ITER blanket module 17 shield block design and analysis

The shield block reference design of the typical ITER blanket module has a number of grave disadvantages, precarious with relation to nuclear safety of the reactor. The main problems may arise when innage of the parallel cooling passages both in the first wall and in the shield block. Vapor locking in a radial channel with flow insert driver is very probable. Another problem, as a result of the same reason, is draining and dehydration of the coolant system. Then the highly dense packing of the radial channels in the collector array brings an essential flow irregularity. Customary as a rule, the lack of coolant is observed in the last channels, nearest to the outside, most heated surface of the shield block. A local boiling is possible in these dead spaces of coolant system. In consequence of the radial flow irregularity the cooling in the upper box header, directly under the first wall, may be extremely poor. Among the other imperfections one should note the large frontal figured lids, which overburden at welding and give to rise of stresses and shrinkages, and as a result, the large share of irreparable spoilage. The paper represents an alternative design of the shield block coolant system with predominantly sequential flow circuit. The cooling channels are drilled from the frontal side as inclined transverse holes. The open drilling ends are combined in pairs with milled grooves and welded with small lids. This gain the following advantages: the lids may have smaller thickness (7 mm instead 20 mm), the cooling passengers are placed closer to the lateral and upper sides and make cooling better, the welding stress and shrinkages are reduced, there are no any dead spaces of coolant, and the water fillup and draining are substantially improved. The listed hydraulic and thermo mechanical problems have been analysed with help of 3D models in ANSYS CFX program. The models include both the cooling space filled by water and the solid part of shield block. Thus the conjugate hydraulic and thermo structural analysis is solved simultaneously with account of real geometry and local flow turbulence. The results of the analysis are assumed as a basis of design modification to eliminate the existent disadvantages of the reference design. (orig.)