Development of Mechanical Pipe-Connection Design for DEMO

Round 1

Reviewer 1 Report

Dear Authors,

I read with care the manuscript titled “Development of Mechanical Pipe Connection Design for DEMO” to be published in Journal of Nuclear Engineering. It reports a study dealing with the development of a novel type of pipe connection to be adopted in DEMO.

An initial design is proposed and investigated. Some improvements are thus proposed and investigated as well by means of dedicated finite element analyses. Nevertheless, the description of numerical models, loads and boundary conditions is totally missing, while results are presented in a really synthetic manner.

Thus, I believe that the work could be suitable for the publication in Journal of Nuclear Engineering only after major revisions.

Comments for author File: Comments.pdf

Author Response

Dear Reviewer,

 

Thank you very much for your comments and input. We have carefully considered your remarks and have corrected the manuscript accordingly.

 

 Dear Authors,

I read with care the manuscript titled “Development of Mechanical Pipe Connection Design for DEMO” to be published in Journal of Nuclear Engineering. It reports a study dealing with the development of a novel type of pipe connection to be adopted in DEMO.

An initial design is proposed and investigated. Some improvements are thus proposed and investigated as well by means of dedicated finite element analyses. Nevertheless, the description of numerical models, loads and boundary conditions is totally missing, while results are presented in a really synthetic manner.

Thus, I believe that the work could be suitable for the publication in Journal of Nuclear Engineering only after major revisions.

Global remarks

• With the exception of Figure 2, all other figures are not cited in the text. Please cite each figure you show and try to describe them.

All figures are now mentioned and their contents described as they should be.

• Structural analysis: the description of FEA numerical models, adopted loads and boundary conditions is completely missing. It is hard to judge obtained results with information reported in the paper. Moreover, what piping system are authors investigating? From adopted pressure values (9.6 MPa) it seems that are those relevant to the HCPB BB (coolant pressure of 8 MPa). What happens in case of WCLL BB where the coolant pressure is equal to 15.5 MPa (and design pressure is equal to 17.8 MPa)?

The FEA model and boundary conditions are now included. This can be found in lines 248 through 262.

Please revise deeply these sections, adding more details and references on the aforementioned points.

• Consider to merge sections 5 and 6 could be merged in a unique section.

The manuscript is now restructured according to your remarks.

Detailed remarks

2. Basic Considerations

• Figure 1 is not cited in the text. What is the relevance of this figure? Is the adoption of some of the sealings reported in the picture foreseen for DEMO? Some references are found in section 3, maybe figure 1 could be moved after this section.

Explanations have been added to complement the figure.

• It seems that a typo occurred in the penultimate bullet: “Only of passive mechanical…”

This has been corrected in line 66

4. Structural analysis

• Lines from 68 to 70 are confused, please try to improve this part.

This has been corrected.

5. Improvement

• Lines from 89 to 91, describing the spring configuration is not very clear. Please modify this part.

The spring configuration is now included in figure 6.

Author Response File: Author Response.pdf

Reviewer 2 Report

Dear Authors,

I have read with care the proposed paper titled “Development of Mechanical Pipe Connection Design for DEMO”. My general feeling is that you did a good work, trying to obtain a sound design for a MPC for DEMO, but its presentation given in this paper is quite poor and should be significantly improved. A huge work is necessary, in my opinion, to enlarge the presentation of the performed numerical analysis, describing in detail the models, the loading conditions and the assumptions as well as adequately motivating the rationale behind them. Attention should be also paid to the discussion on the results of the analysis, which is practically missing. The provided pictures are not enough if not accompanied by a critical discussion. The link in between the different sections is often missing or weak, and the terms of comparison (design criteria? numerical requirements? other figures of merit?) used to compare the design options and improve it are not clearly motivated and discussed. Moreover, last but not least, the reference list should be enlarged in order to give the context which the work has been developed in, highlighting its link with the overall DEMO in-vessel component design.

For these reasons, I think that this paper can be published in Journal of Nuclear Engineering only after a major revision. You can find my main remarks in the following.

