# Optimized Water Distillation Layout for Detritiation Purpose
## 4 Conclusions  
The research presented in this paper follows the design activity carried out in 2022 on the Coolant Purification System of the EU-DEMO WCLL BB. In that activity, the water distillation was selected as the most promising technology for the detritiation of the primary coolant due to its intrinsic simplicity and safety. However, concern about the power consumption were highlighted. The present work deals with the assessment of best procedure to reduce power consumption of this system using Heat Pump-Assisted Distillation technologies.  
First of all, a review of the HPAD developed and tested in the industry was conducted, and the most suitable solutions for the EU-DEMO water CPS were identified based on qualitative considerations. Then, a quantitative analysis was carried out with Aspen Plus in order to compare design and performances of the HPADs with the Standalone Distillation. To do this, HTO thermodynamic properties set was collected from the literature and added in Aspen Plus. Then, parametric studies were performed with Aspen Plus to optimize  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Parameter** & **Unit** & **STD** & **MVR** & **TVR-CMP** \\ \hline Reboiler power & kW & 1517.39 * & – & – \\ Condenser power & kW & 1517.72 & 163.79 & 120.80 \\ Compressor power & kW & – & 163.49 & 120.50 \\ Total power saving & \% & – & 78.4 & 84.1 \\ \hline \hline \end{tabular}
* Waste heat from CVCS.  
\end{table}
Table 6: Power consumption for the Standalone Distillation.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Parameter** & **Unit** & **STD** & **MVR** & **TVR-CMP** \\ \hline Required heat transfer area & m\({}^{2}\) & 23.3 & 29.8 & 24.16 \\ Excess surface & \% & 32 & 29 & 7 \\ Tube Outer Diameter (OD) & mm & 25.4 & 30 & 30 \\ Pitch & mm & 31.75 & 37.5 & 37.5 \\ Shell OD & mm & 525 & 610 & 914 \\ Tube length & mm & 2850 & 2550 & 2100 \\ Number of tubes & – & 140 & 166 & 425 \\ Shell-side free volume & m\({}^{3}\) & 0.39 & 0.42 & 0.72 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Comparison of the reboiler rigorous design for the STD, the MVR, and the TVR-CMP.  
the operation of the two selected HPADs, i.e., the MVR and the TVR-CMP. Finally, the optimized configurations were compared with the STD, assessing the possibility to obtain a conspicuous power saving (around 80%) with both the considered HPADs. A further figure of merit considered in the assessment was the size of the reboiler, being this component the most relevant in terms of tritium inventory.  
From this analysis, the MVR concept has been recognized as the most promising solution representing an excellent compromise in terms of power saving and tritium inventory of the system. Future works will be dedicated to the investigation of the compatibility between the compressor and tritiated steam and on the control procedures for the MVR concept.  
Conceptualization, V.N. and A.S.; methodology, V.N. and A.S.; software, V.N.; validation, V.N.; formalism analysis, V.N.; investigation, V.N.; resources, A.S.; data curation, V.N. and A.S.; writing--original draft preparation, V.N. and A.S.; writing--review and editing, V.N. and A.S.; visualization, V.N. and A.S.; supervision, A.S.; project administration, A.S.; funding acquisition, A.S. All authors have read and agreed to the published version of the manuscript.  
This work has been carried out within the framework of the EUROfusion Consortium, funded by the European Union via the Euratom Research and Training Programme (Grant Agreement No 101052200--EUROfusion). Views and opinions expressed are, however, those of the author(s) only and do not necessarily reflect those of the European Union or the European Commission. Neither the European Union nor the European Commission can be held responsible for them.  
Not applicable.