Comment by cestith
1 day ago
A MSTR only needs uranium-233, uranium-235, or plutonium to start. It then produces uranium-233 as part of its fuel cycle as thorium is input.
Given current found reserves and the current rate of use, the world has about 40 to 50 years of natural gas. Thorium used in molten salt thorium reactors would provide electricity for 60 billion years or so if we could actually extract all of it. That's 10 billion years or more if it provided all human energy consumption. Of course there's a limit to extraction, but it is over three times as common as uranium.
Also, besides thorium one can mix in partial amounts of other fuels, including uranium and plutonium. There is no runaway meltdown risk, as the fission is actively managed rather than actively suppressed. Fuel is spent more completely. The waste products are smaller, less radioactive, and have far shorter half-lives.
Then of course we're always getting slightly closer to productive fusion reactors.
These technologies along with solar PV, solar thermal, hydro, wind, geothermal, wave power, and batteries likely all have a place in the future.
There's a decent chance that at some point in the future residential customers will pay for the connection and only commercial or industrial customers will actually be metered. That's not because companies want to give up additional revenue. It's because at some point the cost of meters, tracking usage, and competitive advertising about who has the cheapest plans costs more than the power the typical customer uses above the base charge.
How can the waste product be less radioactive if it has a shorter half-life?
It contains a different mix of elements and isotopes than spent solid fuel rods from light water reactors.
The reactor creates new fissile material while it runs, then fissions that. The new fissile material is recycled into the reactor. Even actinides can largely be recycled into the fuel stream. The fuel and coolant being a liquid mixture allows a lot of chemical processing and returning parts of the initial waste back into the reactor more fully.
The waste that's actually handled for storage tends to have a lower proportion of fission byproducts that carry their own radioactivity, but some traces of highly active sources. I've read cesium, strontium, iodine, xenon, krypton, barium, and various noble metals are the bulk of the waste. Some of that cesium will be cesium-137. Some of the strontium will be strontium-90.
Solid rods from a light water reactor are not even nearly completely spent before they become too degraded for producing electricity. They contain cesium-137 and strontium-90 too but along with uranium-235, plutonium-239, americium-241, neptunium237, and curium at the time they're ready for storage. Small parts of this can be reprocessed rather than stored, but often for nuclear weapons. Having solid rods also makes it more difficult to separate elements.
MSTR waste is dangerous, but for about three hundred years. The radiation involved tends to be largely gamma, but from a very small portion of the waste rather than the bulk of the mass. Light water reactor waste can be dangerous for tens of thousands of years, producing alpha, beta, and gamma from most of the mass of the waste. The alpha and beta radiation will last tens of millennia.
I guess if you abused terminology to scale by risk then, something decaying faster but by a different mechandism could be “less radioactive”, e.g., for external exposure, an alpha emitter with a shorter half-life might be “less (dangerously) radioactive” than a beta emitter (of course, the reverse would be true for internal exposure.)
Can’t really think of any other way to rationalize that combination.