What is ThorCon?
ThorCon is the trade name for a hybrid thorium/uranium liquid fuel fission power plant being designed and marketed by ThorCon International. It is a molten salt reactor.
Is ThorCon a small modular reactor (SMR)?
Yes. Small Modular Reactor is a term usually applied to solid fuel, light water reactors generating up to 300 MW of power. Each ThorCon power module can generate 250 MW of electric power.
Who will finance, build, and operate ThorCon power plants?
ThorCon International will form consortia with investors and national businesses to build fission power plants to sell electricity in developing nations seeking ample, reliable electric power, cheaper than coal.
What is the fuel?
What is liquid fuel?
Liquid fuel was first conceived by Oak Ridge National Laboratory as an alternative to the water-cooled, zirconium-clad uranium oxide solid fuel rods used in light water reactors. Thorium and uranium fluorides are dissolved in molten salt. ThorCon molten salt is a mix of fluorides of beryllium and sodium heated to 560-700°C. The fuel flows through the reactor vessel (the Pot) where it fissions and gets hotter, then through a pump and heat exchanger to cool it and deliver the thermal energy, then recirculates.
What are the advantages of liquid fuel over solid fuel?
Liquid fluoride salts enjoy several advantages over zirconium-clad solid oxide fuel including: tolerates much higher temperatures without damage, can be rapidly reconfigured by draining to move the fuel away from the moderator absolutely ensuring the fission reactions stop and into a configuration which readily loses decay heat, not pressurized or near any pressurized water that can push fission products into the environment, chemically binds up the two most difficult fission products strontium and cesium so they will not volatilize, easy to maintain fuel homogeneity because the circulation mixes the fuel to burn evenly, no excess reactivity needed and no burnable poisons so efficient in the use of valuable neutrons, easy to remove xenon fission products which otherwise deplete neutrons and complicate reactor control.
Isn’t fluorine corrosive?
Fluorine gas is very reactive, combining with almost any other element. Once combined as a fluoride, the resultant salt is very stable. Sodium fluoride is in toothpaste. After 4 years of operation at Oak Ridge, the molten fluoride salts did corrode the prototype metal reactor vessel (Pot) to a depth of 0.1 mm. In ThorCon corrosion is controlled by managing the redox potential and by changing out the Pot after 4 years of use.
Don’t new fuel designs require many years of testing in special high-neutron-flux reactors?
Yes, for solid-fuel rods. No, for liquid fuels. Solid fuels rods contain solid uranium oxide pellets that are stacked inside zirconium metal pipes to protect from the corrosive effects of the cooling water heated to 315°C and pressurized to 153 atmospheres. The interior of the fuel pellet can reach 1400°C, so there are large temperature gradients, stresses and strains that much be carefully engineered for and tested. In ThorCon the uranium fission takes place in the cooling liquid. Oak Ridge demonstrated this in two prototype molten salt reactors.
Doesn’t graphite distort from exposure to neutrons?
Yes, the graphite moderator planks in ThorCon shrink and swell during years of neutron irradiation. Graphite is not structural. The graphite restraint system accommodates these changes and also temperature changes. Based on Oak Ridge testing, the graphite lifetime exceeds four years; the ThorCon Pot with the graphite is only used for 4 years before being swapped out.
How can ThorCon claim an 80 year life for the power plant?
The only parts of the power plant that are subjected to neutron irradiation are within the Can. The Can is used for 4 years, idled in the plant for 4 years, then transferred by CanShip to a Can Recycling Facility for inspection and refurbishment. The rest of the power plant can be maintained with standard industrial practices.
How do you keep the underground steel plant structure from rusting?
Both the ThorConLand and ThorConIsle versions are built with steel-concrete-steel sandwich walls, of thickness 25-1000-25 mm. The outer steel layer is in contact with groundwater or seawater. The steel is coated and also protected from galvanic corrosion using impressed current cathodic protection and other techniques common in the marine industry.
How long will it take to build and test the first ThorCon?
We expect 36 months will be required to complete the detailed design, build the pre-fission version and conduct temperature and pressure testing. Thereafter an additional year will be required before fueling and fissioning can begin. We plan to deliver power to the grid after 60 months. This depends on a national regulator participating in the test-then-license process. After 72 months we expect to obtain a license to build more commercial power plants.
How long will it take to deploy production versions?
Two years from receipt of a firm order; transmission lines, permitting, siting, cooling are local limiting issues.
Will we run out of uranium?
ThorCon requires 1093 kg of U-235 feed per GW-year with a net U-235 consumption of 448 kg per GW-y. A standard light water reactor requires about 1150 kg/GW-y of U-235 with a net consumption of 850 kg/GW-y. The difference in net consumption is due to ThorCon’s 40% higher thermal efficiency, removal of Xe-135, and the production of U-233 from thorium.
