Accelerated nuclear power deployment requires early coordination on design choices to ensure new technologies remain unattractive for weapons development.
During a period when the effects of climate change are pushing the world towards more sustainable forms of energy production, nuclear power has emerged as a suitable option in many states that had not previously planned for new nuclear energy systems. One example is Sweden, which is now considering the deployment of small modular reactors in the coming years. At the same time, increasing geopolitical uncertainty and growing concerns over war in Europe have led many states to place nuclear non-proliferation high on the agenda.
Proliferation resistance is important when discussing deploying new reactors such as small modular reactors (SMRs), because the technology can introduce novelties into a country’s nuclear fuel cycle that may increase proliferation risks and, therefore, require dedicated solutions. For example, new characteristics for Sweden¹ may include load-following reactors, cogeneration of district heating, hydrogen production, dry storage of used nuclear fuel and new deployment sites located near population centres or within industrial parks. From a research point of view, it is urgent to understand if and how these developments influence proliferation risks and what measures could be implemented to mitigate them. This publication presents the results of a proliferation resistance assessment of deploying light water SMRs in Sweden, using the dedicated INPRO methodology developed by the International Atomic Energy Agency (IAEA).²
Nuclear safeguards serving non-proliferation
The international treaty commonly known as the Non-Proliferation Treaty (NPT)³ has divided the world into nuclear weapon states and non-nuclear weapon States to unite them under the global effort to stop the spread of nuclear weapons, known under the term ‘nuclear non-proliferation.’ The main objectives of the NPT are to prevent the spread of nuclear weapons, encourage the peaceful use of nuclear applications and promote efforts on nuclear disarmament.
Almost all countries in the world are parties to the NPT and are required to conclude a Safeguards Agreement with the IAEA, which allows for a country’s nuclear technology and nuclear materials to be safeguarded under international monitoring. Therefore, nuclear safeguards rely on verification measures such as nuclear material accountancy and control, inventory taking, application of seals on technology/materials, video surveillance, and on-site inspections. The people performing the verification are nuclear safeguards inspectors from IAEA,⁴ regional regulators such as Euratom (for European Union Member States),⁵ and national regulators such as the Swedish Radiation Safety Authority⁶ in Sweden.
Nuclear safeguards are, in essence, extrinsic measures applied to verify the usage of nuclear capabilities only for peaceful activities. There are, however, ways to design and develop new facilities so that they are inherently less attractive for proliferation purposes. Examples are nuclear reactors with fuel that is inaccessible during operation, nuclear material quantity, form and composition that would make it unsuitable for use in nuclear weapons, or nuclear facility layouts with a reduced number of access points.⁷ These intrinsic features, along with complementary extrinsic measures, build up resistance to proliferation in the nuclear energy system of a state and ensure that its civilian nuclear fuel cycle remains peaceful.
Early considerations of proliferation resistance
A suitable tool for designing a proliferation-resistant nuclear fuel cycle is the methodology developed and maintained by the IAEA through the International Project on Innovative Nuclear Reactors and Fuel Cycles (INPRO).⁸ The INPRO methodology can be used to assess the sustainability of proliferation resistance in a nuclear energy system, thereby encouraging actions to strengthen the system where needed. Both extrinsic measures and intrinsic features must be considered and aligned to ensure the development of a system that does not introduce unaddressed proliferation risks. For example, if one country decides to deploy an SMR, a proliferation resistance assessment could include studies on the nuclear technology, the nuclear facility layout, and how the deployment would harmonise with existing regulations and policies supporting non-proliferation.
A nuclear energy system includes more than the reactor and its fuel; it also contains the front-end activities related to fuel fabrication and the back-end activities associated with managing used nuclear fuel. The involved organisations, such as facility owners and operators, designers and constructors, national safeguards regulators, and the research community, collectively influence the fuel cycle design and technology selections. Therefore, they can shape a low proliferation attractiveness of the fuel cycle components by selecting and developing technologies with proliferation-resistant characteristics.
If dialogue begins early between these actors and the safeguards inspectors (IAEA, Euratom), a Safeguards by Design⁹ (SbD) process can be initiated. SbD is a collaborative approach that enables the full integration of international safeguards considerations into the design, planning, construction, operation and decommissioning of nuclear facilities.10 The stakeholders of the SbD process can increase awareness and promote more proliferation-resistant solutions for the system. SbD is officially supported by Euratom through Commission Regulation no. 974 from 202511 and by the IAEA.
Big steps towards deploying new nuclear reactors in Sweden
Since the 1970s, Sweden has become a state relying heavily on commercial nuclear reactors for electricity production. Today, however, only six of the original 12 large-scale commercial reactors remain in operation. The current reactors are based on light water technology and located at the Forsmark, Ringhals, and Oskarshamn nuclear sites.
