Air Ingress Analyses on a High Temperature Gas-Cooled Reactor

Abstract

A loss-of-coolant accident is one of the design-basis accidents for a high-temperature gas-cooled reactor (HTGR). Following the depressurization of helium in the core, if the accident is not mitigated, there exists the potential for air to enter the core through the break and oxidize the in-core graphite structure in the modular pebble bed reactor (MPBR). This paper presents the results of the graphite oxidation model developed as part of the Idaho National Engineering and Environmental Laboratory’s Directed Research and Development effort. Although gas reactors have been developed in the past with limited success, the innovations of modularity and integrated state-of-art control systems coupled with improved fuel design and a pebble bed core make this design potentially very attractive from an economic and technical perspective. A schematic diagram of a reference design of the MPBR has been established at a major component level (INEEL & MIT, 1999). Steady-state and transient thermal hydraulics models will be produced with key parameters established for these conditions for all major components. Development of an integrated plant model to allow for transient analysis on a more sophisticated level is now being developed. In this paper, preliminary results of the hypothetical air ingress are presented. A graphite oxidation model was developed to determine temperature and the control mechanism in the spherical graphite geometry.