Safety and Environmental Assessment for Laser IFE

1
Safety and Environmental Assessment for Laser IFE

• S. Reyes, J. F. Latkowski
• Lawrence Livermore National Laboratory

Laser IFE Meeting November 13-14, 2001 Crowne
Plaza Hotel, Pleasanton, CA Work performed
under the auspices of the U. S. Department of
Energy by University of California Lawrence
Livermore National Laboratory under Contract
W-7405-Eng-48
2
LLNL is addressing critical issues for laser IFE
safety and environment

• Safety and environmental attractiveness is a key
  requirement for the success of laser IFE
• We are using the SOMBRERO laser driven conceptual
  design to perform safety and environmental
  analyses
• Design uses a low activation material (C/C
  composite) for chamber structures
• Xe gas atmosphere used to protect FW from target
  emissions

• Blanket consists of a moving bed of solid Li2O
  particles flowing in a He carrier gas through the
  chamber

3
We have recently performed analyses to address
key safety issues

• Oxidation of graphite chamber structures may be a
  concern in case of air ingress event (reaction
  rate seems to be significant even at T ? 1000 ºC)
• passive safety feature should be easy to
  implement (inert gas released from tank by
  rupture disk failure when a differential pressure
  is reached)
• protective coatings for C/C composites (Si-B-C
  coatings)
• alternative materials for FW and/or blanket
  structures
• The activation products for Xe are the main
  contributors to accident dose, possible solutions
  are
• removal of I and Cs by the chamber vacuum system
• alternative gas such as Kr
• Other than Xe, the most important contributor to
  accident dose is the HTO
• tritium trapped in FW/blanket may be greater than
  1 kg (need experimental data)
• simple modifications in the confinement building
  material would enhance HTO condensation on walls,
  reducing off-site dose

4
We are currently assessing waste management
options for laser IFE

• The importance of safe handing of radioactive
  waste for the protection of human health and the
  environment has long been recognized
• Traditionally, studies for IFE have used Waste
  Disposal Rating (WDR) as the preferred waste
  management index
• WDR lt 1 means that radioactive material qualifies
  for shallow land burial
• Even in the case of low activation materials,
  there are concerns about space limitations and
  negative public perception of large volumes of
  waste
• There is a growing international motivation to
  develop a fusion waste management system that
  maximizes the amount of fusion materials that can
  be unconditionally cleared or recycled

5
The concept of clearance allows for new waste
management options

• The IAEA has proposed clearance levels for
  radioactive waste below which regulatory control
  may be relinquished
• Clearance implies that radiation hazards
  associated are trivial so that the final
  destination of materials (recycle, reuse, surface
  disposal) is not known in advance
• We have implemented the calculation of Clearance
  Indexes (CIs) using current IAEA clearance
  limits
• The CI for a material containing n different
  nuclides is calculated as
• CI ? An/Ln
• where An is the activity due to the nuclide and
  Ln is the clearance limit for the nuclide
• CI 1 means it is possible to clear the material

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We have calculated Clearance Indexes for the
SOMBRERO design

• We have upgraded the neutron activation code ACAB
  to include a new subroutine for calculation of
  CIs

• A detailed 3-D model of SOMBRERO has been used
  for neutron transport calculations
• We have used ACAB to simulate activation of
  materials after 30 years-operation
• Results have been obtained for WDRs and CIs for
  every plant component and for every isotope

SOMBRERO 3-D model for neutronics analysis
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Results show that SOMBRERO meets criteria for
shallow land burial

• The first wall and blanket easily meet waste
  disposal rating criterion of WDR lt 1
• The concrete building also meets criterion,
  although it represents a volume of ? 105 m3
• Due to their exposure to line-of-sight neutrons,
  the neutron dumps have the highest WDR (? 0.5)
• However, the neutron dumps are unimportant from
  the waste volume perspective (they are 0.1 of
  the building shell volume)

