RELAP5 Modeling of the HTTR-GT/H₂ Secondary System and Turbomachinery

This work describes the development of a RELAP5-3D model of the HTTR-GT/H2 plant secondary system, a designed upgrade to the High Temperature engineering Test Reactor (HTTR) for the purpose of demonstrating power production via closed-circuit gas turbine (GT) and hydrogen generation via the sulfur-iodine process. The RELAP5-3D model presently includes detailed models of several of the heat exchangers in the secondary system as well as the turbomachinery, which includes two compressors and two gas turbines connected to a common shaft and motor. The predictions of the model agreed well with design parameters in both sole power generation and hydrogen co-generation modes in most instances. Both the turbomachinery and heat exchanger models rely on extensive customization via RELAP5-3D control variables, and these implementations are outlined in detail. Potential improvements to the RELAP5-3D turbine model are discussed. (author)