 

 

Abstract

·                 Double dot at the end. Please correct it.

 

 

Introduction

·                 The introduction is too brief. The scope of the work is not clearly stated, as well as the followed methodology and the structure of the paper. Moreover, the context in which the work has been developed should be given making use of proper reference, to fully frame the presented work into the EUROfusion activities aimed at achieving the DEMO design. In fact, the development of mechanical Pipe Connection Design for DEMO is pivotal to improve and complement the design of the main in vessel components, such as Breeding Blanket, Divertor and, consequently, the relevant Primary Heat Transfer Systems. Therefore, this link between the work here presented and the general scope of in-vessel components design should be stressed and enforced to put more emphasis on the topic addressed in this paper. To this scope, some reference papers could be:

 

Arena, P. et al. The DEMO Water-Cooled Lead–Lithium Breeding Blanket: Design Status at the End of the Pre-Conceptual Design Phase. Appl. Sci. 2021, 11, 11592. https://doi.org/10.3390/ app112411592;

 

Moscato, I: et al., Tokamak cooling systems and power conversion system options, Fusion Engineering and Design, 2022, 178, 113093. https://doi.org/10.1016/j.fusengdes.2022.113093;

 

Boccaccini, L.V. et al., Status of maturation of critical technologies and systems design: Breeding blanket, Fusion Engineering and Design, 2022, 179, 113116, https://doi.org/10.1016/j.fusengdes.2022.113116.

 

You, Y.H., Divertor of the European DEMO: Engineering and technologies for power exhaust, Fusion Engineering and Design, 2022, 175, 113010. https://doi.org/10.1016/j.fusengdes.2022.113010.

 

·                 Moreover, you state that “the concept itself is not novel”. Hence, could you please add some references showing the other field of applications of the proposed concept? Do some studies on its reliability, showing for instance its soundness, exist? Should be the case, it would be nice to mention them (making use of reference if necessary) in order to support this statement and enforcing the idea to adopt this approach also for DEMO.

 

 

2. Basic Considerations

·                 The capture of requirements is a good starting point to design an interface system as a pipe connection system is. Also in this case, as the systems engineering approach has been used several times in DEMO design (and in BB design particularly), some references could be used in support, to enforce the link between the work here reported and the general DEMO design approach. Some suggestions:

 

G. Bongioví, et al., Systems engineering activities supporting the heating & current drive and fuelling lines systems integration in the European DEMO breeding blanket, Fusion Engineering and Design, 147, 111265, 2019. DOI: 10.1016/j.fusengdes.2019.111265.

 

G. A. Spagnuolo, et al., Systems Engineering approach in support to the breeding blanket design. Fusion Engineering and Design, 146, Part A, pp. 31-35, 2019. DOI: 10.1016/j.fusengdes.2018.11.016.

 

G. Bongioví, et al., Concept selection of the automated inspection and maintenance test unit for the EU DEMO using a novel fuzzy-based decision support tool, Fusion Engineering and Design, 148, 111324, 2019. DOI: 10.1016/j.fusengdes.2019.111324.

 

·                 Lastly, figure 1 is not mentioned in the text and its content is not explained. Each figure should be mentioned at least once and the content should be described and/or commented to provide additional information to the reader. Moreover, the data reported in this figure only refer to gas. It could seem that you developed this connection system only for HCPB BB, as WCLL BB does not foresee any gas coolant. You should clarify this aspect.

 

 

3. Concept design

·                 The main components shown in Figure 2 should be indicated and briefly described in the text. If possible, the main dimensions should be indicated. In particular, the initial dimensions of the component that will be modified in the further steps are necessary to ease the comprehension and highlight the work done.

 

 

4. Structural analysis

·                 This section must be significantly enlarged. Information on the FEM models set-up, the loads definition and boundary conditions must be given. Indication on the assumed temperature conditions is missing and it is pivotal.

