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Due to the challenging nature of its loading conditions and developmental status, it is desirable
that the divertor system not be classified as a safety-class system. However, since the divertor
structure will become radioactive and its plasma-facing surfaces will become contaminated with
absorbed tritium, the impact of the divertor system on other safety-class systems must be
The goal of the divertor design should be that a single failure of the divertor system does
not threaten any in-vessel or ex-vessel safety-class system. The divertor system design should
prevent damage to safety-class components, which might include the vacuum vessel, fueling
and vacuum pumping system piping, and in-vessel coolant system pipes. If this goal cannot be
met and individual components within the divertor system are designated as safety-class, the
design guidance listed in Section 6.1 should apply to these components. Divertor components
designated as safety-class should be designed, fabricated, inspected, and tested in accordance
with an approved structural acceptance criteria. Because the divertor environment and material
candidates differ significantly from more conventional applications with regard to (1) handling
the high, steady-state heat and energetic particle fluxes on the surface of the divertor target,
(2) withstanding the intense thermal and electromagnetic loads during plasma disruptions, and
(3) experiencing fluences of high-energy neutrons leading to property changes, embrittlement,
and irradiation-induced creep, existing safety-related codes are largely inapplicable. The design
of the divertor should meet the safety design criteria of this Standard and should employ a
design and analysis methodology that is consistent with a recognized safety-related code.
Design standards and practices for non-safety-class divertor components are not addressed in
this document.
b. Special considerations for divertors
In addition to conventional materials and effects, special consideration of the following
items, which are unique to the fusion divertor environment, must be included in the design and
analysis of the divertor and in defining appropriate design practices and criteria:
1. Armor Tile Materials--Many of the armor tile material candidates considered for
use in protecting the divertor target structure are brittle metals or nonmetals. The
behavior of these materials and their influence on the structures to which they are
attached must be considered in evaluating the integrity of the coolant confinement
2. Erosion and Redeposition--Reduced or increased armor tile thickness due to
erosion or redeposition of previously eroded material could have a significant
effect on the thermal stresses in the coolant containment structure to which the
armor tiles are attached.
3. Plasma Disruptions/VDEs--The transient dynamic mechanical and thermal effects
during plasma disruptions/VDEs, which are extremely intense but of very short
duration, must be considered in evaluating the integrity of the divertor structure
and in defining appropriate structural design criteria.

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