Page 255 - Fundamentals of Magnetic Thermonuclear Reactor Design

236 Fundamentals of Magnetic Thermonuclear Reactor Design

2
2
−4
of armour will be ∼1 m . A tile measures 2.5 × 10 m at most. Then, the
above observation that the loss of one tile is allowable is correct, but to the
extent that the loss of one tile and the resultant heat flow redistribution do not
induce avalanche-like damage of neighbouring tiles.
As a result of irregularities occurring due to tile partial detachment or defor-
mation at the tile–plasma interface, prominent parts become overheated, which
entails a series of damages, as shown in Fig. 7.8G and H). Such irregularities are
allowable if there is no direct contact with the plasma. For plasma-facing FW
components, the largest permissible vertical displacement of one tile against
another must be within 0.3 mm, while the difference in height between neigh-
bouring ICCs may be up to 3 mm.
Another thing worthy of consideration is the impact produced by the armour
on the heat-sink panels’ operating conditions. Transient events, such as current
disruptions, may make the panels exposed to extreme heat fluxes with resultant
overheating and even melting of their surfaces. This, in turn, may initiate sur-
face cracking. However, ITER design requirements forbid any cracks on any
structural components containing a forced-flow cooling system. The width-to-
height ratio must be as small as technologically permissible to decrease the heat
loads on the nonarmoured part of panels (Fig. 7.8F).
The design and technological solutions for the heat sink panels, load-bearing
structures and collectors must also meet requirements, such as the ‘absolute’
leak-tightness (total number of uncontrollable gas leaks through the many-kilo-
3
−8
metre-long welding joints and cooling channels must be within 1.10 Pа m /s.
In-chamber components must not experience deformations that may give rise to
irregularities and local curvatures of plasma-facing surfaces. Fastener assem-
blies must be designed with online remote replacement capability. Despite the
radiation-induced degradation of the piping material, the opportunity to her-
metically weld on replaceable ICCs from time to time must be provided.
The difficulties listed emphasise the need to comprehensively evaluate and
analyse the design solutions from the thermal mechanics perspective.

7.4 NEXT-GENERATION REACTOR FIRST WALL
7.4.1 Challenges

The engineering ideas implemented in the ITER functional systems have raised
reactor-making to the heights of technical mastery. However, the ITER is just
an experimental machine, and its characteristics are far from the projected pa-
rameters of a demonstrational reactor [7] to say nothing about a commercial
power reactor!
We further make some simple comparisons (Table 7.5). The plasma column
sizes and divertor target areas being similar, the DEMO reactor plasma will be
hotter. In addition, the DEMO’s first wall will be exposed to a heat flow of much
greater strength and density, while the cycle active phase will be many times