Bereitstellung, Qualifizierung und Mischung typischer LWR-Störfallaerosole mit Brandaerosolen

• Generation, qualification and composition of typical LWR severe accident aerosols with soot

Wellding, Jan; Allelein, Hans-Josef (Thesis advisor); Abel, Dirk (Thesis advisor)

Aachen : RWTH Aachen University (2020, 2021)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2020

Abstract

The possibility of severe accidents is the main impediment for nuclear energy being accepted as a carbon dioxide-free source of energy. To limit the consequences of such incidents the understanding of aerosol behaviour is of high significance. Due to their ability of being mobilized, these fission products are the reason for long lasting, external effects, like land contamination. Although associated questions, regarding formation and aging processes or transportation and deposition mechanisms, have been part of the reactor safety research for a long time, plenty of details have not yet been solved. The knowledge gained so far represents the basics for system codes, which are supposed to calculate the trend of accidents and their potential effects. This thesis provides executed experiments for the processes and mechanisms mentioned above, pointing out the characteristics and behaviour of typical severe accident aerosols of light water reactors and their mixing in particular. These experiments clearly show, that the particle size distribution of a multi-component aerosol, not aged, is characterized by the particle size distribution of the starting aerosols. This fact also leads to the conclusion, that the chemical composition of an aerosol is a function of the particle size. With this understanding, that the radiological characteristics are substance-specific and practically all deposition mechanisms are led back to a function of the particle size, there is an immense significance regarding a potential source term. Because of this fact, the activity of a severe accident aerosol can not just be determined via its mass, it rather must be looked at considering the particle size distribution. The executed experiments reveal, that interactions between fire aerosols and typical severe accident aerosols do not lead to any unusual variations of the particle size and do also show a simple superposition of the particle size distributions. Furthermore, the conducted deposition experiments, for the first time, provide experimental data proving, that calculations, with the system code COCOSYS, show the right trend for concentration ranges, where no data for validation was present yet.