Page 245 - Fundamentals of Magnetic Thermonuclear Reactor Design

226 Fundamentals of Magnetic Thermonuclear Reactor Design

The FW stress–strain state is generally analysed using 3D simulations
(Chapter 12). Lifetime projections are necessary for structural components con-
taining forced-flow cooling channels. Such components should have an at least
2× margin for projected deformations and a number of operation cycles should
be at least 20× smaller than that derived from the low-cycle fatigue curve.
During the final design stage, a detailed design work and optimisation aimed
at a better definition of system design specifications and the ICC engineering and
physical characteristics should be carried out. This includes the consideration of is-
sues related to safety analysis (e.g. minimisation of tritium accumulating in the ar-
mour/coolant and particulates deposition in slots), as well as the issues of fabrica-
tion, installation, mounting and dismantling of different components, prevention of
the loss of coolant, destruction and loss of the armour tiles and other emergencies.

7.3 ITER FIRST WALL
Numerical simulation, experimental adjustment and comprehensive testing of
the ITER’s first-wall components were part of an extensive international re-
search collaboration programme [4]. This work will continue during ITER’s
operation.
The scope of the said programme is governed by the complexity, unique-
ness and high cost of the FW components, and the fact that it is impossible to
reproduce experimentally at the ‘pre-reactor’ stage or to simulate the destructive
factors comprehensively. The hallmarks of this research are the following:
l Its highly interdisciplinary, integrative nature.
l The technical solutions’ variability and high probability of implementation
due to the many prospective modes of the reactor operation and FW compo-
nents replacement while the reactor is still operating.
l Utilisation of large-scale electro-physical devices and special equipment in-
tended for modelling or simulation of the plasma’s negative effects on the
first wall; and opportunity to use the research site as venue for in-chamber
component manufacturing operations.

7.3.1 First-Wall Components
The ITER divertor uses 54 water-cooled ‘cassette assemblies’, each of which
has a supporting structure that carries plasma-facing components, that is, the
inner and outer divertor targets, the liner and the dome (Fig. 7.4). The cassette
assemblies act as a common water collector for PFCs and local neutron shield
for the vacuum chamber. The divertor design is optimised such that three re-
quirements are met: (1) no direct contact between a cassette body and plasma,
(2) minimal flow into the plasma of the neutral gas generated due to divertor
plasma neutralisation and (3) a vacuum duct to pumps with sufficient gas-ki-
netic conductivity.
A divertor target has two distinct parts: the upper, bent one (the baffle), and
the lower, straight one, crossed by the separatrix (the vertical target).