Axisymmetric finite-element analysis of aconcrete biological shield exposed to neutron radiation

Abstract

This paper presents development of an axisymmetric finite-element (FE) model of the concrete biological shield (CBS) of a VVER-440/213 reactor. Long-term neutron exposure causes radiation-induced volumetric expansion (RIVE) of aggregates, which is introduced in the analysis as a homogeneous eigenstrain driven by neutron fluence. The analysis aims to determine the initiation and further propagation of damage (cracks) with RIVE treated as the primary load effect. Acalibrated Mazars-μ damage model for concrete is implemented to describe the material nonlinear behavior. The analysis predicts the first occurrence of damage after ∼6 years, localized near the inner surface in the upper part of the section, with subsequent propagation vertically along the height and eventually toward the outer surface. Compared with selected studies (where the damage occurs after ≈12–15 years to first damage), the presented axisymmetric local-damage formulation is conservative, consistent with the omission of creep/temperature effects and nonlocal damage regularization. The findings therefore confirm and motivate subsequent 3D model, nonlocal approach and creep-coupled analysis.