Development of Analytical Procedures for Chemical Characterization of Substrates for the Production of TRISO Coated Particles as Nuclear Fuel in High Temperature Gas-Cooled Reactors

Round 1

Reviewer 1 Report

This paper provides an analytical technique of trace elements in materials with regard to the TRISO coating. Trace elements in the organic liquids and solid materials were analyzed by an ICP-MS and NAA, respectively. In contrast, numerous papers for the determination using an ICP-MS and NAA have been reported so far. It is, therefore, hard to find out the novelty in the analytical protocol. The evaluation of trace elements in the materials give great impact for the TRISO coating and is much important for the sake of this work. This paper cannot be accepted without the evaluation.

1. Introduction
In this work, gasoline, extraction gasoline, ethanol, ammonia solution, HMTA, silicone oil were analyzed. I think pyrolytic carbon and silicon carbide should be analyzed as well as these material. Describe the reason why these material were analyzed, and pyrolytic carbon and silicon carbide were not analyzed. In addition, describe what process requires these materials (gasoline, etc) in the manufacturing process of the TRISO coated fuel particles.

2. Materials and Methods
It would be kind for reader if there is a section of samples in which sample materials is described. And, describe that the liquid samples and solid samples were analyzed by an ICP-MS and NAA, respectively.
Please refer to relating references. Numerous papers about analyses using an ICP-MS and NAA have been published so far.

L60-61
The novelty of the analyses in the work should be described briefly. And, why is the chemical characterization of materials important? The chemical impurities in TRISO are heavily activated by neutron capture reaction when the fuel is burned. After the use of the fuel, it seems uranium will be recovered and coating material will be discarded. Is there a procedure in the disposal of the coating material relating with activation level? Describe the importance of the chemical characterization.

L74-76
Heating of the mixture of c.HNO3 and organic material would sometimes make explosion. It seems a quite dangerous process. Or, residues obtained after evaporation were dissolved in HNO3? Please check.

Fig. 1, 5, 6, 7
Describe what the author tells with these figures. These figures should be removed if the figures are not used for the discussion.

Table 2
N.D. in Table 1 should be replaced by the detection limits written in Table 2.

L180
What is "the newly developed analytical method"? Details should be described by comparing conventional method.

L186-L202
This description should be included in Sec.2.

L206-L318
This description should be included in Sec.2.

As described above, the evaluation of trace elements in the materials is required. Describe the details.

L91, L105
Section number is duplicated. Please check.

L56, L81, L91, L168, L176, L186, L214
Check indenting.

Author Response

This paper provides an analytical technique of trace elements in materials with regard to the TRISO coating. Trace elements in the organic liquids and solid materials were analyzed by an ICP-MS and NAA, respectively. In contrast, numerous papers for the determination using an ICP-MS and NAA have been reported so far. It is, therefore, hard to find out the novelty in the analytical protocol. The evaluation of trace elements in the materials give great impact for the TRISO coating and is much important for the sake of this work. This paper cannot be accepted without the evaluation.

This is obviously true the general statement that numerous papers for the determination using ICP-MS and NAA analytical techniques have been reported so far. However each of these papers is specific, because it concerns various elements, various materials, various type of matrix, various level of elemental content etc. To some extent, each of them always brings something new. For this reason, the fact that there are a lot articles on analytical methods is very favorable for analytical community. The more articles, the better, because in this situation is much easier to match an analytical method suitable as much as possible for a given analyzed material. We believe that our work can make a small contribution to analytical knowledge. We are specialists in the field of analytical chemistry and the main aim of our work was to develop analytical methods which enable determination of elements at the lowest possible level of content. An assessment of the impact of impurities on the TRISO fuel should be a subject of completely separate investigations carried out by appropriate specialists.

 

1. 
   Introduction
   In this work, gasoline, extraction gasoline, ethanol, ammonia solution, HMTA, silicone oil were analyzed. I think pyrolytic carbon and silicon carbide should be analyzed as well as these material. Describe the reason why these material were analyzed, and pyrolytic carbon and silicon carbide were not analyzed. In addition, describe what process requires these materials (gasoline, etc) in the manufacturing process of the TRISO coated fuel particles.

