THERMO-MECHANICAL AND FRACTURE ASSESSMENT BY FE MODELING FOR THE CRITICAL COMPONENTS OF THE DEMO NUCLEAR FUSION REACTOR

NUCLEAR FUSION REPRESENTS ONE OF THE MOST PROMISING PATHWAYS TOWARD SUSTAINABLE, LARGE-SCALE, AND LOW-IMPACT ENERGY PRODUCTION. HOWEVER, THE EXTREME OPERATIONAL CONDITIONS WITHIN FUSION REACTORS, CHARACTERIZED BY ELEVATED TEMPERATURES, INTENSE NEUTRON IRRADIATION, AND SEVERE MECHANICAL AND MAGNETIC LOADS, POSE SIGNIFICANT CHALLENGES FOR THE STRUCTURAL INTEGRITY AND LONG-TERM RELIABILITY OF REACTOR COMPONENTS. THIS DOCTORAL WORK HAS BEEN DEVELOPED ALONG TWO COMPLEMENTARY AND PARALLEL RESEARCH LINES, CONDUCTED RESPECTIVELY WITHIN THE ACADEMIC FRAMEWORK OF THE UNIVERSITY OF SALERNO AND IN COLLABORATION WITH THE ENGINEERING COMPANY LT CALCOLI AS PART OF AN INDUSTRIAL PARTNERSHIP. WITHIN THE ACADEMIC RESEARCH, THE FOCUS WAS PLACED ON FRACTURE MECHANICS APPLIED TO THE DIVERTOR OF THE DEMO FUSION REACTOR, ONE OF ITS MOST CRITICAL STRUCTURAL COMPONENTS. A COMPREHENSIVE FINITE ELEMENT (FE) MODEL WAS DEVELOPED TO CAPTURE THE THERMO-MECHANICAL RESPONSE OF THE DIVERTOR UNDER REALISTIC OPERATING LOADS. USING SUBMODELING AND LINEAR ELASTIC FRACTURE MECHANICS (LEFM) APPROACHES, STATIONARY SEMI-ELLIPTICAL CRACKS WERE INTRODUCED TO ASSESS STRESS INTENSITY FACTORS (SIFS) AND IDENTIFY THE MOST CRITICAL REGIONS. THE STUDY WAS FURTHER EXTENDED TO SIMULATE CRACK PROPAGATION UNDER MULTI-STEP LOADING CONDITIONS, ALLOWING FATIGUE LIFE ESTIMATION THROUGH PARIS’ LAW AND THE PREDICTION OF THE NUMBER OF CYCLES REQUIRED TO REACH CRITICAL CRACK SIZES. ADDITIONALLY, AN ELASTOPLASTIC MATERIAL MODEL WAS IMPLEMENTED TO EVALUATE THE DEVIATION OF THE STRUCTURAL RESPONSE FROM THE LINEAR ELASTIC ASSUMPTION, WHILE A MULTI-CRACK GROWTH ANALYSIS WAS PERFORMED TO INVESTIGATE THE SIMULTANEOUS PRESENCE OF TWO CRACKS LOCATED IN ADJACENT CRITICAL REGIONS. THE OBTAINED RESULTS IDENTIFIED THE MOST VULNERABLE DIVERTOR ZONES AND DEMONSTRATED THE SENSITIVITY OF CRACK GROWTH TO THERMAL GRADIENTS AND COMBINED LOADING EFFECTS. IN PARALLEL, THE INDUSTRIAL RESEARCH CONDUCTED WITH LT CALCOLI FOCUSED ON THE THERMO-MECHANICAL DESIGN AND ANALYSIS OF A ROBOTIC ARM INTENDED FOR THE MAINTENANCE OF THE DEMO BREEDING BLANKET, OPERATING UNDER SEVERE THERMAL CONDITIONS. THE STUDY ASSESSED THE STRUCTURAL RESPONSE OF THE MANIPULATOR TO HIGH HEAT CONDUCTIVE AND CONVECTIVE FLUXES ORIGINATING RESPECTIVELY FROM THE BLANKET AND THE SURROUNDING ENVIRONMENT, AND EXPLORED DESIGN AND MATERIAL OPTIMIZATION STRATEGIES TO ENHANCE HEAT RESISTANCE AND ACHIEVE A MORE UNIFORM TEMPERATURE DISTRIBUTION. BEYOND THE SPECIFIC RESULTS OBTAINED IN EACH RESEARCH LINE, THE ORIGINAL CONTRIBUTION OF THIS WORK LIES IN THE DEVELOPMENT OF AN INTEGRATED METHODOLOGY FOR ASSESSING THE STRUCTURAL INTEGRITY OF FUSION REACTOR COMPONENTS UNDER REALISTIC OPERATIONAL CONDITIONS. THE COMBINED USE OF THE SUBMODELING TECHNIQUES, FRACTURE MECHANICS AND LIFETIME ASSESSMENT ANALYSES ESTABLISHES A PREDICTIVE FRAMEWORK CAPABLE OF CAPTURING COMPLEX LOADING INTERACTIONS AND REALISTIC OPERATING CONDITIONS MORE ACCURATELY THAN CONVENTIONAL APPROACHES. THE INTEGRATION OF THESE TWO RESEARCH DIRECTIONS YIELDS A COMPREHENSIVE CONTRIBUTION TO THE STRUCTURAL SAFETY, DURABILITY, AND MAINTAINABILITY OF NEXT-GENERATION FUSION REACTORS, SUPPORTING THEIR RELIABLE AND SUSTAINABLE DEVELOPMENT.