Effects of process-generated hydrogen on RPV walls

5. Hydrogen production in PWR

• PR H 2 O 2 = − RR 4 + RR 9 − RR 19 − RR 20 + RR 24 + RR 25 + RR 26 − RR 29 − 2 ∗ RR 30 + RR 32 − RR 34 − RR 40 − RR 44 − RR 45 − RR 46 + RR 47 + E H 2 O 2 • PR HO − 2 = RR 6 − RR 14 + RR 27 + RR 28 + RR 29 − RR 32 − RR 35 − RR 38 + RR 39 + RR 42 + RR 46 + RR 48 + E HO − 2 • R HO 2 = − RR 6 − RR 10 + RR 19 + RR 21 − RR 22 + RR 23 − RR 33 − RR 44 − RR 47 + E HO 2 • R O − = RR 36 − RR 37 + RR 38 + E O − • R O = RR 40 − 2 ∗ RR 41 + E O • R O 2 − 2 = − RR 42 + RR 43 + E O 2 − 2 • R Li + = − RR 49 + RR 50 − RR 5 1 + RR 52 • R LiOH = RR 49 − RR 50 • R LiB(OH) 4 = RR 51 − RR 52 • R B(OH) 3 = − RR 53 + RR 54 − 2 ∗ RR 55 + 2 ∗ RR 5 6 − 3 ∗ RR 57 + 3 ∗ RR 58 − 4 ∗ RR 59 + 4 ∗ RR 60 • R B(OH) − 4 = − RR 51 + RR 52 + RR 53 − RR 54 • R B 2 (OH) − 7 = RR 55 − RR 56 • R B 3 (OH) − 10 = RR 57 − RR 58 • R B 4 (OH) 2 − 14 = RR 59 − RR 60 The production rates, R i , are the time derivatives of the concentration of specie i. The concentrations of each of the species can be interpreted as a set of ordinary differential equations. These equations are solved in the code using the classical Runge-Kutta method of fourth order. The initial step size in the calculation is set to 10 − 8 s and increases every step with a factor 1.5. This small initial time step is chosen for the stability of the system, as some of the starting concentrations are far from the steady state concentrations. 5.4.2 Stability of the model Before one can start using the model for the calculation of the concentration for each of the species, the stability of the system must be checked. More specifically the time needed for the system to reach a steady state condition, if reached at all. To check this, the system will be simulated for the extreme conditions of the primary water chemistry and see its influence on the time needed to reach a steady state concentration. 52