Accident-Tolerant Barriers for Fuel Road Cladding of CANDU Nuclear Reactor

Round 1

Reviewer 1 Report

Quality of paper needs significant improvement, results are contradictory to manuscript description. Inadequate methodology explaination.

 

Please refer to the following items needing revision:

 

Line 53: might need rewording of sentence, nuclear energy does not prevent CO2 emissions 

 

Line 67: loss of coolant accident (LOCA)

 

Line 103: test parameters description, introduce again in methodology and include pressure. Was the samples removed under pressure or allowed to cooled? What was the heating cycle for the experiments? How were the samples mounted in the autoclave?

 

Section 2.1: it is important to identify Cr layer thickness 

 

Line 106: define EB-PVD

 

Line 122: include description of test setup conditions in autoclave. Current context description in sufficient. 

 

Line 176: power law

 

Figure 1: please include standard deviations of data since 3 samples are removed every 504hrs

 

Indicate location of analysis of sample in Figure 2 (surface or cross section) and indicate that they are optical images. Is it surface or cross section? If surface what happened to the colors as shown in figure 3

 

Line 191: keep Zy-4 consistent throughout manuscript 

 

Line 206: confusing sentence, please re write

 

Line 218: contradicting results from SEM results showing 2um of Cr oxide layer in comparison to 100nm described in context

 

Figure 5: cannot see scale description 

 

Figure 5: please include SEM image at time 0

 

Table 2: include time 0 elemental composition, possibly include standard deviation in multiple point scans since SEM EDS usually has quite a high discrepancy across various point. Will also be good if point locations are indicated on SEM image

 

Line 248-249: show pre test oxidation numbers in table 2 to support claim

 

Line 256: the SEM EDS data will show bulk data of beam voltage use is high. Reduce the incident beam voltage value and you will get more information from the surface.

 

Line 256: SEM line scans shows chromium oxides contradicting context

 

SEM section: indicate if images are back scatter or secondary electron images

Figure 6: seems like a secondary electrons image, please change to back scatter electron image if so, also indicate resin and bulk

 

Figure 6c: how is the layer thickness defined? 3.57um arrow looks like it should be longer.

 

Figure 7: redraw charts, unable to see scale numbers

 

Figure 7: use wt% or at% instead of counts

 

Figure 7: Cu and Zr line colors too close, please change

 

Figure 7: it seems that the SEM line scans tells you that the layer is made up of chromium oxide and not zirconium oxide. Contradictory to the description 

 

Line 281-282: this sentence does not reflect the supported context given. There’s no zirconium oxide layer as shown in EDS line scan results. And minimal Zr on the outer surface. Please re-write

 

Line 298-299: these results are not in agreement with SEM data. For Sample 3042hr, please look into more characterization, the increase in ZrO2 peak can also indicate the break down of Cr layer, which suggests that coating is not sustainable for long exposures times. However, SEM results shows higher Cr layer and it seems that it is pretty uniform. Please either recheck SEM or XRD analysis again. Like mentioned in text, specimens are not flat, X ray beam penetration might just not be at the highest convex location.

 

Section 3.3.2: my understanding for these electrochemical tests are done ex situ post exposure test at ambient conditions? And also different from the pH10.5 lithiated solution?

 

What is the difference between this “0.05 M boric acid and 0.001 M borax solution” and pH 10.5 solution?

 

Line 330: is non-autoclaved sample time 0 sample?

 

Table 3: it would be best to insert a row to separate units from description, first row of table is very messy currently most likely due to formatting, not by authors 

 

Section 3.3.2: Describe difference of roles between Rcoat and Roxide in the equivalent circuit. 

 

PD scans need be conducted in the same environment to reflect actual corrosion rates of studied medium, not in room temperature and different solution.

 

Major issues:

Improper use on choice of words

Abbreviations need to be introduced first

Author Response

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Reviewer 2 Report

The article presents the results of the tests and evaluation related to the corrosion behaviour of a thin chromium coating, deposited by Electron Beam Physical Vapor Deposition on Zircalloy-4. The tests were carried out by applying three electrochemical methods: potentiodynamic measurements, EIS, and OCP 18 variation. The authors noted that a plateau appears on the weight gain evolution, and the oxidation kinetics generate a cubic oxidation law, both of which indicate a stabilization of the corrosion. They observed a relatively uniform distribution of hydrides along the samples, in the horizontal direction, and that the coatings with thickness from 2 to 3 µm are still adherent and maintain integrity. Thus, their electrochemical results indicate better corrosion behaviour after some time of autoclaving.

