Research Needs for Magnetic Fusion Energy Sciences - US Burning ...

• Proposing integrated safety design approaches. For example, removing safety constraints
from in-vessel components to the extent possible and evolving coordinated and
comprehensive radiological confinement boundaries. safety issues served as a common
link among system design teams.
• assisting system designers with safety assessments. The performance of each system in
normal, off-normal, and accident situations is the responsibility of the designers.
• assessing the design of systems with respect to their impact on other systems, so that
safety experts focused on potential events could evaluate where one system affects
another and system interconnections.
• identifying potential safety issues early in the design, and performing safety research and
development activities.
• iterating on the functions above so that new design specifications or data were incorporated,
problems with one system would be balanced elsewhere, and a coordinated confinement
system design evolved as the various system source terms and their interactions with
systems were better understood.
a key safety decision made early in the iteR project was to shift the safety burden away from
plasma physics, plasma control, diagnostics, the divertor, first wall/blanket, and magnets to vessels,
heat transport systems, and the tritium plant. by definition, iteR’s physics and plasma facing
components would be experimental, and an iteR objective was to maximize the flexibility of
testing and experimentation during operation. This approach reduced the safety risk by removing
all safety needs from the components and systems whose behaviors are least known. as a result,
no plasma facing components served as part of the radiological control boundary, and wide allowances
were preserved in case of their failure. The iteR safety design did, however, require limiting
the in-vessel inventory of dust and tritium, thereby placing greater safety burden on the first
confinement boundary.
one of the important design integration issues was defining the first confinement boundary.
choice of the vacuum vessel was a logical alternative that took advantage of preexisting fusion design
approaches of high quality and high reliability vacuum vessels. The vacuum vessel can meet
the low failure rate criteria with robust construction and double walls that confined tritium, neutron
activated materials, and chemically toxic materials. Unfortunately, there are many vacuum
vessel penetrations that are necessary to operate the tokamak. The integration challenge was determining
the boundary perimeter for these penetrations. The designers required many vacuum
vessel interfaces to the vacuum pumping system, the radiofrequency plasma heating systems, the
fueling system, the diagnostics and their ports, penetrations for cooling system piping, and the
maintenance access ports with port plugs. all of these systems extended the vacuum vessel strong
barrier boundary and are potential natural bypasses of the strong barrier. hence, safety integration
became increasingly important with each of the systems that penetrated the strong barrier.
as concepts mature and safety considerations are elucidated during safety integration through
design, the areas for safety research and development will be refined. however, there are several
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