1. LLNL 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.

2. LLNL chambers work spans three areas Chamber and systems design Safety & environmental analyses Molecular dynamics simulations

3. 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

4. Many constraints need to be considered in 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?

5. Example: Scaling maximum surface temperature of W armor 1D temperature for surface heat flux qo applied starting at t = 0. k = thermal conductivity,  thermal  diffusivity, 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/Rw 2.5 Assuming T max occurs at t ~  p  Surface temp at t =  p

6. Simple scaling compares favorably to Blanchard’s results 50  m W, No gas, Y = 154 MJ, To ~ 500C Tmelt Blanchard pts Scaling eqn. Next steps: - Add effect of gas fill - Need more calcs at various yields - Scaling parameters important to other constraints

7. 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), F i = m i a i = -  V(r 1,r 2,…, r N ) Given an interatomic potential. We have available, the Embedded Atom Method (EAM) potentials of Finnis-Sinclair and Ackland, V(r 1,r 2,…, r N ) = V R + V E Where V R is a repulsive pairwise contribution, and V E is the embedding energy of an atom in an electron gas, with the form, V E (  i ) = (∑ ij  (r ij )) 1/2 Where  (r ij ) are the individual neighbor contributions to the embedding electron density

8. 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

9. Analyses: Voronoi cell analysis to 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 LatticesVoronoi Cell for BCC Lattices Zero-occupancy denote a vacancy Double-occupancy denotes an interstitial

10. Example: 2 keV recoil in FCC metal 0.76 psec 2.76 psec4.76 psec 6.76 psec 8.76 psec18.76 psec White = Interstitial (Dumb-bell)Magenta = Vacancy

11. 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

12. Activation calculations have been completed for 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

13. Waste disposal ratings have been calculated for 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/CW-3Re/SiC W-3Re/ ferritic steel armor N/A5.4E-015.3E-01 first wall 7.5E-046.2E-033.9E-01 blanket structures 9.7E-051.1E-045.9E-02

14. Waste disposal ratings have been calculated for 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/CW-3Re/SiC W-3Re/ ferritic steel armor N/A5.4E-015.3E-01 first wall 7.5E-046.2E-033.9E-01 blanket structures 9.7E-051.1E-045.9E-02 Similar analyses needed as function of Re content, impurities, chamber radius, etc.

15. MDS Parallelization by Spatial Decomposition mcr13mcr14mcr15mcr16 mcr29mcr30mcr31mcr32 mcr45mcr46mcr47mcr48 mcr61mcr62mcr63mcr64 Data Environment Hardware An Array of Link Cells Link-Cell Decomposition Spatial Decomposition Link-Cell Sizes are based on cutoff- lengths (4.4A for W)

16. Questions for Alison: 1 st slide/1 st 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?