8
We have obtained CIs for every component for up
to 100 years of cooling

• Neither component qualifies for clearance,
  however the concrete building has the lowest
  index
• Ability to clear the building would be highly
  beneficial because of the enormous waste volume
  that it represents

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Calculations have been performed for alternative
building materials and thickness

• Concrete composition should avoid critical
  isotopes from waste point of view (long-lived
  nuclides)
• Increasing the thickness of the walls reduces
  clearance index but increases total plant cost

10
Laser IFE presents unique challenges to the
development of structural materials

• All materials in a fusion power plant are subject
  to SE considerations
• Ideally, a material would be cleared
  unconditionally following its lifetime in the
  power plant
• If clearing is not possible then recycling is the
  second option
• criterion for remote recycling is the contact
  dose rate (CDR), which must be lt 20 mSv/h
  following 50 years of radioactive decay
• hands-on recycling would require a CDR below 25
  mSv/h
• If a material is not eligible for recycling the
  next best option is disposal via shallow land
  burial, which is evaluated using the WDR
• Finally, a material must meet the accident safety
  criterion (dose lt 10 mSv) so that it does not
  result in an unacceptably high accident dose

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We intend to provide SE guidance for target and
chamber designers

• We have performed analyses in order to provide
  guidance for selection of chamber and target
  materials from a SE perspective
• CDR and WDR results have been obtained for all
  naturally occurring elements from lithium to
  bismuth at the SOMBRERO chamber wall
• using the elemental values in the table, one can
  derive an approximate value for an actual
  material
• the table does not include results for accident
  doses given that these are accident- and
  material-dependent
• Target materials have been evaluated in a similar
  manner
• CDR criterion for dose is that recycling
  equipment could withstand 30 Mgy
• WDR is evaluated in the same way as for chamber
  wall
• accident dose is evaluated using a dose limit of
  5 mSv (the other 5 mSv is allocated to tritium
  releases) and release fraction calculated with
  MELCOR

