Class

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Class 14 NSEN 619 Partitioning and Transmutation

• Objective is to accelerate the fission of
  actinides
• Np-237, Pu-238, Pu-239, Pu-240, Am-241,
  Cm-242-248.
• Also, some envision transmuting long lived
  fission and activation products
• Tc-99, I-129, Nb-94.
• Partitioning is necessary in order to remove some
  fission products that might otherwise poison the
  reactor (absorb neutrons without producing
  replacement neutrons.
• See also http//web.mit.edu/22.76/www/moltensalt/o
  ptimization.pdf

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Partitioning and Transmutation

• Separation of actinides and fission products from
  Spent Fuel.
• Recycle Uranium and Plutonium (just like the
  Breeder Reactor).
• Return the minor actinides and fission products
  to high neutron flux and burn them.
• i.e., Transmute them to less long-lived isotopes
  or non-radioactive isotopes.
• This is what ANL-W was doing and Japan, France
  and England are still pursuing.
• Internet is a rich resource for P-T information.

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Who was/is working on PT

• See textbook, pages 242-259, and 315-317
• Argonne and ANL-W began this work in the mid
  1950s and were shut down in late 1990s
• Pyrometallurgical, pages 249-259
• Molten-salt, pages 258-259, 315-317.
• See the NEA website
• http//www.nea.fr/html/pt/projectslinks.htm

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Partitioning and Transmutation   The term
partitioning and transmutation refers to
partitioning all of the actinides from the fuel,
and making a second generation fuel from the
actinides and placing them back in the reactor
and burning them again. Each time an actinide
picks up a neutron, it becomes more unstable and
has a shorter half-life. Picking up the neutron
is technically activation, but it has earned the
term, here, of transmuting it. The upside and the
downside is that the fuel becomes progressively
more radioactive. It is not necessarily an
effective method of burning up fission products.
It is an integral part of the breeder reactor
concept. The following slides come from a
presentation by Robert Benedict of Argonne-West.
They deal with a non-aqueous method recycling
plutonium fuel of the type that EBR-II was
designed to burn. The process could be used for
LWR fuel also but not in such a closed loop
cycle. The process is based on electrochemically
separating the actinides from the fission
products in a 500?C molten sodium chloride bath
with a molten cadmium electrode in the bottom of
the melt. The process works in part because the
free energies of the various chlorides are
separated by significant gaps (see the free
energy chart.) The waste product (the fission
products in the chloride salt would be forced
into a zeolite matrix and sintered. A grandiose
scheme, but funding was terminated several years
ago.
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Transmutation Processes

• Neutron capture makes the nucleus more unstable
  (see the chart of the nuclides).
• High energy neutrons stimulate fission
• There are two processes, one in which the nucleus
  picks up neutrons and then becomes fissionable
  (U-238 gt Pu-239, for example) in the other, the
  high energy neutron adds energy necessary for
  prompt fission.
• Proton capture (makes the nucleus more stable).
• High energy gamma capture (triggers decay).

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What Kind of Systems

• Processes 1 and 2 (previous Slide) occur in LWR
  or BR (ANL, Japanese, European) whether intended
  or not, the degree to which it occurs (by design)
  may make the reactor a normal fission reactor, a
  breeder, or a transmutator.
• Processes 3 and 4 are accelerator based (ORNL and
  PNNL).
• The primary proposal to remove weapons grade Pu
  has been to use it as LWR fuel MOX, which is
  partially a transmutation process.

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Partitioning Objective
8
Partitioning Proposals

• Solvent extraction using molten metals as the
  solvent. Immiscible metal phases, or use a
  combination of molten metal and molten salt.
• Use distillation in molten metal or molten salt
  systems systems.
• Metal fuel, dissolve in some molten metal (zinc,
  magnesium, mercury, cadmium, silver.
• Rely on differences in solubility or volatility
  (see text book around p. 250).
• Take advantages of chloride chemistry instead of
  aqueous acid base chemistry.

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From Development of Partitioning and
Transmutation Technology for Long-Lived Nuclides,
Tadashi Inoue, et al., CREI (Japan)
This is just one partitioning option, but is
similar to the ANL-W.
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The Plan

• Assume metal fuel, as was used in the IFR, (as
  opposed to oxide fuels in the LWR BWR reactors).

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From http//itumagill.fzk.de/ADS/ITU/PT_final.ht
m Karlsruhe, Germany
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Why will it work?

