Dynamic analysis of the 'cut-and-cover' type underground nuclear reactor containment

El-Tahan, Hussein Wahba Mohamed (1977) Dynamic analysis of the 'cut-and-cover' type underground nuclear reactor containment. Masters thesis, Memorial University of Newfoundland.

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Abstract

Nonlinear dynamic structure-medium interaction for ‘cut-and-cover type’ underground nuclear reactor containments is studied for earthquake excitation. The structure considered is a reinforced concrete containment for a 1100 - MWe power plant buried in a dense sand medium. The analysis has been carried out using the recently developed computer programmes: LUSH (plane-strain finite element), and SHAKE (one-dimensional wave propagation analysis). The high frequency ranges, which must be considered in the study of soil-structure interaction for nuclear power plants, and the nonlinear soil behaviour during strong earthquakes are adequately taken into account in this study. -- Parametric studies for the response of the containment and the surrounding medium are carried out for: 1) containment shape (high horseshoe, flat horseshoe and semi-circular roof-vertical walls), 2) relative stiffness of the containment and the medium, 3) depth of burial of the containment (shallow, intermediate and deep embedments), 4) relative stiffness of the medium and filling material (original fill, loose sand, stabilized sand and reinforced earth), 5) thickness of the backfill jackets (10ft. and 70ft.), 6) isolation of the containment using energy absorbing jackets around the containment (polyurethane foam and foamed concrete), and 7) type of surrounding medium (sand and rock). Comparative studies are presented for rock vs. sand siting and aboveground vs. underground siting in sand. -- The response values determined are: i) time history of acceleration, displacement and stresses, ii) maximum stresses and maximum accelerations, and iii) acceleration response spectra. Plotting of these results using the CALCOMP Plotter involved writing of twelve computer programmes. -- The results indicate that: i) The high horseshoe shape is the best among the three shapes considered decreasing the containment stresses by 10-20%, ii) Flexible containments are better than rigid ones, iii) Successive reductions in containment stresses to 67% of the initial values are associated with each additional 70ft. embedment depth, iv) The relative stiffness of the filling material and the medium has the most significant effect on the response. The lower the modulus of elasticity of the filling material, the greater is the reduction in the containment and medium stresses. A filling material with stiffness 30% lower than that of the medium, reduces the stresses by 30% in the containment, and about 20% in the medium, v) Using a jacket of energy absorbing material (polyurethane foam) in a sand medium reduces the containment and medium stresses by 65% and 40% respectively, vi) A reduction in the containment stresses of about 20% is achieved using a reinforced earth jacket, vii) Increasing the width of the backfill side-cover increases the stresses in the containment and the medium, viii) The response values of the medium near the containment are considerably affected by the interaction. The interaction effect is larger for aboveground siting, and ix) A containment in the sand medium is subjected to dynamic loading higher than that for a rock medium. -- Recommendations are made for further studies to account for more realistic modelling and material behaviour, and more complex plant configuration and structural details.

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