Thorium reactors and radioactive waste

As I mentioned in my first posting on thorium reactors, this is a huge topic that deserves a careful discussion – even four postings isn’t enough to do justice to the topic, but it’s a good start. So this will be my last posting on thorium reactors for now, but I might come back to the topic in the future if it seems appropriate. And for this week’s posting I thought I’d take a look at one of the persistent bugbears of commercial nuclear power, and another area in which aficionados of the thorium cycle claim a great advantage. But the best way to get started is to go over where radioactive waste comes from and we’ll go from there. And, incidentally, I should add here that I’ve generated and processed my share of radioactive waste in the Navy and in civilian life (hospital and university waste primarily, in addition to some remediation projects). Although some radioactive waste can be highly dangerous, most of the waste I’ve generated, processed, and handled has been very low-level and quite safe. Dangerously radioactive materials are the exception rather than the rule.

In a reactor there are three basic sources of radioactive waste – activation products, fission products, and transuranic materials. Activation products come from neutron bombardment of stable atoms – adding a neutron, say, to stable cobalt-59 turns it into radioactive cobalt-60. This can happen with any stable atom in the neutron-rich environment of a reactor core – even the water used to cool the reactor core can capture neutrons to form radioactive tritium, and any air dissolved in the water can become neutron-activated as well. But in a nuclear reactor the majority of activation products come from the metals that make up the reactor itself – cobalt (added to some metals to harden them), iron (in the steel pipes and components), manganese (added to high-strength steels), and more. And when the steel suffers from wear and tear, the corrosion and wear products that flake off from the pipes and other components can collect in low-flow parts of the plant or are filtered out by the water purification system – this is a major source of radioactive waste. Luckily, neutron activation products are usually relatively short-lived and decay away over a period of months or years – at most a few decades. Since the formation of activation products is a function of neutron flux (which all reactors have) and the chemical composition of the reactor components (which all reactors have), we can expect that both conventional and thorium-cycle reactors will produce similar suites of activation products. On the other hand, since the molten salt reactors operate at lower pressures, it might be possible to alter the makeup of the metals that comprise the reactor vessel, pipes, and other components – in a reactor that operates at near-atmospheric pressures. it might be possible to adjust the metallurgy to a mix that produces fewer of the longer-lived nuclides.

Fission products are another form of radioactive waste. Hit an atom of U-235 (or U-233) with a neutron and it’s likely to split into two parts (the fission fragments), both of which will be radioactive atoms. While we can’t predict in advance what fission fragments will result from splitting any individual atoms, there are some patterns that we can see. For example, while fission products can have any atomic mass between about 70 and 166 atomic mass units (1 amu is a little less than the mass of a single proton), most of the fission products cluster around atomic masses in the 130s and the 90s. What’s happening is that the atoms split, but not exactly in half, and some neutrons are given off as well. Anyhow – what this means in practical terms is that every uranium atom that fissions produces two radioactive fission product atoms.

In a conventional uranium reactor the atoms of uranium fuel are sealed within a clad that contains not only the fuel but the fission fragments as well. So under normal circumstances the fission fragments will remain locked away – some will leak out, but not many. On the other hand, if there is a defect in the cladding the fission products can escape into the coolant. Either way the fission products will add to the radioactivity of either the spent fuel (if the clad remains intact) or of the reactor plant itself (if the clad leaks). Luckily, with a very few exceptions, the fission products from both U-235 and U-233 fission are fairly short-lived. In fact, there are only 8 nuclides that are both long-lived and produced in abundance – these include some that are pretty well-known (Cs-137 and Cs-134) as well as some lesser-known nuclides (Tc-99, and Kr-85). These are the nuclides that can make spent reactor fuel dangerously radioactive, and some of these (the cesium nuclides) are among those still hanging around in Japan.

If you have a Chart of the Nuclides handy you can look up the fission product yields for U-233, U-235, and Pu-239 – this will tell you, for example, that fissioning U-235 produces something with a mass of 137 amu about 6.19% of the time while a fission fragment of this mass occurs slightly more frequently (6.76) when U-233 fissions. MOst fission products are short-lived so this 137-amu atom will decay merrily away through short-lived nuclides until it reaches Cs-137, with a half-life of 30 years. So by looking at the long-lived nuclides in any atomic mass along with the frequency with which atoms of this mass are produced we can work out a profile for our radioactive waste.