In recent years, the Swedish government has made considerable efforts to enable the deployment of new nuclear power. Such efforts are shown through government inquiries related to improving the licensing process for nuclear reactors,12 the development of financing models for state aid in new nuclear investments,13 and investigations related to future back-end and waste management.14 Also, the interest in new nuclear power in the industry has increased with time. In 2024, the state-owned company Vattenfall announced plans to explore building new nuclear power in the form of light water SMRs at the Värö Peninsula, adjacent to the Ringhals nuclear site.15 Thus, a significant step was taken towards realising Sweden’s first new nuclear reactors in decades.
Against this background, a proliferation resistance assessment of new nuclear deployment in Sweden has become highly relevant, motivating the recent research carried out within the ANItA competence centre.16 The work consists of an INPRO assessment conducted to investigate if and how the deployment of SMRs would affect the proliferation resistance of the Swedish nuclear energy system, and to identify what actions can be taken to minimise proliferation risks. The following sections summarise key elements of that work.
Proliferation resistance assessment for introducing SMRs in Sweden
The versatility of the INPRO methodology allows it to be applied on both national-level (general view including all nuclear facilities in a country) and facility-level assessments. The nuclear energy system under evaluation includes the current operational reactors in Sweden and a hypothetical SMR deployment scenario consisting of three light water SMR units and a dry intermediate storage facility at the Forsmark nuclear site. The scenario considers the dry storage of used nuclear fuel since the existing nuclear waste management solutions are licensed only for the operating reactors. The assessment also takes into account the size of the SMR and its usage in electricity production, resembling Vattenfall’s plans for the Ringhals nuclear site.
According to the INPRO methodology, the considered SMR deployment scenario needs to be assessed against five requirements: 1) the state’s legal framework on non-proliferation should be adequate; 2) the attractiveness of nuclear technology and nuclear material should be low; 3) IAEA nuclear safeguards should be facilitated through system design; 4) multiple measures to deter diversion and misuse of materials and technology should be incorporated; 5) optimisation of proliferation resistance in the design should be officially approved. These requirements make up the sustainability pillars that ensure long-term proliferation resistance, and meeting them requires a combination of extrinsic measures and intrinsic design features. In this publication, we focus on the first three requirements.
Extrinsic measures
Sweden’s legal framework has a strong commitment to the non-proliferation regime by having adopted adequate national legislation and European regulations.17 In addition, Sweden employs an open nuclear fuel cycle, where used nuclear fuel will be disposed of in the deep geological repository at Forsmark,18 thus limiting access to highly attractive material such as plutonium. Other important extrinsic features are the international and multilateral ownership of nuclear power plants and the international dependency on fresh nuclear fuel, which prevent the Swedish state from becoming the sole owner of the nuclear fuel cycle. Furthermore, our study case17 shows that existing safeguards measures are implemented effectively at the Forsmark site through detailed safeguards procedures that can be adapted to include new SMR units. However, one extrinsic measure that Sweden should implement is to request an IAEA Safeguards and SSAC (State System of Accounting for and Control of Nuclear Material) Advisory Service Mission.19 Such a mission would help determine if sufficient financial and human resources are allocated to support safeguarding the existing nuclear facilities and other planned deployments.
Intrinsic features
For the second requirement, the attractiveness of the nuclear technology and the available nuclear material in terms of quantity were evaluated. The latter evaluation was done for fresh and used nuclear fuel. The attractiveness scale used in the assessment has the following reference levels: Very Low, Low, Moderate, High, and Very High, according to the INPRO methodology.
In terms of nuclear technology, the considered hypothetical SMR is based on designs that are not fundamentally different from the current Swedish reactors. The scenario assumes light water reactor technology, a smaller reactor core with less nuclear fuel, baseload operation and fresh fuel with the same enrichment as the one used today. Current technology employed in Sweden is already rated to have a High attractiveness level due to the presence of nuclear reactors and remote fuel handling capabilities,20 and this level would not increase with the deployment of additional reactors. Nevertheless, this attractiveness level is not problematic if the state meets its safeguards commitments established by the legal framework, which is the case in Sweden, given its consistent record of fulfilled inspections.21 It is therefore reasonable to conclude that Sweden can deploy additional reactors without further increasing proliferation risks, as the methodology also indicates.
