Qualitative Reliability Issues for Solid and Liquid Wall Fusion Design Page: 4 of 66
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Some members of the magnetic fusion community have suggested that conventional solid wall
armor for magnetic fusion is not reliable enough to make the overall fusion plant economically
attractive, and they have suggested design alternatives such as liquid self-renewing walls. Other
members of the magnetic fusion community believe that strides have been made in solid walls
and are dubious of the technical feasibility of liquid walls. Such feasibility issues may not be
overcome even if the overall availability of liquid wall systems were greater than that of
conventional solid walls. A quantitative analysis of the availability of these two approaches
cannot be performed because there is inadequate design detail at the present time. A preliminary
qualitative examination of the reliability issues associated with solid and liquid walls can be
useful to help understand the strengths and weaknesses of each approach, and to highlight areas
for further study.
This report presents a preliminary examination of qualitative reliability issues of solid wall and
liquid wall fusion designs. A comparative failure modes and effects analysis (FMEA) approach
was used to identify the different reliability issues for the two design concepts. Very generalized
designs were used for the evaluation. Using the results of the FMEA method, the following eight
issues of importance were identified: coolant pump reliability, vacuum quality, liquid wall nozzle
reliability, maintenance downtime issues, responses to loss of vacuum accidents (that is, vacuum
component failures), responses to loss of coolant accidents (that is, piping failures), helium
pumping ability for vacuum cleanliness, and natural circulation of reactor coolant.
There are vast differences in system design approaches at the first wall. In solid wall designs,
the in-vessel system consists of large wall modules with cooling passages (such as the SiC
passages in advanced tokamak designs), headers, and module mounts. In liquid wall designs, the
first wall is an open surface, and the remainder of the in-vessel system consists of a small
number of flow nozzles, flow vanes, and electrically insulated substrate plates. This trade-off
initially appears to be very positive since the number of components and their complexity are
greatly reduced. However, the overall availability of the liquid wall system is now determined
not by passive component wall modules, but the active pump component. Thus, for liquid wall
systems, the overall availability is determined by the flow loop. Of course, the solid wall
systems need operating pumps as well to allow system operation, but the consequences of an off-
normal flow event are less severe for low afterheat solid walls since the solid wall modules are
designed for replacement if they are damaged.
Table S-1 shows how this initial list of important features compared between designs. The
comparison highlights these reliability issues; some can be changed by design. Others may be
altered by feedback from testing. The remainder of the liquid wall flow system must be designed
and analyzed for reliability in design before numerical comparisons of plant availability are
made. The liquid wall idea should be investigated for its merits, and for the possibility of use in
conjunction with solid walls, as in the Advanced Limiter-divertor Plasma facing Systems
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Cadwallader, Lee Charles. Qualitative Reliability Issues for Solid and Liquid Wall Fusion Design, report, January 1, 2001; [Idaho Falls, Idaho]. (digital.library.unt.edu/ark:/67531/metadc878553/m1/4/: accessed January 17, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.