Innovative extinction photometry for the characterisation of multicomponent-aerosol and humidity measurement (IN-EX). Sub-project D. TDLAS based humidity measurements in mixed phase systems for nuclear safety research. Final report

The joint INEX project's purpose was the development of optical measurement technologies. These were then used to characterise the challenging process conditions during a loss of coolant accident during a severe nuclear incident. Measuring Instruments were developed, which permit in-situ measurements of particle concentrations and relative humidity under those conditions. The responsibility of subproject D was the development of a TDLAS (tunable diode laser absorption spectroscopy) based hygrometer and to perform its characterisation at the test stand at Forschungszentrum Juelich (FZJ). The atmosphere to be analysed consists of a mixture of different gases like helium, hydrogen, nitrogen or air at temperatures of up to 200 C, pressure of up to 8 bar (gauge) and humidity of up to 100 %r.H. During such a loss of coolant accident a plurality of liquid and solid components in the containment. Characteristic non-radioactive substances which were available and used in the test stands were substances like caesium hydroxide, caesium iodide, silver and tin dioxide. This composition posed challenges to the in this subproject developed hygrometer. On this account a small test chamber was build up to simulate individual challenges like temperature, pressure and high particle load before measuring in the test stand at Forschungszentrum Juelich. In addition to the experiments at Forschungszentrum Juelich, which constitute the core of this project, the TDL-Hygrometer was deployed in another series of experiments in the REKO-4 at Forschungszentrum Juelich. This experiment investigates the proper functioning of the system in hydrogen-loaded atmospheres. This is of fundamental importance in the context of nuclear safety research.