## 4 Discussion
### Significance of Reactions  
The significance of reactions was assessed based on the integrated (up to 100 s) contributions \(R\) of individual reactions, expressed in mol\(\cdot\)kg\({}^{-1}\). Reactions contributing in less than 1\(\cdot\)10\({}^{-4}\) mol\(\cdot\)kg\({}^{-1}\), which is the lowest integrated production rate at 1 kGy\(\cdot\)s\({}^{-1}\) (Table 1), were considered insignificant. Simulation performed for the dose rate 1 kGy\(\cdot\)s\({}^{-1}\) showed that skipping reactions (1), (22), (47), (52), (53), (55), and (56) results in a relative error of the steady-state concentrations of radiolytic products below 0.1%, for all the systems studied. The most significant are equilibrium reactions, but the assessment of their importance should take into account a net contribution of each equilibrium, expressed as a difference between the integrated contributions of forwarding and backward reactions. Figure 6 shows net contributions calculated for neutral water, alkaline solution, neutral and alkaline solutions containing 3\(\cdot\)10\({}^{-5}\) mol\(\cdot\)kg\({}^{-1}\) H\({}_{2}\). The upper part presents net contributions R24-R25, R38-R39, R40-R41, R42-R43 of equilibria (24) \(\leftrightarrow\) (25), (38) \(\leftrightarrow\) (39), (40) \(\leftrightarrow\) (41), (42) \(\leftrightarrow\) (43), obtained for gamma and fast neutron irradiation, whereas the lower part refers  
Figure 5: Simulated response of the steady state concentration of O\({}_{2}\) to hydrogen added to neutral water at 300 \({}^{\circ}\)C (black) and to alkaline solution containing 2\(\cdot\)10\({}^{-4}\) mol kg\({}^{-1}\) OH\({}^{-}\) ions (blue): (**a**) dose rate 1 kGy\(\cdot\)s\({}^{-1}\); (**b**) dose rate 10 kGy\(\cdot\)s\({}^{-1}\). Solid and dashed lines refer to fast neutron and gamma radiolysis, respectively. \begin{table}
\begin{tabular}{c c c} \hline
**Oxidant/Solution** & \
\begin{tabular}{c} **1 kGy\(\cdot\)s\({}^{-1}\)** \\ **Neutron \(\gamma\)-Radiolysis** \\ \end{tabular} &
\begin{tabular}{c} **10 kGy\(\cdot\)s\({}^{-1}\)** \\ **Neutron \(\gamma\)-Radiolysis** \\ \end{tabular} \\ \hline H\({}_{2}\)O\({}_{2}\)/neutral & 8.8\(\cdot\)10\({}^{0}\) 3.1\(\cdot\)10\({}^{0}\) & 4.2\(\cdot\)10\({}^{0}\) 2.4\(\cdot\)10\({}^{0}\) \\ H\({}_{2}\)O\({}_{2}\)/alkaline & 8.5\(\cdot\)10\({}^{2}\) 1.4\(\cdot\)10\({}^{2}\) & 6.5\(\cdot\)10\({}^{2}\) 1.0\(\cdot\)10\({}^{2}\) \\ \hline O\({}_{2}\)/neutral & 4.2\(\cdot\)10\({}^{2}\) 2.7\(\cdot\)10\({}^{2}\) & 1.5\(\cdot\)10\({}^{2}\) 1.1\(\cdot\)10\({}^{2}\) \\ O\({}_{2}\)/alkaline & 2.2\(\cdot\)10\({}^{6}\) 5.0\(\cdot\)10\({}^{6}\) & 8.7\(\cdot\)10\({}^{5}\) 1.4\(\cdot\)10\({}^{6}\) \\ \hline \end{tabular}
\end{table} 
Table 3: Effectiveness of hydrogen addition expressed as a ratio of the steady-state concentration in the absence of extra hydrogen and in the solution containing 1.5\(\cdot\)10\({}^{-4}\) mol\(\cdot\)kg\({}^{-1}\) H\({}_{2}\). to equilibria (26) \(\leftrightarrow\) (27), (28) \(\leftrightarrow\) (29), (34) \(\leftrightarrow\) (35), (36) \(\leftrightarrow\) (37). Net contributions R30-R31, R32-R33, R49-R50 are of the order of \(10^{-7}\)-\(10^{-5}\) mol\(\cdot\)kg\({}^{-1}\) and are not shown in Figure 6.  
Equilibria (24) \(\leftrightarrow\) (25), (26) \(\leftrightarrow\) (27), (28) \(\leftrightarrow\) (29), (36) \(\leftrightarrow\) (37), (38) \(\leftrightarrow\) (39) (40) \(\leftrightarrow\) (41), are shifted to the left, whereas equilibria (34) \(\leftrightarrow\) (35), (42) \(\leftrightarrow\) (43) are shifted to the right. The shift of equilibrium (42) \(\leftrightarrow\) (43) towards reaction (43) is almost independent of the composition of solution and more meaningful in the systems irradiated by fast neutrons. Net contributions of equilibria (40) \(\leftrightarrow\) (41) and (38) \(\leftrightarrow\) (39) are highly enlarged in the alkaline solution containing 3\(\cdot 10^{-5}\) mol\(\cdot\)kg\({}^{-1}\) H\({}_{2}\).