Experimental Assessment of Accident Scenarios for the High Temperature Reactor Fuel System

Abstract

The High Temperature Reactor (HTR) is an advanced reactor concept with particular safety features. Fuel elements are constituted by a graphite matrix containing submm- sized fuel particles with TRISO (tri-isotropic) coating designed to provide high fission product retention [1]. Passive safety features of the HTR include a low power density in the core compared to other reactor designs [2]; this ensures sufficient heat transport in a loss of coolant accident scenario. The temperature during such events would not exceed 1600°C, remaining well below the melting point of the fuel [3]. An experimental assessment of the fuel behaviour under severe accident conditions is necessary to confirm the fission product retention of TRISO coated particles and to validate relevant computer codes. Though helium is used as coolant for the HTR system, additional corrosion effects come into play in case of an in-leakage affecting the primary circuit. The experimental scope of the present work focuses on two key aspects associated with the HTR fuel safety. Fission product retention at high temperatures (up to ~1800°C) is analyzed with the so-called cold finger apparatus (KüFA: Kühlfinger-Apparatur), while the performance of HTR fuel elements in case of air/steam ingress accidents is assessed with a high temperature corrosion apparatus (KORA: Korrosions-Apparatur).