Modern Systems for Nuclear Fuel Storage and Monitoring: An Analysis of Technological Trends, Challenges, and Future Perspectives

Abstract

The storage and monitoring of nuclear fuel, whether spent or fresh, are key components of the nuclear energy life cycle, with significant implications for safety and sustainability. With the global focus on carbon neutrality, interest in advanced management solutions is rising. This paper provides a comprehensive analysis of modern technologies for the design, storage, and monitoring of nuclear fuel, highlighting current trends and future challenges. The study encompasses both spent and fresh nuclear fuel, with a focus on radiological safety, structural integrity, and digital monitoring. Data were organized into the following categories: storage types (wet/dry), monitored parameters, surveillance technologies (sensors, AI, IoT, and Digital Twin), simulation models, and emerging directions. A comparison between fresh and spent fuel shows a clear shift toward intelligent systems using non-invasive sensors, deep-learning algorithms, and decentralized architectures (e.g., blockchain-IoT). Despite progress, challenges remain, such as limited interoperability across system generations and insufficient experimental validation. This paper provides a solid foundation for researchers, suggesting future directions that include the full integration of AI in monitoring, broader numerical simulations for reliability, and the standardization of digital interfaces. These measures could significantly enhance the safety and efficiency of nuclear fuel storage systems.

1. Introduction

In the context of global efforts to reduce greenhouse gas emissions, nuclear energy is promoted as a transitional solution toward a low-carbon energy mix. Electricity generated in nuclear power plants is considered clean energy because the production process does not release carbon dioxide or other compounds that could significantly pollute the environment [1]. The total CO₂ emissions per kWh are comparable to those of wind energy and lower than those of photovoltaics, considering industrial processes such as manufacturing, maintenance, and decommissioning.

In 2022, the European Commission added nuclear energy to the list of eligible sources for green certificate taxation. A key advantage of nuclear energy is its capacity to provide a consistent supply, unlike solar or wind energy, which are intermittent because they depend on weather conditions beyond human control. Nuclear power plants produce large amounts of energy on relatively small land areas, a feature that does not apply to the other two energy sources [2].

Special responsibilities related to safety, traceability, and waste management have been assigned to ensure that this transition toward “green” energy is both achieved and maintained.

The safe storage and monitoring of nuclear fuel, whether irradiated (spent) or unirradiated (fresh), are key components of the nuclear energy life cycle. As nuclear energy regains strategic importance in the international initiative to minimize carbon emissions and advance toward environmentally responsible energy systems, the need for secure long-term storage solutions becomes increasingly critical. Spent nuclear fuel (SNF) remains highly radioactive and thermally active for decades after use, requiring storage systems that ensure radiological shielding, structural integrity, and environmental isolation. Although fresh fuel presents significantly lower risks, it still demands strict requirements for traceability and protection against mechanical, thermal, or chemical degradation [3].

In recent years, nuclear fuel storage has undergone significant evolution through the adoption of advanced solutions and the integration of innovative digital technologies within storage systems. Recent studies demonstrate the effectiveness of dry storage systems equipped with ventilation channels that promote heat dissipation through natural convection. Supporting examples have been published, highlighting the ability to maintain temperatures within safety limits through the use of passive ventilation, combining theoretical modeling with experimental testing.

The recent development of digital technologies has enabled the emergence of innovative solutions, such as dry cask systems with passive cooling [4], IoT networks for distributed monitoring, AI algorithms for structural defect detection [5], and blockchain architectures for data traceability [6]. These technologies hold the promise of transforming storage systems into intelligent, autonomous, and resilient platforms.

Digitalization and IoT are integrated into these systems. Significant challenges in nuclear fuel management, such as data handling and regulatory compliance, can be addressed with hybrid architectures that combine blockchain and IoT technologies.

The primary objective of this article is to provide a comprehensive and up-to-date synthesis of technologies and strategies for the storage and monitoring of nuclear fuel—both fresh and spent—in light of the latest technological advancements and international regulations. Unlike other review articles that focus separately on radiological safety, container engineering, or digital monitoring [3,7], this analysis combines multidisciplinary perspectives: traditional storage methods (wet and dry), emerging technologies (IoT, SCADA, Digital Twin, blockchain), and advanced AI applications for predictive diagnostics and traceability. Moreover, the paper highlights the fundamental differences between the monitoring requirements for spent and fresh fuel. It emphasizes existing gaps in the experimental validation of numerical models and AI applications under real-world conditions.

2. Nuclear Fuel Storage Systems Types

Although most of the examples and studies discussed in this section focus on spent nuclear fuel, considering radiological risks and long-term storage challenges, the analysis also includes systems dedicated to fresh nuclear fuel. This section provides an overview of both storage solutions for fresh fuel, which primarily require protection, traceability, and controlled environmental conditions, and complex systems for interim and final storage of spent fuel, where residual heat dissipation, radiological shielding, and mechanical integrity are essential. This integrated approach enables a comprehensive understanding of the safety challenges and technological solutions applicable throughout the entire nuclear fuel life cycle.

Nuclear fuel goes through several stages, requiring transportation or storage in different types of containers based on the hazard level to personnel and the risk of environmental contamination [8]. To understand the process from natural uranium extraction to its disposal or transfer to specially designed final repositories, the pathways shown in Figure 1 can be followed.

Natural uranium is extracted through mining. After milling, it is carried out near the mining sites. The extracted ore is crushed and chemically processed to separate the uranium, resulting in a compound known as U₃O₈ (triuranium octoxide). The transport containers safeguard both personnel and the environment from exposure to radioactive dust.

Natural uranium contains the isotopes ²³⁵U and ²³⁸U. The heat needed to produce energy in a nuclear reactor is generated through the fission process, which occurs using the ²³⁵U isotope. Most nuclear power plants use fuel enriched to 3–5% ²³⁵U. Since uranium enrichment takes place in gaseous form, U₃O₈ (triuranium octoxide) is converted into UF₆ (uranium hexafluoride). In fuel fabrication facilities, enriched uranium is used to produce the nuclear fuel needed for reactors, which typically utilize either UO₂ (uranium dioxide) or MOX (mixed oxide fuel). Enriched uranium and MOX fuels have different life-cycle resource demands, with enriched uranium requiring the highest total material input and MOX fuel needing fewer resources compared to fresh fuel cycles [9].

