Ref: JNM_2018_309
Title: The influence of external stress/strain on the uranium-hydrogen reaction
Journal: Journal of Nuclear Materials

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Comments from the editors and reviewers:
-Reviewer 1

- Page 2: You swap between H and hydrogen in your text I would stick to one or the other.

Page 3: I would encourage you to reference:

Christopher P. Jones, Thomas B. Scott, James R. Petherbridge, Joseph Glascott,

A surface science study of the initial stages of hydrogen corrosion on uranium metal and the role played by grain microstructure,

Solid State Ionics,

Volume 231,

2013,

Pages 81-86,

ISSN 0167-2738,

https://doi.org/10.1016/j.ssi.2012.11.018.

within the section discussing microstructural features dominating factors in preferred hydride precipition. Since this shows cross-sectional FIB analysis of early stage hydride growths, the relation to the metal-oxide boundary and preferential formation at grain boundaries with high mismatch.

In addition this might be of interest to include

Christopher P. Jones, Thomas B. Scott, James R. Petherbridge,

Structural deformation of metallic uranium surrounding hydride growth sites,

Corrosion Science,

Volume 96,

2015,

Pages 144-151,

ISSN 0010-938X,

https://doi.org/10.1016/j.corsci.2015.04.008.

as it shows direct comparison of the stresses induced within the material as the hydride forms larger growths (>35um diameter), comparing the effect laterally across the surface with sub-surface formation (where the hydride is confined).

Page 3 line 11: "Finely, some of these nuclei rupture" (this should be Finally, some of...)

Page 3 line 25: "We found that bending experiments may allow the resolution to answer these questions" - This is ambiguous, do you mean the resolution of the analysis techniques deployed or the resolved outcome of the bending experiments?

Page 4 line 3: You've stated that the main impurities found were... but haven't mentioned the analysis performed to measure these impurities. Either requires rewording or the data presented

Figure 1 would benefit from a scalebar

Page 5 - the pressure drop is a little meaningless without the cell volume quoted. Ideally you could do with calculating the number of mols of reacted hydrogen gas with the sample and quote a reaction percentage (since the surface area of the sample is known).

Page 5 line 7 - relived should be relieved

Figure 4 says hydration and should be hydriding.

Page 14 line 3 quiet should be quite

Page 15 line 17 - (data not shown) - could you include this please or at least give a reason why it isn't included.

Page 15 line 17 - reviled should be revealed and tweens should be twins

General Point:

The discussion centres around the variation in density of growth centres depending on the stresses present. It would greatly improve the conclusions if image analysis was performed to estimate the percentage of surface coverage of hydride present per unit area as a function of distance from the bend point. This quantitative analysis would be superior to casual observation. This should be relatively straightforward using a freeware program such as imagej for pixel counting with thresholding. There are also tools available that can readily identify shaped features on the surface and would provide improved datasets.

This is an interesting piece of work which builds on the realisation of the community that stress corrosion may well be a valid phenomenon for uranium metal.

1) The overall quality of the English is poor and this means that certain key parts of the discussion and conclusions are confusing or at worst are misleading. This needs a thorough proof read and then rewriting to improve the grammar, clarity and flow.

2) It lacks specific detail about why this is actually important research. Why is stress corrosion important for uranium? Without explaining this then any reader will wonder what the point of doing all the research was.

3) I don't agree with the conclusions as they are slightly misleading. The author has not demonstrated what the actual mechanism is for the observed hydride formation behaviour - is it metallographic or simply related to the failure of the surface oxide layer? Equally, I would argue that they conducted the experiment the wrong way - I would have prepared the sample in a glove box, subjected it to bending and then exposed it to air for a set period in order to form a coherent (non-cracked) oxide. Instead, the author allowed the sample to have some oxidise and then bent it. This would have cracked the oxide making it easy for hydrides to preferentially formed in the cracked regions and equally, it would promote small family hydrides to easily form into large growth centres. THIS MUST be addressed fully in the manuscript and proven or disproven for the manuscript to be publishable. Without addressing this issue then the paper is potentially VERY misleading.

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