My comments are as follows:

1. Authors should emphasize their innovative contribution and approach to the presented issue.

2. A graphic research diagram, workflow, description of the adopted algorithm and research stages seem to be necessary.

3. You need to clearly formulate the purpose of your research in a separate paragraph or even a subsection. Lines 99-103 are not enough.

4.Lines 247 and 353 – space after the tables.

5.Figure 6 – too large letters - (a) etc.

6.Was the research intended to confirm the advantages of the autoclaving process or the presented process or results were original or innovative? It must be written about if they were.

sufficient to publish

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

This manuscript is devoted to studying the Accident tolerant barriers for fuel road cladding of CANDU 2 nuclear reactor. The paper investigates into a key aspect of the nuclear industry - improving the safety of existing nuclear reactors and future designs. The manuscript is well-written and well organized and includes some merits and can be accepted for publication after incorporating following suggestions:

1. Incorporate recent literature into the introduction section.

2. Provide supplier details of isopropyl alcohol, Zy-4 tube, etc in section 2.1.

3. Add more details of microhardness testing in section 2.2.

4. Why density of hydrides was not increased after 3024 h of autoclaving (Fig. 2).

5. Discuss the XRD results in more detail (peak positions, reflection planes, intensity etc.)

6. “formation of zirconium hydrides, which may induce a material hardening effect” Provide suitable references. (Line 233)

7. Explain why polarization resistance of Cr-EBPVD coated Zy-4 sample was increased with increasing autoclaving time in more detail. (Section 3.3.3)

 

8. Add quantitative results in the conclusion section.

Minor editing of English language required.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Revision:

Q4 not answered: deposited pre-test Cr average and standard deviation thickness not added in section 2.1

Q5: define EB-PVD, not reply to reviewers, but define in context. All abbreviations used should be defined.

Q6: Figure 1 research diagram is great, shows clear process.

Q12: Maybe include in context the reason why the color and thickness examined from SEM is not similar? Also it seems that reference did not do actual measurements on the thickness of chromium oxide layer. High resolution SEM is needed to define spatial resolution in nm range. Else, XPS has to be adopted, but it seems that the reference did not really conduct actual measurements on thickness.

Q13: Figure 6 scale, font size is still too small

Q14: Was the same SEM settings used? if that is the case, Zr is showing up on the signals, it either means the the electron beam penetrated through the Cr layer or the Cr deposit layer is not uniform and fully covered.

Q16: I think there's misunderstanding on this question raised. Probe depth from SEM analysis is dependent on the accelerating voltage used. higher voltage = deeper depth, thus reducing accelerating voltage will provide you with more surface level results.

Figure 7 missing a, b, c captions

Q17. "the Cr2O3 layer not being able to be detected even by SEM measurements" - this statement is still contradictory to the results shown in Figure 8, yellow lines from cross section scans clearly shows oxygen, why would authors say chromium oxide layer is not being able to be detected? This does not require XPS analysis. The SEM results presented in figure 8 is sufficient to show the presence of chromium oxide.

Q18 & 19 combined. if results presented in figure 7 is secondary electron image, it would only provide topography information, which is not as useful for a cross-section. It would be best to show back scatter electron image that shows Z (atomic number) contrast.

Q20. Good. figure is much clearer now. you can also reference Ellingham diagram to support your claim. as you can see the gibbs free energy formation for ZrO2 is significantly lower than Cr2O3, and the needed concentration to form ZrO2 is also much lower, which is why ZrO2 layer is beneath Chromium oxide.

Q21: Refer to this reference. The Cr2O3 peaks might be overlapping. 10.1007/s10971-016-4066-4

Q22: Which results are authors referring to with "cross-section shows a deeper presence of chromium after 3024h autoclaving time, which translates to a 4-8 µm range compared to 2-6 µm after the initial 504h autoclaving treatment",? SEM results shows 2-3µm

Q23: If that is the case, the PD results for Figure 13 and Table 4 needs to be amended as they are no longer "primary circuit conditions of CANDU nuclear reactor". For EIS purposes, it is fine because you are only comparing the oxide behavior, however it should not be the case when presenting corrosion potential. this would shift based on the medium scans were made.

 

improved wording. Same comment: please introduce abbreviations before using them for the first time. eg: ebpvd

Author Response

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Reviewer 2 Report

The authors have taken into account my suggestions and doubts. They have thoroughly justified the corrections made that are meet  my expectations. The article is ready for publication.

Author Response

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