Neutronics Plans and Status

1
Neutronics Plans and Status

• Mohamed Sawan
• Fusion Technology Institute
• The University of Wisconsin

FIRE Project Meeting November 7,8, 2002 PPPL
2
Impact of New Design on Neutronics Parameters

• Several design parameters changed as FIRE moved
  from the 2-m machine to the 2.14-m machine
• As a starting point for iteration with other
  design tasks neutronics parameters are scaled for
  the new machine design parameters
• To obtain initial preliminary neutronics
  parameters radial build was assumed not to
  change. Change in IB FW/tiles thickness from 25
  to 38 mm is the only observed change in the
  current design. This increase is mainly to
  accommodate diagnostics and might not impact TF
  shielding

3
Changes in Machine Parameters
4
Scaling of Neutronics Parameters

• FW radii increased by 7 cm IB and 21 cm OB
• Height increased by 14 cm for same plasma
  elongation
• FW area increases by 21
• Average neutron wall loading for DT pulses with
  largest power of 150 MW is reduced by a factor of
  0.62
• Average NWL was 3 MW/m2 for 200 MW DT pulse
• Average NWL in current machine is 1.85 MW/m2
• All parameters that scale with neutron wall
  loading such as flux, nuclear heating, damage
  rates, dose rates, decay heat, etc will reduce by
  38

5
Impact on Cumulative Neutronics Parameters

• Goal is a combined total fusion energy of 5 TJ DT
  and 0.5 TJ DD
• Fluence dependent parameters (e.g., cumulative
  radiation damage, insulator dose, and radwaste
  classification) depend on cumulative FW fluence
  (MW-yr/m2) not fusion energy and will reduce due
  to larger FW area
• Cumulative neutronics parameters reduce by a
  factor of 0.83

6
Impact of Tritium Burnup in DD Pulses

• 2 tritium burnup in DD pulses results in
  production of 14 MeV neutrons while reducing
  number of 2.45 MeV neutrons by 4.8
• 14 MeV neutrons produced are only 2 of the 2.45
  MeV neutrons produced in DD pulses with
  negligible impact on nuclear heating, etc during
  1MW DD pulses. This is only 0.03 of neutrons
  produced in 150 MW DT pulse
• For 5 TJ DT 1.77x1024 14 MeV neutrons produced
• For 0.5 TJ DD 4.07x1023 2.45 MeV and 8.15x1021 14
  MeV neutrons produced
• Impact on fluence dependent parameters is
  negligible

7
Peak Nuclear Heating (W/cm3) for 150MW DT Shots

• For DD pulses with largest fusion power (1 MW),
  neutron wall loading is a factor of 0.003 of that
  for the DT pulses
• Nuclear heating values are at least two orders of
  magnitude lower

8
Nuclear Heating in OB FW/Tiles
Nuclear Heating in OB VV at Midplane
9
Nuclear Heating in Outer Divertor Plate
10
Radial Variation of Nuclear Heating in IB TF at
Midplane
11
Cumulative Damage in FIRE Components reduced by
17

• Peak end-of-life cumulative radiation damage
  values in FIRE components are very low lt 0.03 dpa
  
• He Production in VV lt 1 appm Allowing for
  Rewelding

12
Cumulative Peak Magnet Insulator Dose( 5 TJ DT
Shots and 0.5 TJ DD Shots)
13
Radiation Induced Resistivity in Cu

• Cumulative dpa and fluence in Cu TF coils reduced
  by 17
• Component of resistivity increase from
  transmutation products reduces by 17
• Reduction in dominating resistivity increase from
  displacement damage is smaller because of
  non-linear relation with cumulative dpa.
  Reduction is 12 at front and 17 at back

14
Impact on Activation Results

• Activity and decay heat values at shutdown are
  almost fully dominated by activation during the
  last pulse
• Short term activity, decay heat, and dose rate
  following DT pulses are reduced by 38
• Activity and decay heat generated following D-D
  shots are more than three orders of magnitude
  lower than the D-T shots
• Following DT shots hands-on ex-vessel maintenance
  is possible with
• The 110 cm long steel shield plug in midplane
  ports
• The 20 cm shield at top of TF coil
• Following DD shots immediate access for
  maintenance is possible behind OB VV
• WDR reduced by 17 and all components still
  qualify as Class C LLW (largest WDR is 0.15 for
  OB FW)

15
Plans for FY03

• (1) Perform self-consistent analysis for the 2.14
  m machine
• Update nuclear parameters for the machine
  components (e.g., FW/tiles, VV, divertor,
  magnets)
• This task involves significant iteration with
  other design tasks to converge on a
  self-consistent design
• This task is already underway and preliminary
  results are presented

16
Plans for FY03(Continued)

• (2) Assess the impact of operation schedule and
  possible operation extension on key nuclear
  parameters such as insulator dose
• Dose was calculated for 5 TJ DT and 0.5 TJ DD
• Plans for higher fusion energy are being
  considered
• We need to make sure that the insulator dose does
  not limit that possible extension
• Include 14 MeV neutrons generated during DD
  pulses
• Define required spectra (neutron and gamma) for
  irradiation experiments to properly simulate FIRE
  conditions

17
Plans for FY03(Continued)

• (3) Investigate the effect of 3-D geometry on
  peak insulator dose and other Parameters at IB
  midplane
• Insulator dose is based on 1D model with plasma
  extended uniformly to infinity in the vertical
  direction
• This affects the angular distribution on neutrons
  incident on FW
• Comparison between 1D and 3D results in ARIES
  showed that 1D could overestimate radiation
  damage close to FW by 20-50
• Will perform simple 3D calculations with
  emphasize on conditions at midplane where the
  worst parameters occur. Model does not have to
  include details for other components away from
  midplane
• This tasks starts in April after we get a new
  drawing with revised radial build

18
1-D Neutronics Yield Conservative Peak FW Damage
Parameters

• 3-D results were compared to 1-D results for
  ARIES-ST and ARIES-AT
• 1-D calculations overestimated peak damage
  parameters at FW by up to a factor of 1.6
  depending on the aspect ratio

19
Plans for FY03(Continued)

• (4) Estimate nuclear environment at sensitive
  diagnostics components
• Due to limited resources estimates will be based
  on 1D calculations and appropriate extrapolation
• Calculate the neutron and gamma fluxes and
  absorbed doses for the sensitive components (e.g.
  silica and alumina) at selected locations
• As starting point results given in memo of
  2/25/2002 are to be scaled for new parameters
• Identify a few cases where streaming is critical
  and perform simple 2D calculations

20
Assumed Radial Build
21
Radial Build of FW/Tiles

• Radial build and composition of FW/tiles
• 5 mm Be PFC (90 Be)
• 18 mm Cu tiles (80 Cu)
• 2 mm gasket (50 Cu)
• 25 mm water cooled Cu vessel cladding (80
  Cu, 15 water)

22
Radial Build of Outer Divertor Plate
23
Radial Build of VV

• 1.5 cm thick inner and outer 316SS facesheets
• Space between facesheets includes 60 304SS and
  40 water except in IB region where 11 304SS and
  89 water is used
• VV thickness
• IB midplane 5 cm
• OB midplane 54 cm
• Divertor 12 cm
• 1.5 cm layer of thermal insulation (10
  Microtherm insulation) attached to back of
  coil-side VV facesheet

24
TF Coil Model

• Baseline design with 16 wedged TF coils analyzed
• BeCu used in inner legs and OFHC in outer legs
• 90 packing fraction used in coils
• 304SS coil case used in OB region with 4 cm front
  and 6 cm back thicknesses