Interestingly, the fission product curves for both U-233 and U-235 are pretty much the same – both nuclides are so close in mass that they have similar fission product profiles. In addition, the amount fission products produced are solely a function of the amount of energy a reactor produces – splitting a U-233 atom releases about as much energy as does splitting a U-235 atom, so producing a MW-hr of energy requires splitting the same number of atoms in both cases. And since each fission produces two fission fragments, the same power output will produce about the same number (and radioactivity) of fission products from each of these devices. The bottom line is that fission product production should be more or less a wash when we compare thorium-cycle reactors to their conventional cousins. What makes the molten salt reactors interesting (for both activation and fission products) is the ability to continually filter out these radionuclides – even were the amount of radioactivity produced be the same, in a molten salt reactor they can be removed as the reactor operates, making them easier to deal with.

So – both the thorium-cycle and conventional reactors should produce roughly the same activation and fission products. But where the thorium units shine is in the production of transuranic nuclides – those elements that lie beyond uranium on the periodic table. As mentioned in last week’s post, the transuranics are produced when uranium atoms capture multiple neutrons to form plutonium, americium, and even more exotic elements. Lighter atoms are further away from the heavy transuranics, making them more difficult to produce. And since it’s many of the transuranics that hang around for centuries, this also reduces the length of time that the fuel is dangerous. This same characteristic, then, accounts for two favorable characteristics – the relative lack of plutonium produced by these reactors (making them more proliferation-resistant) and the lower burden of radioactive waste they produce.

In Superfuel, the author also discusses the possibility of using thorium-cycle reactors to “process” existing spent fuel and radioactive waste by using the neutron flux to transmute this waste into shorter-lived nuclides. While this is true in principle, this is something that can be done in any nuclear reactor – it’s a function of the waste being exposed to a neutron flux, and every operating reactor has a plethora of neutrons. But I suspect that, in real life, this is no more likely to be accomplished in a thorium-cycle reactor than it is in today’s reactors – it’s something that’s possible, but I’m not sure how likely it is to take place. But this is not a negative; rather, it’s the lack of a positive.

So, let’s sum this up:

  • Fission products are largely the same for both reactors
  • Activation product production for thorium-cycle reactors might be lower if the less stressful environment (lower pressure) allows the use of alternate materials
  • Production of transuranic nuclides is decidedly lower in thorium-cycle reactors.
  • But the ability to chemically process molten salt (in a homogeneous liquid-fuel core) makes it possible to scrub radioactivity from the fuel on a continuing basis, reducing the build-up of these nuclides over time.

From this it seems reasonable to conclude that thorium-cycle reactors do offer clear advantages over conventional devices in this area, although these advantages might not be as pronounced as the pro-thorium advocates might suggest.

Finally, let’s try to sum up what we’ve discussed in this series of thorium postings.

Reactor design and construction – we are more familiar with building the “conventional” high-pressure and high-temperature water-cooled reactors, so these have an advantage by virtue of experience and familiarity. However, molten-salt thorium reactors can operate effectively at atmospheric pressure and they don’t require many of the components that make our current fleet of nuclear reactors so complex. Overall, the advantage here goes to thorium-cycle reactors because of their potential simplicity and lower mechanical stress (although to be fair it should be noted that it is possible to build liquid-fuel, molten salt-cooled uranium reactors).

Fuel economy – in a thorium-cycle reactor as much as 100% of the atoms are capable of being transmuted into U-233 and fissioned, compared to less than 1% of the atoms in natural uranium. In addition, there are about four times as many thorium atoms as uranium on Earth. Thus, there are more pounds of thorium than of uranium for us to use and each pound contains more fuel atoms. In this category, thorium has a clear advantage.

Proliferation resistance – thorium-cycle reactors produce far less of the plutonium that can be made into weapons compared to uranium reactors, with their high abundance of U-238. In addition, the presence of high-energy gamma radiation from the U-232 decay series and the ability to “poison” the U-233 by adding U-238 adds further complexity to the process of producing nuclear weapons from this type of reactor. The advantage here is also clearly to thorium.

