Homogeneous bubble nucleation limit of mercury under the normal working conditions of the planned European Spallation Source

TL;DR

This paper investigates the likelihood of homogeneous bubble nucleation in liquid mercury under conditions typical of the European Spallation Source, finding that such nucleation is highly improbable despite thermal shocks.

Contribution

It provides a calculation of the critical cluster formation work and nucleation rate for mercury, demonstrating the low probability of temperature-induced homogeneous bubble formation.

Findings

Homogeneous nucleation rates are very low in mercury.

Probability of bubble formation due to temperature shocks is negligible.

Results support the safety of mercury under planned operational conditions.

Abstract

In spallation neutron sources, liquid mercury is the subject of big thermal and pressure shocks, upon adsorbing the proton beam. These changes can cause unstable bubbles in the liquid, which can damage the structural material. While there are methods to deal with the pressure shock, the local temperature shock cannot be avoided. In our paper we calculated the work of the critical cluster formation (i.e. for mercury micro-bubbles) together with the rate of their formation (nucleation rate). It is shown that the homogeneous nucleation rates are very low even after adsorbing several proton pulses, therefore the probability of temperature induced homogeneous bubble nucleation is negligible.