ThorCon nuclear reactor
- See also: Nuclear_power_reconsidered
ThorCon power train. An extra heat exchange loop ensures no leakage of radiation.[2]
Raw material flows and waste at a ThorCon fuel processing plant. Enriched uranium powers the cycle, but most of the energy comes from the more abundant thorium.[3]
Thorcon nuclear reactors are molten salt reactors with a graphite moderator. These reactors (and the entire power plant) are to be manufactured on an assembly line in a shipyard, and delivered via barge to any ocean or major waterway shoreline. The reactors are delivered as a sealed unit and never opened on site. All reactor maintenance and fuel processing is done at a secure location.
This article is a brief summary. For more details see the ThorCon documents[4] and ThorCon's Status Report to the IAEA.[5]
Safety
Accidental overheating. There are salt plugs at the bottom of the reactor vessel that melt if the reactor gets too hot, and allow the fuel to flow out of the reactor into drain tanks, where the fission reaction stops, and the decay heat is absorbed by a "cold wall".[6] There are no safety-critical systems or valves and no electronic or computer systems vulnerable to cyber attack.[7] No operator action is required, and there is nothing an operator can do to stop a safe shutdown. Reactors that meet these requirements are called "walk-away safe".
Leakage of Radioactivity The molten salt is at low pressure, and any leakage from the reactor will quickly solidify. The most troublesome fission products, including iodine-131, strontium-90 and cesium-137, are chemically bound to the salt. There is no pressurized water near the reactor vessel. Leakage to the environment is blocked by three gas-tight barriers - the Can, the Silo, and the Hull.[8] Tritium is captured by getters in inert gas in the power module hall and in the secondary heat exchanger cell. A third salt loop allows any tritium penetrating both heat exchangers to be captured in the third loop.[7] Xenon and krypton bubble out in the header tank, are held in storage tanks until they have decayed to harmless levels, and then cooled, compressed and stored.[9]
Sabotage The hull is a 10ft thick wall of sand with an inch of steel on each side, capable of blocking a jumbo jet with nine-ton engines.[7] Reactivity can be increased only by adding fuel slowly through an orifice inside the silo, out of reach of any rogue operator. The maximum rate of increase in reactivity is enough for load following, but never enough that the reactor can go prompt critical.[7] Should a group of terrorists seize control of the plant and attempt to remove fuelsalt, they would require use of the 500-ton deck crane, which could be easily disabled with small artillery.[10] There is no vulnerability to cyber attack.
Waste Management
All reactor maintenance and fuel processing is done at a secure location.
Average per year for a 500MW plant:[3]
High Level Waste: 13,400kg to dry-cask storage[11]
Medium and Low Level Waste: 343 tonnes of irradiated steel (one of the 4 "cans") shipped out for refurbishment.
Recycled Fuel: 650kg of 19.7% U-235 (33% of total U consumption)
Other: (Medical isotopes, etc.)
The "waste" in the ThorCon fuel cycle is actually valuable fuel for future fast neutron reactors capable of efficiently burning thorium and depleted uranium. This will extend proven resources from centuries to millennia.
Weapons Proliferation
The reactors are delivered as sealed cans and never opened on site. All reactor maintenance and fuel processing is done at a central secure location.
There is no online chemical processing to remove fission products or anything else, and no highly enriched material anywhere — none above 20% U-235.
The sealed cans are inside a high-radiation silo under a heavy concrete lid. Any attempt to get inside the silo can be detected by sensors and security cameras and stopped by local police or military.
Uranium is always low-enriched. Plutonium is always diluted with thorium, in fuel salt with hazardous fission products.[7] Making bombs from this material will be far more difficult than starting from uranium ore.
Cost
The expected cost of a complete power plant will be less than a coal plant of equal power.[12] Everything in the fission island except the structure itself is replaceable. Every four years the sealed reactor and entire primary loop is changed out, returned to a centralized recycling facility, decontaminated, disassembled, inspected, and refurbished. Incipient problems are caught before they can turn into casualties. Thorcon plants with replaceable sealed reactors can operate for 80 years; but, if a ThorCon is decommissioned, the process is little more than pulling out but not replacing all the replaceable parts.[13]
Specs for a 500MW plant:[7]
Plant cost per KW: $1200
Operating cost per KWh: $0.03 (including $0.006 for fuel)
Fuel consumption per day: 5.3kg of 19.7% enriched uranium plus 9.0kg of thorium.[3]
-145 tonnes of natural uranium per GW-year compared to about 250 tonnes for a standard light water reactor
- future re-enrichment of spent fuel will cut this uranium requirement by a third
Initual fuel load (2 cans): 78,000kg NaF-BeF2-ThF4-UF4 (76-12-10.2-1.8 mol %)
Notes and References
- ↑ Fig.10 from Section 1.2 in ThorConIsle
- ↑ ThorCon Power Conversion.
- ↑ 3.0 3.1 3.2 ThorCon Fuel Cycle
- ↑ ThorCon Isle
- ↑ IAEA Advanced Reactors Information System (ARIS) ThorCon_2020.pdf 2020/06/22.
- ↑ The wall is kept "cold" by water that is replenished from a storage tank above the reactor. Circulation is maintained without pumps, because the hot water (or steam) rises in the space around the cold wall.
- ↑ 7.0 7.1 7.2 7.3 7.4 7.5 ThorCon SpecSheet7
- ↑ See section Release resistance in ThorCon Safety
- ↑ ThorCon Drain tank
- ↑ Section 6.2 in ARIS Status Report
- ↑ ThorCon power plants can store up to 80 years of used fuel onboard, using passive air cooling. ThorCon Fuel
- ↑ ThorCon Economics
- ↑ "ThorCon is Fixable" p.1 in ThorConIsle