Page 175 - Fundamentals of Magnetic Thermonuclear Reactor Design

156 Fundamentals of Magnetic Thermonuclear Reactor Design

magnets with the aim of maintaining operation under substantial dynamic
heat loads due to radiation, neutron absorption and magnetic field/current
variations.
Heat loads generated in ITER SC magnets, while in operation, are pulsed
loads, which is a factor of fundamental importance. This makes the oper-
ability and safety of ITER SC magnets and their cryogenic circuits one of the
key problems in tokamak thermal physics. For the purposes of the thermal–
hydraulic analysis, normal operation is taken to mean operation consistent
with a chosen plasma burn scenario, which may include plasma disruption.
Abnormal operation conditions comprise various situations where SC coils
stop being superconductive followed by the energy removal from the magnet
system.
The thermal–hydraulic analysis for the normal operating conditions includes
the following:

1. Simulations of a non-stationary temperature field of the TF magnet, the po-
loidal field (PF) magnets, the CS, the CCs and the support structures;
2. Assessment of the temperature, pressure and SHe mass flow rate variations
along the SC conductors, in the cooling circuits of the support structures,
and in cooling channels of cryogenic accessories (pipes, feeders, heat ex-
changers, etc.).
3. Search for methods to mitigate the pulsed heat loads generated in the TF
and CS MS and transferred to the cryoplant to select the relevant control
strategy and ensure stable and balanced operation of the cryoplant under
such loads.
The study of abnormal operating conditions is aimed at analysing the to-
kamak’s thermal–hydraulic behaviour and efficiency of quench protection in
cases when one or more ITER MS coils (TF, PF, CS or CC) loses its supercon-
ductivity.
This includes the investigation of the following:

1. The normal zone propagation and temperature/pressure rise in the SC coils
under protected and unprotected quenching.
2. Helium evacuation from the SC magnet primary cooling circuit.
In the case of ITER, such issues are mainly investigated numerically with
appropriate mathematical models. Obtained results should help optimise the SC
coil design to provide reliable operation of the magnets.
In the course of ITER activities, many issues relating to a comprehensive
mathematical modelling of the ITER magnets’ thermal–hydraulic behaviour
over a wide range of operational plasma scenarios [18–24] have been innova-
tively resolved. The key feature of constructed full-scale models is that they al-
low the magnets to be examined together with the cryoplant interface. The level
of details in the description of components included in the full-scale models is
variable in conformity with the particular tasks.