RELAP5-3D is a simulation tool that allows users to model the coupled behavior of a nuclear reactor's coolant system and the reactor core for various operational transients and postulated accidents that might occur in a nuclear reactor. RELAP5-3D (Reactor Excursion and Leak Analysis Program) can be used for reactor safety analysis, reactor design, simulator training of operators, and as an educational tool by universities. RELAP5-3D was developed at Idaho National Laboratory to address the pressing need for reactor safety analysis and continues to be developed through the United States Department of Energy and the International RELAP5 Users Group (IRUG) with over $3 million invested annually. The code is distributed through INL's Technology Deployment Office and is licensed to numerous universities, governments, and corporations worldwide.
Background RELAP5-3D is an outgrowth of the one-dimensional RELAP5/MOD3 code developed at Idaho National Laboratory (INL) for the U.S. Nuclear Regulatory Commission (NRC). The U.S. Department of Energy (DOE) began sponsoring additional RELAP5 development in the early 1980s to meet its own reactor safety assessment needs. Following the Chernobyl disaster, DOE undertook a re-assessment of the safety of all its test and production reactors throughout the United States. The RELAP5 code was chosen as the thermal-hydraulic analysis tool because of its widespread acceptance. The application of RELAP5 to various reactor designs created the need for new modeling capabilities. In particular, the analysis of the Savannah River reactors necessitated a three-dimensional flow model. Later, under laboratory-discretionary funding, multi-dimensional reactor kinetics were added. Up until the end of 1995, INL maintained NRC and DOE versions of the code in a single source code that could be partitioned before compilation. It became clear by then, however, that the efficiencies realized by the maintenance of a single source were being overcome by the extra effort required to accommodate sometimes conflicting requirements. The code was therefore "split" into two versions—one for NRC and the other for DOE. The DOE version maintained all of the capabilities and validation history of the predecessor code, plus the added capabilities that had been sponsored by the DOE before and after the split. The most prominent attribute that distinguishes the DOE code from the NRC code is the fully integrated, multi-dimensional thermal-hydraulic and kinetic modeling capability in the DOE code. This removes any restrictions on the applicability of the code to the full range of postulated reactor accidents. Other enhancements include a new matrix solver, additional water properties, and improved time advancement for greater robustness.
Features
Modeling Capability RELAP5-3D has multidimensional thermal hydraulics and neutron kinetic modeling capabilities. The multidimensional component in RELAP5-3D was developed to allow the user to accurately model the multidimensional flow behavior that can be exhibited in any component or region of a nuclear reactor coolant system. There is also two dimensional conductive and radiative heat transfer capability and modeling of plant trips and control systems. RELAP5-3D allows for the simulation of the full range of reactor transients and postulated accidents, including: Trips and controls Component models (pumps, valves, separators, branches, etc.) Operational transients Startup and shutdown Maneuvers (e.g. change in power level, starting/tripping pump) Small and large break Loss Of Coolant Accidents (LOCA) Anticipated Transient Without Scram (ATWS) Loss of offsite power Loss of feedwater Loss of flow Light Water Reactors (PWR, BWR, APWR, ABWR, etc.) Heavy Water Reactors (e.g. CANDU reactor) Gas-cooled Reactors (VHTGR, NGNP) Liquid metal cooled reactors Molten-salt cooled reactors
Hydrodynamic Model RELAP5-3D is a transient, two-fluid model for flow of a two-phase vapor/gas-liquid mixture that can contain non-condensable components in the vapor/gas phase and/or a soluble component in the liquid phase. The multi-dimensional component in RELAP5-3D was developed to allow the user to more accurately model the multi-dimensional flow behavior that can be exhibited in any component or region of an LWR system. Typically, this will be the lower plenum, core, upper plenum and downcomer regions of an LWR. However, the model is general, and is not restricted to use in the reactor vessel. The component defines a one, two, or three-dimensional array of volumes and the internal junctions connecting them. The geometry can be either Cartesian (x, y, z) or cylindrical (r, q, z). An orthogonal, three-dimensional grid is defined by mesh interval input data in each of the three coordinate directions. The functionality of the multi-dimensional component has been under testing and refinement since it was first applied to study the K reactor at Savannah River in the early 1990s. A set of ten verification test cases with closed form solutions are used to demonstrate the correctness of the numerical formulation for the conservation equations. Recent developments have updated the programming language to FORTRAN 95 and incorporated viscous effects in multi-dimensional hydrodynamic models. Currently, RELAP5-3D contains 27 different working fluids including:
Light water (e.g. 1967, 1984, and 1995 steam tables) Heavy water Gases (e.g. helium and carbon dioxide) Molten salts (e.g. FLiBe and FLiNaK) Liquid metals (e.g. sodium and lead-bismuth eutectic) Alternative fluids (e.g. glycerin and ammonia) Refrigerants (e.g. R-134a) Working fluids allow single-phase, two-phase, and supercritical applications.
Thermal Model Heat structures provided in RELAP5-3D permit calculation of heat transferred across solid boundaries of hydrodynamic volumes. Modeling capabilities of heat structures are general and include fuel pins or plates with nuclear or electrical heating, heat transfer across steam generator tubes, and heat transfer from pipe and vessel walls. Temperature-dependent and space-dependent thermal conductivities and volumetric heat capacities are provided in tabular or functional form either from built-in or user-supplied data. There is also a radiative/conductive enclosure model, for which the user may supply/view conductance factors.
… excerpt ends here. Continue reading the full article.