Radioactive waste – both reactors produce similar fission product profiles. The production of activation products depends on whether or not the lower pressures and potentially simpler reactor design permit the use of alternate materials that are less likely to produce radioactive waste. However, thorium-cycle reactors produce far fewer of the more problematic transuranic nuclides, giving them an advantage in this category as well. In addition, the ability to process liquid fuel on a continuing basis and, thus, to sequester the fission and activation products on a continuing basis adds to this advantage.

My conclusion from all of this is that there is a clear advantage to using thorium-cycle reactors, especially in a world that needs baseline energy production without carbon dioxide emissions. If all that stands in our way is the reluctance of Congress to fund this novel technology (not new tech since it’s been around for more than a half-century) and the reluctance of the existing nuclear utilities to experiment with a new style of reactor then we really need to try to get past the entrenched status quo to try to build some of these things. Maybe we can take notes from the Indians and Chinese as they get their own thorium programs up and running.

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24 Responses to “Thorium reactors and radioactive waste”

  1. Elling Disen September 7, 2012 at 12:11 PM #

    This is a well written introduction to the subject. Allow some details :

    1) MSR can be used with an without thorium. There are designs for MSRs running on LEU and SNF, with and without the U content. Fluid fuel can be mixes of the Th-U and U-Pu cycles. But since Th meets several hurdles in the established U fuel rod food chain, Th is likely to be used industrially in MSRs.

    2) The proliferation resistance offered by U232 is conditioned on design. Since all U can be simply removed from a batch of salt, a quantity of fertile Pa can be held up over months to result in rather pure U233. The presence of safeguards, poisonous and glowing hot chemistry as well as other radiotoxic nuclides should close this window but the specifics remain to be hammered out.

  2. Robert Hargraves September 7, 2012 at 1:02 PM #

    Besides Superfuel, there is another new book on the liquid fluoride thorium reactor, THORIUM: energy cheaper than coal, described at http://www.thoriumenergycheaperthancoal.com.

    The thesis is that the compact, low pressure reactor [originally designed to fit on an airplane wing!] if factory-produced, is the least expensive energy source. Because it can be cheaper than coal, it can dissuade 7 billion people in 250 countries from burning coal and emitting CO2. We only need to depend on economic self-interest, not carbon taxes or worldwide treaties that have proved to be impossible to negotiate.

    • Douglas September 8, 2012 at 9:26 AM #

      I’d love to read that book, can you publish it on the kindle store too?

  3. Thomas Balsløv September 7, 2012 at 1:03 PM #

    Regarding processing waste in a LFTR:

    It’s only the transuranic waste that can be processed and ONLY in a fast spectrum reactor. All transuranic elements are fissionable, but are not considered fissile. Fissile elements (e.g. U-235) are a subset of fissionable (e.g. U-238).

    That means fissioning transuranic elements can’t be done in any of the current commercial reactors, as they all operate in the thermal end of the neutron spectrum.
    That is where a fast spectrum reactor, e.g. like the FS-LFTR, has a great advantage over conventional reactor designs.
    Such a reactor will be able to use all transuranic elements as fuel and attain very deep burn.

    Best regards
    Thomas Balsløv.

  4. Casey Thormahlen September 7, 2012 at 2:41 PM #

    I think you’re missing a major point which would significantly change your conclusion. U-235 cycle reactors are not relying exclusively on U-235, in fact most of the fuel mass is U-238. The resulting U-238 -> Pu-239 fission products look very different from those of U-235 or U-233. You touch on the transuranics later, but it doesn’t take “several neutron absorptions” to get to Pu-239 in the U-235 cycle. Unless you’re running on very highly enriched uranium.

  5. Julien Martin September 7, 2012 at 3:54 PM #

    The Pu-239 fission rate is extremely poor when dealing with neutrons in the thermal spectrum. You can remove the moderator and achieve a fast-spectrum, however at that point you simultaneously give up your ability to breed additional Pu-239 from u-238 because your capture cross-section for U-238 goes down by almost 2 orders of magnitude.

    What’s worse is that neutron capture will occur almost as much as fission for Pu-239 in the thermal-spectrum. That’s where all the other transuranics come from, and basically chews your neutron economy apart if you’re trying to breed additional Pu-239. Fast breeders had to contend with this problem of Pu-239 only working in the fast spectrum and U-238 only working in the thermal spectrum. It is beyond the capabilities of a light water reactor, and only somewhat within the capabilities of a heavy water system.

