Spent Nuclear Fuel—Waste to Resource, Part 1: Effects of Post-Reactor Cooling Time and Novel Partitioning Strategies in Advanced Reprocessing on Highly Active Waste Volumes in Gen III(+) UOx Fuel Systems
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis work is a speculative (purely desk) study. It does not take into account all the technological complexities and extremely high financial, labor, material and time costs for the practical implementation of this approach. First of all, this concerns the construction of large radiochemical production facilities for the deep separation of high-level waste streams into fractions, the creation of new types of nuclear installations for the transmutation of minor actinides, the costs of long-term temporary storage of isolated radionuclides, and so on.
In addition, it should be noted that more effective forms (matrices) with a higher capacity than glass are proposed for fractionated waste.
I recommend that the authors familiarize themselves with reports of the US Academies of Sciences and the US National Laboratories on this issue:
- National Research Council. 2011. Waste Forms Technology and Performance: Final Report. Washington, DC: The National Academies Press. 308 p. https://doi.org/10.17226/13100.
- National Academies of Sciences, Engineering, and Medicine. 2023. Merits and Viability of Different Nuclear Fuel Cycles and Technology Options and the Waste Aspects of Advanced Nuclear Reactors. Washington, DC: The National Academies Press. https://doi.org/10.17226/26500.
- Closed Fuel Cycle Waste Treatment Strategy. Prepared for U.S. Department of Energy Materials Recovery and Waste Forms Campaign. Compiled By: J.D. Vienna (PNNL). February 27, 2015. FCRD-MRWFD-2015-000674, Rev. 0. PNNL-24114.
Detailed data on the composition of SNF are contained in the reports:
- NEA. Spent Nuclear Fuel Reprocessing Flowsheet; NEA OECD: Paris, France, 2012; 120p.
- Hardin, E.; Hadgu, T.; Clayton, D.; Howard, R.; Greenberg, H.; Blink, J.; Sharma, M.; Sutton, M.; Carter, J.; Dupont, M.; et al. Repository Reference Disposal Concepts and Thermal Load Management Analysis. FCRD-UFD-2012-00219. November 2012.
- Carter, J.T.; Luptak, A.J.; Gastelum, J.; Stockman, C.; Miller, A. Fuel Cycle Potential Waste Inventory for Disposition; Savannah River National Laboratory: Aiken, SC, USA, 2012; 328p.
Despite the rather skeptical attitude towards this article, it can be recommended for publication to maintain attention and continue the discussion on the very important topic of handling SNF and HLW.
Author Response
This work is a speculative (purely desk) study. It does not take into account all the technological complexities and extremely high financial, labor, material and time costs for the practical implementation of this approach. First of all, this concerns the construction of large radiochemical production facilities for the deep separation of high-level waste streams into fractions, the creation of new types of nuclear installations for the transmutation of minor actinides, the costs of long-term temporary storage of isolated radionuclides, and so on.
RESPONSE: We thank the reviewer for taking the time to read and feedback on our article. We acknowledge the challenges we raise in suggesting the concepts within this piece and aim to perform a comprehensive life-cycle analysis of similar options in future, which is beyond the scope of this initial piece. The purpose of this work was primarily to highlight the potential gains in waste managementthat could be made by the addition of FP separations to several baseline SNF reprocessing cases. We have (on the suggestion of some of the other reviewers), slightly amended the titel, abstract, and text in places to discuss the technology readiness of these separations, with appropriate references, and to highlight that Scernarios 1-4 are “base-cases” for comparison.
In addition, it should be noted that more effective forms (matrices) with a higher capacity than glass are proposed for fractionated waste.
I recommend that the authors familiarize themselves with reports of the US Academies of Sciences and the US National Laboratories on this issue:
- National Research Council. 2011. Waste Forms Technology and Performance: Final Report. Washington, DC: The National Academies Press. 308 p. https://doi.org/10.17226/13100.
- National Academies of Sciences, Engineering, and Medicine. 2023. Merits and Viability of Different Nuclear Fuel Cycles and Technology Options and the Waste Aspects of Advanced Nuclear Reactors. Washington, DC: The National Academies Press. https://doi.org/10.17226/26500.
- Closed Fuel Cycle Waste Treatment Strategy. Prepared for U.S. Department of Energy Materials Recovery and Waste Forms Campaign. Compiled By: J.D. Vienna (PNNL). February 27, 2015. FCRD-MRWFD-2015-000674, Rev. 0. PNNL-24114.
