Rough analysis of the unavailability of representative measurement channel groups of the THTR-300 reactor protection system

Automatic translation: As part of the KFA's work on the THTR-3oo approval process, reliability analyzes were carried out by the Institute for Nuclear Safety Research (ISF) for representative measuring channel groups and for emergency cooling initiation signals of the reactor protection system. The measuring channel groups for monitoring the live steam pressure, the room pressure, the hot gas temperature, the hot gas temperature gradient and the feed water mass flow were selected as representative. The unavailability of the emergency cooling initiation signal was determined for the accident ''pipe rupture of a live steam line''. In this accident, the signal is triggered by the two diverse measuring channel groups for monitoring the live steam pressure in the pipeline and the pressure in the room in which the pipeline is installed. The average unavailability of the emergency cooling initiation signal was determined by monthly testing of the measuring channel groups to 3.8 • l0^-7. For incidents in which emergency cooling is requested via the steam generator component protection of all three steam generators of an emergency cooling system and the hot gas temperature in front of the steam generators is above the bridging level of the component protection, an average unavailability of the emergency cooling initiation signal l0^-7 was determined. It was assumed that the unavailability of the emergency cooling initiation signal was caused by the incorrect bridging of the component protection over the hot gas temperature, even though the temperature itself was above the bridging level.