• Because of the nature of chloride free energies
• Note in nest slide how the radionuclide free
  energies are clustered into noble metals, iron to
  zirconium, the actinides and rare earths, and the
  alkalis and alkali earths (Cs and Sr and their
  friends).
• Solubility of chlorides in cadmium note the big
  solubility differences in second future slide.
• Volatility of chlorides could be used to support
  distillation (third future slide).

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Conversion of Aqueous PUREX Wastes to Chlorides

• Denitration
• See the oxide to chloride Figure in the Japanese
  article

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The System

• Complete IFR Cycle.
• Disposal of some fission products in salt or
  salt-loaded zeolites.
• Not all fission or activation products are
  removed.
• Fast reactors are tolerant of contaminants in the
  fuel.

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For a color diagram of this, go to
http//www.nuc.berkeley.edu/designs/ifr/images/ifr
-concept.jpg
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Molten Metal Pyroprocessing

• The following slides were obtained from a 1991
  National Academy of Sciences document,
  GEFR-00898, Actinide Recycle Enhancement
• It describes a molten metal process supporting GE
  and ANLs Advanced Liquid Metal Reactor (ALMR)
  Design, to convert LWR oxide fuel to ALMR metal
  fuel for recycle.
• http//www.nuc.berkeley.edu/gav/almr/01.intro.htm
  l
• The ALMR would have had metal fuel and blanket
• The ALMR was to be a sodium cooled reactor

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Initial Spent Fuel Processing

• Disassemble grid spacers and end fittings.
• Chop fuel rods into short (1/2 1 in) pieces
• Alternatively subject the fuel segments to
  oxidative and reducing atmospheres at elevated
  temperature to loosen and fracture the fuel.
• Mechanically shake the fuel from the segments.
• Heating the chopped fuel removes iodine,
  carbon-14, and the fission gases.
• The metal waste will be combined with the electro
  refining (ER) waste.
• Kr and Xe are captured in a cryogenic process and
  loaded in pressurized tanks for storage and
  disposal.
• Iodine is captured on silver impregnated zeolite
  and C-14 is precipitated as calcium carbonate.
• Tritium is removed as tritiated water, absorbed
  on molecular sieves (zeolites), and packaged for
  disposal.

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Reprocessing

• The oxide fuel is dispersed in a molten (800 C)
  CaCl2 /CaF2 salt along with calcium metal and
  reduced to a metal.
• The reduced metals are dissolved in a molten Cu -
  40 Mg - Ca receiver alloy.
• Uranium exceeds the solubility limits in this
  receiver alloy and precipitates out as a solid
  metal.
• Pu, other actinides, rare-earths, and noble metal
  fission products accumulate in the receiver
  alloy.
• The the alkali metals (Rb and Cs), alkali-earths
  (Sr and Ba),and remaining iodine and bromine
  accumulate in the CaCl2/CaF2 salt.
• The salt contains CaO from the reduction process.
  The CaO is electrolytically reduced to metal for
  reuse.
• Some salt is drained off to prevent buildup of
  fission products.

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Similar, but not identical to that described on
the preceding slide.
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Recovering Plutonium

• The metals in the receiver alloy are removed by
  contacting the receiver alloy with a transport
  salt 50 MgCl2 - 30 NaCl - 20 KCl. Pu, Np,
  Am, and Cm are oxidized and displace the
  magnesium from the MgCl2, dissolve into the salt,
  and the Mg dissolves in the alloy.
• The salt which now contains Pu, Np, Am, and Cm,
  is contacted with an acceptor alloy of Cd-Mg,
  where they are reduced and go into solution, but
  no rare earths and noble metal fission products.
• Note this is just a solvent-solvent extraction
  process using 800 C molten salt and molten
  metals.

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Purification

• The actinides are separated from the acceptor
  alloys by distilling the Cd-Mg alloy.
• The electrorefining process described above is
  then used to purify the final metal uranium and
  actinide product.
• NO WATER ALLOWED!
• Because there is no water to enhance criticality,
  containers typically can have 20 or 30 kg of
  fissile material!

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EPILOGUE

• Breeder reactors were canceled because of the
  concern for a plutonium economy.
• IFR promised a plutonium economy without
  recoverable plutonium.
• IFR was canceled.
• France-England and Japan continue.
• Issues not discussed in this class.
• Reactivity
• Conversion efficiency
• Reactor design.