Ultimate load behaviour of internally pressurized 'cut-and-cover' orthotropic reactor containment

Ahmad, Mohamed Fouad Abdel Meneim (1979) Ultimate load behaviour of internally pressurized 'cut-and-cover' orthotropic reactor containment. Masters thesis, Memorial University of Newfoundland.

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Abstract

Nonlinear static and dynamic analyses are presented for 'cut-and-cover’ type underground reinforced concrete nuclear reactor containments subjected to internal pressurization. A nonlinear anisotropic model has been adapted and incorporated into a general linear and nonlinear, static and dynamic finite element analysis programme, NONSAP, to account for the orthotropic behaviour of reinforced concrete. The load increment required in elastoplastic static analysis, and the time interval, as well as the boundary simulation of infinite or semi-infinite continuum in dynamic analysis, are adequately taken into account in this study. Numerical investigations of the stability of equilibrium iteration procedure to reduce the divergence of the incremental solution from the true solution, are also presented. -- Parametric studies for the static response of the containment are carried out for: 1) stiffness of backfill (original and stabilized sandy loam fill with different cement ratios, 2%, 6%, and 10%); 2) thickness of backfill (2.5, 7.5, 12.5, and 18.5m); 3) percentage of reinforcing steel (#18 bars @ .25m, #18 bars @ .35m, #14 bars @ .35m, and plain concrete); 4) thickness of containment (1.25, 1.5, 2, and 2.5m) and; 5) different types of surrounding medium (sandy loam, clay, sand stone, and silty clay). The response values determined are: i) maximum positive vertical displacement, ii) maximum negative vertical displacement, iii) vertical and horizontal displacement, iv) stress-displacement relation at the point of maximum stress concentration. The results confirm the effect of the different parameters on the response of the containment. The stiffness of backfill and the containment thickness have the greatest effect. The reinforcement effect is amplified when plastic flow commences. -- Dynamic analysis is carried out to study the response of a containment to a typical pressure-time function following a Loss-of-Coolant-Accident (LOCA). A disturbance in displacements and stresses, is observed immediately after pressure decreases for two seconds after which the response becomes steadystate.

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