For the storage and transport of nuclear fuel during the production phase, good mechanical protection is required, as the fuel is only mildly radioactive and does not involve additional constraints. After the fuel assemblies are loaded into the reactor and the fission process begins, they are stored in wet storage containers for several years. Cooling pools represent the first and most widespread storage solution for spent nuclear fuel, typically located near the reactors. Water serves simultaneously as a cooling agent, maintaining the temperature below approximately 35 °C, and as a natural shield against gamma and neutron radiation [7].

After the cooling period in the pool, the following steps include loading into containers, dry storage, reprocessing options, or final disposal [10].

In the intermediate storage of spent nuclear fuel, stainless steel containers function as modular and efficient components for corrosion protection and ease of handling. Using a dry cask prototype equipped with two vertically mounted internal stainless-steel canisters inside a concrete overpack with passive natural ventilation, the temperature was kept within safety limits, confirming the practicality of handling [11].

Final geological disposal containers are built to endure thousands of years in underground repositories and are constructed from carbon steel with a special coating or copper. Spent fuel is highly radioactive and requires a long-term period of isolation in a final storage location. Significant investments and long implementation times are needed to develop both new nuclear reactor technologies and final disposal facilities. Finland has become a pioneer in this field by obtaining the license for a geological repository for final storage [12].

2.1. Dry Storage Systems

A dry storage system for radioactive nuclear waste consists of a container with a tubular shell, into which a nuclear waste storage canister is inserted. One end of the shell is sealed with a welded lid, while the other end has a sealed closure. Some lids may also include secondary pressure-retaining barriers around the canister or areas most vulnerable to failure under certain conditions [13].

Figure 2 illustrates the main components: the lid, the shell, the base plate, the storage canister structure, the sealing and closure lids, fastening elements, the cooling system, and the shielding for radiological safety protection.

The secure sealing of radioactive materials in dry storage containers can be accomplished using a double-lid system. A study was also conducted on a dry storage system using a concrete container for spent Deuterium Uranium fuel from CANDU-type reactors. The temperature history during the operational period is determined using a validated thermal analysis model for this container. This allows the assessment of degradation behavior as a function of the spent fuel temperature [14].

Some patented equipment documents are available for the United States [15], and Europe [16] but the design for both models is the same and open for study. Both technical documents list Krishna P. Singh as the inventor and Holtec International as the manufacturer.

Table 1. Types of containers used for dry storage.

No.	Name/ Manufacturer	Purpose	Construction Materials	Monitored Parameters	Key Aspects	Ref.
1	CASTOR 1000/19 GNS	transport and storage	-Steel; -Shielding: ductile cast iron; -Neutron moderator: polyethylene rods; -Capacity: 19 fuel assemblies.	-Temperature; -Internal pressure; -Sealing; -Lid integrity.	It offers a high level of radiological safety during storage or transport. Adequate protection is provided by using suitable construction materials. The modular structure facilitates easier handling and storage.	[17]
2	CONSTOR/GNS	transport and storage	-Walls are of sandwich type: steel–concrete–steel; -Designed for high-level radioactive waste.	-Temperature; -Heat load distribution; -Mechanical deformation.	These systems offer excellent shielding and provide strong protection against thermal and mechanical stresses.	[18]
3	HI STAR 100/Holtec International	transport and storage	-Cylindrical body made of carbon steel; -Shielding with lead.	-Temperature; -Leak detection indicated by helium loss; -Structural stresses.	A dependable storage system operated under pre-set vacuum conditions. Shows high performance in accident scenario tests.	[19]
4	Korad 21	transport and storage	-Structure made of stainless steel; -Protective concrete layers against radiation.	-Temperature; -Structural integrity; -Radiation shielding; -Subcriticality.	Modular system allows for efficient and safe storage, with a durable structure that provides protection under extreme external conditions.	[20]
5	Hi STORM 100/ Holtec International	storage	-Body made of steel and concrete; -Inner storage canister made of stainless steel.	-Temperature; -Airflow in the passive cooling system; -Corrosion due to external environmental exposure.	Robust system with highly effective passive cooling. Nuclear fuel integrity is properly maintained over an extended period.	[21]
6	MAGNASTOR/ NAC International	storage	-Body made of carbon steel; -Storage canister made of aluminum alloy; -Lead shielding; -High storage capacity.	-Temperature; -Internal pressure; -Radiation level; -Leak detection	The system is designed to ensure the secure long-term storage of large quantities.	[22]
7	TN 32/ Transnuclear INC	storage	-Body made of carbon steel; -Lead shielding; -Capacity: 32 PWR fuel assemblies.	-Temperature; -Radiation level; -Pressure; -Mechanical integrity through periodic inspections.	Reliable long-term system operating under controlled environmental conditions, retaining its protective functions even after extended periods of use.	[23]
8	HI-STORM FW/ Holtec International	storage	-Body made of steel and concrete; -Designed with high resistance to flooding and strong winds.	-Temperature; -Integrity under external factors (wind, rain).	System with excellent stability and long-lasting reliability, tested under harsh weather conditions.	[24]

lists the materials used in dry storage containers, the monitored parameters, and important aspects related to their application, based on a synthesis of various storage system models. This highlights the variety of available dry storage options and illustrates how different design configurations and materials are used to meet complex safety requirements related to radioactivity, structural integrity, and heat transfer.

The analysis highlights that modern systems, such as CASTOR, CONSTOR, HI-STORM, and MAGNASTOR, combine materials with complementary properties (stainless steel, reinforced concrete, lead, and aluminum alloys) and are equipped with redundant sealing and monitoring systems to prevent radioactive leaks and maintain fuel stability over extended periods. At the same time, modular design and adaptability to harsh external conditions (flooding, wind, corrosion) reflect a clear evolution toward durable and flexible systems. This synthesis confirms that, although the basic principles of dry storage are shared, each technology offers specific solutions for enhancing the safety, transportation, and handling of spent nuclear fuel, contributing to the diversification and strengthening of global nuclear infrastructure.