The World Nuclear Association reckons current uranium reserves are 5.9 million tons at $130 per kg uranium. If, for sake of argument, we assume 4 million tons were available to ThorCon and no re-enrichment, then we have 19,200 GW-y of uranium. If we start turning out 100 one GW ThorCons per year, then we are into a 100+200+300+400+… = 100*n*(n+1)/2 series. At year 19, we will have used up our 4 million tons. At this point, nearly 2000 one GW ThorCons will be producing about half the world’s electricity while generating no SO2, no NOx, no ash, and nil CO2. ThorCon will have been spectacularly successful.
This fleet will then be eating into the remaining reserves at the rate of 416,000 tons per year. Re-enriching the used fuel back to 20% equivalent will halve this burn rate. If reserves were static, we’d run out of uranium in another 20 years, about 50 years from now. But the reserves will not be static. ThorCon will push up the real price of uranium and new reserves will be developed. Known low grade sources such as phosphate deposits, enrichment tailings, and coal ash will be exploited. Doubling the cost of uranium from $100 per kg to $200 increases ThorCon’s levelized cost of electricity by 0.2 cents per kWh. Advances in extraction technology always seem to outpace the predictions. For example, the sea contains about 4.6 billion tons of uranium. River flows add about 32,000 tons of uranium to the ocean each year.
Doesn’t being near a navigable waterway limit ThorCon’s market?
No. ThorCon fission power plants must be located so they can be serviced by ocean-going ships that replace Cans and fuel salt casks. Presently 50% of the world’s population lives within 100 km of the sea. Three quarters of the world’s cities are near the sea. ThorCon CanShips can service plants on most major rivers. The CanShip is 150 m long, 23 m beam, 14 m air draft, with a river draft of 2.5 m.
High voltage direct current (HVDC) long distance transmission lines operate near 1 million volts potential. Compared to AC transmission lines they lose less energy because of lessened dielectric losses. HVDC transmission lines as long as 2300 km operate in South America, and a 3300 km line operates in China. Nearly all inland cities are within the reach of an HVDC transmission line from a CanShip-navigable waterway.
Why is the capital cost so low?
Thanks to high temperature, ThorCon uses the same, competitively-sourced, $500/kW, high efficiency, supercritical steam turbine-generator as a modern coal plant. Thanks to low pressure, ThorCon avoids reinforced concrete and 9-inch-thick forgings. Thanks to liquid fuel, ThorCon can move fuel around with a pump. No exacting fuel pin fabrication nor complex reshuffling refueling systems are required. Coal plants are more massive because the energy density of coal fuel is so low compared to uranium. A one-GW coal plant must pulverize 10,000 tons/day of coal and dispose of over 1000 tons/day of ash.
Why is the electricity production cost so low?
In addition to ThorCon’s low capital costs, ThorCon uranium fuel costs are a third of coal fuel costs. ThorCon liquid fuel uranium costs less than LWR solid uranium oxide fuel rods that require precision manufacturing. Thorium costs are relatively trivial. Staffing costs will be modest because the passive safety systems prevent any operator actions from creating a dangerous situation.
Must shipyards handle radioactive materials?
No. Shipyards building ThorCon fission power plants need no special licenses or skills to handle radioactive materials. After a ThorCon is installed and pre-tested, uranium and thorium fuel will be supplied to the plant in fuel transport casks transported by ship.
How do you know it will work?
ThorCon is a molten salt reactor. Oak Ridge National Laboratory built two molten salt reactors in the 1970s; the second operated for 4 years. The team analyzed the experiences and furthered the design. All this research was well documented and is posted publicly. The ThorCon design team draws heavily on this information.
Today the ThorCon team has fast computers and powerful software that simulates fuel fission, heat transfer, fluid flows, and materials properties. There is no new technology in the ThorCon design; it is an assemblage of well-understood technologies. Certainly this new fission reactor will require rigorous testing, just as new airplanes must be tested before the FAA licenses them for commercial use.
Why aren’t you doing this in the US?
It’s too expensive and time consuming. In 2015 our team did visit the Nuclear Regulatory Commission and the Department of Energy to discuss building the first ThorCon in Washington state at the Hanford Reservation, the site of nuclear reactors used to produce plutonium for weapons. The Pacific Northwest National Laboratory is there. We found it would take too much time and money. Since then the GAO has estimated that it would cost a billion dollars and take a decade or more before the NRC would decide to grant a license to build ThorCon. In August 2016 former NRC chair Allison Macfarlane confirmed in MIT Technology Review that it would take 20 years and $1 to 2 billion dollars to reach the design certification point.
How will the nuclear regulator establish licensing rules?
Instead of licensing based on theoretical risk analyses and extensive computer modeling with prescribed document submissions and approvals, we advocate test-then-license. We plan to work closely with the national regulator during construction and rigorous testing of the ThorCon fission power plant. When testing is completed and the regulator becomes familiar with the new design, the regulator can establish rules to license new such power plants for commercial service.
Can ThorCon change power as demand changes or weather-dependent generators start and stop?