 

·                 How can you state (lines 62 and 63) that “Hub and clamp concept studies show that the design is feasible and the clamping mechanism can withstand the operation pressure and all first seal failure” ? Did you adopted any set of structural criteria ? Or you used numerical limit values derived from requirements collected in section 2) ? You should add information on this point.

 

·                 Moreover, Figure 3 is never mentioned (it should be at least once) and its content should be described and commented. Here, in Fig. 3 b) and 3 c) “seating load” should be “sealing load”. Shouldn’t it? Then, what does Figure 3 a) mean? Did you perform 2D models and analysis, or you used the indicated plane as a symmetry plane to assess only half of the geometric model? Or you performed 3D analysis but you are reporting results on a selected plane? In this latter case, the label “analysis plane” is misleading. In any case, you should add explanations.

·                 In general, the adopted analysis approach and the rationale behind the results presentation must be described and justified.

 

·                 Lastly, legends in Figure 3 are too small and the numbers are hardly readable. Please improve their quality.

 

 

5. Improvement

·                 The most of the comments done for section 4 still hold for this section. The FEM models, the loads and boundary conditions should be described. In general, the presentation of the analysis methodology and of the rationale behind is poor (it is almost missing, actually) and should be significantly enriched.

 

·                 Figure 4 is never mentioned, and its content should be described. Its quality should be improved (typos are present and the legends are hardly readable). In particular, the meaning of Figure 4 a) should be explained as it is not clear what “analysis plane” means (are you reporting results of a 3D analysis on a plane or did you perform a 2D analysis? Whatever is the answer, it must be explained and justified) and the reason why it is now different from the previous section.

 

·                 Moreover, numerical values should be given in lines 78, 79 and 80 to quantify the amount of the modifications. Lastly, it is not clear what rationale has been used to modify the design. Did you use as reference a set of structural design criteria? Or numerical values of the captured requirements? You should clearly describe and motivate the adopted strategy.

 

 

6. Analysis of the Improvement

·                 The use of “design by formulas” is not adequately motivated, since up to this point only “design by analysis” has been followed. Some justifications should be given, considering also that after this point another FEM analysis is performed.

 

·                 Moreover, results reported in table 2 should be commented a bit more in detail focussing on the stress margin against the limits. For instance, as to Clamp Lip Shear Stress, the predicted stress in Assembly conditions is 163.62 MPa and the corresponding limit is 173.6 MPa. Hence, a margin lower than 10 % is calculated and the criterion can be considered as passed even if with a narrow margin. What can we deduce?

 

·                 Looking at the “MPC Stress Value” column, which kind of stress are reported? Are they equivalent stress, maximum or minimum values of stress components? Do they refer to a stress line (i.e. path) or to the whole component? Please give some details on that.

 

·                 Figures 6 and 7 are never mentioned and their content should be explained. Also in this section, information on the FEM model and loads and boundary conditions application should be given. Why are you referring to Tresca equivalent stress whereas in previous analysis you showed Von Mises equivalent stress? This point should be addressed. You should also explain the rationale behind such a kind of results presentation. In particular, results on the gasket should be discussed.

 

·                 The “ticker flange” here is 115 mm thick but in the previous section you stated that the thickness is 110 mm. You should check.

 

 

References

The list of references is quite poor. As the work here presented is fully framed into the EUROfusion activities, some references can be added in support. Some suggestions are given in the previous points. Basically, since the Pipe connection system design is directly connected to remote maintenance and in-vessel components design, this link should be enforced to further highlight the importance of this work.

Author Response

Dear Reviewer,

 

We would like to thank for the rigorous review and detailed feedback. Your remarks helped us to improve the manuscript with a complete rewrite. Please find below our response to your comments:

 

I have read with care the proposed paper titled “Development of Mechanical Pipe Connection Design for DEMO”. My general feeling is that you did a good work, trying to obtain a sound design for a MPC for DEMO, but its presentation given in this paper is quite poor and should be significantly improved. A huge work is necessary, in my opinion, to enlarge the presentation of the performed numerical analysis, describing in detail the

models, the loading conditions and the assumptions as well as adequately motivating the rationale behind them. Attention should be also paid to the discussion on the results of the analysis, which is practically missing. The provided pictures are not enough if not accompanied by a critical discussion. The link in between the different sections is often missing or weak, and the terms of comparison (design criteria? Numerical requirements? other figures of merit?) used to compare the design options and improve it are not clearly motivated and discussed. Moreover, last but not least, the reference list should be enlarged in order to give the context which the work has been developed in, highlighting its link with the overall DEMO invessel component design.

