This document discusses the in-vessel components of fusion reactors, including blankets, shields, and divertors. It covers the functions and design challenges of these components for both magnetic and inertial confinement fusion. The blankets are used to breed tritium fuel and shield the core from neutrons, while divertors extract excess heat and particles from the plasma. Designing effective blankets and shields requires selecting appropriate breeding, cooling, and structural materials that can withstand high neutron fluxes and damage over many years of operation.

1. Introduction to Fusion
Technology Issues
. Lecture II
In-vessel components: Blanket,
shield, Divertor
Prof. Mohamed Sawan
Fusion Technology Institute
University of Wisconsin-Madison
1Lecture IIM. Sawan

2. Outline
• In-Vessel Components
• Magnetic Confinement Blanket,
Shield, Divertor
• Inertial Confinement Blanket, Shield
M. Sawan 2Lecture II

3. MFE and IFE Fusion Reactors are
Complex with Many Components
MFE IFE
M. Sawan 3Lecture II

4. Components of a Tokamak
Reactor
M. Sawan 4Lecture II

5. Breeding Blanket Functions and
Requirements
M. Sawan Lecture II 5

6. Example Fusion Power Flow
M. Sawan Lecture II 6

7. Energy Distribution in Blanket and
Divertor Zones
M. Sawan Lecture II 7

8. M. Sawan 8Lecture II

9. M. Sawan Lecture II 9
Typical Radial Build in MFE Reactor

10. Tritium Breeding in Lithium
10
Two Reactions:
6Li(n,a)t
• Low energy
• Multiplier helps
7Li(n,n’a)t
• High energy
• Competes with
multiplier
• Produces additional
neutron along with
breeding
M. Sawan Lecture II

11. Fusion Facilities beyond ITER Should Breed
Their Own Tritium
 Almost all tritium supply will be used by ITER and FNSF has to be self-
sufficient in tritium in addition to providing initial startup inventory for DEMO
11M. Sawan Lecture II

12. 12
Tritium Breeding Potential of Candidate
Breeders
 Li and LiPb have highest
breeding potential
 Breeders with moderate
breeding potential (Li2O, Flibe)
require moderate amount of
multiplier
 Ceramic breeders have poor
breeding potential and require
significant amount of multiplier
and minimal structure content
 Enriching Li in 6Li is beneficial
when a multiplier is used
 In realistic designs, the
structure, configuration, and
penetrations will degrade the
achievable overall TBR below
the values shown
M. Sawan Lecture II

13. Blanket Breeding Materials
M. Sawan Lecture II 13

14. Issues for Blanket Breeders
M. Sawan Lecture II 14

15. Neutron Multipliers
M. Sawan Lecture II 15

16. Issues for Neutron Multipliers
M. Sawan Lecture II 16

17. Component Damage and Lifetime
M. Sawan Lecture II 17

18. Low Activation Structural Materials
for Fusion
18
Based on safety, waste
disposal and
performance
considerations, the 3
leading candidates are:
Ferritic/martensitic steels
Vanadium alloy
SiC/SiC composites
Lecture IIM. Sawan

19. Issues for Structural Materials
M. Sawan Lecture II 19

20. Blanket Coolants
M. Sawan Lecture II 20

21. SiC/LiPb Blanket Designs
M. Sawan Lecture II 21

22. Helium Cooled Pebble Bed Blanket
M. Sawan Lecture II 22

23. Helium Cooled Lithium Lead Blanket
M. Sawan Lecture II 23

24. Dual Coolant Lithium Lead Blanket
M. Sawan Lecture II 24

25. M. Sawan Lecture II 25

26. M. Sawan Lecture II 26

27. M. Sawan Lecture II 27

28. M. Sawan Lecture II 28

29. Divertors
• To first order, particles
are confined to the
closed field lines
• A divertor uses a
“separatrix” to separate
closed from open field
lines
• W is the lead plasma
facing material with
Carbon Based material
as alternate (retains T)
M. Sawan 29Lecture II

30. Particle Load Summary
• Particles strike walls, leading to sputtering
• Sputtered particles will be pumped or
deposit somewhere in the chamber
• Key issues are
– Particle flux and spectrum
– Sputtering rate and mechanism
– Transport and deposition throughout chamber
M. Sawan 30Lecture II

31. The ITER Divertor
M. Sawan 31Lecture II

32. Candidate Plasma Facing Materials
M. Sawan Lecture II 32
From: V. Barabash, et al., “Selection, Development and Characterization of Plasma Facing Materials for
ITER,” Journal of Nuclear Materials, Vol. 233-237, pp. 718-723 (1996).

33. IFE Chamber Requirements
Establish at a rep rate 1-10 Hz chamber conditions to
allow target injection (or placement in the case of Z-IFE),
beam propagation andengagement at specifications
needed for ignition and high gain (unique for IFE)
Protect the first wall from pulsed, short-ranged target
emissions (x-rays and ion debris), e.g., from intense
thermal spikes and ion damage, or design the FW to
accommodate these threats (unique for IFE)
Capture and transfer power to power conversion system
Breed, recover and recycle tritium to provide a self-
sustained fuelCycle. For IFE, adequate tritium breeding is
typically not the most constraining requirementM. Sawan 33Lecture II

34. Three Categories of IFE Chamber Design
• Dry-wall
– Gas protected
– Magnetically protected
– Engineered surface
• Wetted-wall
• Thick-liquid-wall
M. Sawan 34Lecture II