The parameters monitored in these systems reflect their complex operation and include: temperature to prevent cladding degradation and ensure efficient heat dissipation; internal pressure to detect leaks or gas buildup; mechanical integrity checked through inspections and resistance tests against shocks and vibrations; radiation levels to protect personnel and the environment; and corrosion, especially in containers exposed to external environmental conditions.

Dry storage offers the following advantages [25]:

• Storage in an inert atmosphere prevents fuel corrosion issues;
• Natural cooling without maintenance;
• Low probability of environmental impact contamination;
• Safety measures are simple to put into practice.

Dry storage offers the following disadvantages [3,26];

• Storage buildings or containers are costly; prices vary based on the volume and kind of waste;
• Repairing equipment is complicated when containers are damaged;
• Continuous monitoring with pressure sensors is necessary to detect leaks caused by sealing failures.

2.2. Wet Storage Systems

Immediately after nuclear fuel is extracted from the reactor, it stays hot and radioactive, needing cooling for several years or even decades. The Spent Fuel Pool (SFP) provides a solution that combines thermal cooling and radiation shielding. Storage racks using polymeric neutron absorbers are particularly vulnerable to erosion and can crack when exposed to radiation over time. The deterioration of these materials causes gaps or erosion in nearly all fuel racks made from such materials [27].

The potential of placing the spent fuel pool inside the reactor containment building, instead of traditional external sites, was examined to lower the risks linked to external hazards [28].

Wet storage provides the following benefits [7,29]:

• Storage pools are already accessible nearby reactor;
• Proven technology, all spent fuel is temporarily stored in pools cooling;
• Low-cost storage.

Wet storage presents the following disadvantages [30,31];

• Corrosive environment;
• Potential fuel damage from storage corrosion containers;
• Water purification by filtration;
• The importance of controlling water quality;
• Maintenance of mechanical equipment, such as coolers or pumps, must be conducted over a long period;
• Possibility of radioactive material leaking into the environment pool;
• Possibility of contamination spreading into the environment;
• Before fuel is transported, it must be dried when it is packed in a container.

A comparative analysis between wet and dry storage of spent nuclear fuel reveals significant differences in terms of safety, durability, and operational costs. Wet storage, commonly used right after reactor discharge, offers quick cooling and good radiological shielding, but it also presents high corrosion risks and demands ongoing, expensive maintenance [27]. In contrast, modern dry storage systems, such as passively ventilated casks, provide sturdy structural protection and long-term radiological safety, making them the ideal choice for decades-long storage before being moved to geological repositories [3,4,23]. However, the initial infrastructure costs for dry storage are higher, and its implementation demands careful planning and adherence to international nuclear safety standards [25,26].

A comparative analysis of the two storage types, from the perspectives of radiological safety, corrosion risk, recommended duration, associated costs, and maintenance requirements, is summarized in

Table 2. Overview of Storage Types by Safety and Operational Factors.

No.	Criterium	Wet Storage	Dry Storage	Ref.
1	Radiological Security	Good, immediately after removal from the reactor, water offers cooling and gamma shielding.	Very good in the long term; Containers provide shielding and protection tight sealing.	[7,32]
2	Corrosion Risk	High water is a corrosive environment that needs filtration and chemical treatments.	Low–inert atmosphere (helium/nitrogen) and corrosion-resistant containers.	[27,33]
3	Estimated Storage Period	Temporary solution lasting years to decades for initial cooling.	Long-term solution (lasting decades to centuries) until final geological disposal.	[3,12]
4	Costs	Relatively lower initially (pools already available); However, high maintenance costs.	High initial costs, but low when considering long-term maintenance.	[25,26]
5	Maintenance	High: pumps, filters, continuous water quality monitoring.	Low: passive ventilation systems and periodic structural monitoring.	[4,23]

.

The analysis of nuclear fuel storage system types highlights that both wet and dry storage solutions have evolved steadily to meet increasingly stringent requirements regarding safety, residual heat dissipation, and mechanical integrity. Wet storage remains the initial and most widespread solution for spent fuel, ensuring rapid cooling immediately after removal from the reactor. However, its limitations, including corrosion risks, maintenance demands, and potential for leakage, necessitate a gradual transition toward dry storage. Modern dry cask systems, presented in various configurations and prototypes, demonstrate high reliability, particularly due to passive cooling, corrosion-resistant materials, and modular design. Meanwhile, solutions for fresh fuel focus on traceability and mechanical protection, with less demanding technical requirements, yet crucial for ensuring quality and safety.

3. Monitored Parameters and Monitoring Methods

This study presents a structured review of recent technologies and models used in monitoring nuclear fuel storage and handling. Monitoring nuclear fuel, whether spent or fresh, is a crucial step in managing its life cycle, playing a key role in preventing incidents, extending storage times, and ensuring compliance with international safety standards. The parameters monitored, including temperature, pressure, radiation levels, humidity, corrosion, and structural integrity, offer valuable information for assessing the behavior of the fuel and the long-term storage containers. At the same time, specialized literature indicates that monitoring varies significantly depending on the type of fuel and storage system used, a point that is summarized in this section through a comparative analysis and by presenting the most relevant detection and diagnostics technologies. This approach not only identifies the most critical parameters to monitor but also highlights recent advances in the field of non-invasive surveillance and the digitalization of monitoring processes.

In the context of ensuring the long-term safety of used nuclear fuel storage systems, the graph below, Figure 3, shows the relationship between the key functional requirements for the integrity and security of these systems and the technical measures implemented to meet them. These requirements include secure closure and prevention of radioactive leaks, mechanical strength, radiological protection, maintaining subcriticality, and dissipating residual heat—all of which depend directly on the continuous monitoring of specific parameters such as internal pressure, temperature, radiation, and structural integrity, using modern detection and control methods [3,13,34,35,36].

3.1. Critical Parameters During Storage

Storing spent fuel in wet pools or dry cask storage requires careful monitoring of key parameters to ensure long-term safety and prevent radiation leaks [37].

The parameters monitored during the storage of nuclear fuel are crucial for maintaining the safety and integrity of storage systems throughout their lifespan. Exceeding the permitted limits can cause degradation of the fuel cladding, loss of container sealing, or release of radioactive materials, leading to serious consequences for nuclear safety and the environment. Therefore, identifying and continuously monitoring these parameters is essential for both fresh and spent fuel, especially during long-term storage.

Table 3. Parameters monitored during storage.

