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Thorium Fuel: No Panacea for Nuclear Power

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  • Romi Elnagar
    Thorium Fuel: No Panacea for Nuclear Power Edited on Thu Mar-11-10 12:34 AM by kristopher (Open Access Document) Thorium Fuel: No Panacea for Nuclear Power By
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      Thorium Fuel: No Panacea for Nuclear Power

      Edited on Thu Mar-11-10 12:34 AM by kristopher
      (Open Access Document)

      Thorium Fuel: No Panacea for Nuclear Power
      By Arjun Makhijani and Michele Boyd

      A Fact Sheet Produced by the Institute for Energy and Environmental Research and Physicians for Social Responsibility

      Thorium
      “fuel” has been proposed as an alternative to uranium fuel in nuclear
      reactors. There are not “thorium reactors,” but rather proposals to use
      thorium as a “fuel” in different types of reactors, including existing
      light‐water reactors and various fast breeder reactor designs.

      Thorium, which refers to thorium‐232, is a radioactive metal that is about three times more
      abundant
      than uranium in the natural environment. Large known deposits are in
      Australia, India, and Norway. Some of the largest reserves are found in
      Idaho in the U.S. The primary U.S. company advocating for thorium fuel
      is Thorium Power (www.thoriumpower.com ). Contrary to the claims made or implied by thorium proponents,
      however, thorium doesn’t solve the proliferation, waste, safety, or cost problems of nuclear power, and it still faces major technical hurdles
      for commercialization.


      Not a Proliferation Solution

      Thorium
      is not actually a “fuel” because it is not fissile and therefore cannot
      be used to start or sustain a nuclear chain reaction. A fissile
      material, such as uranium‐235 (U‐235) or plutonium‐239 (which is made in
      reactors from uranium‐238), is required to kick‐start the reaction.
      The enriched uranium fuel or plutonium fuel also maintains the chain
      reaction until enough of the thorium target material has been converted
      into fissile uranium‐233 (U‐233) to take over much or most of the job.
      An advantage of thorium is that it absorbs slow neutrons relatively
      efficiently (compared to uranium‐238) to produce fissile uranium‐233.

      The
      use of enriched uranium or plutonium in thorium fuel has proliferation
      implications. Although U‐235 is found in nature, it is only 0.7 percent
      of natural uranium, so the proportion of U‐235 must be industrially
      increased to make “enriched uranium” for use in reactors. Highly
      enriched uranium and separated plutonium are nuclear weapons materials.

      In addition, U‐233 is as effective as plutonium‐239 for
      making nuclear bombs. In most proposed thorium fuel cycles,
      reprocessing is required to separate out the U‐233 for use in fresh
      fuel. This means that, like uranium fuel with reprocessing,
      bomb‐making material is separated out, making it vulnerable to theft or
      diversion. Some proposed thorium fuel cycles even require 20% enriched
      uranium in order to get the chain reaction started in existing reactors
      using thorium fuel. It takes 90% enrichment to make weapons‐usable
      uranium, but very little additional work is needed to move from 20%
      enrichment to 90% enrichment. Most of the separative work is needed to
      go from natural uranium, which has 0.7% uranium‐235 to 20% U‐235.

      It
      has been claimed that thorium fuel cycles with reprocessing would be
      much less of a proliferation risk because the thorium can be mixed with
      uranium‐238. In this case, fissile uranium‐233 is also mixed with
      non‐fissile uranium‐238. The claim is that if the uranium‐238 content
      is high enough, the mixture cannot be used to make bombs without a
      complex uranium enrichment plant. This is misleading. More uranium‐238
      does dilute the uranium‐233, but it also results in the production of
      more plutonium‐239 as the reactor operates. So the proliferation
      problem remains – either bomb‐usable uranium‐233 or bomb‐usable
      plutonium is created and can be separated out by reprocessing.

