Plan to Develop A First Wall Concept for Laser IFE

We have decided to concentrate on a "front runner" first wall.... HAPL materials and chambers community has chosen tungsten armored- low activation ferritic. 1.Why choose a "Front Runner" approach? A.Focuses our resources. B.Should lead to a workable solution faster 2.Why tungsten/ ferritc? A.Most mature data base...ferritic is nuclear qualified B.Most viable candidate to field on the ETF within the next years. C.Takes advantage of vast body of fission and other fusion work D.Readiness to qualify materials for a nuclear environment E.Can address a lot of the critical issues now a.fabrication, bonding, forming F.Confidence can we model the material’s response to threats a.neutrons, x-rays, and ions? 3.Goal of plan: Assess this approach in archival paper by Dec 31, 2003

ETF FIRST WALL REQUIREMENTS 1. Full laser energy & yield (400 MJ), 5 Hz runs, up to few hours duration: < 0.02 micron erosion/shot 10 5 shots maximum 2. Full laser energy, 10% yield (40 MJ), continuous operation: negligible erosion/shot 10 7 shots or more (1 year lifetime) Design allows annual replacement The first opportunity to fully evaluate the first wall is the Engineering Test Facility... Test multiple blanket concepts, if desired 40cm x 40 cm cooled 2 m radius But our "first" first wall must meet the needs of the ETF

There are some issues with tungsten armored ferritic that can be addressed now 1.Bonding of tungsten to the ferritic steel 2.Operating windows for both the IFE and the ETF chambers. A.Real allowable threshold: roughening vs. melting. 3.The type of tungsten to use: A.Pure or alloy? B.Flat plate or engineered structures? 4.Issue of Helium retention 5.General suitability of W/Fe in a fusion and nuclear system. This is the basis for our plan

Task 1: Bonding of tungsten to ferritic steel a) ORNL: Develop techniques to bond tungsten to steel, based on advanced concepts started last year. Look at bonding W to ODS. Finally, explore concepts for bonding engineered materials. b) UCLA: Investigate techniques to bond engineered materials to ferritic substrate. c) MWG (Nasr, Jake): What modeling can we do to help understand/predict the bond stresses? d) MWG/Wisconsin (Jake): Assess utility of using existing facilities (Electra, ORNL IR source) for thermal fatigue testing of the tungsten/ferritic bond and to study the evolution of the microstructure. Can we get the meaningful thermal stresses and temperature swings?

Task 2: Operating windows for both the IFE and the ETF chambers. What is the real allowable threshold: roughening or melting? 1.MWG/Wisconsin (Jake): Refine model to get prediction of observed RHEPP roughening in tungsten. Does it go on forever? 2.Wisconsin: Perform runs of operating windows for a power plant if we take roughening as the allowable threshold.. 3.Wisconsin: Perform runs to predict erosion for ETF first wall for target optimization and electricity production. 4.Wisconsin: Perform runs to predict erosion for ETF first wall using criteria for reduced yield targets, to allow materials components testing, 5.LLNL (XAPPER), SNL (RHEPP), UCSD. Extended runs with tungsten to establish the long term effects of exposure. Are limits melting or roughening? 6.MWG: Assess three thing related to the planned exposure experiments: A.The value of exposing samples heated to IFE temperatures (1000 ◦C). B.The importance of the ion species in RHEPP C.The issue of scaling exposure times.

Task 3: The type of tungsten to use: Pure or alloy? Flat plate or engineered structures? 1.ORNL(Lance): Provide samples for evaluation on RHEPP, XAPPER, UCSD, and Z. These will include both pure tungsten and tungsten with Re. W-25Re as used in RHEPP tests will have waste disposal problem, whereas W-3Re may prove acceptable. We need to find out if 3% Re maintains higher roughening threshold. 2.UCLA: Develop concept of engineered material armor. 3.UCLA/UCSD: Identify “engineered materials” and try to get some for testing in our facilities. First tests: are damage thresholds are increased. 4.SNL, LLNL, UCSD. Expose the above materials in your facilities. 5.UCLA: Modeling of engineered first wall systems: transient temperature & thermal stress analysis, and finite element thermo-mechanical modeling. 6.ORNL/UCLA: Based on the modeling above, design experiments (maybe with a surrogate for W if suitable samples cannot be obtained now) to study thermal conductivity in engineered tungsten first wall

Task 4: Issue of Helium retention 1.ORNL/MWG: Continue He exposure experiments in a prototypical IFE environment. Can we test UCSB’s claim that the spectrum of He ions spreads out the helium deposition in the material, and that exfoliation is delayed. 2.ORNL/UCLA: Design an experiment to test out hypothesis that an engineered material with small fiber sizes that are small compared to the He migration distance will not retain He. Perform the experiment. Perform modeling support.

Task 5: General suitability of W/Fe in a fusion and nuclear system. 1.MWG (Zinkle): Assess the overall suitability of both a tungsten ferritic first wall and the underlying ferritic structure from the point of view of a nuclear fusion environment. The basic question is, if we assume we can successfully address all the issues above, (i.e. we have a W/Fe bond that survives repeated cyclic stress, an armor that survives the x- ray/ion threat, and a material that gets around He-induced exfoliation.), what are the other issues with neutron damage in a ferritic system? 2.LLNL: Apply MDS modeling to tungsten 3.UCSD: "Spread sheet" analysis of typical parameters expected for an IFE power plant with a tungsten/ferritic wall and a blanket based on ferritic materials. The idea is to get an idea of what the thermal efficiency will be with this type of system, and what are the trade-offs between yield, rep-rate and chamber size. This will extend the earlier UCSD work done for an SiC blanket as part if the ARIES program.