Modeling of the physico-chemical behavior of pollutions in the secondary circuit of nuclear reactors

In the secondary circuit of a PWR, some phenomena such as hideout can lead to a deterioration of the physico-chemical conditions, which is a risk for the primary-secondary confinement barrier in the steam generator. Hideout denotes the concentration increase, due tu boiling, of non volatile chemical species (such as dissolved metals, Na, Cl, PO₄, SO₄, etc.) in specific parts of the steam generator. The aim of this work is to improve the understanding of these phenomena through the physico-chemical modeling of the circuit from the origins of the pollutants to the areas where hideout can take place. The modeling presented in this work puts together the parameters needed for the description of the chemistry and the one-dimensional transport. Among all the elements present inside the secondary circuit, copper is under particular scrutiny because it was identified as susceptible of locally disturbing the redox potential of the steam generator. A new thermodynamic dataset is generated for copper in order to better fit the experimental data from the literature. This is done by gathering data and applying a thermodynamic consistency method described in this work. A hideout experimental campaign with Na-PO₄ as pollutants confirms that copper oxidizes magnetite into hematite or sodium-iron hydroxyphosphate (SIHP), which is harmful to the steam generator. The coupling of the transport and the chemistry code is performed. Among other results, it shows that a significant amount of hematite is formed after just a few minutes of fluid circulation in absence of chemicals other than iron and copper. (author)