  6. Josh September 7, 2012 at 4:35 PM #

    In contrast to plutonium separation, separating U-233 from Th fluoride salts is so easy a third year chemistry student could do it. Simply add hydrofluoric acid, then heat and distill out the resulting U-233 hexafluoride. How does that make thorium reactors “proliferation resistant?”

    • George Lerner September 8, 2012 at 12:24 AM #

      In addition to u-233, you would get all other U — including u-232, which as mentioned in the main article, emits hard gamma rays. Hard enough to destroy the electronics of a bomb; hard enough to kill people working on the bomb. U-232 can be detected on the ground or by satellites.

  7. andrew September 7, 2012 at 4:50 PM #

    There is another way to destroy the waste.

    A hybrid fusion-fission converter such as the one designed at UT Austin.

    http://www.utexas.edu/news/2009/01/27/nuclear_hybrid/

    Andrew

  8. SA Kiteman September 8, 2012 at 12:29 AM #

    Actually, it is the fact the breeding U233 from Th232 also breeds some U232 as well that makes it more resistant. U232 is not something that plays well with neaponry control circuits, or explosives, I’m told.

    • Robert Steinhaus September 8, 2012 at 3:20 AM #

      No nuclear weapon in the US arsenal has ever used any electronics.
      The suggestion that the hard gamma produced from Thorium daughters will destroy some associated electronics and maked impractical a weapon built using U-233 contaminated with U-232 does not take into account the fact that no electronics whatsoever has ever been used in any US weapon.

      Removing U-232 from U-233 is difficult, as it requires an isotopic separation. Most of the radiation (2.6 MeV hard gamma) is actually produced by Tl-208 and other decay daughters of U-232, not the U-232 itself. It is possible to remove Tl-208 and other decay daughters from a sample of U-233+U-232 and make a U-232 contaminated sample “safe” for a period of about 3 weeks and allow handling by nuclear workers including machining and work inside a standard glove box. The chemistry of decay daughter removal was worked out in report ORNL-4731 Laboratory Development of a PRESSURIZED CATION EXCHANGE PROCESS. FOR REMOVING THE DAUGHTERS OF U-232 from U-233
      R. H. Rainey
      http://www.ornl.gov/info/reports/1972/3445605995418.pdf

      • Mark L. September 8, 2012 at 8:43 AM #

        Could you be more specific about what you mean by “no electronics”? Because I’m pretty sure that US nuclear weapons have used, for example, electricity to fire their detonators, so I’m assuming I’m just misunderstanding you.

        • Robert Steinhaus September 8, 2012 at 11:02 AM #

          Mark – I regret that I am not permitted to describe any details of the firing mechanism of US weapons (even though I am retired, I am still bound by security related limits).
          Suffice it to say, literally, no electronics have ever been permitted to be incorporated in any US weapon retained in the arsenal.
          Electronics may be a critical part of the delivery systems (missiles, etc) but electronics are not parts (and have never been parts) of actual warheads themselves.

        • Mark L. September 8, 2012 at 11:14 AM #

          I understand. Thanks for taking the time.

          • Robert Steinhaus September 10, 2012 at 4:10 PM #

            Sadly, it is not true that the 2.6 MeV penetrating gamma produced from U-232 decay daughters makes U-233 based weapons impossible. One of the reasons is that NO US nuclear weapons have ever incorporated ANY electronics (at all).

            LLNL recently declassified information about some aspects of the arming mechanism used in US nuclear weapons. The following picture
            https://str.llnl.gov/Mar12/images/obrien3.jpg

            is of a mechanical safe arming detonator (MSAD) which prevents accidental or unintended detonation of a nuclear warhead. An MSAD arming device is all mechanical, and uses NO electronics.
            An MSAD is closer to an old mechanical watch mechanism in the way it is constructed, and it is a device like this that controls the detonation of US nuclear ordinance.
            No US weapon that has ever been in the US arsenal has ever used any electronics whatsoever, so arguments based on the damage 2.6 MeV gamma radiation would do to electronics is not relevant for US weapons designs.
            More info – https://str.llnl.gov/Mar12/pdfs/3.12.pdf

  9. Robert Steinhaus September 8, 2012 at 2:11 AM #

    I would like to complement the author, Dr. Y, on a fine and balanced series of articles on Thorium reactors that I hope is widely read and enjoyed.

