FX2-TH, 2-D Multigroup Neutron Diffusion in X-Y, R-Z and R-Theta Geometry with Thermal Feedback

1 - Description of problem or function: FX2-TH solves the steady-state and time-dependent two-dimensional multigroup neutron diffusion equations with thermal and hydraulic feedback. The following geometry options are available: x, r, x-y, r-z, theta-r, and triangular. FX2-TH contains two basic thermal and hydraulic models: a simple adiabatic fuel temperature calculation and a more detailed model consisting of an explicit representation of fuel pin, gap, clad, and coolant. FX2-TH allows feedback effects from both fuel temperature (Doppler) and coolant temperature (density) changes. The code is designed for nuclear reactor analysis. 2 - Method of solution: The multigroup diffusion equations are discretized in space using mesh-centered finite differences. The steady-state solution of these equations is found by accelerating a fission source iteration through the use of Chebyshev polynomials. The neutron fluxes for each energy group at each power iteration are found using the successive line over-relaxation method. A consistent set of steady-state conditions is established by iterating between the steady-state neutronics and thermal-hydraulics equations. The time-dependent solution is then found using the improved quasistatic method. The shape calculations required by the quasistatic method utilize the same calculational methods as described above for the steady-state calculation. 3 - Restrictions on the complexity of the problem: Variable dimensioning is used throughout the program so that computer storage requirements depend on a variety of problem parameters. The amount of memory required can range from 300 K bytes for a small problem up to the maximum limit of computer storage for very large problems