Page 410 - Fundamentals of Magnetic Thermonuclear Reactor Design

388 Fundamentals of Magnetic Thermonuclear Reactor Design

this reason, any damage of those parts raises the risk of coolant leakage into the
vacuum chamber and an emergency shutdown of the reactor. The FW and diver-
tor plates’ cladding represents a different case, as it can be repeatedly repaired
and replaced while the reactor is still in operation. Moreover, a partial loss of
cladding does not necessarily lead to the tokamak shutdown. The requirements
for the operating conditions of in-chamber components’ steel parts are relatively
mild, as steels are definitely superior to copper alloys in terms of mechanical
strength and fatigue resistance.
As ITER is subject to cyclic mechanical stresses, its structural materials must
be resistive to cyclic loads. The basic concepts related to the MFR’s structural
and functional materials and the results of experimental research of ITER steel
and alloy properties are summarised next. Many of the relevant studies were
carried out in 1990–2010 under a technological collaboration programme of the
Efremov Institute and the Oak Ridge National Laboratory (USA). Experimental
findings concerning the little-explored radiation endurance of copper alloys are
particularly interesting.
Information about material radiation properties, given later, mostly reflects
the results of mockup experiments on fission reactors. The issue of their phe-
nomenological adequacy is beyond the scope of this book.
The existing database on MFR materials is far from complete, and a compre-
hensive research in this area is still underway. The list of materials under study
is extending. For example, the potential of multilayer structures and composi-
tions based on graphite, carbides and nitrides (C + TiC, C + Cr C , SiC + Al,
2 3
SiC + Si, Si N , AlN, and BN) is investigated.
4
3
The launch of ITER will give a strong impetus to conceive solutions to this
problem and proceed from the MFR radiation landscape fission-based imitations to
full-scale realistic experiments. We risk suggesting that the solution will be found
through a targeted synthesis of materials with preset combinations of properties.
Fifty years of experience in radiation materials science suggests that the
advent of new power devices necessarily leads to important discoveries.
Phenomena such as low-temperature and helium-induced embrittlement were
discovered while running the thermal reactors, and the radiative swelling effect
was noticed when breeder reactors came into operation. The creation of the first
fusion reactor is very likely to offer the opportunity of continued discovery of
new radiation-induced phenomena—maybe associated with the fast accumula-
tion of transmutation products or the specificity of radiation defect propagation,
associated with a harder radiation spectrum in fusion reactors compared with
fission reactors. The future that knows what it has in store for us is not so distant!

13.2 SELECTION CRITERIA
Factors affecting the MFR’s structural and functional materials are quite diverse.
One can deduce from Table 13.1, which summarises potential causes of impair-
ment of the FW materials, that the key selection criteria for MFR’s structural
and functional materials should include the following: