Molten salt reactor vs fluoride salt-cooled reactor
The most common classification error in advanced nuclear, and the one the vocabulary behind this site originally got wrong. Both use molten salt. Only one dissolves the fuel in it.
Molten salt reactor (MSR)
Fuel DISSOLVED in the salt, which in most designs is fuel carrier and coolant at once. Distinct from a salt-cooled reactor with solid fuel; the two are often confused. Moderator, where one is used at all, is a separate design choice from the salt: thermal-spectrum MSRs are typically graphite-moderated, fast-spectrum MSRs carry no moderator.
2 devices · 12 organisations · 1 measurements
Fluoride salt-cooled high-temperature reactor (FHR)
Molten salt COOLANT with solid fuel, typically TRISO, and a separate solid moderator, usually graphite. Kairos Power's KP-FHR is the reference example.
2 devices · 1 organisation · 1 measurements
Differences
| Molten salt reactor (MSR) | Fluoride salt-cooled high-temperature reactor (FHR) | |
|---|---|---|
| Where the fuel is | Dissolved in the salt. The fuel and the coolant are the same fluid. | Solid TRISO pellets. The salt only removes heat. |
| Why it matters | Fuel can be processed online and the reactor cannot melt down in the conventional sense, because the core is already liquid. | Fuel behaves like conventional solid fuel. The safety case rests on TRISO particles retaining fission products, not on the coolant. |
| Fission product handling | Fission products are in the circulating salt, so the entire primary loop is highly radioactive. | Fission products stay in the fuel particles. The salt loop is far cleaner. |
| Licensing consequence | A liquid-fuelled reactor challenges regulatory frameworks written for solid fuel. | Closer to existing precedent, because the fuel form is familiar. |
| The error to avoid | Salt-fuelled. | Salt-COOLED. Kairos Power is an FHR: describing it as a molten salt reactor gets the fuel form exactly wrong. |