This is not true that pyrolytic carbon and silicon carbide were not analyzed. They were analyzed by NAA and the results are presented and discussed with details in the chapter 3.2. Gasoline, extraction gasoline, ethanol, ammonia solution, HMTA, silicone oil are the reagents used in the sol-gel process aimed at obtaining spherical nuclear fuel precursors.

 

2. Materials and Methods
   It would be kind for reader if there is a section of samples in which sample materials is described. And, describe that the liquid samples and solid samples were analyzed by an ICP-MS and NAA, respectively.
   Please refer to relating references. Numerous papers about analyses using an ICP-MS and NAA have been published so far.

In the Introduction section one sentence was added which materials were analyzed by ICP-MS and which ones by NAA (L65-67). Regarding numerous analytical publications, it has already been mentioned above.

 

L60-61
The novelty of the analyses in the work should be described briefly. And, why is the chemical characterization of materials important? The chemical impurities in TRISO are heavily activated by neutron capture reaction when the fuel is burned. After the use of the fuel, it seems uranium will be recovered and coating material will be discarded. Is there a procedure in the disposal of the coating material relating with activation level? Describe the importance of the chemical characterization.

Regarding the novelty, it was discussed in more detail above. The importance of the chemical characterization was emphasized in the introduction (L56-61).

 

L74-76
Heating of the mixture of c.HNO3 and organic material would sometimes make explosion. It seems a quite dangerous process. Or, residues obtained after evaporation were dissolved in HNO3? Please check.

It is very difficult to agree with this comment. Nitric acid is commonly used in analytical chemistry for the digestion process of analyzed materials, including also organic samples.

 

Fig. 1, 5, 6, 7
Describe what the author tells with these figures. These figures should be removed if the figures are not used for the discussion.

In our opinion the gamma-ray spectra of analyzed materials (uranyl nitrate, pyrolytic carbon and silicon carbide) should be included in the article. They illustrate the presence of radionuclides in the analyzed materials. The resulting conclusions are discussed (L286-297).

 

Table 2
N.D. in Table 1 should be replaced by the detection limits written in Table 2.

The abbreviation “nd” (not detected) is often used in publications dealing with analytical chemistry.

 

L180
What is "the newly developed analytical method"? Details should be described by comparing conventional method.

The newly developed analytical method relies in many cases to some extent on existing published methods, but includes newly developed fragments (e.g. digestion procedure, detection technique, type of material analyzed, etc.). As explained (L182-185), when publishing such a method, one should take into account the estimation of the uncertainty of the obtained results.

 

L186-L202
This description should be included in Sec.2.

We do not agree. This fragment is a part of discussion.

L206-L318
This description should be included in Sec.2.

As above.

As described above, the evaluation of trace elements in the materials is required. Describe the details.

We do not quite understand this statement. Quantitative results of the content of trace elements in the examined materials are presented in Table 1 and 3.

L91, L105
Section number is duplicated. Please check.

Yes, it was duplicated. The appropriate correction has been made.

L56, L81, L91, L168, L176, L186, L214
Check indenting.

Indenting was corrected as indicated.

Reviewer 2 Report

Comments/corrections in more detail:

Abstract:

• “source of electricity”, suggest to add “process heat” as this the unique feature of HTRs
• “spherical grains of uranium kernel”, grain is here the wrong expression, it’s the kernel of a particle, and it’s not a uranium kernel, but a uranium oxide (or carbide or UCO) kernel, you might say a kernel containing uranium fuel.
• “Separate, where…, and separate using…” sounds somewhat awkward. What you mean by “separate” in this context?

