1. Basic concepts

1.1 Hydraulic diameter

One of the special features of the nuclear industry, and of the pressurized water reactor (PWR) in particular, lies in the complex geometries of the core, vessel and all reactor components, where water flows in a confined but open environment with high levels of transverse exchange.

A simplified approach commonly used in hydraulics (compared to fluid mechanics) considers unidirectional flows in circular pipes. In order to use for any flow geometry the results of hydraulics established in circular pipes, we use Chézy's formulation which determines an equivalent hydraulic diameter D _h taking into account the fluid passage area A and the wetted perimeter $$