Numerical Simulation of Accident Scenario in HTGR (Pebble Bed Reactor) Using COMSOL® Code

Abstract

High Temperature Gas Cooled Reactor (HTGR) development and operation is expanding in the United Kingdom, Russia, USA (Generation IV Reactors), and France (Pebble Bed Modular Reactor, PBMR). A prototype pebble bed reactor producing 10 MW thermal, High Temperature Reactor (HTR-10) is in operation in China. However, the general public remains skeptical of the safety and the perceived dangers of possible accidents. Of particular concern are blockages caused by local variations in flow and heat transfer that lead to hot spots within the bed. This paper models the accident scenario resulting from blockages due to the retention of dust in the coolant gas or from the rupture of one or more fuel particles used in the High Temperature Gas Cooled (Pebble Bed) Nuclear Reactors using the commercially available computer code COMSOL. Numerical modeling of flow and heat transfer in a packed bed produces an Elliptical Non-Linear Partial Differential equation that requires custom made computer codes. Previously published results obtained from the use of a custom-made verified computer code are limited to one accident scenario and involve considerable modification to study different accident scenarios. Thus the use of a commercially available computer code that can simulate many different accident scenarios is of considerable advantage. Further, this paper compares numerical solutions obtained from custom-made computer code with COMSOL simulation and discusses the advantages and limitations of both codes.