    I would like to suggest that some consideration be given in any future Thorium articles to the potential of Thorium Ignited Fusion Reactors (Thorium Ignited PACER) which are a practical style of nuclear power generation that uses Thorium but produces most of its energy from the fusion of Deuterium and Tritium. Thorium Ignited PACER Fusion Reactors also have exceptional characteristics when it comes to efficient utilization of Thorium fissile fuel and generate little nuclear waste.

    Senior nuclear designer at the Lawrence Livermore National Laboratory, Dr. Ralph Moir, led LLNL Molten Salt PACER fusion design efforts. Dr. Moir published “PACER Revisited” which describes LLNL final version of this practical Thorium Ignited Fusion power generation system.
    http://www.osti.gov/bridge/purl.cover.jsp?purl=/6718615-nhbbsq/

    A Comparative Waste Generation study of Coal, Thorium LFTR, and Fission Ignited Fusion PACER Reactors while producing 1 GWe of electrical energy for 1 year

    Coal Fossil Fuel in a 1GWe Coal Fired Power Plant
    Coal Energy Density: 2.9 x 10^7 J/kg
    Fuel Consumed by 1000-MWe Plant: 7,300,000 kg/day
    2666325 metric tons per year
    Waste Produced:
    19466 metric tons of CO2/day
    7,109,956 metric tons of CO2/year

    Thorium/U-233 Fission in a 1GWe LFTR
    Thorium Fission Fuel Energy Density: 8.2 x 10^13 J/kg
    Fuel Consumed by 1000-MWe Plant: 2.7 kg/day or about 1 metric ton of Th-232 per year
    Waste:
    2.7 kg/day (fission products)
    980 kg (fission products) and about 20 kg (Minor Actinide)/ year

    (Thorium Ignited) D-T Fusion in a 1GWe Fusion Reactor
    D-T Fusion Fuel Energy Density: 3.4 x 10^14 J/kg
    D-T Fusion Fuel Consumed by 1000-MWe Plant: 0.6 kg/day or about 100 kg of Deuterium and 150 kg of Tritium or about 0.25 metric tons of fusion fuel consumed per year
    Waste:
    0.54 kg/day (non-radioactive) He-4
    200 kg of (non-radioactive) He-4 produced per year
    (While non-radioactive helium is the only nuclear waste produced by D-T fusion, a profusion of 14.1 MeV fusion neutrons will activate the materials of a fusion reactor target chamber over time – low neutron activation materials are preferred)
    Source: Per Peterson “Overview of the Science and Technology”
    It takes one thousand kilograms of Thorium to produce 1 GW of electrical power for a year in a LFTR and this power production from Thorium results in 1 ton of fission product nuclear waste.

    Fusion Enhanced Thorium Fuel Cycle (Thorium PACER) uses U-233 from the Thorium fuel cycle to create the conditions needed for practical ignition of Deuterium-Tritium plasma via nuclear fusion.

    In D-T fusion
    Deuterium + Tritium –> Helium-4 + Neutrons + Energy

    The nuclear waste of D-T Fusion is only non-radioactive Helium and 1/20th the amount of Thorium fission products from the U-233 fission igniter.

    • Mark L. September 8, 2012 at 8:42 AM #

      I’m a little concerned about the proliferation implications of generating electricity from nuclear explosives.

  10. Kirk Dorius September 8, 2012 at 11:42 AM #

    A key waste advantage of molten salt reactors is the ability to continuously extract, separate and commercialize many of the fission products, excluding them from the waste stream.

  11. Rich Pickens September 8, 2012 at 11:46 AM #

    It’s weird watching so many people fooled by the thorium fantasy and then clinging on to it like some religious cult.

    http://www.joabbess.com/2011/10/26/thorium-trolls-hypnotise-environmentalists/

    • Toby October 12, 2012 at 8:24 PM #

      Would you care to enlighten us on that further? To me it seems weird that so many are convinced we can run an industrialised economy entirely from windmills, whilst in reality the spiralling energy costs in the here and now are sending most people to the wall.