In terms of nuclear material availability, additional fresh fuel would need to be transferred to the site every year, and used fuel would accumulate over time at the dry storage facility, being first stored short-term in water cooling ponds, and then transferred into dry casks to be stored at the site for up to 80 years (the estimated lifetime of some of the current SMR designs). Assuming each SMR unit is refuelled every three years, the estimated additional quantities of fresh fuel would not significantly impact the amounts currently handled in Sweden, and the attractiveness level would remain Moderate. Likewise, while the used fuel from the three SMR units would be stored for up to one year in the cooling ponds, the attractiveness level would not increase from High, which is already given by the annual inventory of used fuel from the large-scale reactors at Forsmark.20
However, a very significant impact would be seen at the Forsmark site due to the cumulative effects of used fuel being stored at the dry storage facility over time. Since the dry storage facility is hypothetically going to be co-located with the SMR units, after three years of operation, the inventory there would reach a High level. In 30 years (within the lifetime of the SMR units), the attractiveness level would become Very High, adding to the nuclear energy system another ‘hot spot’ for attractiveness, as is the used fuel inventory at the national Central Interim Storage Facility for Spent Nuclear Fuel (Clab). Therefore, to enhance proliferation resistance, Sweden should consider some recommendations derived from the methodology, such as enabling a safeguards-by-design process when planning for deployment. The process might include discussions among the designer, operator, safeguards inspectors, research community, and the regulator to determine and approve a facility layout that can be properly and efficiently safeguarded. Such a layout should allow for a clear nuclear material flow, and an adequate placement, sealing and surveillance of dry storage casks for the given attractiveness of nuclear material.
In conclusion
The assessed attractiveness levels for technology (High) and nuclear fuel (fresh: Moderate, used: High and Very High) are the result of combining the currently safeguarded nuclear energy system with a hypothetical SMR deployment. These findings do not constitute a barrier for nuclear power or new reactor deployment, especially for a country with a well-functioning Comprehensive Safeguards Agreement in place. Instead, they highlight what to consider when designing an energy system to be as proliferation-resistant as possible, leveraging experience from previous safeguards implementation. However, as more nuclear installations and more nuclear material become available, the burden on safeguards inspectors increases, and sufficient resources must be allocated for the task to make monitoring and verification efforts acceptable. For this reason, collaboration between stakeholders is of utmost importance to optimise the design of the nuclear energy system in terms of proliferation resistance.
Based on these current findings, nuclear proliferation risks associated with the construction and licensing of new small modular reactors in Sweden appear to be manageable. However, further research is planned on designing a proliferation-resistant SMR facility for the deployment scenario, as it would be valuable to identify potential intrinsic features for integration into its layout, as well as extrinsic measures that safeguards inspectors might recommend. In addition, work is underway to examine a more detailed operational scenario for determining if and how different SMR operation modes, such as load-following for electricity production or district heating, might influence the composition of used fuel and, thereby, affect the quantity and attractiveness of nuclear material.
Acknowledgement
This work has been carried out within the framework of the ANItA collaboration and has been financially supported by the Swedish Energy Agency under project number 52680-1. Also, the work has been partially funded by the Swedish Radiation Safety Authority under the competence support project number SSM2023-4386. The authors would like to express their gratitude to Sofia Nilsson (Vattenfall), Felicia Thune (Forsmark Kraftgrupp AB), and the INPRO Section (IAEA).
References
- SMR designs suitable for Sweden’s future electricity production needs, Innovation News Network
- INPRO Methodology, IAEA
- Treaty on the Non-Proliferation of Nuclear Weapons (NPT), IAEA
- Department of Safeguards, IAEA
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- Swedish Radiation Safety Authority
- INPRO Methodology for a Sustainability Assessment of Nuclear Energy Systems: Proliferation Resistance, INPRO Manual, IAEA Nuclear Energy Series, (draft publication), IAEA, Vienna (2023)
- International Project on Innovative Nuclear Reactors and Fuel Cycles (INPRO), IAEA
- Safeguards by design, IAEA
- Christos KOUTSOGIANNOPOULOS, Safeguards-By-Design, presentation, Euratom Member States Training, EURATOM, Luxembourg (2025)
- Commission Regulation (Euratom) 2025/974 of 26 May 2025 on the application of Euratom safeguards
- SOU 2025:7, New nuclear power in Sweden – more efficient licensing procedures and appropriate fees, Regeringskansliet
- How the support model for financing new nuclear energy works, Government Offices of Sweden
- SOU 2025:104, New nuclear power in Sweden – an integrated framework for managing radioactive waste
- Vattenfall takes the next step for new nuclear power at Ringhals in Sweden, Vattenfall
- ANItA, Uppsala University
- C. Olaru, E. Branger, and S. Grape, ‘Integration of Small Modular Reactors in the Swedish Nuclear Energy System: A Proliferation Resistance Study’, presented at the International Conference on Small Modular Reactors and their Applications, 21-25 October, 2024, Vienna, Austria, 2024
- The Spent Fuel Repository, SKB
- IAEA SSAC Advisory Service, IAEA
- C. Olaru, E. Branger, S. Grape, and D. Montano Trombetta ‘The Swedish Perspective on Safeguarding SMRs in Future Nuclear Energy Systems: A Proliferation Resistance Study using the INPRO Methodology’, manuscript in writing
- Drawing safeguards conclusions, IAEA
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