Whole-core transient analysis methodology for prismatic high temperature gas reactors

A new transient thermalhydraulic method for simulating prismatic high temperature gas cooled reactors (HTGRs) during a loss-of-forced-circulation (LOFC) accident is presented. Whole-core, three-dimensional temperature profiles are computed at an individual fuel pin and lattice assembly block levels. A method that computes the fluid mass, velocity (momentum), and energy throughout a transient is implemented using a well-documented, semi-implicit pressure-correction scheme. Models for reactor cavity cooling system (RCCS) heat transfer and decay heat generation are also included. Pressurized (P-LOFC) and de-pressurized (D-LOFC) accidents are simulated. This method provides two significant advantages over available thermalhydraulic analysis techniques. The first is its ability to compute whole-core results and capture the important transient core-level phenomena such as bypass flow and heat redistribution into the reflector assemblies after reactor SCRAM. The second is its ability to compute each fuel assembly in detail, computing the heat rates and temperature profiles for every fuel pin, graphite, and coolant channel. These features produce realistic, 3-D transient results for prismatic HTGRs during a LOFC. A RELAP model is also developed and implemented for the HTGR. The limitations of existing methods for the simulation of the prismatic fuel are identified and the need for and novelty of the present method are highlighted.