Hybrid Small Modular Reactor—Renewable Systems for Smart Cities: A Simulation-Based Assessment for Clean and Resilient Urban Energy Transitions

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1. The life cycle assessment framework has obvious flaws. Table 4 zeroes out operational emissions from nuclear energy, which is too ideal and should actually include emissions from mining, enrichment, construction and so on. The International Atomic Energy Agency (IAEA) data show that typical life cycle emissions are about 12g CO2/kWh, while the paper incorrectly cites "operational emissions" as the full life cycle data. This leads to an overestimation of emission reduction.
2. The economic model ignores some cost elements such as insurance and decommissioning.
3. The policy recommendations lack implementation paths.
4. The table should be standardized as a three-line table.
5. There are redundant yellow border lines in Figure 5.

Author Response

First of all, I would like to thank you for your thorough review of our paper (energies-3771849) and helpful comments to improve it.

 

Reviewer 1

Comments to the Authors
1. The life cycle assessment framework has obvious flaws. Table 4 zeroes out operational emissions from nuclear energy, which is too ideal and should actually include emissions from mining, enrichment, construction and so on. The International Atomic Energy Agency (IAEA) data show that typical life cycle emissions are about 12g CO2/kWh, while the paper incorrectly cites "operational emissions" as the full life cycle data. This leads to an overestimation of emission reduction.

2. The economic model ignores some cost elements such as insurance and decommissioning.
3. The policy recommendations lack implementation paths.
4. The table should be standardized as a three-line table.
5. There are redundant yellow border lines in Figure 5.

 

To Reviewer 1:

            Thank you very much for your review and valuable remarks.

 

1. The life cycle assessment framework has obvious flaws. Table 4 zeroes out operational emissions from nuclear energy, which is too ideal and should actually include emissions from mining, enrichment, construction and so on. The International Atomic Energy Agency (IAEA) data show that typical life cycle emissions are about 12g CO2/kWh, while the paper incorrectly cites "operational emissions" as the full life cycle data. This leads to an overestimation of emission reduction.

- We thank the reviewer for the insightful observation. In the original version of Table 4, the emission factor for SMR was incorrectly stated as 0 gCO₂/kWh, reflecting only operational emissions. We fully agree that this underestimates the true life-cycle impact. As suggested, we have updated the emission factor to 12 gCO₂/kWh, in line with the International Atomic Energy Agency (IAEA) and IEA (2023) estimates, which include mining, enrichment, construction, operation, and decommissioning. A clarification note has also been added below Table 4 to explicitly address this correction. As a result, all emission-related calculations and scenario interpretations remain valid but reflect more realistic carbon accounting for nuclear systems.

2. The economic model ignores some cost elements such as insurance and decommissioning.

- We appreciate the reviewer’s important observation regarding omitted cost elements in the economic model. Indeed, in the current version, some long-term and external cost components — particularly insurance, decommissioning, and waste management — are not explicitly modeled in the LCOE estimates for SMR.

We acknowledge this limitation and have revised the manuscript to include a clarification note stating that such costs are currently excluded but will be integrated in future model iterations. We also highlight that in many countries, these costs are often handled through state-level instruments or embedded in regulatory frameworks, which creates variability across jurisdictions.

3. The policy recommendations lack implementation paths.

- Thank you for highlighting this critical gap. We agree that effective policy recommendations require not only conceptual proposals but also realistic implementation paths. To address this, we have expanded the “Policy Implications” section to outline concrete policy mechanisms and actions. These include regulatory innovation (e.g., licensing sandboxes for SMRs), targeted fiscal incentives (e.g., tax credits for hybrid systems), and capacity-building strategies. These additions aim to bridge the gap between modeling insights and actionable policy design.

4. The table should be standardized as a three-line table.

- Thank you for the formatting recommendation. In response, we have reformatted the relevant tables according to the three-line table standard, ensuring consistency and clarity. All internal lines have been removed, and only the top, header-bottom, and final horizontal rules are retained, following journal guidelines.

5. There are redundant yellow border lines in Figure 5.

- Thank you for pointing this out. We have removed the redundant yellow border lines from Figure 5 to improve the visual clarity and ensure consistency with the overall design style. The revised figure is now free of unnecessary graphical elements.

 

 Thank you very much for your remarks and comments. They were very useful for me to emphasize the main tasks and contributions of the manuscript, and also to focus the attention of the readers on the new and unique elements.

Reviewer 2 Report

Comments and Suggestions for Authors

Thank you for the opportunity to review this manuscript. The topic is timely and relevant, and the work provides valuable insights. However, there are a few issues that should be addressed to improve the clarity, consistency, and overall quality of the paper. My detailed comments are as follows:

1. Section Titles (2.2 and 2.3):
   The titles of Sections 2.2 and 2.3 are currently the same, which appears to be a mistake. The title of Section 2.3 should be revised to reflect its specific content—perhaps "Construction Phase" would be a suitable alternative.

2. Table 4 – CO₂ Emissions:
   In Table 4, the CO₂ emissions for solar PV include the full life cycle, whereas those for SMR do not appear to account for construction and decommissioning. This inconsistency is problematic and may lead to a biased comparison. The rationale for this discrepancy should be clearly explained. Furthermore, it seems that the emissions associated with batteries do not include production and disposal processes. Please clarify this point and consider revising the table or the accompanying explanation for consistency.

