Background and objective

The seismic assessment of nuclear structures under Design Extension Conditions (DEC) requires an understanding of structural behaviour beyond the conventional elastic design range. Under severe earthquake loading, nonlinear behaviour may develop in reinforced-concrete structures, resulting in cracking, stiffness degradation, reinforcement yielding, redistribution of internal forces and the progressive development of structural damage.

For the LEANDREA SMR-LFR demonstrator, understanding this behaviour is important for evaluating the structural response and available margins of the reactor building containment under severe seismic conditions.

The objective of this Master’s thesis is to numerically investigate the nonlinear seismic response of the LEANDREA SMR-LFR reactor building containment structures under Design Extension Condition earthquake loading, with particular attention to the initiation, distribution and progression of structural damage.

A nonlinear finite element model representative of the LEANDREA reactor building containment structures will be developed and subjected to seismic loading representative of DEC conditions. The study will investigate the evolution of structural response from the elastic range into the nonlinear domain and evaluate the extent and localization of damage under increasing levels of seismic demand.

Main activities

The Master’s thesis will include:

• Review of the relevant requirements and methodologies for the seismic assessment of nuclear civil structures under Design Extension Conditions.
• Review of appropriate methodologies for the nonlinear seismic analysis of reinforced concrete reactor building containment structures.
• Development of a nonlinear finite element model representative of the LEANDREA SMR-LFR reactor building containment structures.
• Definition and calibration of appropriate nonlinear material models for: reinforced concrete, concrete cracking and crushing, reinforcing-steel yielding, stiffness and strength degradation, where applicable.
• Definition and selection of appropriate DEC seismic input for the numerical analyses.
• Performance of nonlinear dynamic seismic analyses of the LEANDREA SMR-LFR reactor building containment structures.
• Investigation of the transition from elastic to nonlinear structural behaviour.
• Assessment of the initiation, localization and propagation of structural damage.
• Evaluation of relevant response parameters, including:  displacements and inter-storey/drift response; stresses and strains, concrete cracking and damage, reinforcement yielding, redistribution of internal forces. residual deformations, where relevant.
• Performance of sensitivity analyses using different levels of seismic demand to investigate the evolution and extent of damage with increasing earthquake intensity.
• Identification of critical structural regions and potential governing failure mechanisms.
• Assessment of the structural margins and overall stability of the LEANDREA SMR-LFR reactor building containment structures under DEC seismic conditions.
• Identification of recommendations for further detailed analyses and future design development of the LEANDREA SMR-LFR reactor building containment structures.

Student profile

The thesis is intended for a student enrolled in a Master’s-level Civil Engineering programme.