About the volatility of boron in aqueous solutions of borates with vapour in relevance to BWR-Reactors

摘要

In BWR-reactors a boron injection system is installed to control a total or partial ATWS accident. The injected boron will be spread in the fluid and some of the boron will leave the reactor with the exhausted vapour. To analyse the lost of boron with the vapour is the great aim of this thesis. The volatility of the boron solution was measured by experiments in a little autoclave vessel up to 330 °C and 13 MPa and in a circulation loop called BORAN up to 225 °C and 2.5 MPa.In the two test facilities different boron compounds in solution were analysed. Mostly, solutions of Disodium-Pentaborat are used because only this compound will be injected in BWR-reactors as a high concentrated solution. The boron concentration in the vapour depends mainly on temperature and void fraction of the two-phase-flow. The volatility can take values about some percent. As well the reason of the volatility of the analysed solutions will be discussed within a chemical background.