3. Line 590 – Power Import/Export Explanation:
   On Line 590, the manuscript refers to power import/export exchanges. A more detailed explanation of this aspect is needed. Specifically, the conditions under which such exchanges are possible should be clarified, as this aspect appears to be limited or constrained in the model.

Author Response

First of all, I would like to thank you for your thorough review of our paper (energies-3771849) and helpful comments to improve it.

Reviewer 2

Comments to the Authors

Thank you for the opportunity to review this manuscript. The topic is timely and relevant, and the work provides valuable insights. However, there are a few issues that should be addressed to improve the clarity, consistency, and overall quality of the paper. My detailed comments are as follows:

Section Titles (2.2 and 2.3):

The titles of Sections 2.2 and 2.3 are currently the same, which appears to be a mistake. The title of Section 2.3 should be revised to reflect its specific content—perhaps "Construction Phase" would be a suitable alternative.

Table 4 – CO₂ Emissions:

In Table 4, the CO₂ emissions for solar PV include the full life cycle, whereas those for SMR do not appear to account for construction and decommissioning. This inconsistency is problematic and may lead to a biased comparison. The rationale for this discrepancy should be clearly explained. Furthermore, it seems that the emissions associated with batteries do not include production and disposal processes. Please clarify this point and consider revising the table or the accompanying explanation for consistency.

Line 590 – Power Import/Export Explanation:

On Line 590, the manuscript refers to power import/export exchanges. A more detailed explanation of this aspect is needed. Specifically, the conditions under which such exchanges are possible should be clarified, as this aspect appears to be limited or constrained in the model.

 

 

To Reviewer 2:

            Thank you for your review and valuable remarks.

 

1. Section Titles (2.2 and 2.3):

The titles of Sections 2.2 and 2.3 are currently the same, which appears to be a mistake. The title of Section 2.3 should be revised to reflect its specific content—perhaps "Construction Phase" would be a suitable alternative.

- We appreciate the reviewer’s careful reading and constructive observation. Indeed, the title of Section 2.3 was mistakenly duplicated from Section 2.2. We have corrected this by renaming Section 2.3 to “Construction Phase of SMR Deployment”, which better reflects the content discussing the actual implementation of small modular reactors that have progressed beyond the design phase. Section 2.2 remains titled “Engineering Design and Licensing Preparation” to accurately capture the earlier development stage. This revision improves both clarity and consistency in the manuscript structure.

2. Table 4 – CO₂ Emissions:

In Table 4, the CO₂ emissions for solar PV include the full life cycle, whereas those for SMR do not appear to account for construction and decommissioning. This inconsistency is problematic and may lead to a biased comparison. The rationale for this discrepancy should be clearly explained. Furthermore, it seems that the emissions associated with batteries do not include production and disposal processes. Please clarify this point and consider revising the table or the accompanying explanation for consistency.

- Thank you for this valuable and well-founded comment. We fully agree that consistency in life cycle assessment (LCA) boundaries is critical for a fair comparison of CO₂ emissions across technologies. In the original version of Table 4, the emissions for solar PV were based on full LCA data (including manufacturing, construction, and disposal), whereas those for SMR referred only to operational-phase emissions, excluding construction, fuel processing, and decommissioning. Similarly, battery-related emissions did not account for production and end-of-life management.

To address this inconsistency and improve transparency:

- Table 4 has been revised to include life cycle CO₂ emission values for all technologies, based on reputable sources such as IAEA, IPCC, and NREL.

- The caption and accompanying explanation in the manuscript have been updated to clarify the scope of emissions (e.g., operational vs. full life cycle).

Where full LCA data are not uniformly available (e.g., for some advanced SMR projects), we have explicitly stated the assumptions and limitations used in estimating emissions.

We believe these changes improve the comparability and scientific validity of the table and better reflect the environmental impacts of each technology.

3. Line 590 – Power Import/Export Explanation:

On Line 590, the manuscript refers to power import/export exchanges. A more detailed explanation of this aspect is needed. Specifically, the conditions under which such exchanges are possible should be clarified, as this aspect appears to be limited or constrained in the model.

- We appreciate the reviewer’s attention to this important point. Indeed, the original explanation of the power import/export mechanism was insufficiently detailed. To address this, we have revised the corresponding paragraph in the manuscript to clarify that:

- Power import/export is modeled as a conditional process governed by system balance constraints within the hybrid energy system.

- Import occurs when local generation (SMR, PV, battery) cannot meet the demand, and grid access is available.

- Export is only possible when there is surplus generation and sufficient grid connectivity.

The model assumes a constrained grid capacity, reflecting the limitations of remote or semi-islanded regions, and includes maximum import/export thresholds as boundary conditions in the optimization process. Additionally, economic penalties for import and limited incentives for export are incorporated to reflect market realities.

We believe this clarification improves the realism and transparency of the modeling assumptions and helps readers understand the functional role of grid exchange in the hybrid configuration.

 

Thank you very much for your remarks and comments. They were very useful for me to emphasize the main tasks and contributions of the manuscript, and also to focus the attention of the readers on the new and unique elements.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

It can be accepted.