No.	Monitored Parameter	Description	Ref.
1	The temperature of the fuel and the container in which it is stored	The temperature must stay below 400 °C to avoid degrading the fuel rods. Exceeding these values may cause chemical reactions like oxidation, followed by the breaking of the fuel rods. Monitoring this parameter is crucial, especially in dry casks, because heat dissipates passively.	[38]
2	The dose of radiation	It must be monitored for the safety of the operators. They should not receive more than the maximum allowable dose to avoid any adverse health effects. Radiation monitoring must also be conducted to detect any breaches in the integrity of the containers. An increase in radiation levels indicates the containers are degrading.	[39]
3	The internal pressure of the container	If the tightness of the container is affected, the pressure changes. This phenomenon suggests that accumulations of radioactive gases or hydrogen are produced from reactions with residual water. The increase in pressure is due to modifications to the vessel’s structure.	[40]
4	Corrosion of exterior surfaces	If containers are stored outdoors, particles from the environment can cause corrosion of stainless steel or other metal materials. Corrosion reduces the strength of the container structure. When stored in a damp climate, these problems can occur much more frequently. Therefore, this storage method is not recommended for prolonged periods.	[33]
5	Humidity	If moisture exists inside the container, corrosion could happen. That is why it is vacuumed several times. If this vacuum drying process is not performed properly, the leftover moisture can also impact the fuel tubes and generate H2, which can become hazardous in large quantities.	[41]
6	Fuel integrity	If the nuclear fuel cladding is compromised, fission products may escape. Quickly detecting structural degradation is crucial because the cladding can crack under thermal stresses.	[34]

lists the most critical parameters, along with bibliographic sources supporting their roles in evaluating the safety and reliability of storage systems.

The results summarized in Table 3 confirm the importance of ongoing monitoring of critical parameters to ensure the safety of storage systems. However, monitoring needs vary significantly depending on the specific type of nuclear fuel: fresh or spent, an aspect rarely addressed in the literature.

Fresh fuel poses fewer risks, mainly requiring monitoring of environmental conditions and ensuring traceability, while spent fuel involves significant dangers due to radioactivity, residual heat, and cladding deterioration.

Considering the significant differences in the physical and chemical structures that occur after nuclear fuel has been used in the reactor compared to fresh fuel,

Table 4. Comparison of fresh/spent fuel.

No.	Monitored Characteristics	Fresh Fuel	Spent Fuel
1	Radioactivity	Reduced emissions.	High radioactivity: requires shielding, cooling, and personnel protection [42].
2	Heat generation	Very small.	A prolonged period must be applied to a cooling method due to residual heat [43].
3	Physical-chemical state	Excellent stability; the material remains unchanged mainly unless external factors intervene.	The potential for chemical reactions caused by gases and fission products [32].
4	Risk of contamination	Very low.	Raised because of potential cracks in the fuel tanks [44].
5	Storage period	Small: until their introduction into the reactor.	Considerable: decades of years [32].
6	The objective of monitoring	Ensuring the environmental conditions and fuel traceability.	Maintaining container integrity to prevent radioactive leaks and support continuous assessment [44].
7	Monitored parameters	Temperature, humidity, internal pressure, and traceability of fuel rods.	Temperature, emitted radiation, pressure, corrosion, tube and container integrity, vibrations [44].
8	The complexity of monitoring	Reduced: sensors and automation equipment are used for everyday working environments.	Raised: continuous monitoring is implemented with complex and redundant equipment [44].
9	Monitoring equipment	Thermocouples, thermoresistances, humidity sensors, tables, or RFID for traceability.	Gamma/neutron detectors, acoustic and vibration systems, gas monitoring systems, etc. [45].

provides a comparison between the two types of fuel, highlighting each one’s specific characteristics.

Oettingen [43] demonstrated that, although used nuclear fuel remains highly radiotoxic for approximately 130,000 years, a validated methodology exists that enables estimates for managing all stages of nuclear fuel, from production to final disposal storage.

Sun et al. [44] analyze radiation monitoring in a spent nuclear fuel reprocessing plant using fuzzy methods and fault tree analysis. It provides a practical resource prioritization scheme, showing that the extraction workshop and the central control room are the most critical areas for nuclear safety security.

The paper [32] offers a preliminary yet essential assessment of the risks involved in storing spent nuclear fuel in Ukraine, focusing on Zaporizhzhia and Chernobyl. The analysis combines nuclear data, decay models, and geotechnical/hydrological studies, demonstrating that infrastructure issues and a lack of cooling water can lead to high-risk situations.

Although the specialized literature focuses almost exclusively on spent nuclear fuel, since it presents the most significant safety and monitoring issues, this section also covers aspects related to fresh fuel. The mentions regarding the parameters and requirements for fresh fuel are based on both deduction and comparative synthesis, grounded in its physicochemical characteristics and low level of radioactivity, as well as on the recommendations included in the IAEA standards and guidelines [46,47,48].

The monitoring parameters from

Table 5. The minimum set of requirements that ensures safe management of nuclear fuel.

No.	Parameter	Device	Description	Ref.
1	Temperature	Thermocouples/ Temperature Sensors	Preventing the contraction or expansion of materials that could compromise the integrity of nuclear fuel.	[46]
2	Humidity	Humidity sensors	The metal components and casings are exposed to corrosion, and humidity must be monitored to prevent it from contributing to the phenomenon.
3	Internal pressure	Pressure sensors	Gas accumulations can be observed when the internal pressure changes. A sign of seal failure in the system is when the internal pressure drops.
4	The level of radiation	Radiation detectors	To prevent personnel in the storage area from being exposed to a high dose of radiation, the radiation level must be checked, and any potential contamination in that area must be identified.	[47]
5	Positioning and inventory of the fuel	Fuel traceability systems	The production batch, technical details, and other information about the nuclear material must not be lost during storage or transportation. That is why traceability must be maintained with strict precision.	[48]
6	Structural integrity	Visual inspection	The integrity of the structure and the absence of cracks or deformations must be checked regularly.

represent the minimum set of requirements that ensure safe management of nuclear fuel. These parameters are applicable to both fresh and spent fuel. However, in the case of fresh fuel, they are generally sufficient due to its lower radiological risk. For spent fuel, the same parameters are only the baseline, which must be expanded with stricter monitoring measures as it is described in the comparison made in Table 4.