  12. Robert Steinhaus September 8, 2012 at 1:11 PM #

    Mark – There is no nuclear technology on planet earth that is proliferation proof. There are nuclear technologies that are significantly more proliferation resistant.

    PACER is real fusion that works and produces GWe levels of energy. While PACER technology does peacefully extend technology that originated in the weapons area, it has some significant advantages over current nuclear power generation in terms of nuclear risks.

    Proliferation strengths of PACER -
    1) PACER devices operate in the Fusion Enhanced Thorium Fuel Cycle. U233 that is bred in PACER Thorium blankets with fast fusion neutrons would be highly contaminated with U-232. Such fissile material would be dangerous to remove from the PACER reactor and would be easy to track with radiation instruments, including orbiting satellites.
    2) PACER is designed to not allow removal of any material from the PACER cavern. The PACER cavern is substantial (9 inch thick steel liner combined with a 36″ thick reinforced concrete shell), it would not be an easy matter to cut into and penetrate a PACER reactor buried 300 feet underground and enter that high radiation environment to try to steal fissile material.
    3) No fissile materials are shipped around the country to support the operation of PACER. PACER’s fuel’s include a small flow of fertile Thorium (about 1/20th the amount as a similar size Thorium LFTR having the same power rating) and a supply of Lithium (PACER requires about 2 grams of tritium per shot and a PACER Reactor generates this from exposing Lithium to fusion neutrons) and deuterium separated from sea water. The Fusion process is more energy dense in power production than any other power generating technology, and less sensitive nuclear material has to be transported to support an operating PACER Fusion reactor than any other reactor technology producing similar levels of power.
    4) PACER devices are built in a factory like automobiles (a pacer device is small and only about 50 – 200 lbs. in weight). A PACER device, as shipped from the factory to a PACER power plant, is just casting and sheet metal, not significantly more dangerous from a proliferation standpoint than a Maytag washer or other sheet metal product. No PACER device is ever shipped in a condition where it is fitted with nuclear materials (the U-233 micro-pit and D-T gasses are added just in time to the PACER device immediately before it is used in the PACER Reactor).
    5) The vast majority (~95%) of the Power produced by PACER each shot is from fusion produced from about 1 gram of deuterium (separated from sea water) and about 2 grams of Tritium (produced by exposing Lithium to fusion neutrons on a previous PACER shot).
    6) Buried at a depth of 300 feet underground, a PACER Fusion Reactor is more hardened to terrorist attack than any existing above mounted nuclear reactor. It would be more difficult to break into a PACER cavern with a 9 inch thick steel liner combined with a 36″ thick reinforced concrete shell buried at a depth of 300 ft, than any existing above ground mounted reactor.
    7) PACER requires less fissile material to start-up generating power at a 1 GWe level than any other nuclear power system.
    It requires the following quantities of fissile to start up competing 1 GWe nuclear power generating technology:
    Integral Fast Reactor = 15,000 kilograms
    PWR = 5,000 kilograms
    Thorium LFTR = 800 kilograms of U-233
    PACER Fusion Device = 10 kg of U-233

    The low ambient pressure operation (< 1atm prior to shot and less than 30atm at peak), low tritium inventory (tritium is not soluble in Flibe salt – gaseous tritium can be nearly completely pumped out of PACER after each shot to serve as fuel for a future shot, and the lowest fissile inventory of all nuclear power generating systems operating at the same power level should aid in satisfying safety concerns.

    It is necessary to ship only 1/80th the amount of fissile to start up a PACER Fusion power plant as a Thorium LFTR. It requires shipping only 1/500th the amount of fissile to initially start-up a PACER Fusion Reactor as a conventional LWR.

    • Mark L. September 8, 2012 at 1:59 PM #

      Look, you obviously know way more about this than I do, so maybe I’m making a fool out of myself here. But this is still a piece of technology that involves the regular manufacture of nuclear explosives. It’s not terrorists that worry me here, it’s governments, governments whose policies and alliances might change after the PACER unit is set up. Specifically, there are a lot of developing countries in need of large quantities of energy and who we would rather not have access to nuclear weapons, and there doesn’t seem to be any obvious way to keep them from building PACERs if we’re building them. As you say, no piece of nuclear technology is proliferation-proof, but with a LFTR – or an LWR or IFR – you can’t just take some of the fuel out of the reactor and drop it on somebody. A 2-kT PACER shot is pretty puny by nuclear weapons standards, but it’s still a nuclear bomb.

