Analysis of the Thermo-Mechanical Behaviour of the EU DEMO Water-Cooled Lithium Lead Central Outboard Blanket Segment under an Optimized Thermal Field

Abstract

Within the framework of the EUROfusion research activities on the DEMO Water-Cooled Lithium Lead (WCLL) Breeding Blanket (BB) design, a research study was performed to preliminarily optimize, from the thermal point of view, the WCLL Central Outboard Blanket (COB) segment in order to investigate its structural behaviour under a realistic thermal field. In particular, a study of thermal analyses was performed to optimize the Double Walled Tubes and Segment Box cooling channels’ geometric configurations along the poloidal extension of the WCLL COB segment, in order to obtain a spatial temperature distribution fulfilling the thermal design requirement. Then, the thermo-mechanical analysis of the WCLL COB segment under Normal Operation (NO, representing nominal conditions), Upper Vertical Displacements Event (UVDE, representing a plasma disruption event) and Over-Pressurization (OP, representing an in-box loss of coolant accident) scenarios were carried out, assuming the previously obtained thermal field, to realistically predict displacement and stress fields. Finally, a stress linearization procedure allowed comparing the stress values obtained in some critical regions of the structure with the criteria prescribed by the reference design standard RCC-MRx. A theoretical–numerical approach based on the Finite Element Method (FEM) was followed using the commercial code Abaqus v. 6.14.

Preliminary thermal optimization and investigation of the overall structural behaviour of the EU-DEMO water-cooled lead lithium left outboard blanket segment

“…It has to be highlighted that this represents a first guess for the WCLL LOB segment, since no detailed thermal studies have been yet carried out for a lateral blanket segment. Concerning the DWTs spatial arrangement, on the basis of the outcomes found in the thermal optimization study performed for the WCLL Central Outboard Blanket (COB) segment [8], the alternative cross-24 and cross-26 DWTs layouts (foreseeing, respectively, 24 and 26 tubes per elementary cell, Figure 3) have been adopted for the WCLL LOB equatorial region. Since, unlike the COB segment, the LOB segment layout presents asymmetrical SWs and its equatorial region is larger than the COB one (Figure 4), the original cross-24 and cross-26 DWTs layout conceived for the COB segment have been properly modified, by moving, re-shaping and slightly re-sizing the DWTs in order to adapt them to the peculiarities of the LOB segment geometry.…”

“…The campaign of thermal analysis previously described has allowed predicting a thermal field within the equatorial region of the WCLL LOB segment compliant with the suggested thermal requirements. Afterwards, an interpolation procedure has been purposely set-up in order to find a set of polynomial functions capable of representing the thermal field arising within the equatorial region with a remarkable level of confidence [8] [15]. Then, the found functions have been used to obtain a 3D thermal field for the whole WCLL LOB segment.…”

Structural assessment of the EU-DEMO water-cooled lead lithium central outboard blanket segment adopting the sub-modelling technique

“…The study of an entire segment is particularly onerous from both a computational and a modelling effort standpoint due to its size and the complexity of details it is made up. Therefore, in order to speed up the calculations and to make the mesh procedure easier, a complete assessment of the structural behaviour of the COB segment has been carried out [4] simplifying the model and removing some structural details, as the Segment Box cooling channels. In the above-mentioned work, the evaluation of the structural performances of some regions, as the toroidal-radial and poloidal-radial Stiffening Plates, in terms of RCC-MRx design criteria fulfilment, has been presented.…”

“…Then, the present work is intended as a follow-up to the previous one [4]. Once investigated the overall structural behaviour of the WCLL COB segment under nominal and accidental loading scenarios, the sub-modelling technique has been adopted to assess in detail the structural performances of some regions of interest of the segment.…”

Thermo-Mechanical Analysis and Design Update of the Top Cap Region of the DEMO Water-Cooled Lithium Lead Central Outboard Blanket Segment

“…Displacement field applied to the model lower surface, obtained from the analysis of the thermo-mechanical behavior of the whole WCLL COB segment [21], in order to simulate the effect of the rest of the COB segment on the investigated region. In particular, depending on the scenario, the appropriate displacement field is extracted from the corresponding COB analysis and applied to the present model.…”