Nuclear Fission

Nuclear fission will continue to play an increasingly important role in meeting our energy needs in the short term (say over the next 50 years). There is just no other energy source presently available that can replace fossil fuels fast enough.

We have created large quantities of nuclear waste that will take tens of thousands of years to decay. Yucca mountain storage for 20,000 years is not a viable solution. Civilizations do not last tens of thousands of years.

The PUREX reprocessing cycle recovers only uranium and plutonium and extracts only 5% of the energy potential of the initial uranium or thorium fuel.

PUREX processing produces pure uranium and plutonium that can be used to make bombs.

Pyrometallic reprocessing combined with generation VI reactors can extract 95% of the potential energy from nuclear fuel, producing only 5% of the waste which decays to safe levels in 300 years instead of 20,000. Uranium, plutonium and the rest of the actinides are extracted together. This combination can then be re-used in a sodium cooled fast reactor but is unsuitable for nuclear weapons.

Reactor Image

Uranium 235 and plutonium 239 are fissionable with slow neutrons in conventional reactors but many of the other actinides are not. All actinides are fissionable in a sodium cooled fast reactor.

After the actinides are extracted from spent fuel the remaining waste consists of fission products which decay to safe levels within 300 years.

Building pyrometallic reprocessing facilities and generation IV sodium cooled fast reactor turns our nuclear waste burden into a vast energy resource for current and future generations.

Yucca mountain would make an excellent location for a generation IV reactor farm. The repository was already designed to contain wastes for ten thousand years, it could also contain a potential nuclear accident should the reactors not live up to the safety expectations of their designers.

By locating a large number of reactors in one location we can reduce the overall expense of the operation. The same reprocessing facilities can be used to process spent fuel for all the reactors eliminating any risks associated with the transportation of high level radioactive wastes and the fission products that will be left can be stored on site. When it is time for the reactors to be decommissioned, they too will already be at a nuclear waste storage facility.

I encourage you to write your congress critters and suggest this. An energy rich America will be an economically prosperous America, and we can export this technology to foreign countries reducing the risk of nuclear proliferation abroad will allowing it’s use for power generation displacing fossil fuel power generation and greenhouse gases.

4 thoughts on “Nuclear Fission

  1. Hi Robert,

    You might want to learn more about the liquid-fluoride reactor, which can operate on a thermal-neutron spectrum and with non-volatile core fluids (salts instead of metallic sodium). When operated with uranium-233 generated from thorium, the liquid-fluoride reactor produces essentially no transuranics. Furthermore, since it uses salts instead of metallic sodium, it avoids all the issues with sodium-water fires that bedevil the liquid-metal fast breeder concept.

    Energy from Thorium

    Thorium is abundant and can be completely converted to energy in the reactor.

  2. While I believe that the safety issues associate with liquid sodium cooled reactors are substantial, and even though good design can mitigate most risk of radiation release, reliability problems related to sodium reactivity with atmosphere and water remain an issue, and it is for the safety reasons that I suggested reactor farm in what was intended to be the Yucca mountain repository.

    I would further suggest other reactors be sited underground at locations where water table contamination in the event of loss of containment would not occur.

    Not to dismiss your suggestion but one of my primary concerns is that we find a way to use up the existing actinides that we’ve created in water cooled reactors before we intentionally create more.

    I would also suggest that the pyrometallic / fast neutron fuel cycle can also incorporate Thorium.

    But you are correct in as much as sodium cooled reactors have been plagued with sodium leaks, sodium-air fires, sodium-water fires, and that fast reactors are more prone to rapid reactivity excursions.

  3. Hi Robert,

    I agree with you that we should be building a reactor farm at Yucca Mountain instead of a waste repository. I also agree that you need fast-spectrum reactors to destroy transuranic waste. But rather than using the sodium-cooled fast reactor, which has a multitude of safety issues, I am very intrigued with the liquid-chloride reactor concept, which is another kind of molten-salt reactor. I believe the chloride reactor could be built in ways that would be far safer and simpler than the sodium-cooled solid-core reactor.

    Whereas the liquid-fluoride reactor optimizes as a thermal-spectrum reactor that can run on thorium (with a conversion ratio of > 1.0), the liquid-chloride reactor is a very fast spectrum reactor designed to destroy transuranics. I think we should build a few chloride reactors to destroy all the transuranics we’ve produced in light-water reactors, breed U-233 from thorium using the excess neutrons these chloride reactors will produce, then use the U-233 to start literally thousands of fluoride reactors which will then run exclusively on thorium.

  4. Out of curiousity, do you know specifically what chloride salt is use? Is it sodium-chloride or some other chloride? Do you know the melting and boiling points? The heat carrying capacity relative to liquid metals?
    Can metallic fuel rods and fuel be used with liquid salts or is the corrosiveness too high?

    I think we have to build some sort of fast spectrum reactor to destroy existing transuranics but I do not know what the best technology is.

    There is also the helium cooled very high temperature reactors but those strike me as a disaster waiting to happen given the relatively low heat carrying capacity of helium. But the high outlet temperatures translate into high efficiencies.

    You had mentioned reactivity excursions with fast reactors. I can see two contributing factors to this problem.

    One, you don’t have the time it takes to slow (thermalize) fast neutrons as you would in a thermal reactor so that delay is eliminated from the reactivity escalation.

    Two, in a thermal reactor that is water moderated, steam is a less efficient moderator and so you have a negative void coefficient, that is when the reactivity level increases, more steam is produced and the effectiveness of the moderator is reduced and so the reaction is dampened. But in a fast reactor where moderation is not desired, if the cooling medium, say liquid sodium, acts as a moderator or just absorbs neutrons to any degree, if boiling is reached, the voids are going to slow/absorb neutrons less increasing the rate of reaction creating a positive void coefficient. That positive feedback only destablizes things further which would seem to hold a strong potential for rapidly increasing reactivity and destruction of the reactor core.

    But a number of these reactors have been operated and the major problems with the liquid sodium cooled reactors so far seems to have been leaks in the plumbing resulting in sodium reacting with atmosphere or leaks in the secondary heat exchanger resulting in sodium reacting with water. These cases the major hazards have not been nuclear but chemical.

    The corrosive nature of salts and the lower heat carrying capacity, the chemical reactivity of liquid sodium with atmosphere and water, both of these are engineering problems. I do not know which is more difficult.

    With the very high temperature helium cooled reactors I would imagine loss of forced coolant would have a high probability of core destruction?

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