Dynamic Modeling and Simulation of a High-Temperature Gas Cooled Pebble-Bed Reactor

Abstract

A coupled neutronics-thermohydraulic model for the high temperature gas cooled pebble-bed reactor, PNP-500, was developed using the special purpose block oriented simulation language - DSNP. The model developed was tested and included in the DSNP modules library, and then used in the full scale simulation of the PNP-500 power plant. The core of the pebble-bed reactor contains about 5x10⁶ graphite spheres seeded with coated UO₂ particles. Several perturbations were introduced into the simulation. The major conclusion drawn from the results is that the thermodynamic response of the reactor is very slow due to the very large heat capacity of the core. The core response time is measured in hours rather than in seconds and minutes. The slow response of the core makes the PNP-500 a very stable and safe reactor.