing an Integrated Molten Salt Reactor.
But the ThorCon takes a different tack on manufacturing. It would be completely manufactured in 150 to 500 ton blocks in a shipyard, assembled, then towed to the site, producing order of magnitude improvements in productivity, quality control, and build time.
ThorCon’s genesis is in ship production, one of the few industries up to snuff for building large complicated technologies. The Hellespont Fairfax, the largest double hull tanker ever built, is one of eight ships built by ThorCon’s predecessor company. She was built in less than 12 months and cost 89 million dollars in 2002.
ThorCon is designed to bring shipyard quality and productivity to fission power. But ThorCon’s structure is simpler and much more repetitive than a large ship. The fission island employs steel plate, sandwich walls filled with concrete or sand. This results in a strong, air-tight, ductile building, all simple flat plate. A properly implemented panel line will be able to produce these blocks using less than 2 man-hours per ton of steel.
Each ThorCon plant is based on one or more hulls, each containing two 250 MWe power modules, a 500 MW super-critical turbogenerator, gas insulated switchgear (GIS), a decay heat pond, and auxiliaries (see figure above). The fission island is at the forward end of the hull. Aft of the fission island is the Steam Generating Cell (SGC). Aft of the SGC is the turbine hall, which contains the turbogenerator, exciter, condensers, feedheaters, pumps, and condensate treatment.
A single large reactor yard can turn out twenty gigawatts of ThorCon power plants per year, providing clean, reliable, CO2-free electricity at 3¢/kWh - cheaper than coal.
Operation of molten salt reactors are inherently easy. Rather than attempt to build components that last 40 or more years in an extremely harsh environment with little maintenance, ThorCon is designed to have all key parts regularly replaced, with little interruption in power output.
Every four years the entire primary loop is changed out, returned to a centralized recycling facility, decontaminated, disassembled, inspected, and refurbished. Upgrades can be introduced without significantly disrupting power generation
Of course, this reactor, like most SMRs, is walk-away-safe. The public will not embrace anything else. Since ThorCon fuel is a liquid salt, if the reactor overheats for whatever reason, ThorCon will shut itself down, and passively handle the decay heat. No power, no machinery, no operator action is required. This is built into the reactor physics.
The operators, or even any bad actors, can do nothing to prevent safe shutdown and cooling. The spilled fuel merely flows to a drain tank where it is passively cooled. The troublesome fission products, including I-131, Sr-90 and Cs-137, are chemically bound to the salt. They will end up in the drain tank as well.
ThorCon combines a strongly negative temperature coefficient with a massive temperature safety margin between the operating temperature of 700°C and the fuelsalt’s boiling temperature (1430°C).
The plant is also an extremely strong structure. It cannot not be penetrated even by a Boeing jet in a perpendicular impact at 400 knots. The hull, which is a double barrier, is only one of at least three gas tight barriers between the fuel salt and the atmosphere. The Can silo is a gas tight structure; and the Can itself is a gas tight structure. All these must be breached to allow a release.
But even if they were, there is no internal dispersal mechanism. The ThorCon reactor operates at near-ambient pressure, about the same as a backyard garden hose. In the event of a primary loop rupture, there is little pressure energy and no phase change from liquid to gaseous. The spilled fuelsalt merely flows to the drain tank where it is passively cooled and hardens into solid salt.
ThorCon is a thorium converter. The initial fuel charge is largely thorium. During the eight year fuel cycle, a portion of the fertile thorium is converted to fissile U-233 which then becomes part of the fuel. Each ThorCon will require only about 5 kg of 19.7% enriched uranium and 9 kg of thorium per day, on average, to produce 4,000,000,000 kWh of non-intermittent, dispatchable, pollution-free, CO2-free electricity each year.
All the while generating only one cask of waste every four years. It’s easy to forget that a normal coal plant takes 10,000 tons of coal each day, or just under 15,000,000 tons in that same 4-year period.
ThorCon’s net consumption of uranium is less than half that of a traditional reactor, because of its higher thermal efficiency, removal of Xe-135, and U-233 production from thorium.
Since we need to triple nuclear power in the world within 20 years in order to have any hope of mitigating the worst effects of global warming, along with bringing up renewables as fast as possible, this is a nice way to go sailing into that future.
