For performance evaluation of existing reinforced concrete members under irradiation conditions, a numerical code called "DEVICE" (Damage EValuation for Irradiated ConcretE), which takes into account the heat, moisture, and radiation transport coupled with cement hydration, is proposed. This code is composed of the established computational cement-based material (CCBM) model and the one-dimensional deterministic transport Sn code "ANISN". In the proposed model, temperature-dependent irradiation-induced expansion of aggregate minerals and resultant strength deterioration of concrete are introduced. Currently, the knowledge and modeling of irradiation-induced expansion of aggregate mineral is limited only for α-quartz. DEVICE was used for evaluating the strength distribution of the decommissioned plant Japan Power Demonstration Reactor (JPDR). Compressive strength distribution in a concrete biological shielding (CBS) wall of the JPDR was obtained by core sampling, and the compressive loading test results were compared with the calculation results. This comparison proved the practicality potential of DEVICE to predict the concrete strength distribution in a CBS. In addition, concrete strength change and its distribution in a CBS of an anonymous two-loop pressurized water reactor was simulated by DEVICE. The contributing factors for the change in the distribution of concrete strength at the inner surface of the CBS are discussed. Furthermore, the ways of integrity evaluation other than the existing allowable fast neutron fluence method are proposed and discussed as follows: 1) mineral composition-based allowable fast neutron fluence; 2) strength prediction at the inner surface based on the expansion of mineral composition of aggregates and the lower limit curve of the ratio of compressive strength of the specimen after irradiation (Fc) to that of the reference specimen (Fco) as a function of concrete expansion; and 3) direct numerical calculation for seismic performance by considering irradiation-induced volume expansion and degradation of concrete.
Reliable estimation of surface fault displacements is crucial to the safety of nuclear power plant facilities. It is necessary to develop a numerical method for the estimation. In the study, we develop a finite element method in which the following two functions are implemented: (1) a symplectic time integration of an explicit scheme to properly conserve the energy of the system; and (2) rigorously formulated joint elements of high order. The finite element method is enhanced with parallel computing capability. We apply the developed method to solve simple three-dimensional models of faults embedded in a rock mass. It includes a comparison of results from quasi-static and dynamic simulations and investigation of the sensitivity of results to the shear stiffness on faults. In the study, we propose capacity computing with a quasi-static simulation for uncertainty quantification.
A parallel finite element method (FEM) based on high-fidelity models for solving diverse earthquake engineering problems is presented. Its key feature is a parallel solver that is tuned to solve large-scale wave equations. Tensorial material constitutive relations of concrete and soil and sophisticated nonlinear joint elements are implemented to broaden the applicability of the parallel FEM. The performance of the proposed parallel FEM is demonstrated for three examples; namely, seismic response, liquefaction, and surface earthquake fault analyses. A high-fidelity model was constructed for each analysis, and the numerical results were validated against observed data. The performance of the proposed parallel FEM approach was evaluated in terms of the resolution of the simulated results.Ensemble computing based on approximately a hundred high-fidelity models is useful for cases where there are considerable uncertainties regarding the material properties.
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