Project Conference Call

3 September 1997



Participants:

(DOE) - Wiffen
(UCSD) Mau, Tillack, Wang
(PPPL) - Jardin, Reiersen
(GA) -
(UW) El-Guebaly
(FPA) -
(RPI) - Steiner
(ANL) Sze
(MDA) Waganer

Administrative

The date of the next project meeting was affirmed as Thursday, Sept 25 and Friday, 26. It was suggested the last day be concluded by 4:00 to allow adequate time for return flights. Steve Jardin has provided the following arrangements:

Dai-Kai Sze will host an informal breakfast briefing and information exchange for the ARIES Engineering Group at the Novotel restaurant on Friday, 26 September, approximately 1 1/2 hours before the start of the ARIES meeting. The topic will be progress on the US-Japan collaboration in fusion blanket technology.

An Engineering Conference Call is scheduled for next Wednesday, 10 September, at 11:30 CDT, 314-232-8169.

Mark Tillack noted that he would like to collect the preprint ARIES papers to be presented at the upcoming SOFE Conference and then publish the collection. Also provide electronic copies if available to be included in the ARIES Web Site. The FED report is presently in the process of being printed. Arrangements have been made to have several colored figures within each section. The Stellerator Report and the ARIES-RS Assessment Report are close to being finished.

Plasma Physics

Steve Jardin noted that the results from the physics analyses indicate that plasma parameters are improved as the aspect ratio is increased from A = 1.2 to 1.4, and then to 1.6. He suggested, and others agreed, that we should examine other larger aspect ratios until we find the optimal aspect ratio (based upon both physics and engineering considerations). Thus, the aspect ratio of 1.8 will be investigated and the equilibrium results will be reported at the upcoming meeting. As the aspect ratio reaches values of approximately 1.6 or greater, the need to provide an inboard breeding capability will be necessary. The Engineering Group should provide a guideline as to the minimum aspect ratio that will require inboard breeding. Then a trade study could be accomplished over a range of aspect ratios. Laila El-Guebaly noted that a pure inboard shield could be as thin as 15-20 cm whereas an inboard breeding blanket would be thicker.

Steve Jardin reported some progress on the free-boundary equilibrium problem. The TSC equilibrium code previously did not converge at low-A conditions, perhaps due to excessive coil currents. Chuck Kessel is working on a code modification that will improve code convergence. According to Steve Jardin, T.K. Mau is collaborating with Bob Miller of GA on the start-up equilibrium conditions. They are looking at anaspect ratio of 1.6 and a bootstrap current of 90% (as opposed to 99%) to obtain a more stable beta.

Mark Tillack asked about the progress of the definition of the edge physics. Steve Jardin felt confident that a radiative mantle could be used in a low-aspect ratio device to (help?) average the radiative heat between the divertor and the first wall. This is supported by current experiments on tokamak devices. He also thought that most of the energy in the divertor would be directed to the outer strike points, a result also seen on current tokamaks. Wayne Reiersen asked if the plasma would behave as a limiter, ala NSTX or would it be more of a divertor plasma. Steve could not answer as to which would be more likely, but he said he would present analysis results for both types at the September meeting. Wayne was also concerned as to the configuration of the first wall so he could begin to design a compatible divertor and the inboard shield (or blanket). Dai-Kai Sze said that several types of first wall and blanket designs are being evaluated and no decision has been made.

Engineering

Center Post - Mark Tillack mentioned there are several different design options for the center post, all of which are closely integrated with the choices for the outboard first wall and blanket design. The considerations are safety, performance, waste, and cost. A low-temperature water-cooled (<150oC), copper CP would raise embrittlement questions (brittle design conditions). A higher temperature water-cooled (250-300oC), copper CP would help reduce embrittlement concerns, but the strength and fracture toughness would be reduced (ductile design conditions). (Subsequently, D-K stated a minimum coolant temperature of 300oC would be necessary for effective utilization of the removed CP heat.) A lithium-cooled CP is possible if the outboard first wall and blanket were similarly cooled. A lithium-lead CP cooled with helium is also possible if the first wall and blanket were compatible.

Configuration and Maintenance - Mark Tillack reviewed the three configuration and maintenance options being considered. Generally the CP is envisioned to be removed and replaced vertically with the remainder of the power core being undisturbed. The favored CP maintenance approach is from below to minimize the building size and the ability to contain any radioactive contaminants. The maintenance of the bulk of the power core can be accomplished vertically, horizontally between TF coils, and horizontally including removal of the TF coils. Removal of the core vertically upwards is not favored as it significantly increases the cost of the building and the size of the bridge crane. Moving the core downward has been investigated to some degree, and it seems a more feasible approach at a lower cost. The ARIES-RS approach is thought to be feasible, given the outboard legs of the TF coils are moved sufficiently outboard. Because of the significant effort applied in the ARIES-RS design, only a minimal effort is being applied to this approach for the low aspect ratio design. The current analysis effort is on the approach of employing a demountable TF coil joint and moving a portion of the TF coil aside to gain access to the core. One key question is exactly where is the vacuum vessel to be located?

Blanket and Thermal Conversion - Dai-Kai reviewed the most likely blanket options of (1) a lithium blanket, vanadium structure, and lithium coolant and (2) a lithium-lead blanket, ferritic steel structure, and helium coolant. The lithium-cooled blanket would likely be coupled with a Rankine steam cycle whereas the helium-cooled blanket would be coupled with a closed Brayton cycle.

High Heat Flux Components - Mark Tillack noted that there are three classes of divertor designs being considered: (1) conventional as typified by the ITER approach of a copper substrate, steel pipes, and water coolant; (2) advanced as proposed by ARIES-RS; and (3) exotic such as liquid metal surfaces (films, jets or drops, or porous films). Since the first and second approaches have been previously investigated in some depth, the latter is being assessed at the present time.

Neutronics- Laila El-Guebaly stated that she needs to know the configuration and location of the vacuum vessel. Mark Tillack said that within the constraints of the inboard shield, the shield could be configured to be a vacuum vessel.

She noted that she had received a memo stating that the ferritic steel DPA limits for commercial fusion applications would be similar to that of vanadium, which is 200 dpa. An action item was identified for the University of Wisconsin to determine the creep rate versus primary stress for both irradiated ferritic steel and vanadium.

Safety Analyses - Operation of the center post at high temperature (>300oC) may result in excessive temperatures during LOCA (700-800oC). UW will determine the resultant LOCA temperatures for the center post and other high temperature components for the case where the coil bus acts as a heat sink for the centerpost during LOCA.

Systems Studies

Ron Miller was not on the conference call, but the subject of the cost of power supplies being assumed in the system code was raised. The assumption was thought to be $1/W but Wayne Reiersen will check what PPPL was assuming for the NSTX. Meanwhile, Ron Miller should check on the capital cost of the power supplies assumed in the systems code.

Wayne Reiersen raised the question about the straight or shaped centerpost being in the engineering analyses and the system code strawman. He suggested that a trade study be conducted to assess the cost/benefits. The Engineering Group should also assess the impact of a shaped versus straight center post.

Alternate Applications

Les Waganer informed the group of his alternate fusion product applications presentation at the Fusion Power Associates "Pathways to Fusion Power" symposium held at Snowmass Village, CO, on 27-29 August 1997. The presentation was a condensed version of the updated results recently shown to the DOE Office of Fusion Energy Sciences. The purpose of the symposium was to explore the potential pathways and markets for fusion.

Other ARIES presentations at the FPA symposium were by Farrokh Najmabadi, who gave the results of the ARIES-RS study, and Ron Miller, who presented information about the economic viability of fusion in the electric power marketplace. Page