According to the IAEA Safety Standards Series No. SSG-63: Design of Fuel Handling and Storage Systems for Nuclear Power Plants [48], the management of fresh nuclear fuel must meet specific requirements to ensure nuclear and radiological safety. Hence, it is essential to regulate control, and restrict nuclear reactivity by properly arranging the assemblies and, if needed, employing neutron-absorbing materials, even when the fresh fuel does not produce substantial residual heat. Furthermore, conditions for controlled handling and storage are established, including designated areas for reception and inspection, with monitoring of temperature, humidity, and ventilation, as well as measures to prevent contamination. In cases where fresh fuel contains materials from reprocessing, the guideline requires applying appropriate radiological screening to keep personnel doses below regulated limits. Additionally, full traceability must be maintained by recording the identity of each fuel assembly and managing movement control procedures. Finally, all structures, systems, and components involved are classified according to their importance for safety and subjected to strict quality control.

In conclusion, monitoring fresh nuclear fuel depends on a limited set of parameters focused on environmental conditions and traceability, reflecting the lower risks associated with it compared to spent fuel. Although its radioactivity level is much lower, tracking temperature, humidity, internal pressure, radiation levels, and structural integrity is crucial to prevent material degradation and protect personnel. Additionally, strict traceability of each fuel batch helps ensure compliance with nuclear security standards and prevents the loss of critical information. Therefore, even though the requirements for fresh fuel are less strict than those for SNF, they are an essential part of responsible nuclear material management.

3.2. Monitoring Technologies

The monitoring of nuclear fuel, whether fresh or spent, requires the use of various technologies, from established traditional methods to emerging solutions based on artificial intelligence and non-invasive sensors.

Table 6. The techniques and tools employed for monitoring nuclear fuel.

No.	Equipment	Method Description	Ref.
1	Raman spectrometer	Using the spectrometer, the chemical composition of uranium oxide (UO2) is monitored. It can lose oxygen at high temperatures, which may lead to the formation of triuranium octoxide (U3O8), indicating fuel degradation.	[34]
2	EMAT system	The EMAT system generates waves within the metal walls of the container and measures the vibration frequencies. These frequencies increase as internal pressure rises. A precision acoustic microphone can detect vibrations near the container. This method is contactless and non-destructive, making it an ideal choice.	[49]
3	Ultrasonic sensors	Using ultrasonic sensors allows for non-invasive monitoring of a canister’s internal conditions. This enables the observation of whether a proper vacuum has been achieved, the detection of temperature variations, or the identification of residual water vapors that could compromise the container’s integrity.	[50]
4	Thermocouples/ Temperature Sensors	To prevent fuel degradation, monitor the temperature to avoid reaching levels that could compromise its structural integrity.	[51]
5	Electronic microscopy (SEM)	SEM microscopy is used for detailed analysis of fuel cladding surfaces. It reveals defects that are not visible with traditional methods and provides detailed images of the microstructure of nuclear materials.	[52]
6	XRD Analysis	XRD analysis is used to study the crystal structure of nuclear materials.	[53]
7	FEM	The finite element method is employed to analyze the mechanical and thermal behaviors of nuclear fuel.	[54]
8	EDS	A non-destructive technique used to analyze the elemental chemical composition of surface oxides on nuclear fuel cladding.	[55]
9	FTIR + vacuum drying	Creating a vacuum and generating heat are used to remove moisture, thereby preventing corrosion.	[53]
10	ICP-MS	For nuclear fuel analysis, ICP-MS with an ultrasonic nebulizer is employed. It checks the purity of the fuel and analyzes the isotopic ratios. For samples with very low uranium concentrations, this method remains effective and can be used to analyze all elements from the periodic table, not just uranium.	[56]
11	Ionization chamber	The ionization chamber is designed to detect particles produced in nuclear reactions involving radioactive ions. Using inclined electrodes improves the detector’s response time.	[57]
12	Geiger-Muller Counter	Geiger-Muller counters are used to improve the accuracy of radiation monitoring.	[58]
13	Scintillation detector	Scintillation detectors are crucial for identifying nuclear materials. Their precision improves because they efficiently distinguish between signals from neutrons and gamma radiation.	[59]
14	Muon detector	The trajectories of cosmic muons are diverted when they pass through materials of different densities. Using algorithms and 3D reconstruction, an image of the internal structure of the cask can be created without opening it. This helps determine if nuclear fuel is present.	[60]

summarizes these methods and equipment, showing how recent research has diversified and refined diagnostic techniques and tools to meet current safety and traceability standards. The integration of modern technologies, such as Raman spectroscopy, ultrasonic sensors, or systems based on muography, reflects the trend toward more precise and automated monitoring, aiming to support traditional practices and decrease reliance on manual checks. This presentation offers a clear overview of the available instruments, highlighting the complementarity between established and innovative approaches.

The analysis of the methods summarized in Table 6 shows that, although many methods are available for monitoring nuclear fuel, their usefulness mainly depends on the type of fuel and the specific storage conditions.

4. Technological Trends in Storage Systems

This section examines emerging technological trends in nuclear fuel storage, emphasizing the integration of IoT, artificial intelligence, blockchain, and Digital Twin technologies for secure monitoring and traceability, the use of non-invasive sensors and drones for advanced diagnostics, and the role of numerical simulations in the design and safety assessment of storage systems.

A study published in May 2025 [61] provides a comprehensive overview of blockchain and IoT applications in spent nuclear fuel (SNF) management, highlighting how these technologies can address challenges related to transparency, security, and confidentiality. The authors analyze existing case studies (such as SLAFKA and Sellafield) and compare proposed architectures, highlighting the advantages of using technologies like zero-knowledge proofs for data protection. The review concludes that blockchain and IoT are promising solutions for SNF monitoring and traceability; however, their implementation requires further validation, standardized testing, and international cooperation to ensure both public trust and compliance with nuclear regulations. Yessenbayev et al. [6] present a prototype implemented on a private Ethereum network, tested in a pseudo-real case in Korea, demonstrating the feasibility of real-time monitoring of nuclear waste containers using IoT sensors. While the first emphasizes conceptual analysis and security architectures, the latter offers practical validation, establishing the foundation for potential large-scale applications.

