## 1 Introduction  
Within the framework of the conceptual design of the EU-DEMO Breeding Blanket (BB) [1, 2], the University of Palermo is involved in the design of the Water-Cooled Lithium Lead (WCLL) BB foreseen for the European DEMO fusion reactor. One of the main objectives of the research activity is the development of a geometric layout for the WCLL Central Outboard Blanket (COB) segment robust enough to fulfil all the prescribed design requirements. To this purpose, the assessment of its thermo-mechanical behaviour under different loading conditions plays a key role and, in this regard, the availability of a realistic and detailed thermal field for the whole WCLL COB segment is pivotal. Nevertheless, the WCLL COB design presented at the end of the pre-conceptual phase [3] was not mature enough to allow reliable thermal-hydraulic assessments for the prediction of its thermal field. In any case, such an analysis would require a huge modelling effort, followed by a tremendous computational burden, which would entail the adoption of strong assumptions leading to a certain margin of uncertainties in the results [4]. Hence, an alternative procedure was developed [5] and applied in this study in order to predict a reliable 3D thermal field for the WCLL COB without performing its full thermal-hydraulic analysis, taking into account the radial and poloidal dependence of the thermal loads (namely, nuclear heating and heat flux on the FW surface).  
Afterwards, once the 3D thermal field of the WCLL COB segment was predicted, its structural behaviour was evaluated under different steady-state loading scenarios. First,the Normal Operation (NO) scenario, representing the normal operating conditions and thus falling under service Level A of the RCC-MRx [6] structural design code, was taken into account. Secondly, proper accidental loading scenarios were set-up, derived from two off-normal reference events: the Upper Vertical Displacements Event (UVDE) and the in-box Loss of Coolant Accident (LOCA). The UVDE is an abnormal event reproducing a plasma disruption due to an uncontrolled vertical motion of the plasma volume, classified as Level C. In contrast, the in-box LOCA is the design-driving accident for the BB and therefore it is classified as Level D in the RCC-MRx design code. Its associated loading conditions form the Over-Pressurization (OP) steady state loading scenario. The thermomechanical behaviour of the whole WCLL COB segment was therefore assessed in terms of displacement and equivalent von Mises stress fields. Moreover, a stress linearization procedure was performed within some critical regions, in order to evaluate the stress level by means of the design rules prescribed by the French nuclear code RCC-MRx, currently the primary reference for the DEMO reactor.  
A theoretical-numerical approach based on the Finite Element Method (FEM) was followed. The commercial code Abaqus v. 6.14 [7], considered as one of the reference FEM codes by the international scientific community involved in the nuclear fusion research, was utilized. The obtained results are presented herein and critically discussed. To this end, the adopted methodology and the structure of the paper are reported in the Section 2.