35. Blanket Design in IFE Chamber
 Blanket design options used in MFE can be
used in IFE
 Surface heat flux is higher at FW in IFE
requiring more attention and using liquid
walls is an attractive option
 Flowing liquid metals can be utilized due to
lack of MHD effects
 Space is not constrained allowing using
thicker blankets with potential for higher TBR
M. Sawan 35Lecture II

36. Target Neutronics
• Initial split of energy from DT fusion energy is 14.1 MeVn and a
3.5 MeVa
• In IFE target, DT fuel is heated and compressed to extremely
high densities before ignition and neutron fuel interactions
cannot be neglected
• Softening of neutron spectrum, neutron multiplication, and
gamma production occur
• Energy deposited by neutrons and gamma heats target and
ultimately takes the form of radiated x-rays and expanding
ionic debris
• Spectra of neutron and gamma photons emitted from the
target represent the source term for subsequent blanket
neutronics, shielding, and activation calculations
M. Sawan 36Lecture II

37. Energy Spectra of Source Neutrons and
Gammas from HAPL Target
Target spectrum from LASNEX results (Perkins, LLNL)
M. Sawan 37Lecture II

38. HAPL Blanket Thermal Power
for 1836 MW Fusion Power (5 Hz Rep Rate)
Total Thermal Power 1878 MW
Volumetric
Nuclear
Heating
1548 MW
Ion Energy
Dissipation
307 MW
X-rays
Surface
Heating
23 MW
 Blanket coverage 91.6%
 Target yield 367.1 MJ (274.3 n, 0.017 , 4.94 x-ray, 87.84 ions)
 70% of ion energy dissipated resistively in blanket
• Thermal power in water-cooled 50 cm thickshieldis only3 MW
M. Sawan 38Lecture II

39. Examples of Recent Chamber Designs
M. Sawan 39Lecture II

40. Dry Wall Examples
M. Sawan 40Lecture II

41. Wetted Wall Examples
M. Sawan 41Lecture II

42. Thick Liquid Wall Examples
M. Sawan 42Lecture II

43. Impact of Wall Protection Scheme on
Neutronics Features
• Various IFE wall protection methods influence the FW/blanket
design and neutronics features
– Dry wall (e.g., SOMBRERO, SIRIUS-P)
– Wetted wall (e.g., HIBALL, PROMETHEUS-L)
– Liquid wall (e.g., HYLIFE)
• Blanket neutronics features of dry wall and wetted wall designs are
identical since thin liquid sheet in wetted wall provides negligible
neutron attenuation
• Thick liquid wall concepts have different neutronics features due to
protection of blanket structure by thick liquid layer and elimination
of structure in thick breeding liquid layer
M. Sawan 43Lecture II

44. Biological Shield Requirement
• Biological shield is needed outside the chamber to maintain occupational biological
dose rate <25 mSv/houtside building during operation
• Required shield thickness depends on location of shield and material used in
components between target and shield
• 2.5-3.5 m thick steel re-enforced concrete shield is needed
• If allowed by maintenance approach, significant reduction in shield volume and cost
is realized by placing the biological shield as close as possible to the chamber
LIBRA-SP
1.2 m FS/LiPb blanket
M. Sawan 44Lecture II

45. Beam Line Penetration Shielding
Penetrations in IFE chamber required for ions or laser
transport from driver to target
Measures must be taken to protect the vital components
from streaming radiation
Shielding issues are different for the two drivers considered
• Laser
• HIB
M. Sawan 45Lecture II

46. Shielding of Final Optics in Laser Driven IFE
• Final laser optics located in direct line-of-sight of source neutrons experience
largest radiation damage
• Damage level in these components can be reduced only by moving them
farther from target
• Damage contributed mostly by direct source neutrons
Dielectric coated mirrors
Sensitive to neutron radiation that degrades optical transmission of
dielectric material, decomposes dielectric materials, and destroys interfaces
between dielectric layers
Removing them from line-of-sight of target neutrons prolongs their lifetime
Grazing incidence metallic mirrors (GIMM)
More radiation resistant and can be used in direct line-of-sight
Lifetime of GIMM is limited by mirror deformation from swelling and creep
that leads to defocusing of laser beam
M. Sawan 46Lecture II

47. SOMBRERO Building
Lifetime of dielectric
coated FF mirror
increases with trap aspect
ratio, distance from
target, and neutron
fluence limit
M. Sawan 47Lecture II

48. 48
Final Optics in HAPL
Bio-Shield
Turning (M3)
GIMM (M1)
Beam Duct
Focusing (M2)
Shield
Blanket
M. Sawan Lecture II

49. 49
Fast Neutron Flux Distribution in Final Optics of HAPL
SiC GIMM
M2M3
Flux(n/cm2s)
M. Sawan Lecture II

50. Shielding of Final Focusing Magnets in HIBALL
• Final focusing system consists of set of quadrupole magnets (usually superconducting)
• Shielding provided between the ion beam and the final focusing magnets
• Shield configuration should not interfere with the ion beam envelope
Effective shield configuration
developed for HIBALL and utilized in
OSIRIS
Radiation effects in magnets can be
reduced by about three orders of
magnitude by tapering inner surface
of shield along direct line-of-sight of
source neutrons
All direct source neutrons impinge on
neutron dumps at optimized location
that minimizes magnet damage
Magnets are lifetime components
M. Sawan 50Lecture II