 

Chap 1:

• “countries that expect energy deficits”, correct, but it includes also countries which are changing their energy economy towards minimizing use of fossil fuels.
• TRISO “triple coated isotropic particles”, suggest to us the commonly used expression “tristructural isotropic (TRISO) coated fuel particle”
• “deposition of PyC and SiC coatings at high temperature”. “High” temperature is always relative. But here you imply the wrong impression. The big progress made with the invention of the SiC layer was that its deposition temperature is much lower compared to the previously used BISO coating which resulted in much cleaner fuel (lower contamination level).
• “the author’s concept” -> “the authors’ concept”

 

Chap 2.2:

• “digestion to test” -> “digestion were transferred to test”

 

Chap 2.4:

• “Ns/st is the net peak area” , I don’t understand “area” in this context, as N is a dimensionless number.

 

Chap 3.1:

• 1, both text and caption talk about temperature and pressure only. What is the meaning of “Pressure Power  Program” ? Your pressure scale goes up to 90 bar, but values are floating just little above zero, and you cannot really read any data. If not important, then drop this curve. And, by the way, the official unit for pressure is Pa (or MPa)
• “should be assessment” -> “should be an assessment”
• “in what extent” -> “to what extent”
• “Ishikawa’s” -> “Ishikawa”
• “so-called the fishbone diagram” -> “so-called fishbone diagram”
• Never heard of an Ishikawa diagram before, according to Google a quality management to analyze cause-effect problems, but I don’t understand the meaning of the Cx axis, a kind of progress or what ? And which problem you want to solve in your context? Uncertainties? Suggest to provide some reference for Ishikawa.
• When you come up with results of 5% for Th and U and 10% for other elements, what were your assumptions for the single values of uncertainties Ui, and what were your assumptions based upon?

 

Chap 3.2:

• “is consisted” -> “consists”
• “silica carbide” -> “silicon carbide”

 

Chap 4: is missing !!

 

Chap 5:

• Your “Conclusions” do not contain any conclusions, it is a pure summary. Here I would like to read, in addition to your summary, what you have learned from your experiments. This is then the basis to decide in which direction you will proceed in future.

 

 

Overall comment:

Your paper gives me the impression that you have an excellent set of experimental tools for material analysis at hand and that you are able to handle it decently. If I am not mistaken, you have applied your procedures to the raw materials (educts) needed for the manufacturing of HTR fuel elements. So your results have, in first approximation, nothing to do with the quality of HTR fuel, they are just a demonstration of the quality of your experimental devices. Statements on the fuel quality you only achieve if you take your material samples directly from manufactured particles or fuel spheres to examine impurity levels and their changes with the manufacture process. One focus of your future work, if possible, might be on the U and Th impurity levels of the oPyC and matrix material, because they are sources of activity outside the SiC enclosure, and here data would be needed in the ppb range.

Author Response

Abstract:

• “source of electricity”, suggest to add “process heat” as this the unique feature of HTRs

In the revised manuscript the words: process heat have been added (L16).

 

• “spherical grains of uranium kernel”, grain is here the wrong expression, it’s the kernel of a particle, and it’s not a uranium kernel, but a uranium oxide (or carbide or UCO) kernel, you might say a kernel containing uranium fuel

Yes, we agree. This is kernel of UO₂ or UC₂ or UCO. Appropriate correction has been made (L17).

 

• “Separate, where…, and separate using…” sounds somewhat awkward. What you mean by “separate” in this context?

We meant two different analytical procedures. Indeed, the wording in the original manuscript was somewhat imprecise. For the sake of clarity, the sentence has been worded differently (L23-24).

 

Chap 1:

• “countries that expect energy deficits”, correct, but it includes also countries which are changing their energy economy towards minimizing use of fossil fuels.

Of course, the issue of minimizing fossil fuels should also be taken into account. The sentence has been modified accordingly (L37-40).

 

• TRISO “triple coated isotropic particles”, suggest to us the commonly used expression “tristructural isotropic (TRISO) coated fuel particle”

The expression has been corrected accordingly (L41-42).

 

• “deposition of PyC and SiC coatings at high temperature”. “High” temperature is always relative. But here you imply the wrong impression. The big progress made with the invention of the SiC layer was that its deposition temperature is much lower compared to the previously used BISO coating which resulted in much cleaner fuel (lower contamination level).

