llnl chambers activities presented by: jeff latkowski chambers team: ryan abbott, alison kubota,...

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




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?

llnl chambers activities presented by: jeff latkowski chambers team: ryan abbott, alison kubota,...

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