  If fusion power reactors are to be feasible, it will still be necessary to
convert the energy of the nuclear reaction into usable form. The heat produced
will be removed from the reactor core by a primary coolant, which might be
water, helium, molten lithium-lead, molten lithium-containing salt, or CO2. The
heat could then be transferred to a conventional Rankine cycle or Brayton (gas
turbine) cycle. Alternatively it could be used for thermochemical processes
such as producing hydrogen or other transport fuels. Fusion presents new
problems because of the high energy neutrons released. These affect the
selection of materials and the operating temperature, ultimately determining
the choice of coolant and working cycle. The limited temperature ranges allowed
by present day irradiated structural materials, combined with the large
internal power demand of the plant, will limit the overall thermal efficiency.
The operating conditions of the fusion power source, the materials, coolant,
and energy conversion system will all need to be closely integrated.