 

Abstract

• Double dot at the end. Please correct it.

Corrected at line 18

 

Introduction

• The introduction is too brief. The scope of the work is not clearly stated, as well as the followed methodology and the structure of the paper. Moreover, the context in which the work has been developed should be given making use of proper reference, to fully frame the presented work into the EUROfusion activities aimed at achieving the DEMO design. In fact, the development of mechanical Pipe Connection Design for DEMO

is pivotal to improve and complement the design of the main in vessel components, such as Breeding Blanket, Divertor and, consequently, the relevant Primary Heat Transfer Systems. Therefore, this link between the work here presented and the general scope of in-vessel components design should be stressed and enforced to put more emphasis on the topic addressed in this paper. To this scope, some reference papers

could be:

 

Arena, P. et al. The DEMO Water-Cooled Lead–Lithium Breeding

Blanket: Design Status at the End of the Pre-Conceptual Design

Phase. Appl. Sci. 2021, 11, 11592. https://doi.org/10.3390/

app112411592;

Moscato, I: et al., Tokamak cooling systems and power

conversion system options, Fusion Engineering and Design,

2022, 178, 113093. https://doi.org/10.1016

/j.fusengdes.2022.113093;

Boccaccini, L.V. et al., Status of maturation of critical

technologies and systems design: Breeding blanket, Fusion

Engineering and Design, 2022, 179, 113116, https://doi.org

/10.1016/j.fusengdes.2022.113116.

You, Y.H., Divertor of the European DEMO: Engineering and

technologies for power exhaust, Fusion Engineering and Design,

2022, 175, 113010. https://doi.org/10.1016

/j.fusengdes.2022.113010.

 

The introduction has been completely overhauled to include your points. Citations are included to show this work’s context in the DEMO project.

 

Moreover, you state that “the concept itself is not novel”. Hence, could you please add some references showing the other field of applications of the proposed concept? Do some studies on its reliability, showing for instance its soundness, exist? Should be the case, it would be nice to mention them (making use of reference if necessary) in order to support this statement and enforcing the idea to adopt this approach also for DEMO.

 

Citations have been included to support the information.

 

Basic Considerations

• The capture of requirements is a good starting point to design an interface system as a pipe connection system is. Also in this case, as the systems engineering approach has been used several times in DEMO design (and in BB design particularly), some references could be used in support, to enforce the link between the work here reported and the general DEMO design approach. Some suggestions:

1. Bongioví, et al., Systems engineering activities supporting the

heating & current drive and fuelling lines systems integration in

the European DEMO breeding blanket, Fusion Engineering and

Design, 147, 111265, 2019. DOI:

10.1016/j.fusengdes.2019.111265.

 

1. A. Spagnuolo, et al., Systems Engineering approach in

support to the breeding blanket design. Fusion Engineering and

Design, 146, Part A, pp. 31-35, 2019. DOI:

10.1016/j.fusengdes.2018.11.016.

 

1. Bongioví, et al., Concept selection of the automated

inspection and maintenance test unit for the EU DEMO using a

novel fuzzy-based decision support tool, Fusion Engineering and

Design, 148, 111324, 2019. DOI:

10.1016/j.fusengdes.2019.111324.

Thank you for your suggestions. The design requirements have been expanded and citations in the DEMO context have been added. Lines 34 - 68

 

• Lastly, figure 1 is not mentioned in the text and its content is not explained. Each figure should be mentioned at least once and the content should be described and/or commented to provide additional information to the reader. Moreover, the data reported in this figure only refer to gas. It could seem that you developed this connection system only for HCPB BB, as WCLL BB does not foresee any gas coolant. You should clarify this aspect.