      You say the reactor would be extremely difficult to break into, but does that really apply if you’re the owner-operator? There must be some way to maintain it, some way to move material in and out of the reactor, to refuel it if nothing else. Also – and I understand completely if you can’t comment on this – it seems like there’s no way we could sell this abroad without giving away a lot of classified bomb information, including the Teller-Ulam design.

      Anyway, it’s an interesting idea, and I’m open to changing my mind. But the proliferation aspects of this really concern me.

      • Robert Steinhaus September 8, 2012 at 3:23 PM #

        Mark – You could easily be right about Thorium Ignited PACER fusion.
        PACER is after all currently sidelined technology that you will not even hear
        discussed in hardcore nuke geek circles, even
        though it is in truth the only kind of nuclear fusion that actually works today and could safely produce prodigious amounts of power for any Country that adopted it.

        None of the fusion concepts that DOE and the Western democracies pour money into have the slightest chance of producing the energy it takes to run the fusion experiments for at least several decades and commercial forms of these fusion concepts are probably at least 50 years away. PACER would reliably produce Gigawatt levels of useful power in under 5 years with very low technical risk (all of the essential components of the PACER system, the devices and the artificial caverns/tunnels, have already been built and carefully tested and demonstrated by LLNL and LANL at the Nevada Test Site).

        Why keep up the fiction that fusion is something that we will not be able to do for at least another 50 years. In fact, PACER style fusion has been demonstrated successfully over 50 years ago, and it remains the practical style of fusion, using fission to ignite the D-T fusion plasma, that remains the style of fusion that can actually be built and produce real energy today (more power out than the power it takes to run the fusion experiment).

        PACER would, among other things, extend the
        useful lifetime of the Thorium resource on earth. If we used Thorium in LFTRs to provide all of the power consumed on the planet while raising the worldwide per capita use of power to 6 kilowatts per person (the consumption currently enjoyed in Europe) to provide everyone on earth a chance for a decent life and fair access to energy, we would
        need to generate about 42 Terawatts of power (6
        KW per person x 7 billion persons = 42 Terawatts)
        then we have enough Thorium from known
        guaranteed proven sources [1] to supply the needs of the planet for a about 62 years. Using Thorium in a PACER reactor extends the Thorium resource by 20 times (95% of the energy from PACER is produced from Deuterium-Tritium fusion while only 5% is produced from Thorium/U-233 fission) so the Thorium resource would last 20 x 62 or 1240 years (presuming stable population and 6 Kw per capita power consumption). Whatever the amount of time the world’s Thorium resources ultimately will last, the worldwide Thorium resource can be extended in time by at least a factor of 20X by using the Thorium in a PACER fusion reactor while burning the Thorium together with the Deuterium and Lithium (used to make Tritium) in the seas.
        [1] – IAEA worldwide estimate of Thorium
        resource is 2,610,000 metric tonnes
        http://www.world-nuclear.org/info/inf62.html

        • Robert Steinhaus September 8, 2012 at 3:37 PM #

          ***Correction (and apology)***
          To produce Power from PACER at a 1 GWe level would require igniting a device every 1/2 hour burning about 10 grams of deuterium (separated from sea water) and about 16 grams of Tritium (produced by exposing Lithium to fusion neutrons on a previous PACER shot).

          The fuel to produce D-T fusion is cheap, accessible to all nations, and is almost inexhaustible. In addition to this, only a tiny amount of fuel is required: operating a D-T fusion commercial power station of 1GW(e) power output for a year requires only 250 kg of deuterium tritium fuel. It requires about 250,000 kilograms of natural uranium to produce the enriched fuel needed to produce the same 1GW-year of energy in a LWR. Similarly, it would require 1000 kilograms of Thorium in a LFTR to produce the same 1GW-year of energy.

          The total lithium content of seawater is very large and is estimated as 230 billion metric tonnes, while the quantity of deuterium in the world’s oceans is estimated at 4.6 x 10^13 metric tonnes. The stoichiometric ratio of Deuterium to Tritium is 2 to 3 by weight.

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