RESPONSE: We have added a comment in Section 2.2 citing and referring back to these works and how they could be contextually used to support the results presented here. Our values are likely acceptable compromises between density and heat load on a potential repository, but relatively comparable with different systems of the same relative loading for mass/volume and heat output. This is explained in our amended methods section.
Detailed data on the composition of SNF are contained in the reports:
- NEA. Spent Nuclear Fuel Reprocessing Flowsheet; NEA OECD: Paris, France, 2012; 120p.
- Hardin, E.; Hadgu, T.; Clayton, D.; Howard, R.; Greenberg, H.; Blink, J.; Sharma, M.; Sutton, M.; Carter, J.; Dupont, M.; et al. Repository Reference Disposal Concepts and Thermal Load Management Analysis. FCRD-UFD-2012-00219. November 2012.
- Carter, J.T.; Luptak, A.J.; Gastelum, J.; Stockman, C.; Miller, A. Fuel Cycle Potential Waste Inventory for Disposition; Savannah River National Laboratory: Aiken, SC, USA, 2012; 328p.
RESPONSE: We thank the reviewer for highlighting these additional references. The latter is most definitely of some use in terms of completeness relative to the present work’s source data and will be complimentary for future analyses where additional reactor designs are needed. Where such datasets do exist, they are unfortunately often not particularly easy to find or access. A comment regarding this has been added to Section 2.1 with referral back to the suggested references, where relevant. At this stage it would be unfeasible to rework our entire piece based on this new data, however.
Despite the rather skeptical attitude towards this article, it can be recommended for publication to maintain attention and continue the discussion on the very important topic of handling SNF and HLW.
RESPONSE: Once again we thank the reviewer for taking the time to review and feed back on our work. The contributions from yourselves and the other reviewers help to improve the quality of research like this for the benefit of all in the field.
Reviewer 2 Report
Comments and Suggestions for AuthorsThis paper explores the short-term fuel cycle impacts of a variety of spent fuel reprocessing strategies, benchmarked against a "do-nothing" once-through scenario as the current default.
While I think the overall approach is (mostly) sound, a glaring omission in this paper is a reflection on the considerable amount of prior work that has already been performed in the fuel cycle options evaluation space. This has been an active area of research for easily the last two decades, with numerous studies purporting to demonstrate the comparative benefits of different spent fuel treatment options, many far more comprehensive in time and scope. This study references almost none of them.
The selection of a 30-year old database of calculated spent fuel compositions strikes me as an odd choice, especially in light of modern alternatives. For example, there is the OECD/NEA SFCOMPO database which contains actual measurement data of over 100 commercial fuel assemblies spanning a large range of burnups and decay times. Comprehensive efforts have been carried out by numerous parties to perform estimates of commercial used fuel inventories, such as the "Spent Fuel and Reprocessing Waste Inventory" report (Kaushik Banerjee, Antonio Rigato, Veronica Wilson, PNNL-33938, Rev. 1.1). The ST&NDARDS tool published by the US-DOE contains a comprehensive projection of as-loaded used fuel inventories and calculations of decay heat.
Even notwithstanding these databases, the calculation of used fuel inventories, including aspects such as decay heat and radiological emissions, is trivial with modern tools such as SCALE, OpenMC, etc. Almost all of these codes account for multiple decay modes (including alpha decay, tracking of tertiary fission products, recoverable decay energy, etc.) so it's not clear why one should rely on a manual and limited means of calculating these quantities.
With respect to the study itself, there are numerous studies which have attempted to capture many of the same metrics which at the very least would provide a useful benchmark for comparison. Most notable among these would be "Nuclear Fuel Cycle Evaluation and Screening – Final Report" (INL/EXT-14-31465, available at https://fuelcycleevaluation.inl.gov/SitePages/Home.aspx). Appendix D in particular contains a wealth of information on many comparable metrics for comparable fuel cycles considered. For example, Scenario 1 directly corresponds to EG01 in the E&S study. Scenario 3 would be comparable to EG13 and/or EG21 (depending on the choice of limited or continuous recycle). Scenario 4 is roughly comparable to EG24.
On lines 321-323, the authors make an oblique reference to disposal area requirements for intact used fuel, but there have been numerous studies one could draw upon for land use requirements, too many to individually enumerate here. For example, see: Banu Bulut Acar, H. Okan Zabunoğlu, "Comparison of the once-through and closed nuclear fuel cycles with regard to waste disposal area required in a geological repository," Annals of Nuclear Energy, Volume 60, 2013, Pages 172-180, https://doi.org/10.1016/j.anucene.2013.04.039.
