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Blanket  Chapter | 10    313


                Neutron Characteristics. The chemical compositions of the TBM and DE-
             MO-blanket materials are likely to be the same. However, differences in neutron
             flux loads and the BZ geometry will not allow a straightforward extrapolation
             of the neutron flux density distribution, radiation energy release, and the TBM
             shielding parameters to DEMO-S. Therefore, the main task of neutron tests is
             to verify the computational codes. To accomplish this, one has to measure the
             spatial distribution of the neutron flux and its energy spectrum. Also, it is im-
             portant to build a source of fusion neutrons to prove experimentally the oper-
             ability of materials exposed to neutron fields of the DEMO-S reactor, and the
             special fusion facility used for a durability assessment of DEMO-S in-chamber
             components.
                Thermal Hydraulic Characteristics. Another important TBM testing goal is
             to demonstrate the possibility of obtaining high-potential heat for an efficient
             heat-to-electricity conversion. The TBM coolant temperature range indicated
             in Table 10.4 is more or less the same as in the DEMO-S blanket and can be
             realised with an appropriate coolant flow rate. In a TBM, this coolant flow rate
             will be slower than in the DEMO-S blanket, so a number of experiments should
             be performed to simulate the desired coolant temperature rise and flow rate.
             Desired coolant’s exit temperature can be obtained by varying the inlet tem-
             perature.
                An important blanket design aspect is the analysis of its thermal physics
             condition throughout the operation cycle, including the establishing of burn/
             pause durations. Computations made for different TBM versions suggest that
             a close-to-stationary module temperature is achieved during 400–1000 s when
             plasma is burning and during 700– 850 s when there is a pause. The burn design
             duration in the inductive scenario (400 s) is insufficient for attaining a steady
             temperature state and validating the thermal hydraulic characteristics. Rather, a
             discharge duration of 1000–3000 s, consistent with the non-inductive scenario,
             would be needed.
                Here, again, the experimental adjustment of computational codes is an im-
             portant research goal. To this end, the ITER diagnostic system should include
             instruments to control coolant temperature and flow rate in all channels, as
             well as channel wall temperatures, pressure differences in individual ducts,
             and magnetic induction (for liquid-metal TBMs). Also important are neutron
             and heat flux metrics. Code pre-adjustment will be an off-reactor exercise,
             of course, but a synergy analysis must be conducted through direct reactor
             experiments.
                MHD Characteristics and Properties of Electrical Insulation Barriers. The
             DEMO-S blanket is expected to use electrically insulating coatings (barriers) at
             the duct wall/liquid metal interface. Their purpose is to reduce currents induced
             in the liquid metal and, hence, decrease the MHD pressure drop. This would
             help reduce the mechanical stresses in the structure components, as well as the
             coolant pumping power.
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