Effects of process-generated hydrogen on RPV walls

4.3. Corrosion of the RPV wall

the decreasing B concentration. A schematic representation of this primary water chemistry regime is shown in Figure 4.1. The figure gives the lithium concentration as a function of the boron concentration for a typical fuel cycle in a PWR. [45]

Figure 4.1: Typical primary water chemistry conditions in a PWR during operation at 300 ◦ C. The lithium concentration is given as a function of the boron concentration, which will be adapted to the reactivity of the fuel in the reactor. The grey zone gives the intended concentrations of B and Li in the primary water. [45] It must be noted that the above mentioned pH T ’s in the primary water are measured at high temperature. This is different from the “usual” pH measured at 25 ◦ C. The pH is defined as: pH = − log 10 ( a H + ) (4.2) where a H + is the activity of hydrogen ions, i.e. protons, in the water. This activity is often simplified to the concentration of hydrogen ions, [H + ], expressed in molarity, mol/kg. In water, the concentrations of H + and OH – are linked via the ionic product of water, K W : K W = a H + · a OH − K W = [H + ] · [OH − ] (4.3) This ionic product of water changes significantly with temperature and pressure. As a result, so will the pH of the solution. Marshall and Franck [49] found an equation relating the ionic product of water to the temperature and the density of the water: logK ∗ W = A + B T + C T 2 + D T 3 + ( E + F T + G T 2 ) · log ρ ∗ W (4.4)

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