A modular concept and a computer language for modeling and simulation of a passive boiling water reactor
Frank Möhle · Repository for Publications and Research Data (ETH Zurich) · 2006
A modular concept for the simulation of a general passive boiling water reactor (BWR) pressure vessel and containment system is developed.The model is based on the assumption of slow transients and well mixed gas and liquid in the containments so that ordinary differential equations (ODEs) can be used for the description of the thermalhydraulic phenomena instead of partial differential equations (PDEs).Each module represents a special component of a physical system.A module is written in an advanced formula manipulation language (Maple V) which permits an easy programming of the typically implicitly given ODEs describing this subsystem and their automated transformation into an explicit form required by the subsequent numerical integration.For handling the interaction between different modules a new language (MSDL: Modular System Description Language) and a corresponding compiler have been developed.MSDL is the language to be applied by the user.In his program the user essentially calls the modules written in Maple.The formula manipulation of the relatively small input code in MSDL results in automatically generated Fortran-code of typically several thousand statements.This intermediate code reflects different physical states of the system, which can change during simulation due to discontinuities.The advantage of this new concept is the capability of changing parts of the model with a marginal programming effort.For this kind of application the exact tracking of discontinuities and other events is important.Discontinuities may result from simple changes in inputparameters, all the way to complex changes of the governing model equations at a certain time, e.g. the opening or closing of valves.For the efficient and stable integration of the differential equations, it is an advantage to apply algorithms of variable order and variable step size with automatic stiffness detection and root finding capabilities for the localization of discontinuous events.Either an Adams-Moulton algorithm or a Gear-type integrator are applied, depending on what is most appropriate.After having tested the feasibility of the concept, the number of MSDL-modules has been increased and collected in a library.Finally, the results of a complex simulation is discussed and com-