Page 7, line 346: this is a very specific assumption about the remaining fissile content of used fuel based on a very specific set of assumptions regarding operating history which could easily be tested with actual depletion studies using available computational methods or again, benchmarking against known destructive chemical assay data from resources like SFCOMPO.
Line 393: See EG19 for a potential comparison scenario in the E&S report.
Line 418: Scenario 4 could easily be compared to EG29-32 in the E&S report.
Line 509-512: This doesn't make much sense. Cs/Sr removal would likely occur *downstream* of dissolution and primary solvent extraction.
My general summary comment here is that I think this paper would represent a more substantial contribution instead of re-treading work that has already been substantially investigated prior, if instead the authors focused on the differential benefit of more complex "add-on" processes to conventional PUREX-based reprocessing. First, how do their results compare with prior art? Next, what is the specific value-added for PGM and rare earth recovery? Again, how does this compare to our present understanding?
Author Response
This paper explores the short-term fuel cycle impacts of a variety of spent fuel reprocessing strategies, benchmarked against a "do-nothing" once-through scenario as the current default.
While I think the overall approach is (mostly) sound, a glaring omission in this paper is a reflection on the considerable amount of prior work that has already been performed in the fuel cycle options evaluation space. This has been an active area of research for easily the last two decades, with numerous studies purporting to demonstrate the comparative benefits of different spent fuel treatment options, many far more comprehensive in time and scope. This study references almost none of them.
RESPONSE: We thank the reviewer for taking the time to review and provide feedback for our manuscript and for the references suggested, which we have cited where appropriate. We have reframed the work to account for the intended use of Scenarios 1-4 as base cases and Scenario 5 variations as the primary new data present. The title, abstract and text have been edited to reflect this.
The selection of a 30-year old database of calculated spent fuel compositions strikes me as an odd choice, especially in light of modern alternatives. For example, there is the OECD/NEA SFCOMPO database which contains actual measurement data of over 100 commercial fuel assemblies spanning a large range of burnups and decay times. Comprehensive efforts have been carried out by numerous parties to perform estimates of commercial used fuel inventories, such as the "Spent Fuel and Reprocessing Waste Inventory" report (Kaushik Banerjee, Antonio Rigato, Veronica Wilson, PNNL-33938, Rev. 1.1). The ST&NDARDS tool published by the US-DOE contains a comprehensive projection of as-loaded used fuel inventories and calculations of decay heat.
RESPONSE: We thank the reviewer for highlighting these additional references. We have investigated the SFCOMPO database before, which provides good data for burnup credits but is often (if not totally) incomplete when referring to inactive isotopes, and the other report suggested does not provide detail to the level required for this work. Where such datasets do exist, they are unfortunately often not particularly easy to find or access. A comment regarding this has been added in Section 2.1 with referral back to suggested references where relevant, with some other suggested by one of the other reviewers.
Even notwithstanding these databases, the calculation of used fuel inventories, including aspects such as decay heat and radiological emissions, is trivial with modern tools such as SCALE, OpenMC, etc. Almost all of these codes account for multiple decay modes (including alpha decay, tracking of tertiary fission products, recoverable decay energy, etc.) so it's not clear why one should rely on a manual and limited means of calculating these quantities.
RESPONSE: We are also aware of these codes (SERPENT/FISPIN are used in the UK, usually, where licesnses are available) and their capabilities, but the necessary programming time and computational power needed to run such simulations isn’t always forthcoming, alongside the necessity for similar data handling to that undertaken here. We outlined these challenges in a previous publication (see Holdsworth et al, 2021) and reiterated them in Section 2.1.
With respect to the study itself, there are numerous studies which have attempted to capture many of the same metrics which at the very least would provide a useful benchmark for comparison. Most notable among these would be "Nuclear Fuel Cycle Evaluation and Screening – Final Report" (INL/EXT-14-31465, available at https://fuelcycleevaluation.inl.gov/SitePages/Home.aspx). Appendix D in particular contains a wealth of information on many comparable metrics for comparable fuel cycles considered. For example, Scenario 1 directly corresponds to EG01 in the E&S study. Scenario 3 would be comparable to EG13 and/or EG21 (depending on the choice of limited or continuous recycle). Scenario 4 is roughly comparable to EG24.
RESPONSE: We thank the reviewer for highlighting these studies, they will be useful for future comparison. We have cited and referred back to these in the main manuscript, with the text adjusted accordingly where relevant.
