Chamber Subgroup Question #2 Comments

Neil Morley Fri 25 June 1999 10:50 Subject: Comment 1 Hi Mike and Rich, I think you should include some discussion of the potential of the EVOLVE and refractory metal APEX FW/Blanket concepts for high power density and low failure rates. This seems the perfect place to discuss the advantages of near-isothermal FWs and Blankets and high thermal efficiency. What do you think? Neil

Mohamed Abdou Thurs 8 July 1999 9:07 Subject: Chamber Question 2 Draft Opinion Paper for Comment Dear Mike and Rich, In the spirit of Snowmass, below are some comments on your draft opinion write up for Key Question 2. These comments are my input as a "scientist" (not as a convener). A) Solid Surface PFC 1) Should Plasma edge (pre-sheath) temperature be added as an issue in terms of effects on selection of materials and technology for PFC? 2) On question 8 under "Key Issues" on disruption, do we need to add another part: "can disruptions be accommodated while satisfying other functional requirements (e.g. tritium breeding)? 3) You need a section on opportunities in the next decade to test PFC in existing and planned plasma-based and laboratory facilities. B) First Wall/Blanket Area 1) This section seems to be somewhat long on structural material issues and short on FW/blanket engineering issues. Since the material issues are covered under question 7, we need to make sure the other issues are addressed in Question 2. Examples of areas to be included are: a) solid breeders: this is mentioned as Key issue No. 6 but is not addressed in the text. Improvements such as enhancing thermal conductivity, reducing peak nuclear heating through optimization of Li-6 enrichment in the radial direction, etc. can be good examples of what can be done b) insulators for self-cooled liquid metal concepts and possible advances c) failure modes and rates are critical areas where an assessment and ideas for improvement can be very useful d) bi-metallic loops: can we use refractory alloy in the blanket and "switch" to conventional materials in the heat transport system? UWMAK-III showed the cost of heat transport system with refractory alloys is prohibitive e) Others (hopefully you will get good input from others) 2) I suggest dividing the Evolutionary Concepts (for example in the Table) into two classes: a) traditional concepts with low activation materials (e.g. ARIES, the European concepts, etc.) and b) new concepts where scientists have proposed recently to extend performance, such as the high-temperature refractory alloy concepts (e.g. EVOLVE and He-cooled). 3) In the Table (Performance Characteristics), there are some errors that need to be corrected, especially on the line "average neutron wall loading" - Change ARIES from 5 to 4 (exact value is 3.96). (my Ref. 1) - Change the two EU designs from 3 to 2.2 (Ref. 2) - Check the values for TAURO and ARIES-ST (I do not have them) - Under EVOLVE and He/W/Li, the 10 MW/M2 in APEX is "peak" not "average". Either have a note that it is "peak" or divide by a peaking factor that you designate with a footnote (I suggest 1.4 as a peaking factor). 4) In the Table, the "Surface Heat Flux" values need to be checked and corrected, e.g. - ARIES has surface heat flux of 0.45 MW/m2. ARIES has low fraction of plasma radiation but some come from radiation in the divertor region - EU DEMO designs have surface heat flux of 0.4 MW/m2 (average) and 0.5 MW/m2 maximum. 5) In the Table, I suggest adding a row with the value of the "first wall thickness" used in each case, since it is one of the key factors in determining the maximum wall load and surface heat flux capability and gives the reader some idea of the durability and design margin of the proposed designs. 6) I suggest, if possible, replacing the "Thermal Efficiency" by the values of the coolant exit temperature since it is easier to compare among blanket concepts . 7) I suggest adding the APEX results (my ref. 3) on the wall load limits for low activation materials and for high-temperature refractory alloys. Sec. 2.1.2 of my ref. 3 provides details on assumptions and variations with temperature and other parameters. I recommend adding Table 5 from my Reference 3 because it shows limits separately according to operating temperature and to stress criteria separately (useful also to quantify the impact of your section on design criteria). It also shows the importance of coolant/structure interface temperature on the allowable wall load. I am attaching a copy of the APEX paper (ref. 3) for your convenience. It is also available on the APEX web site at www.fusion.ucla.edu under publications (and, of course, in the Journal of Fusion Engineering and Design). 8) In the conclusion section (before the references; item 1 should be changed. The first part of the sentence should say vanadium alloys and the wall load values should be adjusted lower (or you can say "peak"). State the wall load limits for ferritics and SiC (Ref. 2 and 3 give values). State for what wall thickness and fraction of the alpha power radiated to the wall since they strongly affect neutron wall load limits. 9) I do not have your reference 7. Can I receive a copy? If it is an ISFNT-5 paper, then I assume it has not been reviewed yet? Is this correct? Under what assumptions can a Li/V system have 10 MW/m2 neutron wall load and 2 MW/m2 surface heat flux? This appears to be very different from all other studies and it warrants explanation if it is going to be quoted. 10) I would change the key issues list to be called key questions for evolutionary concepts since they are not really posed as issues (minor point). Final Note Thanks for the opportunity to provide my comments as a "scientist". Please let me know if I can help in any way. References 1. Special Issues for ARIES-RS (several articles), Fusion Engineering and Design, Volume 38 (December 1997) 2. Several Reports and papers on detailed EU blanket designs; for example, M. Dalle Donne, et al., "European DEMO BOT Solid Breeder Blanket", KfK5429 (November 1994) 3. M. Abdou and the APEX Team, "Exploring novel high power density concepts for attractive fusion systems", Fusion Engineering and Design, volume 45, pp 145-167 (1999).