## 5 Conclusions  
In this study, Monte Carlo track chemistry simulations were used to calculate the \(G\) values for the primary radiolytic species in pure, de-aerated water irradiated by monoenergetic 2-MeV neutrons at temperatures ranging from 300 to 600 \({}^{\circ}\)C, maintaining a constant pressure of 25 MPa. These conditions reflect those anticipated in proposed SCWRs and their smaller modular variants. The fast neutron yields were derived by primarily considering the first three elastically scattered recoil protons generated by the incident neutron, with initial energies of 1.264, 0.465, and 0.171 MeV, while effects from oxygen ion recoils were omitted.  
Our simulations shed light on the radiolytic formation of chemical species such as \(\mathrm{e^{-}}_{\mathrm{aq}}\), H\({}^{\bullet}\), H\({}_{2}\), \({}^{\bullet}\)OH, and H\({}_{2}\)O\({}_{2}\) over a time-frame from \(\sim\)1 ps to 1 ms. A comparison with low-LET radiation data underscored the high-LET nature of fast neutrons. A significant finding from our study was the pronounced increase in \(G\)(\({}^{\bullet}\)OH) and \(G\)(H\({}_{2}\)), alongside a notable decrease in \(G\)(\({}^{\bullet}\)), during the homogeneous chemical stage of radiolysis. This change is attributed to the oxidation of water by H\({}^{\bullet}\) atoms, following the reaction H\({}^{\bullet}\) + H\({}_{2}\)O \(\rightarrow\)\({}^{\bullet}\)OH + H\({}_{2}\). This reaction serves as a substantial source of H\({}_{2}\), potentially reducing the necessity to add excess hydrogen to the reactor's coolant to mitigate the net radiolyticproduction of oxidizing species. Our simulations also indicated that unlike in subcritical water, \(G\)(H\({}_{2}\)O\({}_{2}\)) remains very low in low-density SCW, implying that H\({}_{2}\)O\({}_{2}\) is less likely to contribute significantly to oxidative stress under these conditions.  
The findings of this study could greatly influence water-chemistry management in proposed SCWRs and SCW-SMRs, which is vital for evaluating and mitigating corrosion risks to reactor materials, especially over long-term operation. Further experimental data are needed to more accurately characterize the temperature dependence of radiolytic yields, to validate our modeling calculations more comprehensively, and to clarify the potential role of the reaction of H\({}^{\bullet}\) atoms with water at high temperatures.  
M.S.H.B.: validation, formal analysis, investigation, data curation, writing--original draft preparation. J.M.: methodology, software, validation, resources, supervision. A.S.: methodology, formal analysis, investigation. J.-P.J.-G.: conceptualization, methodology, validation, formal analysis, resources, reviewing and editing the final version of the manuscript, supervision, project administration, funding acquisition. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Natural Sciences and Engineering Research Council of Canada-Canadian Nuclear Safety Commission (NSERC-CNSC) Small Modular Reactors Research Grant Initiative (funding reference number: ALLRP 580463-2022).  
Not applicable.  
Data Availability Statement: Data generated or analyzed during this study are provided in full within the article.  
[PERSON] is the recipient of an M.Sc. scholarship from the \"Programme de bourses d'excellence aux etudes superieures\" of the Universite de Sherbrooke. The research showcased in this work was honored with the third prize at the ALEA poster presentation competition, which took place at the Universite de Sherbrooke on 18 June 2024. This recognition underscores the scientific merit of the study within a competitive academic setting, highlighting its relevance and potential impact in the field.  
The authors declare no conflicts of interest.