Yes. ThorCon can change generated power at 5% per minute. Reducing the molten salt pump motor speeds reduces the heat moved to the steam turbine that turns the electric generator. With less heat removed, the fuel salt temperature rises slightly and the fission slows, solely due to the physical properties of the salt, moderating graphite, and Pot. The process is reversed to increase power.
In an ordinary LWR nuclear reactor, the fission product xenon-135 is produced within the fuel rods. It builds up, with a half-life of 9 hours. It strongly absorbs neutrons, requiring compensating increases in fission rates. When power generation is reduced, less Xe is created, but as the prior level of Xe decays, fewer neutrons are absorbed, and reactivity perversely increases. Managing this requires skilled operators during power changes.
In ThorCon, most of the produced Xe-135 is removed from the liquid fuel by the off-gas recovery system, so that neutrons are not absorbed by Xe in the Pot where fission takes place. This removes the xenon instability and also makes ThorCon more fuel-efficient than an LWR.
Do you need US permission to build foreign fission power plants?
No, but US laws limit the transfer of nuclear materials and technology. There are fewer restrictions for transfers to countries that have signed the Nonproliferation Treaty and also signed bilateral 123 agreements with the US. ThorCon intellectual property is guarded as trade secret information, requiring non-disclosure agreements. The US DOE National Nuclear Security Administration affirms that export of ThorCon information to Indonesia is correctly registered under 10 CFR Part 810.
Where’s the containment dome?
The large, reinforced concrete containment dome over an ordinary LWR is to contain the volume of steam that might be released if the high-temperature cooling water, pressurized to 150 atmospheres, were to breach its piping. That steam might contain radioactive contaminants. In ThorCon, the radioactive fuel salt flowing through the primary loop (Pot, pump, primary heat exchanger) is at garden-hose pressure. In a breach there is little propulsive force. The primary loop is contained within the Can. The Can is contained within the silo cooling wall. The silo cooling wall is contained within the silo hall. The silo hall is underground. There are three to four containment barriers retaining radioactive material in any casualty.
What about the waste?
ThorCon will generate about 1 cubic meter of high level radioactive waste for every GW-year of generated power. Every 8 years, a 1 GW ThorCon will return 220 tons of used fuelsalt to the Fuelsalt Handling Facility, 25 tons per GW-y. The fuel will be kept in dry cask storage for a period of time.
ThorCon has designed future fissile re-injection technology, Uranium will be separated from the fuel salt via fluoride volatility, the same process that was used in the enrichment step. That will remove about 2 tons of 9% LEU from the waste stream. This uranium can be used as is as part of the initial fuel charge for other ThorCon plants or, better yet, re-enriched to 20% LEU equivalent. Most fission products will then be removed from the uranium-depleted fuel salt. The resulting recovered salt leaves behind a residue of ThF4 containing about 103 kg of transuranics and 789 kg of fission products, or about 1.1 cubic meters for long-term sequestration. The recovered salt will be re-injected with LEU then returned as new fuel to ThorCon plants.
What happens in an earthquake or tsunami?
Ships at sea are designed to operate in storms with wind and waves that can generate accelerations up to 1.0 g. The similar design of the ThorCon power ptlant is designed for 0.8 pga (peak ground acceleration). Restrain systems within the Can protect the Pot and piping against such earthquake acceleration. The Can itself rests on elastomeric bearings.
Should a tsunami engulf the ThorCon power plant, the fission plant proper is sealed from the waves with heavy hatches on a deck made of a steel-concrete-steel sandwich. The ThorConLand version is underground but weighted sufficiently not to float up. The ThorConIsle version is sufficiently ballasted down that it will remain in place during flooding. The halls containing the steam turbine and the electric generator are above ground, potentially exposed to damage from a tsunami.
How is the plant decommissioned?
In normal operation Cans are normally swapped out on a 4 year cycle, transported by the CanShip. To decommission the plant the Cans are simply removed after their normal four-year waiting period and returned to the Can Recycling Facility. Radioactive fuel salt is returned to the Fuel Processing Facility in fuel casks, also using normal practice. The plant can be reused, deconstructed, or filled in and buried.
How rapidly can you build and install ThorCon fission power plants?
A modest shipyard could build 20 1-GW ThorCon fission power plants per year. After prototype/demonstration success and commercial licensing, the planned elapsed time from firm order to delivering electric power is two years, depending principally on licensing, site preparation and transmission line construction. ThorCon block construction technology is compatible with existing shipyard construction facilities. A 1-GW ThorCon power plant is much smaller than a tanker ship. There is global capacity to produce up to 100 1-GW power plants per year.
How can ThorCon help check global warming?
Each 1 GW ThorCon plant saves 8 Mt of annual CO2 emissions from avoided new coal power plants.
How can ThorCon help developing nations’ people achieve prosperity?
Keys to prosperity for developing nations include transportation, clean water, education, property rights, good government, and electric power. Each 1 kWh of electricity correlates with $4 of gross domestic product. Electrification is necessary (but not sufficient) for prosperity. Each 1 GW ThorCon plant enables $32 billion of added GDP.
Is it safe?
Yes. See the safety sheet in the Answers section.