Together, the two studies outline a strong direction for integrating emerging digital technologies into the long-term management of spent nuclear fuel (SNF).

Using residual neural networks (ResNet) for corrosion detection on dry storage canisters allows for highly accurate image classification as either corroded or intact, reducing personnel exposure and inspection time [5].

Neutron tomography has been combined with machine learning algorithms and convolutional neural networks (CNNs) to reconstruct images of the interior of storage containers. This method enables the accurate identification of gaps or missing fuel assemblies, even during scans shorter than two hours [62].

A 3D CFD model was employed to analyze the thermal behavior and airflow inside the HI-STORM 100 dry storage cask. Two gas models were compared. The ideal gas model provided more accurate results, closer to experimental values, especially in high-temperature regions of the cask. The other model underestimated peak temperatures and the internal heat distribution. The system was analyzed for a cooling period of 10–55 years, and the analysis showed that temperature and airflow gradually decreased as the residual heat of the spent fuel diminished. This offers an optimized framework for simulating and designing dry storage casks, thereby minimizing errors in temperature and airflow distribution estimates. The correct choice of gas models in CFD simulations is vital for accurate predictions and enhanced system safety [63].

The validation of the fuel rod arrangement pattern in a fresh nuclear fuel storage cask was analyzed using the Yonsei Single Photon Emission Computed Tomography system (YSECT)—Yonsei University, Wonju, Republic of Korea. To evaluate the YSECT prototype’s performance, images were taken for three fuel rod arrangement models in a 6 × 6 matrix using two image reconstruction algorithms. The gamma-ray characteristics of freshly enriched 4.3% UO₂ were analyzed by recording the energy spectrum with a trans-SPEC-N HPGe detector (ORTEC AMETEK, Oak Ridge, TN, USA) over a 300 s measurement period. The image intensity at the locations corresponding to fuel rods in the assembly was high. The images showed ring shapes and weak symmetry in the patterns. These effects were caused by the uniformity of gamma-ray detection across the 256 channels, the lower-than-ideal sampling rate of the projection images during detector rotation compared to simulation conditions, and the slight misalignment of the rotation axes [64].

Based on these emerging trends, the analysis further concentrates on two main development areas: the integration of digital solutions for automation and control, and the adoption of non-invasive technologies for advanced diagnostics and monitoring, each helping to enhance the safety and efficiency of storage systems.

4.1. Automated Process Control Using Digital Technologies

In the context of increasingly stringent safety and efficiency standards, automation and digital control have become vital in managing spent nuclear fuel, allowing real-time monitoring of key parameters and significantly reducing the risk of human error.

Data collected from equipment installed on nuclear storage systems is much more accurate when gathered automatically through digital technologies. Manual collection by operators can cause errors during either acquisition or interpretation. Digitalization is crucial for ensuring the traceability of each fuel assembly. As nuclear safety regulations become more stringent and operational optimization is better achieved through automation, digitalization of processes becomes essential. Digital Twin (DT) technology allows for the optimization and development of new equipment designs, as well as the evaluation and validation of processes [65].

At the same time, solutions based on the Internet of Things (IoT) and intelligent monitoring systems allow for real-time collection and analysis of key parameters from storage containers, helping to reduce risks and improve operational efficiency [66,67,68,69,70,71]. Other recent applications of artificial intelligence, such as text similarity analysis models [72] can further support traceability and the management of complex documentation associated with the nuclear fuel cycle, although this is not detailed in this section.

Sensors are vital for measuring process parameters, such as pressure, humidity, temperature, and system vibrations. When selecting the type of sensor to be used, it is necessary to consider the area where it will be installed, as it may need to withstand high humidity, elevated temperatures, or strong vibrations. These sensors can be installed in cooling pools, storage halls, or even inside containers and dry storage casks [73].

SCADA (Supervisory Control and Data Acquisition) and DCS (Distributed Control Systems) architectures are used to gather and centralize data from sensors. They allow operators to visualize, interpret, control, or record data from the system in real time. These systems can be configured to be user-friendly and easy to operate by the personnel managing them [74].

At the first level of the SCADA architecture, sensors detect process parameters in real time. Using this data, actuators execute commands based on instructions programmed into Programmable Logic Controllers (PLCs) to maintain process stability. The next level involves the communication network, where data is transmitted to a central computer. At the top of the SCADA architecture is the master station, which serves as the system’s central control point. This computer gathers data from the installation and displays it via the human–machine interface. Operators use the HMI (Human–Machine Interface) to monitor system performance, adjust settings, or respond to alerts [74].

Monitoring interfaces offer an easy-to-understand view of the system’s status at the time of inquiry, in the past, or as an average of the monitored parameters. Monitoring can be performed locally or remotely, and interfaces can be tailored to make the data more understandable for the user. The data can be shown on a process computer or sent remotely, as long as security protocols allow it. For cybersecurity analysis, de Brito and de Sousa developed an open-source testbed based on the Modbus protocol. ScadaBR was used as the HMI interface for data visualization and graphical screen development. The system allows recording values in a database, enabling the study of data over long periods [75].

A data acquisition platform can automatically generate reports for a specified period, highlight specific events during abnormal operating conditions, or when parameters approach predefined alarm levels thresholds. The format in which they are archived can be adapted according to user requirements. One can choose to view the data in file types such as ‘.csv’, ‘.xml’, ‘.html’, ‘.pdf’, etc., and they can be archived in secure systems for later analysis [76].

Digital technologies are used because they enable more accurate and easily accessible traceability, ensure proper execution of operational workflows, improve measurement and reporting precision, and provide easier access to historical data logs.

Industrial automation systems and Internet of Things (IoT) technologies are perfect for nuclear fuel monitoring because they enable continuous monitoring, real-time analysis, and automatic intervention, if necessary, instead of relying on periodic inspections, provided such responses are preconfigured [66].

Communication can be established using networks such as LoRaWAN, ZigBee, NB-IoT, or even industrial 5G networks. The performance of these networks in electromagnetically shielded environments has shown high reliability under such challenging conditions [67].

