C. Bathke, M. Billone, L. Bromberg, L. El-Guebaly, D. Lee, R. Miller, I. Sviatoslavsky, D-K Sze, M. Tillack, L. Waganer, X. Wang, C. Wong
Mark Tillack reviewed the response to last week's hour-plus DOE briefing given by Farrokh Najmabadi, Steve Jardin, and Mark Tillack with Bob Conn also in attendance. The intent was to acquaint DOE managers of our general system study results and the intended direction and scope of the renamed Fusion Concept Studies team. Anne Davies and John Willis were not available, however several senior level OFES managers were in attendance. The material was well received and the response indicated general agreement with our intended direction and scope. It was suggested we could address both short-term (3 month) and longer-term (12-18 month) types of investigations. The LAR and RS studies were noted as being representative of what could be done by the team. C. Wong requested a copy of the presentation materials be sent to the Starlite groups to help guide them in preparation of 1997 grant requests.
Review and Discussion of Strawman Engineering Input Parameters
Mark Tillack suggested Laila El-Guebaly review the engineering input parameters along with the source of the data and a brief discussion of rationale for data values. The group then had a more in-depth discussion and resolution/action items for specific areas.
First Wall and Blanket - There was no change in the composition or dimensions in the FW/B -changes will await results of El-Guebaly's 3-D calculations. The usage of the FENDL library further reduces the allowable fluence from 12 to 11 MW/m2/y (previously it had been 16.4). This change slightly reduced the component lifetime which will likely impact the availability and the replacement cost. Dai-Kai Sze expressed concern that the lifetime of the vanadium structure is becoming a problem. With a peak loading of 5.7 MW/m2, this yields a full power life of approximately 2 years. M. Billone explained that, in lieu of a detailed design and structural analysis, he based his lifetime estimate (150 dpa) on the assumption that the maximum operating primary membrane stress is equal to the maximum allowable primary stress (110 MPa). If one is able to predict the design-specific operating stresses, a revised set of lifetime criteria (curves) can be devised for design development (lifetime vs. operating stress). He will provide these data within two weeks. D-K Sze indicated that Jake Blanchard would be able to provide preliminary stress data for the blanket after the March meeting which would enable a more refined lifetime estimate for the next strawman.
The group examined the determining factors for the peak-to-average neutron wall loading and the peak neutron wall loading. There was discussion about what could be done to reduce those values. Per C. Bathke, the peak neutron wall loading is determined, in part, by the aspect ratio. C. Bathke agreed to conduct a "What if" trade study to assess the impact of increasing the aspect ratio on other important plant parameters.
Shield - The shield has been reoptimized for the 20-cm IB and 30-cm OB vacuum vessel thicknesses. With the use of more efficient materials (WC + B4C) and the closer placement of shielding materials to the magnet, the IB shield is 5 cm thinner. However, the OB shield was unchanged. The divertor region needs to be evaluated in detail to determine if there is sufficient shielding by the divertor components to retain a life-of-plant rating for the related permanent shield components. Otherwise a thin replaceable shield will be required under the divertor. Laila is planning to use WC + B4C plates within the inboard vacuum vessel walls for additional shielding. The 4-cm thick tungsten vertical stability shell will be incorporated in the input along with the variation of the shield thickness with wall loading.
Divertor - Igor Sviatoslavsky estimated the preliminary composition of the divertor to be 7% V, 6% Li, 0.6% W, and 86% void, subject to more detailed design. Per Igor, these data include the structure. Clement Wong is planning a two-year divertor life similar to that for the FW/B. The radiative divertor is to be designed to deliver a maximum heat flux of 5 MW/m2 in the divertor region with injection of both argon and neon . The related impurity level in the core plasma would deliver an overall radiative heat flux (rather) uniformly to the first wall of 0.5 MW/m2. At present, only the OB divertor region has an open slot for vacuum pumping. GA is preparing to conduct a 3D Monte Carlo analysis on the divertor slots to determine the peak heating. Thanh Hua of ANL will start on the heat transport calculations based upon the preliminary data provided.
I. Sviatoslavsky has developed a structural support system for the divertor. D-K Sze determined the piping sizes for use in the detailed development of the internal and external divertor design configurations by X. Wang and D. Lee. C. Wong is continuing to define the specific divertor surfaces to accomplish the interactive requirements.
Vacuum Vessel - Laila summarized the VV materials and thicknesses. D. Lee reviewed the assumptions and results of the scoping stress analysis. For single wall vessels of 3, 5, and 10 cm thick; 3 cm and 5 cm were unacceptable and 10 cm was generally acceptable except in local areas on the port walls where local reinforcements would be required. Fabrication, assembly, and buckling considerations would mandate that a double-walled vessel be used (3 cm walls spaced 20 and 30 cm apart with stiffing ribs or bulkheads). The innerspace will be used for a heating gas and shielding plates.
D. Lee asked for confirmation of the recommended bakeout temperature for the vacuum vessel. F. Najmabadi had been suggesting 250 C as the bakeout temperature which was used in the stress analysis. Many of the call participants preferred 300 C to 400 C temperatures as the efficiency of outgassing is strongly dependent upon temperature. On the other hand, the strength of the structural material (316LN) is lessened at elevated temperatures. As a trial number, a bakeout of 300 C was adopted pending further data analysis.
Magnets - Per L. Bromberg, there is no need for a coil case. Rather, use the coil pack, wrapped with electrical insulation and a thermal protection blanket. Laila noted that mylar would not have an acceptable lifetime from a radiation standpoint. Leslie agreed to try to find suitable alternative materials. After Leslie left the call, we discussed the need to have a liquid-nitrogen-cooled thermal shield. But a subsequent, private conversation revealed that Leslie did not want an LN2 cooled thermal shield; instead he recommended a multi-layer super insulation with no active cooling.
Cryostat - Laila noted the composition and thickness of the cryostat in the code inputs. Dennis asked for a confirmation of the "bell jar" approach as opposed to the "close-fitting" cryostat. A very interactive discussion ensued centered around cost, ability to fabricate, cooling requirements, maintainability, and prior design approaches. It was recommended that a smaller group, including Bromberg and Lee, hold a telecon to resolve the approach. [A telecon later on 2/28/96 between Bromberg, Lee, and Waganer discussed the magnets and cryostat design requirements and proposed approaches. The recommendations were documented by D. Lee via e-mail.]