| For a complete understanding of the behavior of a nuclear reactor, a detailed description of its neutron population is required. The general integro-differential form of the Boltzmann transport equation, written in terms of neutron density in seven-dimensional phasespace, describes a balance between various nuclear processes affecting the neutron population. During the last decade, the development of advanced reactor designs required, and the exponential increase in computer power allowed more accurate solutions of the Boltzmann transport equation.;This dissertation describes the development of a methodology called MOCHA (which stands for the A&barbelow;dvanced M&barbelow;ethod O&barbelow;f CHaracteristic), its implementation in the MAGGENTA-MOC computer code, and its application in a number of assembly and cell calculations. The MOCHA methodology presents an attempt to satisfy the need imposed by advanced reactor designs by providing the computational ability to account for all heterogeneities within the fuel assembly, the capability of general geometry simulation, the flexibility in energy-group structure, the capability of multi-assembly simulation, accurate burn-up calculation, and linearly anisotropic scattering approximation.;In comparison with the existing lattice physics codes, MOCHA has the following advantages: an easy description of arbitrary domains, a geometry-independent ray tracing, a linearly anisotropic scattering treatment, a flexible cross section processing, a fast and memory efficient solution methodology, and a graphical user interface. The MOCHA methodology as implemented in the MAGGENTA-MOC code has been tested on a number of benchmark problems. The results show that the methodology is internally consistent (k-infinite results within 0.3% of similar codes), and it gives highly accurate solutions in comparison with other published results (k-infinite results within 0.8% of other codes). Finally, the numerical results show that the anisotropic features of the MOCHA system, while slow, still provide accurate results when compared to published data. Thus, MOCHA is a methodology for analyzing advanced nuclear reactor core designs with all of their complexities. |