The temperatures range at which the coatings are formed (1250 – 1500 °C) has been given (48).

 

• “the author’s concept” -> “the authors’ concept” Corrected (L55)

 

Chap 2.2:

• “digestion to test” -> “digestion were transferred to test”

Indeed, two words missed. Corrected (L91-92).

Chap 2.4:

• “Ns/st is the net peak area” , I don’t understand “area” in this context, as N is a dimensionless number.

N_s/st is the net peak area and corresponds to number of counts registered for the isotope of interest during the gamma ray spectrometric measurement. If we divide it by the measurement time, we will obtain the activity i.e. counts per seconds according to eq. 2.

 

Chap 3.1:

• 1, both text and caption talk about temperature and pressure only. What is the meaning of “Pressure Power  Program” ? Your pressure scale goes up to 90 bar, but values are floating just little above zero, and you cannot really read any data. If not important, then drop this curve. And, by the way, the official unit for pressure is Pa (or MPa)

The meanings of the presented plots are as follows: “Pressure” means the pressure inside the vessels change vs. time. “Power” means the power of the magnetron change vs. time. “Program” shows the programmed maximum temperature values. The pressure change (maximum a few bars) indicates the digestion reaction had gentle course. The presented picture is original, generated by the device and the pressure units are expressed in bars.

 

• “should be assessment” -> “should be an assessment” Corrected (L183)

 

•  “in what extent” -> “to what extent” Corrected (L183)

 

• “Ishikawa’s” -> “Ishikawa” Corrected (L187)

 

• “so-called the fishbone diagram” -> “so-called fishbone diagram” Corrected (L188)
• Never heard of an Ishikawa diagram before, according to Google a quality management to analyze cause-effect problems, but I don’t understand the meaning of the Cx axis, a kind of progress or what ? And which problem you want to solve in your context? Uncertainties? Suggest to provide some reference for Ishikawa.

The Ishikawa diagram is a useful tool to identify the sources of uncertainty of results. It is used in many fields, including analytical chemistry to estimate the uncertainty budget of results. C_x is the content of the given analyte in the analyzed material. This supplement has been added in the description of Figs. 2 and 8 (L190-191 and L316-317). References regarding Ishikawa have been given (L187, L369 and L375).

 

• When you come up with results of 5% for Th and U and 10% for other elements, what were your assumptions for the single values of uncertainties Ui, and what were your assumptions based upon?

Individual uncertainties have been estimated experimentally or on the basis of manufacturers' data, as described in the article (L196-197).

 

Chap 3.2:

• “is consisted” -> “consists” Corrected (L227).
• “silica carbide” -> “silicon carbide” Corrected (L278).

 

Chap 4: is missing !!

Chapters 3 and 4 have been merged into one unit entitled “Results and Discussion”.

 

Chap 5:

• Your “Conclusions” do not contain any conclusions, it is a pure summary. Here I would like to read, in addition to your summary, what you have learned from your experiments. This is then the basis to decide in which direction you will proceed in future.

Conclusions have been thoroughly revised.

 

Overall comment:

Your paper gives me the impression that you have an excellent set of experimental tools for material analysis at hand and that you are able to handle it decently. If I am not mistaken, you have applied your procedures to the raw materials (educts) needed for the manufacturing of HTR fuel elements. So your results have, in first approximation, nothing to do with the quality of HTR fuel, they are just a demonstration of the quality of your experimental devices. Statements on the fuel quality you only achieve if you take your material samples directly from manufactured particles or fuel spheres to examine impurity levels and their changes with the manufacture process. One focus of your future work, if possible, might be on the U and Th impurity levels of the oPyC and matrix material, because they are sources of activity outside the SiC enclosure, and here data would be needed in the ppb range.

 

Thank you very much for your valuable comments. On their basis, we have made significant corrections, which allowed us to eliminate some inaccuracies in the article. The developed procedures described in the article concern the chemical characteristics of the substrates used in the production of TRISO fuel. In the near future, after some modifications, we plan to adapt them to the chemical analysis of the produced TRISO particles as well.