On lines 321-323, the authors make an oblique reference to disposal area requirements for intact used fuel, but there have been numerous studies one could draw upon for land use requirements, too many to individually enumerate here. For example, see: Banu Bulut Acar, H. Okan Zabunoğlu, "Comparison of the once-through and closed nuclear fuel cycles with regard to waste disposal area required in a geological repository," Annals of Nuclear Energy, Volume 60, 2013, Pages 172-180, https://doi.org/10.1016/j.anucene.2013.04.039.
RESPONSE: We have referred readers to the suggested article and cites this as suggested. As this is not the focus of our study, we will not further investigate this at this time but may revisit in future works.
Page 7, line 346: this is a very specific assumption about the remaining fissile content of used fuel based on a very specific set of assumptions regarding operating history which could easily be tested with actual depletion studies using available computational methods or again, benchmarking against known destructive chemical assay data from resources like SFCOMPO.
RESPONSE: We acknowledge that there is some speculation about the usability of RepU in various reactor types, but we plan to investigate this in future – this scenario being akin to a slightly more developed DUPIC process – removing everything but U and sending that for more fissioning in a CANDU reactor. Our preliminary results (omitted from this work due to size constraints) indicate a ~40% improvement in performance over NatU in that reactor system (based on SERPENT simulations). This is the next planned work in this series, once we’ve finished running the simulations and interpreting the data – how best to use the recovered U, U+Pu, or U+TRU. The references suggested by yourself and other reviewers will greatly improve the quality of future works.
Line 393: See EG19 for a potential comparison scenario in the E&S report.
RESPONSE: Report referenced as suggested and text amended.
Line 418: Scenario 4 could easily be compared to EG29-32 in the E&S report.
RESPONSE: Report referenced as suggested and text amended.
Line 509-512: This doesn't make much sense. Cs/Sr removal would likely occur *downstream* of dissolution and primary solvent extraction.
RESPONSE: Our previous works have highlighted the benefits of Cs and Sr separations upstream of any solvent extraction processes, aiming to directly capture the high heat radionlucides (as referred to by Forsberg) from dissolver liquor early on in PUREX/similar flowsheets to address numerous operational challenges therein by essentially eliminating solvent degradation, amongst other benefits. We have demonstrated that selective separations are possible directly from dissolved SNF before the U and (simulant) Pu have been removed using a chromatographic/ion exchange approach using AMP-PAN for Cs - this being far simpler to implement than the FPEX solvent extraction process or similar.
My general summary comment here is that I think this paper would represent a more substantial contribution instead of re-treading work that has already been substantially investigated prior, if instead the authors focused on the differential benefit of more complex "add-on" processes to conventional PUREX-based reprocessing. First, how do their results compare with prior art? Next, what is the specific value-added for PGM and rare earth recovery? Again, how does this compare to our present understanding?
RESPONSE: It was our intention to emphasise the benefits of the FP separations over the standard PUREX process and variations thereof up to the current “state of the art” with MA separations. We have amended the abstract and introduction to this effect, highlighting that Scenarios 1-4 are, in essence, the “base cases” and the variations of Scenario 5 are the important new data here. We have added Section 3.9 at the request of yourself and one of the other reviewers, providing a cursory overview of the masses and direct values of PGMs and REEs that could be recovered from a typical SNF reprocessing plant. The indirect value that could be recovered (H2 production, heat, offsetting GDF capacity, etc.) by partitioning/using the HHRs will require significant further work and will be investigated in future, as these are much more complex to calculate.
We would once again like to thank the reviewer for feeding back on this work and helping to improve the quality of it for readers in the field, your contributions are very helpful.
Reviewer 3 Report
Comments and Suggestions for AuthorsThe manuscript by Holdsworth, et al. offers a comparison of different nuclear waste reprocessing schemes, comparing the ability to remove isotopes and the corresponding impact on the longevity and volume of radioactive waste. I think it offers a nice comparison, but I have a few recommendations and corrections.
One of the main drivers limiting the expansion of reprocessing (in addition to political factors) is economic ones. The manuscript would be significantly improved if the authors considered the financial ramifications of each scenario. (1) What is the economic cost (estimated) of each reprocessing scenario per unit mass? And how does this compare to existing costs for storage? (2) What is the potential economic benefit from capturing the isotopes in the fuel? i.e. how much economic benefit from capturing the U and Pu? Or how about the rare earth elements or metals? Offering an economic point of view would give great support to the manuscript.