      Further, while an enrichment plant is needed to separate U‐233 from
      U‐238, it would take less separative work to do so than enriching
      natural uranium. This is because U‐233 is five atomic weight units
      lighter than U‐238, compared to only three for U‐235. It is true that
      such enrichment would not be a straightforward matter because the U‐233
      is contaminated with U‐232, which is highly radioactive and has very
      radioactive radionuclides in its decay chain. The
      radiation‐dose‐related problems associated with separating U‐233 from
      U‐238 and then handling the U‐233 would be considerable and more complex
      than enriching natural uranium for the purpose of bomb making. But in
      principle, the separation can be done, especially if worker safety is
      not a primary concern; the resulting U‐233 can be used to make bombs.
      There is just no way to avoid proliferation problems associated with
      thorium fuel cycles that involve reprocessing. Thorium fuel cycles
      without reprocessing would offer the same temptation to reprocess as
      today’s once‐through uranium fuel cycles.


      Not a Waste Solution

      Proponents
      claim that thorium fuel significantly reduces the volume, weight and
      long‐term radiotoxicity of spent fuel. Using thorium in a nuclear
      reactor creates radioactive waste that proponents claim would only have
      to be isolated from the environment for 500 years, as opposed to the
      irradiated uranium‐only fuel that remains dangerous for hundreds of
      thousands of years. This claim is wrong. The fission of thorium
      creates long‐lived fission products like technetium‐99 (half‐life over
      200,000 years). While the mix of fission products is somewhat different
      than with uranium fuel, the same range of fission products is created.
      With or without reprocessing, these fission products have to be
      disposed of in a geologic repository.

      If the spent fuel is
      not reprocessed, thorium‐232 is very‐long lived (half‐life:14 billion
      years) and its decay products will build up over time in the spent fuel.
      This will make the spent fuel quite radiotoxic, in addition to all the
      fission products in it. It should also be noted that inhalation of a
      unit of radioactivity of thorium‐232 or thorium‐228 (which is also
      present as a decay product of thorium‐232) produces a far higher dose,
      especially to certain organs, than the inhalation of uranium containing
      the same amount of radioactivity. For instance, the bone surface dose
      from breathing the an amount (mass) of insoluble thorium is about 200
      times that of breathing the same mass of uranium.

      Finally, the
      use of thorium also creates waste at the front end of the fuel cycle.
      The radioactivity associated with these is expected to be considerably
      less than that associated with a comparable amount of uranium milling.
      However, mine wastes will pose long‐term hazards, as in the case of
      uranium mining. There are also often hazardous non‐radioactive metals
      in both thorium and uranium mill tailings.


      Ongoing Technical Problems

      Research
      and development of thorium fuel has been undertaken in Germany, India,
      Japan, Russia, the UK and the U.S. for more than half a century. Besi
      des remote fuel fabrication and issues at the front end of the fuel
      cycle, thorium‐U‐233 breeder reactors produce fuel (“breed”) much more
      slowly than uranium‐plutonium‐239 breeders. This leads to technical
      complications. India is sometimes cited as the country that has
      successfully developed thorium fuel. In fact, India has been trying to
      develop a thorium breeder fuel cycle for decades but has not yet done so
      commercially.

      One reason reprocessing thorium fuel cycles
      haven’t been successful is that uranium‐232 (U‐232) is created along
      with uranium‐233. U‐232, which has a half‐life of about 70 years, is
      extremely radioactive and is therefore very dangerous in small
      quantities: a single small particle in a lung would exceed legal
      radiation standards for the general public. U‐232 also has highly
      radioactive decay products. Therefore, fabricating fuel with U‐233 is
      very expensive and difficult.


      Not an Economic Solution

      Thorium
      may be abundant and possess certain technical advantages, but it does
      not mean that it is economical. Compared to uranium, thorium fuel cycle
      is likely to be even more costly. In a once‐through mode, it will need
      both uranium enrichment (or plutonium separation) and thorium target
      rod production. In a breeder configuration, it will need reprocessing,
      which is costly. In addition, as noted, inhalati on of thorium‐232
      produces a higher dose than the same amount of uranium‐238 (either by
      radioactivity or by weight).

      Reprocessed thorium creates even
      more risks due to the highly radioactive U‐232 created in the reactor.
      This makes worker protection more difficult and expensive for a given
      level of annual dose. Finally, the use of thorium also creates waste at
      the front end of the fuel cycle. The radioactivity associated with
      these is expected to be considerably less than that associated with a
      comparable amount of uranium milling. However, mine wastes will pose
      long‐term hazards, as in the case of uranium mining. There are also
      often hazardous non‐radioactive metals in both thorium and uranium mill
      tailings.

      Fact sheet completed in January 2009
      Updated July 2009

      http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=115x235481

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