All figures are now mentioned and their contents described as they should be. The target blanket design and reasoning behind the choice are now explained. Lines 47 - 55

 

3. Concept design

• The main components shown in Figure 2 should be indicated and briefly described in the text. If possible, the main dimensions should be indicated. In particular, the initial dimensions of the component that will be modified in the further steps are necessary to ease the comprehension and highlight the work done.

 

All components are now described, with the main dimensions included in table 2.

 

4. Structural analysis

• This section must be significantly enlarged. Information on the FEM models set-up, the loads definition and boundary conditions must be given. Indication on the assumed temperature conditions is missing and it is pivotal. How can you state (lines 62 and 63) that “Hub and clamp concept studies show that the design is feasible and the clamping mechanism can withstand the operation pressure and all first seal failure” ? Did you adopted any set of structural criteria ? Or you used numerical limit values derived from requirements collected in section 2) ? You should add information on this point.

This section has been overhauled. The FEM setup and load cases have been described and figures have been added to improve comprehension. Lines 107 - 122

• Moreover, Figure 3 is never mentioned (it should be at least once) and its content should be described and commented. Here, in Fig. 3 b) and 3 c) “seating load” should be “sealing load”. Shouldn’t it? Then, what does Figure 3 a) mean? Did you perform 2D models and analysis, or you used the indicated plane as a symmetry plane to assess only half of the geometric model? Or you performed 3D analysis but you are reporting results on a selected plane? In this latter case, the label “analysis plane” is misleading. In any case, you should add explanations.

This section has been overhauled. Figure 3 and 4 (now figure 4 and 5) have been correctly mentioned in the body of the section. We have noticed that due to translation error that “analysis plane” is not correct term, we should have used “cross-section” plane (which is what it is now called in the description) which would describe the picture better

• In general, the adopted analysis approach and the rationale behind the results presentation must be described and justified.

The analysis approach and the rationale has been expanded in line 123-141.

• Lastly, legends in Figure 3 are too small and the numbers are hardly readable. Please improve their quality.

The figure has been replaced to improve readability.

 

5. Improvement

• The most of the comments done for section 4 still hold for this section. The FEM models, the loads and boundary conditions should be described. In general, the presentation of the analysis methodology and of the rationale behind is poor (it is almost missing, actually) and should be significantly enriched. Figure 4 is never mentioned, and its content should be described. Its quality should be improved (typos are present and the legends are hardly readable). In particular, the meaning of Figure 4 a) should be explained as it is not clear what “analysis plane” means (are you reporting results of a 3D analysis on a plane or did you perform a 2D analysis? Whatever is the answer, it must be explained and justified) and the reason why it is now different from the previous section. Moreover, numerical values should be given in lines 78, 79 and 80 to quantify the amount of the modifications. Lastly, it is not clear what rationale has been used to modify the design. Did you use as reference a set of structural design criteria? Or numerical values of the captured requirements? You should clearly describe and motivate the adopted strategy.

The analysis plane is basically a section plane across the 3D FEA. This is now corrected to be more clear. The figures  are now better captioned.

The improvement section now been rewritten for the purpose of clarity. With the FEM analysis of the improved model now moved into section 6

 

 

6. Analysis of the Improvement

• The use of “design by formulas” is not adequately motivated, since up to this point only “design by analysis” has been followed. Some justifications should be given, considering also that after this point another FEM analysis is performed.

We have made efforts to make it clearer why the design by formulas was not suitable for the case of multi-pipe MPCs. Lines 195 – 225.

• Moreover, results reported in table 2 should be commented a bit more in detail focussing on the stress margin against the limits. For instance, as to Clamp Lip Shear Stress, the predicted stress in Assembly conditions is 163.62 MPa and the corresponding limit is 173.6 MPa. Hence, a margin lower than 10 % is calculated and the criterion can be considered as passed even if with a narrow margin. What can we deduce?

