Mechanical analysis of a model of the breeding blanket of net in faulted conditions

Abstract

This paper has been prepared in the framework of the safety analysis of a breeding blanket proposed for NET (Next European Torus). The basic features of the system are the following:

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  Li₁₇Pb₈₃ as breeder;

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  pressurized (5 MPa) water as coolant;

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  AISI 316 SS as structural material.

The breeding blanket consists of 24 segments with an angular opening of 15° placed side by side in the toroidal direction and arranged in the inboard and outboard part of the plasma chamber. The outboard part of the segment is presently under development, and two different design options are proposed:

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  a modular concept in which the breeding units (arranged in five rows and four columns), named modules, look like boxes;

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  a tubular concept in which the breeding units are tubes bent in the poloidal direction.

In both concepts the vessel of the breeding unit must operate as the first barrier against the accident propagation in case of a pipe break in the unit's cooling system.

The mechanical behaviour of the modular concept, loaded by the pressure transient due to such a pipe break, has been investigated and is presented in detail. The analysis of the results, taking into account material non-linearities, fluid-structure interactions and dynamic effects, shows that the structural reliability of the module vessel cannot be guaranteed, and suggests to continue the development of the tubular concept for which a much better mechanical behaviour is expected.