Effect of spray properties on aerosol scavenging efficiency with water mist

Abstract

In the foreseen decommissioning plans of damaged Fukushima Daiichi reactors, submicron aerosol particles will be generated when retrieving fuel debris from reactor buildings by cutting it into small pieces. A multi-nozzle spray system will be used to scavenge these aerosol particles inside the primary containment vessel. To improve the aerosol removal efficiency of the multi-nozzle spray system, it is now necessary to study the aerosol removal performance by different single spray nozzles with different spray properties (spray angle, droplet velocity, etc.). To improve the aerosol scavenging efficiency, a new method with water mist was proposed to aggregate with aerosol particles and form large-sized coagulated aerosol-mist particle clusters, which can subsequently be removed by spray with higher efficiency. In this study, the effect of spray properties on aerosol removal efficiency with preexisting water mist was investigated using three different spray nozzles. The experimental results showed that a larger droplet velocity led to stronger vortex circulation and faster gaseous entrainment from outer spray area into spray region, resulting in a smaller circulation period of gas entrainment by spray and higher aerosol removal efficiency. The numerical simulations of aerosol removal by different spray nozzles without mist were also conducted to provide more insights into the aerosol removal process. By comparing the experiment and simulation results, it is found that the accumulated spray water in the lower plenum of the vessel and the water film formed on the vessel sidewalls also contributed to aerosol removal, especially for the particles with large Stokes numbers.

Copyright © 2021 American Association for Aerosol Research

EDITOR:

• Yannis Drossinos

Disclosure statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Additional information

Funding

This work was financially supported by the Nuclear Energy Science & Technology and Human Resource Development Project of the Japan Atomic Energy Agency/Collaborative Laboratories for Advanced Decommissioning Science [number 31I049].