The Neutronics of

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The Neutronics of Heavy Ion Fusion Chambers
Jeff Latkowski and Susana Reyes 15th Heavy Ion
Inertial Fusion Symposium Princeton, NJ June 9,
2004 Work performed under the auspices of the U.
S. Department of Energy by Lawrence Livermore
National Laboratory under Contract W-7405-Eng-48.
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Neutron transport affects a varietyof components
and raises a set of issues
FinalFocusMagnets
First Structural Wall
Hohlraum
Liquidblanket
Capsule
Blanket
Radius
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Neutron transport affects a varietyof components
and raises a set of issues
Neutron energymultiplication
Isochoric heating
Neutron activation
Radiation damage
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Neutron transport affects a varietyof components
and raises a set of issues
Output spectra
Neutron energymultiplication
Boosts power above (10-20 fusion output typical)
Isochoric heating
Neutron activation
Radiation damage
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Neutron transport affects a varietyof components
and raises a set of issues
Neutron energymultiplication
Affects liquid break-up chamber clearing
Isochoric heating
Imparts stresses to the first structural wall
other components
Neutron activation
Radiation damage
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Neutron transport affects a varietyof components
and raises a set of issues
Neutron energymultiplication
Isochoric heating
Tritium breeding
Transmutation products
Neutron activation
Radiological safety
Waste management
Radiation damage
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Neutron transport affects a varietyof components
and raises a set of issues
Neutron energymultiplication
Isochoric heating
Neutron activation
Component performance
Maintenance requirements
Radiation damage
Component lifetime
Waste management
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In selection of a liquid, thetritium breeding
ratio is a key issue

• TBR of 1.1 is needed to cover uncertainties and
  losses
• Decay
• Leakage
• 3-D effects
• Nuclear data
• Dont want to begtgt1.1, but relatively easy to
  reduce theTBR

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Liquid thicknesses are selected to provide
adequate protection to the first structural wall

• Lifetime limits (in displacements per atom) for
  structural materials of interest
• SS304 25 dpa(0.83 dpa/y)
• ODS-FS 200 dpa(6.7 dpa/y)
• 304-PCA might be a path to ?100 dpa

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Reweldability is desirable but probably not
achievable for wall at reasonable thicknesses

• Reweldability limit (issue is cracking) is 1 appm
  He
• Welding to 10 appm He may be possible with stress
  modified welding technique

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The waste disposal rating (WDR) is a measureof
the level of activation within a component

• WDR is calculated as the ratio of concentration
  to a concentration limit, summed over all
  radionuclides
• WDR lt1 indicates disposal via shallow land burial
  possible

WDR for SS304 first structural wall after 30 FPY
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The waste disposal rating does not uniformly
decrease with increasing liquid thickness
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The neutron spectrum changes considerablyin its
magnitude but only a little in its shape
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The waste disposal rating is a measureof the
level of activation within a component

• WDR peaks after 10 years of irradiation
• Beyond the peak, 98Mo depletion occurs and WDR
  begins to fall
• 93Nb depletion occurs even earlier

WDR during irradiation for SS304 wall behind 30
cm of flinabe
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The waste disposal rating does not uniformly
decrease with increasing liquid thickness
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Radiation damage to and transmutationof the
first structural wall

• An important issue for fusion is the ratio of the
  He production rate to the displacements per atom
  (dpa) rate
• Fission-based neutron sources do not produce
  nearly as much helium as is produced in a fusion
  system (0.1 appm He/dpa)
• For a dry wall fusion system 10 appm He produced
  for each dpa
• Leaves fission-based neutron sources as
  inappropriate tools for study of dry wall fusion
  neutron damage
• The use of thick-liquids, however, significantly
  increases opportunities for the use of currently
  available fission-based neutron sources ? main
  advantage is not a change in the He/dpa ratio,
  but in the reduction of the dpa rate, which
  allows accelerated damage testing

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An important issue is the ratioof He production
rate to dpa rate
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It is possible to alter He/dpa ratioin existing
irradiation facilities

• Greenwood Graczyk report enhanced He production
  from 55Fe in ferritic materials ? can
  isotopically enrich samples (expensive)
• Longest et al. began use of Hf shields in HFIR to
  achieve 14 appm He/dpa ? gives desired ratio, but
  reduces overall damage transmutation rates
• Investigation of other dopants or other means to
  alter the He/dpa ratio is warranted

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Summary

• There are a variety of neutronics issues that
  must be considered for heavy ion fusion systems
• Neutron interactions in the target
• Neutron activation transmutation reactions
• Isochoric heating
• Radiation damage
• The various technical issues strongly affect
  important areas of power plant operation
• Chamber clearing
• Radiological safety
• Component reliability performance
• Waste management
• Economics