Vacuum Vessel

DOE-STD-6003-96

pipe. It is likely that several (2 to 3) confinement barriers will be needed to confine in-vessel

radioactive and toxic materials. The design of successive confinement barriers must therefore

ensure that each separate barrier be independent. This independence should be preserved

during normal and off-normal events. For example, the design-basis earthquake will cause off-

normal loading to all fusion island components, and it should be verified that concentric penetra-

tions from multiple confinement barriers do not have mutual interactions that result in exceeding

specified leak rates.

6.2.1.1 Vacuum Vessel

The vacuum vessel is normally the primary confinement system for in-vessel radioactive

and toxic materials. It is, for the tokamak configuration, a torus-shaped container usually made

of a metal or metallic alloy, and its volume is up to several times the plasma volume. It can be

thin-walled or thick-walled. It may be double-walled with coolant passages in the annulus. The

perimeter of the vacuum vessel is outfitted with a number of ports (extensions) for mounting

hardware for plasma fueling, plasma heating, plasma conditioning, plasma diagnostics, vacuum

pumping, and blanket/divertor maintenance. These ports can vary in size and shape and are

usually located above, below, and on the horizontal plane as well as on top and bottom of the

vacuum vessel. It may be of all-welded, continuous construction or use bolts between segments

with vacuum seals at the joints.

If the safety analysis indicates that vacuum vessel is a primary confinement barrier to

meet the evaluation guidelines, the robustness of the barrier will be defined in the safety analy-

sis and implemented in the design. In performing this public safety function, the vacuum vessel

should be classified as a safety-class system. Hardware internal or adjacent to the vacuum ves-

sel whose credible failure could result in evaluation guidelines being exceeded should be classi-

fied as safety-class. If the vacuum vessel is not considered a confinement barrier in the safety

analysis, those vacuum vessel components whose single failure results in loss of capability of

another safety-class system to perform its safety function should be designated as safety-class

components.

If the safety analysis requires that the vacuum vessel be a confinement barrier, the follow-

ing safety features should be considered:

The vacuum vessel serves as the first barrier for tritium and tritiated compounds, radioac-

tive impurities, and activated dust during normal operation, anticipated operational occurrences,

maintenance external to the vessel, and off-normal events.

In addition to the general design guidance in Section 6.1, the following system-specific

design guidance is provided:

a. Confinement Boundary

The vacuum vessel confinement boundary should be defined as the vacuum vessel

proper including attached windows, flanges, and ports and all penetrations up to and including

the first or second isolation valve as appropriate (depending on system pressure and as defined