Gateways gather data from sensors and locally process important parameters, reducing constant transmission and enabling automatic decisions. They utilize edge computing technologies to enable quick decision-making even when the connection to the central server is lost. The collected data can be transmitted to other automatically controlled systems that can operate the ventilation system, cut off the power supply, or isolate certain equipment based on scenarios configured for such abnormal operating conditions [69].

The communication network must be reliable, and if enhanced security is needed, redundancy should be implemented. Wireless networks are used only if protocols al-low, and data is stored on local networks. Archiving in the cloud or on networks with internet access is only permitted if authorized and if these networks are well protected against cyberattacks through encryption, multi-factor authentication, or industrial-grade security firewalls [70].

The primary benefits of integrating IoT include increased monitoring reliability by removing dependence on human intervention, instant responses when critical parameters are exceeded, monitoring of inaccessible areas, and easy integration with SCADA systems or other industrial platforms [71].

Overall, the studies reviewed highlight significant progress in automation and digitalization, showing that integrating these innovative solutions is a practical approach to enhancing the safety, transparency, and efficiency of spent nuclear fuel storage systems.

Therefore, integrating non-invasive sensors and advanced diagnostic technologies provides not only more accurate and real-time monitoring of spent nuclear fuel containers but also significantly reduces operational risks and personnel exposure, thereby reinforcing the foundation for safe and sustainable long-term management.

4.2. Advanced Diagnostic Technologies and Non-Invasive Sensors

Non-invasive sensors and advanced diagnostic technologies are crucial not only for monitoring the safety of spent nuclear fuel containers but also for quality control and traceability of nuclear fuel, ensuring material integrity throughout the entire nuclear fuel cycle.

Autonomous systems can carry out visual, thermographic, and acoustic inspections without operator involvement. Drones can be fitted with cameras and sensors to examine containers in hard-to-reach or high-risk areas. The use of robots that stick to surfaces with magnets is documented, and these robots are capable of moving along the walls of dry storage containers, collecting essential data without requiring disassembly, extra interventions on the equipment, or exposing operators to radiation [77].

Drones are used for the external inspection of industrial tanks to detect corrosion and visual defects. The captured images are processed using quality enhancement algorithms. A two-stage cascaded fuzzy logic approach is applied to differentiate noise (such as shadows, objects, sediments, and vegetation) from actual defects (such as rust). An accuracy of approximately 83% was achieved in rust detection [78]. Sensors such as RGB, thermal, and multispectral ones mounted on UAVs are used to identify surface degradation like cracks, moisture, and corrosion [79,80].

Neural networks are used for automatically detecting corrosion on metallic structures based on images captured by drones (UAVs). In the study, aerial drone images were preprocessed, and corrosion-affected regions were identified and isolated at the pixel level. Simultaneously, another network was trained to classify the images, confirming the presence or absence of defects [81].

Accurate and early detection of corrosion, even in poor lighting conditions or on hard-to-reach surfaces, enhances the safety of containers. Experimental results showed high accuracy (above 90%), making this technology promising for industrial applications where manual inspection is challenging or hazardous [81].

In conclusion, utilizing non-invasive sensors and advanced diagnostic techniques is crucial for enhancing safety and reliability in managing both fresh and spent nuclear fuel, enabling continuous integrity monitoring and risk assessment prevention. Based on this, the next section will examine how numerical modeling and simulation provide a predictive framework for evaluating the long-term behavior of storage systems.

4.3. Advanced Modeling and Simulation for Designing Storage Systems

To support sensor-based monitoring, numerical modeling and simulation provide an indispensable tool for evaluating the long-term behavior of nuclear fuel and storage containers, enabling accurate predictions of heat transfer, structural integrity, and the evolution of degradation processes caused by external factors.

Significant innovations in the analysis and optimization of dry storage systems have been achieved through the use of Computational Fluid Dynamics (CFD) simulations. These models simulate and analyze fluid behavior within various systems and are commonly used for safety evaluations. To ensure correct application, a dedicated guideline has been created to support the proper use of CFD tools, including recommendations for choosing suitable models. Recommended methods include the Reynolds-Averaged Navier–Stokes (RANS), Large Eddy Simulation (LES), and Detached Eddy Simulation (DES) models. The guideline also outlines the numerical approximations used to solve flow equations and discusses potential sources of error [82].

Probabilistic methods have been used to evaluate the risks linked to accidents during nuclear fuel transport. Probabilities were calculated using existing statistical models and data. A software tool was developed to integrate accident scenarios, such as maritime incidents, an aircraft crashing into a storage facility, or accidents during transport from the factory. The goal of these studies was to assess the associated risks. However, the input data are subject to various uncertainties. Ongoing research to reduce these uncertainties aims to improve the accuracy of such models [83].

To ensure measurement accuracy, signal filtering corrections were applied. The issues that arose were identified and resolved, demonstrating the reliability of the proposed solution. This experiment showed that infrared thermography can monitor the manufacturing process of containers in real time, ensuring the homogeneity of the lead layer and preventing structural defects [84].

Spent nuclear fuel (SNF) must be kept at temperatures between 40 °C and 67 °C. If the maximum temperature is exceeded, the cladding can oxidize and crack. Heat transfer and airflow analyses are performed using ANSYS software, while contamination levels can be monitored with CONTAM. Optimization can be carried out using MATLAB [85].

Numerical models used to simulate the behavior of spent nuclear fuel in dry storage include fuel performance codes, hydrogen diffusion and redistribution models, creep models, and other simulations [86]. Creep is a slow deformation that happens when materials are exposed to high temperatures for long periods. The claddings of fuel elements are made of Zircaloy and can change their shape or size due to stresses and heat effects.

Table 7. Main numerical models developed.