The value of 173 already includes the inherent 1.5 safety factor, which is now better conveyed through line 222-228.

• Looking at the “MPC Stress Value” column, which kind of stress are reported? Are they equivalent stress, maximum or minimum values of stress components? Do they refer to a stress line (i.e. path) or to the whole component? Please give some details on that.

The value is the equivalent stress as per ASME standard, which is now better explained in line 206-221

• Figures 6 and 7 are never mentioned and their content should be explained. Also in this section, information on the FEM model and loads and boundary conditions application should be given. Why are you referring to Tresca equivalent stress whereas in previous analysis you showed Von Mises equivalent stress? This point should be addressed. You should also explain the rationale behind such a kind of results presentation. In

particular, results on the gasket should be discussed.

The explanation has been expanded in lines 236 – 253 and additional figures have been added to make the load cases easier to understand

• The “ticker flange” here is 115 mm thick but in the previous section you stated that the thickness is 110 mm. You should check.

The value has been corrected to the correct value.

References

The list of references is quite poor. As the work here presented is fully framed into the EUROfusion activities, some references can be added in support. Some suggestions are given in the previous points. Basically, since the Pipe connection system design is directly connected to remote maintenance and invessel components design, this link should be enforced to further highlight the importance of this work.

The list now includes more references from the DEMO framework. Relevant work has been cited at the appropriate places.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Dear Authors,

I really appreciated the improvements made on the manuscript. The paper is now much more clear and complete, and it will give an important contribution to the development of a multi-pipe MPC for DEMO.

Two solutions are initially investigated and the most promising one has been selected for more detailed analysis and Proof of Principle (PoP) testing. Then, further detailed calculations on this PoP have been carried out.

Thus, I believe that the work could be suitable for the publication in Journal of Nuclear Engineering only after very few minor revisions as reported in the following:

Line 156 ends with blanket section: it is not clear what author are referring to. Probably the correct term to be adopted is blanket segment.

Section 6: consider to introduce the acronym PoP after the first time you mention Proof of Principle

Table 3. In the first line of Allowed Max Stress Value, the “e” letter is present. Probably it is a Typo. Moreover, please consider to add a column where the ratio between calculated and allowable stress is reported. It will help the reader to immediately identify areas not fulfilling the criterion (i.e. values of the ratio higher than 1).

Author Response

Dear Reviewer,

Thank you very much for your review, we appreciate the time you have taken to help us improve the quality of our manuscript.

As per your input, we have made revisions as reported in the following:

Line 156 ends with blanket section: it is not clear what author are referring to. Probably the correct term to be adopted is blanket segment.

Thank you very much for your input. As we are not familiar with the internal designation for the blankets, i am sorry for this confusion. We have changed the term "blanket section" to "blanket segment" as you have suggested, since in the manuscript, the part that we mean is the segments of the blankets on one section of the tokamak.

 

Section 6: consider to introduce the acronym PoP after the first time you mention Proof of Principle

An acronym is now introduced in line 136 and the term Proof-of-Principle is now revered as PoP from line 137 onwards

Table 3. In the first line of Allowed Max Stress Value, the “e” letter is present. Probably it is a Typo. Moreover, please consider to add a column where the ratio between calculated and allowable stress is reported. It will help the reader to immediately identify areas not fulfilling the criterion (i.e. values of the ratio higher than 1).

Thank you very much for your input, to improve clarity we have removed the typo and added a column to show the ratio between the allowable and calculated stress with the ratio above the ratio of 1 marked with the color red.

 

I would like to thank you again for taking your time to review our manuscript.

 

Best Regards,

Reviewer 2 Report

-

Author Response

Dear Reviewer,

Thank you very much for your review, we appreciate the time you have taken to help us improve the quality of our manuscript.

 

Thank you very much for your input, to improve clarity we have done a spell and grammatical changes.

 

I would like to thank you again for taking your time to review our manuscript.

 

Best Regards,