Browsing by Author "Hossain, Abu Sayed Md. Kamal"

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Development of a fast running multidimensional thermal-hydraulic code to be readily coupled with multidimensional neutronic tools, applicable to modular High Temperature Reactors
(2011) Hossain, Abu Sayed Md. Kamal; Lohnert, Günter (Prof. Ph. D.)
Modular High Temperature Reactors (HTRs) are considered as one of the most promising next generation reactors which will fulfill the future energy demand. The inherent safety is the most attractive feature of this type of reactor along with simplicity in design, operation and maintenance. Since the reactor is safe during any accident conditions without the actuation of any external safety systems, it is considered to be a inherently safe reactor. With its offered inherent safety features, the reactor responses solely from the reactor’s physical properties, hence any dangerous situation will be avoided. The inherent safety feature of this reactor depends entirely on the correct design of this reactor. The power density in the core, radius and height of the core, properties of the materials used and its configuration must be chosen in such a way that the decay heat produced in the core during any accident can be released to the surrounding by natural heat transfer phenomena without any help of external safety features. In addition, possible reactivity insertions into the core are limited such that the corresponding temperature increases of the fuels stay always below the fuel’s temperature design limit. Along with its inherent safety feature, the reactor must be designed such a way that it offers a competitive economics. The objective of this endeavor is to develop a fast running/multidimensional code which can be used to analyze, design and safety related issues in modular high temperature reactors. The program shall be generally applicable for modular HTRs (e.g pebble fuel, block fuel elements). Operational conditions with forced cooling as well as accident situations with heat removal by conduction and natural circulation shall be covered. Coupling to a reactor physics code shall be provided to account for the feedback of neutronics and thermal-hydraulics. Emphasis is on capturing essential effects resulting from three-dimensional features (e.g. single control rod withdrawal, power distribution with block-type fuel elements) rather than on a high level of detail, in order to keep computation times reasonably low. In general, we strive for a quick-turn analysis that provides enough insight to make informed decisions that can not wait for the extensive time it takes to conduct in-depth, detailed analyses, e.g. with large CFD models. The porous media approach is applied. The time dependent mass and energy conservation equations and simplified steady-state momentum conservation equations (dominance of friction) are solved for the cooling gas along with the time dependent energy conservation equation for the solid. An appropriate set of constitutive equations (e.g. effective heat conductivity of solid, pressure drop, heat transfer coefficient, etc.) is applied. A finite-volume method is used for the spatial discretisation. A fully implicit method with adaptive time step selection is applied for the temporal integration in transient problems. The capability of the program for simulating both pebble bed and block fuel reactors are demonstrated by calculating two benchmark problems. The capability of the program to couple with a neutronics system is shown by coupling the program with a point kinetics model. Finally, the tool is verified by calculating an experimental benchmark problem.