Reviewer 3 Report

Two different analytical techniques were developed for the chemical characterization of substrates for the production of TRISO coated particles. Each technique is suitable for chemical analysis of different kinds of samples. The article is well written and ready to be published as it is.

Author Response

Thank you very much for your review and opinion.

Round 2

Reviewer 1 Report

Almost all comments were not applied in the revised manuscript. As mentioned in the previous review report, numerous papers about analytical methods have been published so far. In addition, readers hard to find the importance of this work and think what the analytical value means without discussion. 

Therefore, this manuscript should be revised.

Author Response

In accordance with the comments of the reviewer, the Introduction has been corrected with appropriate references to the use of NAA and ICP-MS in the determination of impurities in reactor fuel. A detailed explanation of the overall purpose of our HTGR project is included in the Introduction.

 

Table 2 has been revised as suggested by the reviewer. That is “nd.” changed to "<LOD" (below limit of detection).

 

The gamma ray spectra of the analyzed samples are often presented in the literature and they are an important part of numerous publications concerning the use of NAA for chemical characterization. Based on the spectra, the reader has an idea of what radioisotopes are present in a given analyzed material. Here are some examples of publications:

1. E. Chajduk & R. S. Dybczyński. Highly accurate radiochemical neutron activation analysis of arsenic in biological materials involving selective isolation of arsenic by hybrid and conventional ion exchange. Microchimica Acta (2010) 168 37–44.
2. M. Mohammadzadeha, M. Ajami, A. Shadeghipanah, M. Rezvanifard. A study of neutron activation analysis compared to inductivelycoupled plasma atomic emission spectrometry for geological samples in Iran. Nuclear Engineering and Technology (2018) 50 1349–1354.
3. M. Chand, R. Senthilvadivu, J. S. Brahmaji Rao, G. V. S. Ashok Kumar, R. Kumar. Elemental characterization of coal fly ash using k0‑based IM‑NAA and EDXRF towards its potential utilization and environmental concern. Journal of Radioanalytical and Nuclear Chemistry (2020) 324 1089–1097.
4. L. Hamidatou, H. Slamene, T. Akhal, A. Boulegane. Trace and essential elements determination in baby formulas milk by INAA and k0-INAA techniques. Journal of Radioanalytical and Nuclear Chemistry (2014) 301 659–666.

 

The estimation of uncertainty should be included in Sec. 3, as it is in the manuscript, but not in Sec.2. In articles on newly developed analytical methods, the estimation of the uncertainty of results is commonly placed at the end of chapter “Results and Discussion” after a detailed presentation of the procedure. We adopted this order in our work. The following publications can be cited as examples:

1. B. Markiewicz, A. Sajnóg, W. Lorenc, A.Hanć, I. Komorowicz, J. Suliburska, R. Kocyłowski, D. Barałkiewicz. Multielemental analysis of 18 essential and toxic elements in amnioticfluidsamples by ICP-MS: Full procedure validation and estimation ofmeasurement uncertainty. Talanta (2017) 174 122–130.
2. E. Chajduk & R. S. Dybczyński. Highly accurate radiochemical neutron activation analysis of arsenic in biological materials involving selective isolation of arsenic by hybrid and conventional ion exchange. Microchimica Acta (2010) 168 37–44.
3. R. S. Dybczyński, B. Danko, M. Pyszynska, H. Polkowska-Motrenko. Ratio primary reference measurement procedure (RPRMP) for the determination of iron in biological materials by RNAA. Radiochimica Acta, (2012) 100, 409–416.
4. I. Zuba, & H. Polkowska-Motrenko. Ratio primary reference measurement procedure (RPRMP) for the certification of chromium content in biological materials. Radiochimica Acta, (2019) 107, 141–147.
5. T. Miura, Y. Iinuma, S. Sekimoto. Precise determination of iridium by neutron activation analysis coupled with internal standard method. Journal of Radioanalytical and Nuclear Chemistry (2020) 324 1007–1012.