Page 334 - Fundamentals of Magnetic Thermonuclear Reactor Design

312 Fundamentals of Magnetic Thermonuclear Reactor Design

ITER is a pulsed reactor, in which the plasma burn relative length is within
one-fourth of the total burn-pause cycle. For this reason, one should assess,
when doing design calculations, parameter forecasting and test result analysis
for TBMs, how close the module operation conditions are to quasi-stationary
operation.
The TBMs are much smaller than the DEMO-S hypothetical blanket, as
shown in Table 10.4. These differences suggest the importance of checking the
adequacy of extrapolating the TBM testing results to DEMO-S.
The experimental data amount and the possibility of their correct interpreta-
tion depend on the control and measurement system. Placing the right number
of sensors in a TBM and achieving the desired measurement accuracy is a dif-
ficult engineering task.
With these problems in mind, let us compare the main design characteristics
of a TBM and the DEMO-S blanket. The purpose is to outline the strategy,
algorithm and methodology for analysing individual characteristics and set the
minimum requirements for ITER’s operating conditions.
The comparability of general design principles for a TBM and the DEMO-S
blanket is ensured if there is a uniformity of

l structural and breeding materials,
l coolants and tritium breeders,
l coolant routing configurations and flow regimes, and
l MHD electrical insulation and diffusion barriers.
Tritium Breeding. The tritium breeding technology testing and experi-
mental validation that fusion can make its own fuel are among the main
goals of the TBM testing. Quantitatively it means that a TBR (per unit vol-
ume of the BZ) greater than unity had to be achieved. Lithium enrichment
6
6
with Li raises the TBR. However, even with a 90% Li enrichment, the TBR
is much smaller in TBMs than in DEMO-S. In addition, radiation chemis-
try processes in TBMs are much more influenced by neutron fluxes from
neighbouring (shielding) blanket modules because of the TBMs’ smaller di-
mensions. In this connection, the TBM testing programme provides for the
development and verification of computational codes, which will later be
adapted to DEMO-S. Also, the diagnostic system includes high-precision
instruments, such as tritium flow dynamics, leakage and trapped tritium
measurement devices.
Due to the TBMs’ very low tritium breeding rates, an adequate assessment
of their tritium extraction systems is only possible with a sufficient number of
pulses and sufficient pulse lengths (under the non-inductive and combined dis-
charge modes with serial pulses).
A lithium breeder, characterised by high tritium solubility and negligible tri-
tium loss, allows an extraction system to be enabled upon achieving an adequate
tritium concentration in the module.