## 3 Observations from Leaching Tests in Reducing Conditions
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample (Reducing Agent)** & **Activity (Bq g\({}^{-1}\) UO\({}_{2}\))** & **Observations by the Authors** & **Reference** \\ \hline PWR segment (H\({}_{2}\)) & \(5\times 10^{8}\) & Decreasing rates but propose a fractional & [PERSON] et al. (2011) citing \\
50 MWd kg\({}^{-1}\) U & \(5\times 10^{8}\) & release rate of \(4\times 10^{-7}\) y\({}^{-1}\) & [PERSON] et al. (2012); [PERSON] (2012) \\ \hline PWR powder (H\({}_{2}\)) & \(4.3\times 10^{8}\) & \(3\times 10^{-7}\) y\({}^{-1}\) based on spent fuel powders & [PERSON] et al. (2015) \\
43 MWd kg\({}^{-1}\)U & \(4.1\times 10^{8}\) & Decreasing dissolution rates & [PERSON] et al. (2016) \\ \hline PWR segments (H\({}_{2}\)) & \(4.3\times 10^{8}\) & Decreasing rates over \(>\)1 year & [PERSON] et al. (2017); [PERSON] _et al._ (2017) \\
43 MWd kg\({}^{-1}\)U & \(4.3\times 10^{8}\) & [U] concentrations \(10^{-5}\) to \(5\times 10^{-10}\) M & [PERSON] et al. (2019) \\ \hline PWR fragment (H\({}_{2}\)) & \(1.2\times 10^{9}\) & Decreasing rates followed by steady-state after & Fors (2015) \\
67 MWd kg\({}^{-1}\)U & \(1.2\times 10^{8}\) & 502 days & Fors (2015) \\ \hline PWR fragments (H\({}_{2}\)) & \(4\times 10^{8}\) & Inhibited dissolution rates over 3 years & [PERSON] et al. (2019) \\
40 MWd kg\({}^{-1}\)U & \(1.3\times 10^{9}\) & Decreasing U concentrations reaching U & [PERSON] et al. (2010) \\ \hline MOX irradiated (H\({}_{2}\)) & \(3\times 10^{9}\) & Decreasing U concentrations after 494 days, & [PERSON] et al. (2018) \\
48 MWd t\({}^{-1}\) HM & \(3\times 10^{9}\) & \(\mathrm{\SIUnitSymbolMicro}\) & \(\mathrm{\SIUnitSymbolMicro}\) \\ \hline Irradiated MOX (Fe) & \(3\times 10^{9}\) & \(\mathrm{\SIUnitSymbolMicro}\) & \(\mathrm{\SIUnitSymbolMicro}\) \\
47 MWd t\({}^{-1}\) HM & (beta, gamma \(2.4\times 10^{10}\)) & No signs of oxidative dissolution & Odorowski 2015 (2015) \\ \hline UO\({}_{2}\) un-doped (Fe) & \(1\times 10^{4}\) & No measurable dissolution rate over 1 year & Odorowski 2015 (2015) \\ \hline UO\({}_{2}\) Pu-doped (Fe) & \(3.8\times 10^{9}\) & No measurable dissolution rate over 1 year & Odorowski 2015 (2015) \\ \hline UO\({}_{2}\) Pu-doped (Fe) & \(1.8\times 10^{7}\) & No measurable dissolution rate over 1 year & Odorowski 2015 (2015) \\ \hline Fresh MOX (7\(\%\)Pu) & \(1.3\times 10^{9}\) (beta, \(9.1\times 10^{9}\)) & No measurable dissolution rate over 1 year & Odorowski 2015 (2015) \\ \hline UO\({}_{2}\) un-doped (Fe) & \(1\times 10^{4}\) & \(8.3\times 10^{-8}\) y\({}^{-1}\) (min) & [PERSON] et al. (2015) \\  & \(1.6\times 10^{-6}\) y\({}^{-1}\) (max) & [22] \\ \hline UO\({}_{2}\) U-233-doped 5\(\%\) (Fe) & \(1.6\times 10^{7}\) & \(7.5\times 10^{-8}\) y\({}^{-1}\) (min) & [PERSON] et al. (2015) \\  & \(1.1\times 10^{-6}\) y\({}^{-1}\) (max) & [22] \\ \hline UO\({}_{2}\) U-233-doped 10\(\%\) (Fe) & \(3.1\times 10^{7}\) & \(4.4\times 10^{-8}\) y\({}^{-1}\) (min) & [PERSON] et al. (2015) \\  & \(1.2\times 10^{-6}\) y\({}^{-1}\) (max) & [22] \\ \hline UO\({}_{2}\) U-233-doped 10\(\%\) (H\({}_{2}\)) & \(3.3\times 10^{7}\) & Decreasing total U concentrations over 328 days. No sign of surface oxidation observed. & [PERSON] et al. (2018) \\ \hline \hline \end{tabular}  
* Approximation based on Figure 2-1 in [PERSON] et al. (2011) and assuming 10 years after discharge. \({}^{\mathrm{b}}\) Reported by the authors.  
\end{table} 
Table 1: Summary of release rates in reducing conditions.