Case Study: SIJ Acroni’s Contribution to Nuclear Waste Storage Solutions

At SIJ Acroni, we strive to deliver high-quality steel products with a focus on reduced environmental impact. A key component of our business has been supplying materials to projects of critical importance, including those in the nuclear industry. This case study highlights our collaboration with Holtec, a major supplier for nuclear storage solutions, in providing the steel used for the dry storage system at the Krško Nuclear Power Plant in Slovenia. The system is designed to store spent nuclear fuel, ensuring safety and durability and enhancing environmental responsibility.

Nuclear Energy and Energy Security

Nuclear energy is the most reliable source of clean energy, playing a crucial role in the global shift toward sustainable and secure energy production. Unlike renewable sources, such as wind and solar, which are limited by variable weather conditions, nuclear energy provides a constant output, ensuring grid stability and security.

However, nuclear power plants, like the Krško Nuclear Power Plant, generate highly radioactive spent nuclear fuel, which, although generated in minimal amounts, may pose significant long-term storage challenges. Our expertise and commitment to quality play a crucial role in making nuclear energy safer by ensuring that spent fuel can be securely stored after its use.

Spent nuclear fuel is stored in a cooling water pool following discharge from a reactor core to dissipate heat and provide a shield against radiation. After five years, spent fuel may be transferred to a special dry storage system designed to passively, securely, and safely store spent nuclear fuel without a water pool. Due to exposure to extreme conditions, this dry storage solution must be robust, durable, and radiation-resistant, maintaining its integrity over decades or even centuries. SIJ Acroni’s partnership with Holtec has been crucial in delivering the materials for these advanced storage solutions.

Partnership with Holtec – High-Quality Materials for Nuclear Applications

Since 2010, SIJ Acroni has worked closely with Holtec, supplying stainless steel that meets stringent standards required for nuclear applications. This long-term collaboration has involved regular audits to ensure that our steel meets the specific quality, safety, and durability demands of nuclear storage. We supply Holtec with SINOXX 4301 and SINOXX 4307–austenitic stainless-steel grades AISI 304 and 304L with excellent corrosion resistance. These materials are optimal for nuclear waste storage, retaining mechanical properties across a broad temperature range of –200 to 150 °C. AISI 304 and 304L stainless steels are among the most reliable for nuclear industry applications. The high corrosion resistance and durability of these grades make them ideal for long-term exposure, especially in the demanding context of nuclear waste storage. Additionally, we bring substantial experience in supplying steel for the nuclear industry, having previously delivered materials for critical projects. Our commitment to quality control ensures that every batch meets the highest international standards, aligning with nuclear industry requirements for safety and durability.

Precision Engineering of Storage Systems

For the dry storage systems at Krško, SIJ Acroni provided stainless steel plates measuring 130 mm x 2 m x 2 m. Holtec used these plates to cut 1.5-meter diameter circles, which were then finely machined and welded in pairs to create robust 10-inch (25.4 cm) thick covers. These covers were precisely welded onto cylindrical storage canisters with a diameter of 1.5 meters and heights ranging from 2.5 to 3 meters. To enhance the safety and radiation resistance of the canisters, Holtec employed a layered design, with a 15 mm thick stainless-steel plate covered by a concrete mass to further shield against radiation. The resulting casks with an outer diameter of 4 meters are designed for dry storage and offer a passive air convection system to safely dissipate decay heat from the spent fuel over time. At the same time, the storage casks provide robust protection against external factors.

Each canister holds up to 37 fuel elements, with the Krško Nuclear Power Plant’s dry storage facility offering capacity for 70 storage systems – approximately 2,600 fuel elements. With this capacity, the new dry storage facility will enable the plant to store spent fuel more simply and safely. It will accommodate the plant’s current needs and be sufficient to handle nuclear waste for at least the next 100 years, offering a sustainable interim solution to nuclear waste storage.

Nuclear Safety and Environmental Responsibility

In developing materials for nuclear waste storage, ensuring safety and environmental responsibility are of the highest importance. The high-quality stainless steel which we supply ensures that the storage casks can securely contain potentially hazardous waste with no risk of contamination to the environment. Our materials support Holtec's vision for a passive, spent fuel storage system that requires minimal intervention, further reducing the environmental footprint. The concrete shield, combined with our stainless steel, provides dual layers of protection, enabling safe storage in dry casks that require a low maintenance level.

Conclusion

SIJ Acroni is proud to support the nuclear industry through partnerships that prioritize safety, innovation, and environmental stewardship. Our collaboration with Holtec on the Krško Nuclear Power Plant dry storage system exemplifies our commitment to producing steel solutions that meet the highest quality and safety standards. Such systems play a vital role in the safe storage of spent nuclear fuel, helping protect the environment and ensuring a sustainable future for nuclear energy.