Engineering Group Conference Call

9 January 1997 (Thursday)
10 PST, 12 CST, 1:00 EST
call-in number: 314-232-8169

Fred Dalgren, Laila El-Guebaly, Phil Heitzenroeder, Steve Jardin, Ron Miller, Hutch Neilson, Wayne Reiersen, Don Steiner, Dai Kai Sze, Mark Tillack, Les Waganer, Xueren Wang

Preliminary remarks (Tillack)

The engineering group faces 2 main near-term tasks: Design concept development for the LAR tokamak Inputs to the system study effort

Following the near-term work, we expect to perform some parametric system studies and then probably more detailed design and analyses.

Since the PPPL meeting, people had a chance to meet, brainstorm, and refine their work plans. So the purpose of this CC is to discuss these plans and coordinate between contributors.


Design issues (Tillack)

Preliminary results of the design issues tasks (detailed below) should be presented in the March project meeting.

FW/blanket studies (Sze)

The activities to perform a preliminary examination of the FS/SiC/Li2TiO3/Be/He design were organized and e-mail was sent out. Key issues to be examined include thermal conversion efficiency, SiC cost, breeder selection, and Be issues. The efficiency of the primary blanket system was estimated to be about 58-59%. Usable heat will be extracted from the center post and shield, but the thermal conversion for this recovered heat will be lower due to the lower outlet coolant temperature. Therefore, the gross plant efficiency will be somewhat lower, to be determined.

A question arose regarding the level of extrapolation we can assume in the technology, i.e., what time frame do we expect for the product? M. Tillack replied that we are looking at a commercial plant with at least a 25-year horizon for R&D.

Divertor HHF studies (Wang/Tillack)

UCSD is planning to assess alternative HHF technologies to define more clearly what are the maximum heat loads and plasma conditions which different designs could handle. There will not be sufficient edge physics to perform a "roll-forward" design and analysis. The assessment will include both low-performance designs as well as innovative designs.

Sze asked if we will assume the presence of disruptions in a LAR device. Jardin suggested we use the same assumption as ARIES-RS; namely, that we allow 1 disruption per year. This means we have to design for that condition.

Jardin expressed the opinion that the consequences of a disruption won't be much worse than a conventional tokamak since, even though the current is high, the inductance is lower.

Tillack asked if PPPL can do EM analysis? Heitzenroeder agreed to do some analysis. He mentioned that halo currents in the LAR are probably easier to deal with than in a conventional tokamak, and that they can translate NSTX results to some extent for use in ARIES-ST.

Centerpost design and performance (Heitzenroeder/Reiersen)

PPPL is planning to examine questions related to the trade-offs in CP attractiveness when shielding is added. They intend to develop a centerpost "design code" for trade studies. Using radiation damage and properties inputs from UW and documented experimental results, they will examine questions related to lifetime constraints due to changes in resistivity and Cu embrittlement.

A request was made for references on fracture mechanics, microstructure changes, etc. The paper by Zinkle/Fabritsiev was mentioned as a good source. El-Guebaly suggested that the team's own analysis should also be considered in the assessment of radiation-induced changes.

Some references include:

S. J. Zinkle and S. A. Fabritsiev "Copper Alloys for High Heat Flux Structure Applications," Atomic and Plasma-Interaction Data for Fusion Nuclear Fusion, supplement, Atomic and Plasma-Material Interaction Data for Fusion, Volume 5, pg 163-191.

S. A. Fabritsiev, A. S. Pokrovsky, S. J. Zinkle, and D. J. Edwards "Low-temperature radiation embrittlement of copper alloys" J. Nuclear Mater. 233-237 (1996) 513-518.

S. A. Fabritsiev, A. S. Pokrovsky, S. J. Zinkle, A. F. Rowcliffe, D. J. Edwards, F. A. Garner, V. A. Sandakov, B. N. Singh, and V. R. Barabash Tensile and Electrical Properties of Copper Alloys Irradiated in a Fission Reactor.

IBC concept development (Steiner)

Some additional scoping studies of the IBC concept have been done by D. Steiner since the PPPL meeting with these general results:

R=6m, a=4m, A=1.5
1.5 T on-axis
Na conductor, Li coolant
300 MW ohmic dissipation
250 MW nuclear heating

Reiersen has evaluated the design values produced by Steiner, and agreed that 300 MW of dissipated power is the right "ballpark" for the parameters given.

With the IBC design approach, it is likely that a larger plant will be optimum. But the COE is not necessarily higher.

The primary candidate structural material is V, but FS also is an option. A question was raised on Na/V compatibility. O impurity may transfer to V, which could lead to problems. The life-limiting component will problably be the centerpost structural material.

Tillack asked when results would be available to the ENG group. Steiner indicated he wanted to first refine the numbers, which would take a few weeks.

Tillack indicated that a fair comparison of the IBC with the Cu/water CP with Fe/SiC/He blanket would require self-consistent systems modeling and optimization. Miller indicated he probably could revisit the IBC modeling in the code and do some work in this area.

Steiner indicated the desire to use in-situ insulators to optimize design (e.g., to allow multi-turn coils and to alleviate some other problems). The life-limiting material in the CP would be the structure.

Finally, safety issues related to Na were raised. Steiner is following up on this.

Nuclear aspects of the centerpost (El-Guebaly)

UW is performing a parametric analysis of the shield thickness (between 20-30 cm). Khater did some initial analysis (for 1 MW/m2 at shield thicknesses of 0, 15 and 30 cm) and sent results out by e-mail.

Miller recommended that the level of CP analysis should be based on a real design and sufficient (heterogeneous) detail from the engineering group should be made available on a timely basis. Specifically, the level of detail in the NSTX design for the distribution of the coolant channels would be useful. El-Guebaly replied that the initial neutronics results are based on Igor's heterogeneous design from last year. She will iterate with the PPPL group to develop an arrangement for the coolant channels that meets the neutronics, thermal hydraulics, and mechanical constraints.

El-Guebaly requested the average wall loading values on the CP and on the o/b blanket. Miller agreed to modify the ASC to give these values. They are needed to get the waste disposal rating, total heating in each component, and average change in resistivity. For a standard tokamak, we can scale from the peak values at the midplane to the average value on the i/b and o/b. For the ST however, the situation is different because the drop in the wall loading over the i/b and o/b is large.

PPPL will provide design detail for the CP in the future. A reasonable starting point for the ratio of coolant channel to total area is 30%.

Reiersen asked Miller's opinion about the development of a standalone design code for CP. Miller said he had mixed feelings. There is a need for good modeling, as long as the system code remains compatible with the standalone models.

Configuration & Maintenance (Wang/Tillack)

Mark summarized the plan to examine the maintenance scheme in more detail (e.g., vertical versus horizontal maintenance of the power core) and alter the design if necessary.

Sze suggested that demountable outboard coils are worth considering. Miller agreed that this will improve the design: the 3/2/96 design point was not optimal in part because the ARIES-RS logic was applied to design. He added that the plant factor is also important to consider in configuration/maintenance activities, and would work toward defining the plant factor as a function of design/maintenance approach.

Status of comparison of ARIES-LAR with other LAR designs (Miller)

All data needed to perform the comparison is in hand. It appears likely that the main difference will be due to the different physics assumptions. We are expecting some initial results within a month.

Status of writing (Tillack)

A plea for ARIES-RS chapters was made, especially for summary and conclusions, and for figures, which are most urgent. Some draft chapters are wildly overdue.

FED articles are due Feb. 1 - we plan to publish whatever we have and omit whatever we don't have.