Transcript Radiation Environment at Final Optics of HAPL Mohamed Sawan

Radiation Environment
at Final Optics
of HAPL
Mohamed Sawan
Fusion Technology Institute
University of Wisconsin, Madison, WI
HAPL GIMM Conference Call
February 15, 2006
1
Design Parameters for Baseline HAPL Design
Target yield:
350 MJ
Rep Rate:
5 Hz
Fusion power:
1750 MW
70% of target yield carried by neutrons with 12.4 MeV average energy
Chamber inner radius
10.75 m
Chamber outer radius
12.25 m
NWL @ FW
0.9 MW/m2
GIMM angle of incidence 85°
GIMM distance from target 24 m
GIMM dimensions
3.4 m x 4.05 m
Previous 3-D neutronics calculations performed for final optics
SIRIUS-P with KrF laser and Aluminum GIMM
[M. Sawan, "Three-Dimensional Neutronics Analysis for the Final Optics of the Laser Fusion Power Reactor SIRIUS-P," Proc.
IEEE 16th Symposium on Fusion Engineering, Champaign, IL, Sept. 30- Oct. 5 1995, IEEE Cat. No. 95CH35852, Vol. 1, pp. 29]
Modified version of SOMBRERO with DPSSL and fused silica transmissive
wedges
[S. Reyes, J. Latkowski, and W. Meier, "Radiation Damage and Waste Management Options for the SOMBRERO Final Focus
System and Neutron Dumps”, UCRL-JC-134829, August 1999]
2
 A preliminary estimate of nuclear environment at final optics of HAPL
will be determined by scaling from results of SIRIUS-P
Previous Analysis of SIRIUS-P
SIRIUS-P design parameters used in calculation
2444 MW fusion power
Chamber radius 6.5 m
Blanket/reflector (SiC/Li2O/TiO2) 1.5 m
Internal concrete wall (1.5 m thick) @ 10 m radius
GIMM @ 25 m and FF mirror @ 40 m
GIMM diameter 5 m
GIMM angle of incidence 85°
Containment building @ R = 42 m
Trap diameter 1.3 m and depth 4 m
Containment building is 1.2 m thick increasing to
3.3 m behind neutron trap
GIMM thickness and material in SIRIUS-P
• Total thickness 24 cm thick with front and rear 2 cm thick zones modeled separately
• Front and rear zones have 75% Al6061 and 25% water
• Middle honeycomb structure is 20 cm thick with 0.833 g/cc Al
3
Observations from SIRIUS-P results
• Fast neutron flux at GIMM is contributed mostly by direct source neutrons (only ~4%
from secondary neutrons)
Calculating flux @ GIMM is straightforward
• 50% of flux at FF dielectric mirror contributed by neutron scattering from the GIMM
Relative flux values at FF dielectric:
With trap and GIMM scattering
With trap and transparent GIMM
Without trap and transparent GIMM
In direct line-of-sight of target
1
0.5
10
100
At most a factor of 2 reduction in dielectric mirror flux can be achieved by
reducing GIMM scattering
• Using neutron traps behind the GIMM in the direct line-of-sight of source neutrons
significantly reduces the flux at the FF mirror. Largest reduction is obtained when FF
mirror is placed as close as possible to the containment wall (factor of 3 less
compared to close to trap opening)
• Inclining sides of neutron trap along the line-of-sight of direct source neutrons such
that all source neutrons impinge on bottom of trap reduces chance of secondary
neutrons scattering back from the trap
Geometric considerations more effective for reducing dielectric mirror flux
4
Scaling from results for SIRIUS-P to HAPL Conditions
Fusion power (MW)
1750
GIMM radial location (m)
24
Fast neutron (E>0.1 MeV) flux @ GIMM (n/cm2s)
8.9x1012
(only 4% from secondary neutrons)
Fast neutron fluence per year @GIMM assuming 80%
availability (n/cm2)
2.3x1020
Radial location of dielectric FF mirror (m)
40
Fast Neutron (E>0.1 MeV) Flux @ FF mirror (n/cm2s)
4.3x1010
Fast neutron fluence per year @FF mirror assuming 80%
availability (n/cm2)
1.1x1018
• Assumed similar “open” configuration as in SIRIUS-P
• If beam ducts are used for vacuum and tritium
containment, both components of flux @ FF mirror
(scattering from trap and GIMM) increase and the %
contribution from GIMM scattering increases
• GIMM scattering contribution depends on material
composition, thickness, and size. Effective thickness
seen by neutrons is 11.5 times (1/cos85) the actual
thickness
5
• Flux at lens depends on scattering at the duct inner walls
What can we do to reduce flux at dielectric mirror and lens?
• Use as thin and small size GIMM as possible with minimal support structure
• Use of low density and less scattering, more absorption GIMM material is
preferable (e.g., He cooling instead of water)
• Place FF dielectric mirror as close as possible to containment wall away from trap
opening
• Increase depth of neutron trap as much as feasible
• Incline sides of neutron trap along the line-of-sight of direct source neutrons
• The wall of the beam duct between the chamber and trap can be made of a thin
absorber since we do not need to attenuate neutrons leaking from the blanket that
are much smaller than those reflected from trap
• Line the inner surface of trap and beam duct with strong absorber
In past studies we showed that lining the ducts by 1/4" (0.635 cm) boral
(Al+36% B4C) reduced streaming by an order of magnitude
• Increasing the distance between lens and dielectric mirror helps reducing the flux
at the lens
• 3D calculations with detailed modeling of final optics configuration and GIMM
layered structure will be performed once we converge on a design
6