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Environmental indices resulting from neutron
activation of potential IFE chamber materials
Element CDR (Sv/hr) WDR Element CDR (Sv/hr) WDR Element CDR (Sv/hr) WDR Element CDR (Sv/hr) WDR
Li 0.00E00 0.00E00 V 8.23E-09 1.94E-09 Ru 6.80E-04 1.88E02 Tb 4.69E02 1.81E05
Be 0.00E00 2.95E-05 Cr 3.86E-11 1.43E-11 Rh 3.81E-01 1.01E02 Dy 3.69E-01 8.32E02
B 0.00E00 8.23E-04 Mn 3.20E-12 1.64E-13 Pd 4.82E-01 1.61E02 Ho 9.56E01 3.88E05
C 0.00E00 1.23E-03 Fe 4.00E-04 1.04E-05 Ag 1.20E02 3.52E04 Er 1.79E-01 7.54E02
N 0.00E00 6.43E00 Co 4.83E02 3.49E-01 Cd 4.13E-02 9.16E00 Tm 4.87E-02 2.14E02
O 1.68E-34 5.73E-03 Ni 8.25E00 5.35E-01 In 5.79E-06 2.09E-04 Yb 2.10E-04 2.10E-02
F 4.10E-25 6.04E-04 Cu 4.91E00 3.34E-01 Sn 1.13E-03 9.79E-02 Lu 1.16E-01 3.05E-06
Ne 8.33E-10 2.05E-03 Zn 5.21E-03 1.97E-02 Sb 2.36E-04 5.78E-03 Hf 3.65E-05 2.78E-01
Na 4.64E-03 4.87E-07 Ga 1.04E-10 1.24E-06 Te 3.02E-05 1.55E00 Ta 5.70E-07 4.20E-03
Mg 8.45E-07 6.01E-06 Ge 1.87E-11 8.34E-06 I 3.80E-07 7.21E-04 W 4.33E-07 4.21E-02
Al 1.26E-02 1.83E01 As 7.45E-19 4.12E-06 Xe 1.28E00 9.76E-02 Re 1.21E-04 1.28E01
Si 1.45E-06 1.87E-03 Se 4.06E-08 1.79E01 Cs 1.16E-01 3.35E-04 Os 1.42E-02 1.38E02
P 2.24E-07 3.92E-04 Br 7.62E-05 1.00E00 Ba 1.98E00 1.26E-02 Ir 7.70E00 7.71E04
S 2.78E-10 1.91E-02 Kr 5.39E-01 1.99E00 La 1.40E-03 5.29E-02 Pt 3.88E-04 3.76E00
Cl 3.24E-12 8.98E00 Rb 2.29E-02 3.43E-05 Ce 4.07E-04 8.16E-02 Au 5.32E-07 3.01E-03
Ar 3.07E-07 7.42E00 Sr 1.92E-03 8.05E-04 Pr 4.88E-08 5.32E-04 Hg 2.21E-06 8.78E-03
K 2.05E-05 4.93E00 Y 3.14E-06 8.99E-06 Nd 2.91E-02 1.66E-03 Tl 1.40E-08 1.70E-04
Ca 4.71E-05 2.55E-01 Zr 5.12E-04 1.13E00 Sm 3.19E01 2.78E-01 Pb 3.92E-05 4.55E-02
Sc 2.03E-03 5.24E-04 Nb 2.58E01 7.62E04 Eu 1.05E04 1.52E02 Bi 8.81E00 5.15E03
Ti 3.13E-04 6.22E-05 Mo 9.64E-02 5.80E03 Gd 1.66E00 4.80E02
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Safety and environmental results for potential
target materials
Element Code Element Code Element Code Element Code
Li P V C Ru CW Tb CW
Be P Cr C Rh CW Dy W
Be P Mn C Pd CW Ho W
C P Fe C Ag CW Er CW
N W Co CA Cd CW Tm CW
O P Ni CWA In C Yb P
F P Cu C Sn P Lu C
Ne P Zn C Sb C Hf C
Na C Ga P Te CWA Ta C
Mg C Ge C I C W C
Al CW As C Xe C Re CW
Si P Se CW Cs C Os CW
P P Br CWA Ba C Ir CW
S P Kr W La P Pt W
Cl W Rb C Ce C Au C
Ar W Sr C Pr P Hg P
K W Y C Nd C Tl C
Ca W Zr C Sm CW Pb P
Sc C Nb CW Eu CWA Bi CW
Ti C Mo CW Gd W

• C failed contact dose rate criterion (dose lt
  30 MGy for 30 years, continuous exposure)
• W failed waste management criterion (WDR lt 1)
• A failed accident dose criterion (early dose lt
  5 mSv for 0.3 release)
• P passed all criteria

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Conclusions (I)

• There are key safety issues for laser IFE
• Oxidation of chamber structures during accidents
• Activation of gas Xenon
• Tritium retention in FW and blanket
• Although all the components in SOMBRERO qualify
  for shallow land burial, this option is not very
  attractive given the enormous waste volumes
  involved
• Clearance of the confinement building would
  greatly reduce the total volume of waste to be
  buried, allowing for recycling or reusing of the
  material

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Conclusions (II)

• We have generated SE results for all naturally
  occurring elements from lithium to bismuth to
  provide guidance to chamber and target designers
• For chamber structures one can derive an
  approximate value for an actual material using
  the elemental values and densities
• For target materials, the most limiting criterion
  is the CDR, however, the list can be increased
  either by
• increasing the limit through use of radiation
  hardened components or through periodic
  change-out of failed components
• decreasing the CDR value of each element by
  extending the radioactive decay time

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Future work

• As part of LLNL chamber work, we will continue to
  address safety and environmental issues for
  laser IFE
• Alternative chamber concepts call for
  modifications in the baseline SOMBRERO design,
  which will have to be re-assessed from the safety
  and environment perspective
• As an example, magnetic deflection schemes for
  wall protection from ion damage will require new
  neutron activation calculations for the magnets
• Still much work to do on target fabrication
  facility safety