SUBJECT: Ph.D. Dissertation Defense
BY: Alexander Huning
TIME: Wednesday, July 20, 2016, 1:00 p.m.
PLACE: Boggs, 3-47
TITLE: A Novel Core Analysis Method for Prismatic High Temperature Gas Reactors
COMMITTEE: Dr. Srinivas Garimella, Chair (ME)
Dr. Farzad Rahnema (NRE)
Dr. Mostafa Ghiaasiaan (ME)
Dr. Thomas Fuller (ChBE)
Dr. Laurence Jacobs (ME)


A new transient thermal hydraulic method for simulating prismatic HTGRs during a loss-of-forced-circulation (LOFC) accident is presented. This expands upon the steady state thermal hydraulic methodology presented in the Author’s MS Thesis. However, several key additions have been made. The largest is the addition of a transient analysis method that computes the fluid mass, velocity (momentum), and energy throughout a transient. This is achieved by using a well-documented, semi-implicit pressure-correction scheme. The fluid volumes are assumed to be 1-D to allow for the use of standard heat transfer and pressure drop correlations. Simple transient velocity and pressure boundary conditions are employed. Helium is assumed to be an ideal gas with constant specific heats, which allows for the use of simple thermodynamic relationships to close the fluid model. Models for reactor containment cooling (RCCS) heat transfer and decay heat generation have also been added.Using the method developed here, both the pressurized (P-LOFC) and de-pressurized (D-LOFC) accident have been simulated. Results from these analyses confirm the HTGR’s key safety advantage over all LWRs and most other advanced reactor designs, which is to have passive, indefinite cooling capability for the most limiting accident. A RELAP model has also been developed and tested for the HTGR. This is done to highlight the limitations of existing methods for the simulation of the prismatic fuel and to emphasize the need and novelty of the method developed here. The newly developed method provides two significant advantages over available thermal hydraulic 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 two factors combine to produce realistic, 3-D transient results for prismatic HTGRs during a LOFC.