At the end of the manuscript, I think it would be improved if the authors gave a recommendation or at least summarized the comparison between the methods better? Which is best? What is valued more: reduced mass or volume or radioactivity of the waste?
Can the authors estimate the mass of REEs or PGMs that could be recovered and correspondingly the value?
Is the amount in waste volume given the amount of waste or the volume needed after correcting for the reduced activity and different decay products causing a different volume concentration in a waste storage material, for example?
The manuscript has minor grammatical errors that should be corrected.
This manuscript was focused on fuel to be used in GenIII+ reactors. How much fuel currently falls into this 5 or 10 year post-reactor category and how much fuel will be in this category in the next 10 years? How is this work applicable to newer fuel forms, such as HALEU? A discussion on applicability (in terms of currently how applicable is this, and for future fuel forms) would be a good finishing section for this manuscript.
Author Response
The manuscript by Holdsworth, et al. offers a comparison of different nuclear waste reprocessing schemes, comparing the ability to remove isotopes and the corresponding impact on the longevity and volume of radioactive waste. I think it offers a nice comparison, but I have a few recommendations and corrections.
RESPONSE: We thank the reviewer for taking the time to review our manuscript and provide constructive feedback.
One of the main drivers limiting the expansion of reprocessing (in addition to political factors) is economic ones. The manuscript would be significantly improved if the authors considered the financial ramifications of each scenario. (1) What is the economic cost (estimated) of each reprocessing scenario per unit mass? And how does this compare to existing costs for storage? (2) What is the potential economic benefit from capturing the isotopes in the fuel? i.e. how much economic benefit from capturing the U and Pu? Or how about the rare earth elements or metals? Offering an economic point of view would give great support to the manuscript.
RESPONSE: We acknowledge that we focus only on the waste volumes and decay heats of the suggested separations in this work. Indeed, we do fully plan on performing a thorough socio-economic and environmental life-cycle assessment of these operations in future to address these concerns, which will likely take an order of magnitude or two greater volume of data to achieve. This has been emphasised at several points throughout. As per your comment below, we have added Section 3.9 to address this, at least in part, as any further study is beyond the indended scope of this piece.
At the end of the manuscript, I think it would be improved if the authors gave a recommendation or at least summarized the comparison between the methods better? Which is best? What is valued more: reduced mass or volume or radioactivity of the waste?
RESPONSE: We have amended and expanded the conclusions to account for this.
Can the authors estimate the mass of REEs or PGMs that could be recovered and correspondingly the value?
RESPONSE: We have added Section 3.9 at the request of yourself and one of the other reviewers, providing a cursory overview of the masses and direct values of PGMs and REEs that could be recovered from a typical SNF reprocessing. The indirect value that could be recovered (H2 production, heat, offsetting GDF capacity, etc.) will require significant further work and will be investigated in future.
Is the amount in waste volume given the amount of waste or the volume needed after correcting for the reduced activity and different decay products causing a different volume concentration in a waste storage material, for example?
RESPONSE: We calculated the waste volumes and activities based on the mass of FPs/MAs, etc. to be disposed of in all scenarios other than Scenario 1. This mass was then assumed to be vitrified in glass at 20 wt% (so multiplying the waste mass by 5) to a consistent density (3.33 g/cm3) to get the volume. Specific activities were calculated from the waste mass and modelled istopic composition.
The manuscript has minor grammatical errors that should be corrected.
RESPONSE: These have been corrected throughout along with some minor textual clarifications to improve clarity.
This manuscript was focused on fuel to be used in GenIII+ reactors. How much fuel currently falls into this 5 or 10 year post-reactor category and how much fuel will be in this category in the next 10 years? How is this work applicable to newer fuel forms, such as HALEU? A discussion on applicability (in terms of currently how applicable is this, and for future fuel forms) would be a good finishing section for this manuscript.
RESPONSE: We have added section 3.10 to address this point. There is, unfortunately, very limited data on spent fuel compositions from advanced reactors to support this kind of work, or even knowledge on how best to reprocess it. As this becomes available though, we can assess the impact of our proposed separations on this. One of the other reviewers did highlight an alternative data source that may prove beneficial here.
Once again we would like to thank the reviewer for reading and feeding back on our work to improve its quality.
Round 2
Reviewer 3 Report
Comments and Suggestions for AuthorsPlease remove the Wiki, 2025 citation in the discussion of the amount of spent fuel. I do not consider that an appropriate source, and replace with a peer reviewed source
Author Response
We once again thank the reviewer for taking the time to review our work.
We have exchanged the reference the reviewer requested to be replaced for an IAEA source.
