Thursday, 17 December 2015

A politician asks: can thorium be profitable for Norway?

It will be profitable when done with the right reactor design. Today's PWR, BWR, designs are too expensive. E.g. Hinkley C in Britain is horrendously expensive. ThorCon (a startup company aiming to make molten salt reactors (MSR), using thorium), reckon they can make a safer reactor, within 6 years, for 20% of Hinkley C prices. ThorCon are not unique. There are a host of other startups and molten salt reactor designs: Transatomic Power, Terrestrial Energy, Seaborg Technologies, Flibe Energy, Moltex SSR, Chinese designs, the Russian MOSART, the EVOL MSFR in France, Japanese, and Czech reactors. Bill Gates TerraPower are said to be working on a molten salt reactor too.

Note:

  1. There are 3 practical nuclear fuels (fissile materials): plutonium-239, uranium-235, and uranium-233 (Pu-239, U-235, U-233).
  2. Uranium consists of a natural mixture of two isotopes: U-238 : U-235, in a ratio of 1000 : 7. Only U-235 is fissile. It must generally be concentrated 5 times (or more) to be used as fuel. In a reactor some of the U-238 "breeds" to Pu-239. U-235 is the only naturally occurring fissile material.
  3. There is about 3½ times more thorium available in the world than uranium. Thorium can be 'bred' to make a kind of uranium not found in nature : U-233. (much like Pu-239 is bred from U-238) U-233 performs better than any other fissile material in a thermal nuclear reactor (and 99%+ of reactors are thermal). This is the reason nuclear engineers love it.
  4. A molten salt reactor is a very good natural fit for thorium. Molten salt reactors are also:
    • safer - they do not use water compressed at 80 atmospheres. So the possibility of catastrophes like Chernobyl or Fukushima is eliminated.
    • more efficient - because they operate at much higher temperatures (almost 400ÂșC above a PWR temperature), they convert more heat to electricity
    • potentially less expensive - the intrinsic safety of a MSR allows many expensive safety boondoggles to be dispensed with.
    • for more see: Advantages of molten salt reactors

The magic of thorium is really uranium-233. Poor uranium-233 had all its limelight stolen by the thorium upstart. U-233 has excellent neutronic performance in the thermal neutron spectrum : 90.3% of neutrons hitting a U-233 atom cause fission and release the atom's energy. Only 7.7% of neutrons are wasted (captured and absorbed). The fission : capture ratio (table below) shows that U-233 is 3.1 times better than Pu-239. I'm measuring this performance in terms of fissionable atoms (and neutrons) wasted. The more that are wasted the more difficult it is for nuclear power to be sustainable. To be sustainable we must be able to breed more fissile material from thorium or uranium-238 than we use up in make energy. The couple: thorium and uranium-233 are sustainable in both the thermal and fast neutron spectra.

In practice, uranium-233 can only be made from thorium. That's why thorium is talked about. But it's really about uranium-233.

The relative performance of 3 fissile materials U-233, U235, Pu-239 under thermal neutron bombardment (aka - in a reactor) :

Thermal cross-section (barn)
capturefissiontotal% fissionfission : capture ratio
U-2334553157692.2%11.80
U-2359969279187.5%6.99
Pu-2392691025129479.2%3.81

Now it's not so much that plutonium-239 and uranium-238 don't make a sustainable couple too. They do. But it's U-238 + Pu-239 for the fast neutron spectrum only, but thorium-232 + U-233 for either the fast or thermal neutron spectra.

2 comments:

  1. I would love to see a thorium (U233) molten salt reactor get built. I would also love to see a U-235/238 molten salt reactor, which probably has fewer technical hoops to get through, and basically keep most of the advantages touted.

    Unfortunately a number of thorium proponents have the fundamentally flawed approach of trying to knock the safety of existing plants in order to convince the world-at-large of how good thorium is. Sorry, folks, that's not going to work.

    Nuclear power is safe already, unless you allow the ground to be shifted so that "safe" is restricted to mean the real-world-impossible "zero risk". It's ridiculous to imagine winning the public over to one type of nuclear power by calling other nuclear power methods "unsafe", whether explicitly or implicitly.

    Also, "safety boondoggles" is ill-advised language. I think you mean "elaborate engineered safety barriers". And multi-layered redundant barriers are - like it or not - going to be part of the scene for a while yet.

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    1. You mistake this process of knocking the "safety of existing plants" as some kind of thorium advocate plan. It's not. Everyone, including nuclear engineers, knocks the safety of existing plants; by which I mean water-moderated BWR, PWR and CANDU plants. People who matter are: politicians, regulators, energy executives and journalists. Power plant cost is greatly hiked by the need for highly engineered safety, phobias over radioactivity leaks, ultra precautionary regulators, ... The real issue are costs that makes current nuclear power much more expensive than fossil fuel; we can't make BWR, PWR, CANDU plants very cheap. Nor can we close the fuel cycle with such technology. Patented in 1947, the PWR was a short-term solution to give the US navy nuclear powered submarines. It was never meant to be the model for nuclear reactors. Accidents of history made it so. Innovation was stifled by a combination of ignorance and short-term thinking by energy execs, politicians, regulators, and, even scientists. We mostly gave up trying to build much better fission reactors. Fusion was supposed to replace fission. It never did, and it may never. Now that fission innovation is back in vogue, we'll finally be able to make nuclear power cheap enough to blow everything else out of the water.

      I called the EPR core catcher a boondoggle because it is. Apart from reassuring a German Green Party minister, it has no practical purpose. Other engineering features should prevent reactor solid fuel meltdown; making core catchers irrelevant.

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