Page 445 - Fundamentals of Magnetic Thermonuclear Reactor Design

422 Fundamentals of Magnetic Thermonuclear Reactor Design

l Modest mobilisable radioactive inventories.
l Several lines of physical and functional barriers, which provide radiation
protection.
l Passive means for decay heat removal.

This safety analysis was based on very conservative assumptions about the
severe character of potential hazardous processes, the full mobilisable amount
of tritium and radioactive inventories in case of accident, and so on.
The designers’ conservatism is quite clear. It stems from the fact that ITER is
a first-of-a-kind and an experimental facility, and there are no definitive bench-
marks for the reactor optimisation design. Also, encumbering the project with
additional risks in the form of new, untested technology is certainly undesirable.
The importance of the ITER’s safety issue calls for the use of reliable input
data and computer codes. To this end, further research is necessary, including
the following:
l A better determination of the accumulation rate, mass and mobilisation of
radioactive inventories.
l Development of adequate physical and mathematical models of exchange,
absorption and desorption, diffusion and radiochemical processes, espe-
cially those involving hydrogen isotopes (in particular, the processes of
tritium capture by the FW and the FW conditioning, tritium conversion into
oxides, hydrogen release at accident-induced chemical reaction, in-cryostat
arcing, etc.).
l Improvement and detailed elaboration of the FW cooling computational models.

The reactor’s operational safety assurance requires the development of the
following:
l Express methods for online control of the leak-tightness of vacuum ducts
and gas/water supply lines, and for detection of leaks from plant rooms.
l Methods for preventing and suppressing arcing in the switchgear of power
supply systems.
l Diagnostics methods and means for preventing the magnet spontaneous
transitions from the superconducting to the normal state.
The remaining uncertainties can only be unravelled by experiments on ITER.

14.5 SAFETY OF DEMONSTRATION AND COMMERCIAL
REACTORS
Unlike ITER with its mainly research mission, next-step fusion reactors will work
to unlock the capabilities and the environmental potential of the controlled thermo-
nuclear fusion. The design of such reactors may make use of new and improved
materials and technologies. There is enough time for their development and for
making them commercially available. The priority of operational safety will, of
course, remain, while the regulatory guidelines will become tighter. In addition, the