# Optimized Water Distillation Layout for Detritiation Purpose
## 3 Process Simulations
### Results Summary  
The scope of the activity is to investigate the possibility to adopt a HPAD to reduce the power consumption of the EU-DEMO water CPS. Thus, the principal figure of merit of the analysis is the total power consumption of the system, along with the power saving obtained with the HPAD concepts. Nevertheless, when using tritium (more in general, radioactive product), its inventory must be controlled and limited as much as possible, especially for a machine like EU-DEMO. Focusing on the water CPS, the main contribution to the tritium inventory of the system derives from the reboiler since it is fed with highly tritiated water (around 3.7 \(\times\) 10\({}^{12}\) Bq kg\({}^{-1}\)) coming from the bottom of the WD-CLM [10]. When using the HPAD, additional degrees of freedom are added to the design calculations. For example, the compressor outlet pressure for the MVR concept and the operative and design parameters of the ejector for the TVR-CMP. The rationale behind the optimization of the HPAD parameters is to obtain a reboiler size as close as possible to the reboiler design of the STD while keeping acceptable operating conditions (in terms of temperature and pressure). Thus, the dimensions of the reboiler constitute the first figure of merit considered in the comparison of the different distillation concepts. The rigorous design of the reboilers involved in the STD, MVR, and TVR-CMP was obtained with the Aspen Exchanger Design and Rating (EDR) program, and the main features are collected and compared in Table 5. For all the distillation concepts, a Tubular Exchanger Manufacturers Association (TEMA) horizontal thermosyphon was considered (TEMA type: BGM), where hot fluid (lower content of tritium) passes through the tube-side and the cold tritium-enriched flow rate boils on the shell-side. The most relevant parameter in terms of tritium inventory is the shell-side free volume, where tritium-enriched fluid is collected. As shown in Table 5, the best condition is ensured by the STD even if the reference MVR presents only an 8% increase of the free volume on the shell-side. On the other hand, the operative conditions of the TVR-CMP reference case involved a more significant increase of 85% compared to the STD. Therefore, from the point of view of the tritium inventory, the TVR-CMP is the worst case, whereas the STD and the MVR are comparable. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{\(A_{2}A_{t}\)} & \(w_{a}\) & \(w_{b}\) & \(T_{a}\) & \(T_{3}\) & \(p_{a}\) & \begin{tabular}{c} **Condenser** \\ **Power** \\ **(kW)** \\ \end{tabular} & \
\begin{tabular}{c} **Compressor** \\ **Power** \\ **(kW)** \\ \end{tabular} &
\begin{tabular}{c} **Required Heat Transfer** \\ **Area of Reboiler** \\ **(m2)** \\ \end{tabular} \\ \hline
100 & 324.6 & 1954.29 & 695.3 & 146.3 & 510 & 120.4 & 120.1 & 24.2 \\
50 & 383.15 & 1895.7 & 559.6 & 137.7 & 272 & 110.05 & 109.76 & 26 \\
25 & 499.1 & 1779.7 & 456.9 & 140.05 & 160 & 112.8 & 112.5 & 25.5 \\
15 & 624.57 & 11,654.3 & 396.1 & 145.2 & 116 & 119.1 & 118.89 & 24.4 \\
10 & 755.8 & 1523 & 350.3 & 149.6 & 89 & 124.4 & 124.1 & 23.6 \\
5 & 1019.46 & 1259.4 & 267.3 & 146.6 & 54 & 120.8 & 120.5 & 24.16 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: TVR-CMP CPS: parametric analysis over the ejector area ratio for the outlet pressure of 20 kPa. The comparison of the power consumption and of the power saving ensured by the considered HPADs is presented in Table 6. It is worth emphasizing that, for the STD, the power required by the reboiler is recovered from waste heat from the CVCS, and thus, the HPAD power saving is computed as follows:  
\[PS=\frac{Q_{STD,\;CND}-(Q_{HPAD,CND}+Q_{HPAD,CMP})}{Q_{STD,\;CND}} \tag{9}\]  
where \(PS\) is the power saving, \(Q\) is the power, the subscript \(HPAD\) stands for the MVR or the TVR-CMP, and the subscripts \(CND\) and \(CMP\) are condenser and compressor, respectively.