LLNL Chambers ActivitiesLLNL Chambers Activities
Presented by: Jeff Latkowski
Chambers Team: Ryan Abbott, Alison Kubota,
Wayne Meier, Susana Reyes
April 10, 2003
Work performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.
LLNL chambers work spans three areas
• Chamber and systems design
• Safety & environmental analyses
• Molecular dynamics simulations
Chamber scaling work will eventually be part of a Laser IFE systems code
• Eventual goal is an integrated systems model of an IFE power plant to help select attractive point design(s)
• Focus this year is on scaling relationships for a dry-wall chamber
• Approach is to use simple scaling tied to results from more detailed calculations
Many constraints need to be consideredin the chamber/blanket design
Tungsten armor on ferritic steel wall/blanket• Peak W temp < Tmelt
• Peak Fe temp < Max allowable operating temp
• Pulse to pulse T at W/Fe interface < ? interface integrity constraint?
• Thermal stresses due to avg T across steel wall
• Cylic stresses due to neutron induced pressure pulse in first wall coolant
• Surface roughing due to ion implantation
• Neutron damage
• Others?
Example: Scaling maximum surface temperature of W armor
T x t( ) To2 qo
k t
0.5
expx2
4 t
qoxk
erfcx
2 t
Ts t( ) To2 qo
k t
0.5
qo Y Rw( )fxd Y
Rw2 p
Ts Y Rw p To2 fxd Y
Rw2
0.4
1
p
0.5
1D temperature for surface heat flux qo applied starting at t = 0. k = thermal conductivity, thermaldiffusivity, To = initial temperature
At the surface
Heat flux: fxd = x-ray and debris fraction, Y = target yield, Rw = wall radius, p = pulse length
Since p ~ 1/Rw, Tmax ~ To + Y/Rw2.5 Assuming T max occurs at t ~ p
Surface temp at t = p
Simple scaling compares favorably to Blanchard’s results
50 m W, No gas, Y = 154 MJ, To ~ 500C
5 6 7 8 9 100
1000
2000
3000
4000
5000
6000
First wall radius, m
W s
urfa
ce te
mpe
ratu
re, C
Tmelt
Blanchard pts
Scaling eqn.
Next steps:- Add effect of gas fill- Need more calcs at various yields- Scaling parameters important to other constraints
Molecular dynamics simulations of radiation damage in tungsten chamber materials
During the first year, we will use MDS to evaluate defect production as a function of recoil energy (several to tens of eV)
MDS involves the numerical time-integration of Newton’s equation of motion for an ensemble of N-interacting particles (atoms),
Fi = mi ai = -V(r1,r2,…,rN )
Given an interatomic potential. We have available, the Embedded Atom Method (EAM) potentials of Finnis-Sinclair and Ackland,
V(r1,r2,…,rN ) = VR + VE
Where VR is a repulsive pairwise contribution, and VE is the embedding energy of
an atom in an electron gas, with the form,
VE (i) = (∑ij (rij))1/2
Where (rij) are the individual neighbor contributions to the embedding electron
density
Previous MDS studies in tungsten
Li and Shi, Study of dislocation Motion, EAM (Finnis-Sinclair) potentials
Mundim, et al., Energetics of defect migration, Morse Potential fit to electronic structure data
Komandri, Chandrasekaran and Raff, Study of atomic-scale friction Morse Potentials
Zhong, Nordlund, Ghaly and Averback, Defect production near free-surfaces, 20-30 keV recoils, EAM (Finnis-Sinclair) potentials
Grujicic, Zhao and Krasko, Grain boundary fracture, EAM (Finnis-Sinclair) potentials
Kinney and Guinan, Defect production near surfaces, Morse Potentials
2002
2001
2000
1998
1997
1982
Analyses: Voronoi cell analysisto calculate defects
The Voronoi cell associated with a single atom is the constructed polyhedral volume for which all points contained within the volume are nearest to the associated atom.
Voronoi Cell for FCC Lattices Voronoi Cell for BCC Lattices
Zero-occupancy denote a vacancyDouble-occupancy denotes an interstitial
Example: 2 keV recoil in FCC metal
0.76 psec 2.76 psec 4.76 psec
6.76 psec 8.76 psec 18.76 psec
White = Interstitial (Dumb-bell) Magenta = Vacancy
Activation cross sections may need to be improved for IFE safety assessments
• Previous work has identified isotopes and reactions that are critical for safety & environmental issues
• Preliminary results show that uncertainties in activation cross sections could be significant
• Two methods have been implemented in the ACAB code: – a comprehensive sensitivity-uncertainty analysis method– a Monte Carlo procedure based on simultaneous random sampling
of all the cross sections involved in the problem
• We will determine if any of the uncertainties are large enough to have an impact upon any of our key results and/or conclusions
Activation calculations have been completedfor three FW/blanket concepts
1. Original SOMBRERO concept with 1 cm C/C first wall and C/C blanket
2. W-3Re armor (1 mm) with SiC first wall and blanket
3. W-3Re armor (1 mm) with ferritic steel first wall and blanket
Waste disposal ratings have been calculatedfor each armor/wall/blanket option
• Results assume 1 yr irradiation time• W-3Re components would not meet Class C disposal
requirements unless exposed for <2 years (dominated by Re, which is added for ductility)
• Ferritic steel WDR dominated by Nb, Mo impurities (0.5, 70 wppm, respectively)
WDR C/C W-3Re/SiCW-3Re/
ferritic steel
armor N/A 5.4E-01 5.3E-01
first wall 7.5E-04 6.2E-03 3.9E-01
blanket structures
9.7E-05 1.1E-04 5.9E-02
Waste disposal ratings have been calculatedfor each armor/wall/blanket option
• Results assume 1 yr irradiation time• W-3Re components would not meet Class C disposal
requirements unless exposed for <2 years (dominated by Re, which is added for ductility)
• Ferritic steel WDR dominated by Nb, Mo impurities (0.5, 70 wppm, respectively)
WDR C/C W-3Re/SiCW-3Re/
ferritic steel
armor N/A 5.4E-01 5.3E-01
first wall 7.5E-04 6.2E-03 3.9E-01
blanket structures
9.7E-05 1.1E-04 5.9E-02
Similar analyses needed as function of Re
content, impurities, chamber radius, etc.
MDS Parallelization by Spatial Decomposition
mcr13 mcr14 mcr15 mcr16
mcr29 mcr30 mcr31 mcr32
mcr45 mcr46 mcr47 mcr48
mcr61 mcr62 mcr63 mcr64
Data EnvironmentHardware
An Array of Link CellsLink-Cell Decomposition
Spatial Decomposition
Link-Cell Sizes are based on cutoff-lengths (4.4A for W)
Questions for Alison:
• 1st slide/1st bullet: really several to tens of eV (vs. keV)?
• How/where do we work in experimental validation?
• Have copy of walkthrough description? (Download this)
• Worth going through method of parallelization?
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