No.	Name	Developer	Model Type	Notes	Remarks	Ref.
1	FRAPCON	PNNL– Pacific Northwest National Laboratory	Fuel performance modeling tool	It is used to simulate key parameters, including the internal pressure within fuel rods, the release of fission gases, and the resulting mechanical responses stresses.	Provides time-evolution predictions of nuclear fuel performance for PWR and BWR reactor types.	[87]
2	TRANSURANUS	JRC– Comisia Europeană	Fuel performance modeling tool	It is used to simulate the behavior of spent nuclear fuel.	It is used to study the post-irradiation behavior of materials.	[88]
3	BISON	Idaho National Laboratory	Fuel performance modeling tool	Used for advanced fuel simulation, assessing the impact of temperature on the fuel cladding, as well as the effects of creep and mechanical stresses.	Detailed 3D simulations	[89]
4	TESTA-ROD	Pennsylvania State University	Fuel performance modeling tool	Used for analyzing hydrogen migration within the fuel cladding.	Confirms the presence and retention of hydrogen in the material structure.	[86]
5	FRAPCON-DATING	ORNL– Oak Ridge National Laboratory	Creep behavior simulation model	Advanced FRAPCON model used for fuel lifetime evaluation.	Beyond the standard FRAPCON capabilities, additional functions have been integrated to enable the prediction of creep behavior under dry storage conditions.	[90]
6	EDF	Electricite de France	Creep behavior simulation model	Model used to assess the long-term creep behavior of Zircaloy-4 cladding.	Provides essential design input data for storage development containers.	[91]
7	CIEMAT	Centro de Investigaciones Energeticas, Medioambiantales y Tecnologicas	Creep behavior simulation model	Simplified version of the EDF model, optimized for fuel performance analysis	Low-temperature optimized model for experimental evaluation.	[92]
8	COUNTY	County et al.	Hydrogen diffusion and hydride precipitation model	Examines hydrogen diffusion and precipitation from the cladding.	Validates hydrogen accumulation	[93]
9	LACROIX	Lacroix et al.	Hydrogen diffusion and hydride precipitation model	An improved version of the County model was developed to better observe hydrogen-induced swelling, as the previous model failed to capture this behavior.	Enables estimation of hydrogen-induced swelling and cladding expansion.	[94]
10	Kolesnik	Kolesnik	Hydrogen diffusion and hydride precipitation model	Investigates hydride behavior under mechanical stress.	Investigates the combined effects of creep and hydrogenation on structures integrity.	[95]
11	ORIGEN	Chemical Technology Division of ORNL	Decay and depletion model	Assesses nuclear fuel irradiation and its life cycle.	Delivers accurate estimations of residual heat generation.	[96]
12	ORIGEN 2	Chemical Technology Division of ORNL	Decay and depletion model	An enhanced version of the Origen code that analyzes composition and radioactivity.	Includes data for materials, shielding, and transport.	[96]

presents the main numerical models developed and used for simulations in the nuclear field.

The analysis of the models presented in Table 7 highlights the progressive diversification of simulation tools, from programs focused on isotopic calculations and radiological assessment (e.g., ORIGEN, ORIGEN 2), to advanced applications dedicated to evaluating the mechanical and thermal behavior of nuclear fuel and cladding (FRAPCON, TRANSURANUS, BISON), and more recently, to specialized models that address critical phenomena such as creep and hydride formation [94,95].

The graph in Figure 4 shows the chronological development of simulation models for spent nuclear fuel, beginning with early isotopic inventory codes like ORIGEN in the 1970s, progressing to advanced multiphysics frameworks such as BISON, and culminating in recent specialized models like Kolesnik (2025) [86,87,88,89,90,91,92,93,94,95,96]. This timeline highlights the evolution of computational tools from simple burnup and decay estimates to detailed analyses of thermal, mechanical, and hydrogen-induced degradation—crucial for maintaining the long-term safety of dry storage systems.

Alyokhina examined the structure of an information system designed for use in a dry spent fuel storage facility with ventilated storage casks. To ensure thermal safety, she developed a database structure that includes an algorithm for monitoring spent fuel temperature. Atmospheric factors are crucial, as they can affect the data collected during the monitoring of ventilation air temperature inside the storage cask.

For long-term storage, both wind speed and direction must be considered, as they are important factors. The suggested information system can be used for effective thermal monitoring and data collection to support future studies on the implementation of spent fuel storage aging management programs, continuous safety monitoring, and staff training [97].

In conclusion, although the simulation models analyzed have progressed from basic isotopic inventory tools to advanced frameworks capable of capturing complex thermal, mechanical, and chemical phenomena, they still depend on simplifying assumptions and are constrained by limited experimental data validation. Therefore, while these models represent an indispensable tool for ensuring the long-term safety of spent nuclear fuel storage, their precision and practical applicability must be strengthened through the expansion of experimental databases and international collaborations aimed at harmonizing methodologies.

5. Conclusions and Future Directions

The study confirms that the storage and monitoring of nuclear fuel have significantly evolved through the adoption of digital technologies, passive cooling systems, and advanced non-invasive diagnostic methods, addressing the need for sustainable and efficient solutions. The literature review shows that, although traditional wet and dry storage methods remain key to nuclear infrastructure, they are increasingly enhanced by innovative approaches involving digitalization and artificial intelligence. Examples such as HI-STORM, MAGNASTOR, or TN-32, which use combinations of stainless steel, reinforced concrete, and lead, demonstrate improved resilience to extreme conditions, ensuring passive cooling and long-term radiological safety.

However, technological progress is accompanied by notable gaps: the lack of interoperability between monitoring systems of different generations, few validated implementations of artificial intelligence algorithms, and the insufficient experimental data to confirm predictive numerical models. In addition, current international standards do not fully cover emerging digital methods, which limits the transfer of best practices between states and organizations.

The presented synthesis provides researchers with a comparative framework for fresh and spent nuclear fuel, facilitating the development of predictive models validated through experiments and Digital Twin simulations. For the industry, the results can guide the integration of drones, IoT sensors, and deep learning algorithms from the design phase, contributing to reduced maintenance costs and operational risks. Regarding regulatory bodies, the study emphasizes the need for the development of harmonized international standards for implementing artificial intelligence and blockchain technologies in nuclear monitoring. Additionally, the analysis emphasizes the importance of developing nuclear infrastructures resilient to external risks, capable of reinforcing energy security and enhancing public trust.

Future directions in nuclear fuel storage and monitoring focus on developing interoperable systems that communicate and optimize parameters in real-time, large-scale experimental validation of numerical models and artificial intelligence algorithms, as well as full integration of the Digital Twin concept for predicting behavior under extreme conditions. Additionally, the use of drones, non-invasive sensors, and technologies based on blockchain and IoT can enhance traceability and safety, while optimizing design from the conceptual phase through predictive simulations has the potential to increase the reliability and efficiency of systems in the long run.