As countries with nuclear research reactors look to optimize their spent fuel management practices, many are considering dry storage. Last week, 33 experts from 24 countries met at the IAEA in Vienna for a technical meeting to share experiences in spent fuel management and to improve their practices.
Dry storage involves removing the fuel from storage in water pools to a space where the fuel is surrounded by air or an inert gas. Of the 24 countries present at the meeting that currently operate research reactors, 8 utilize dry storage and another 13 countries, including Egypt, Malaysia and Romania, are considering this option. Their reasons range from dwindling storage capacity in spent fuel pools to a desire for a longer-term solution as facilities for final disposition may not be available for many years and research reactors operate longer than initially planned, producing more spent fuel.
“Dry storage offers a number of advantages, including passive cooling from air, reduced risk of fuel cladding corrosion and the ability to scale up storage space incrementally,” said Frances Marshall, an IAEA nuclear engineer and scientific secretary of the meeting. “It also allows for longer interim storage periods than that afforded by wet storage.”
Research reactors—used for research, development, education and training—produce neutrons for use in industry, medicine, agriculture and forensics, among others. Wet storage of their spent fuel involves placing spent fuel assemblies in a pool at the reactor site for cooling and storage until the final disposition path is determined.
While the safety and reliability of this method is well established, wet storage requires significant, ongoing maintenance. This includes recycling the pool water, which must be constantly monitored for temperature and purity, and periodic fuel inspections. Spent fuel pools also have relatively limited space, which can become an issue after many years of reactor operation.
For dry storage, after an initial period of cooling in the spent fuel pool, spent fuel is dried and then placed in either airtight containers or in an engineered facility which provides confinement, where natural air circulation cools the spent fuel over time. The engineered facilities could be above ground structures, near surface boreholdes, pits or pipes containing arrays of storage cavities suitable for containment of fuel assemblies.
Germany has extensive experience with dry storage dating back to the early 1990s and currently has several dual purpose casks for spent fuel from research and test reactors, with additional casks expected to be added in the near future. “Dry storage has been our primary storage method owing to its passive safety features and relatively minimal maintenance requirements,” said Oliver Bartos, an expert at Gesellschaft für Anlagen- und Reaktorsicherheit (GRS), a non-profit scientific research organisation in Germany. “For countries considering a move to dry storage, deciding on a storage system and cask type based on their specific needs is important together with regulatory considerations for safety and security.”
During the technical meeting, participants were divided into three working groups to review drivers for seeking dry storage solutions, identify gaps in technology options and discuss countries’ needs in this area. They also considered next steps for enhancing cooperation and knowledge sharing with an eye to assisting countries new to dry storage.
“Argentina has concrete silos for the dry storage of commercial spent fuel, but for now we have only utilized wet storage for spent fuel from our research reactors,” said Gabriel Manrique, a technician at Argentina’s Irradiated Fuels Storage Facility of Research Reactors (FACIRI). “However, FACIRI is already 38% full, and with the RA-10 research reactor scheduled to come online in about 5 years, a future storage alternative will be needed.”
South Africa has used dry storage for its research reactor spent fuel for around 25 years. “Sharing knowledge and experience at technical meetings and workshops is highly useful for Member States looking to implement dry storage,” said Suzan Bvumbi, a senior physicist at South Africa’s National Radioactive Waste Disposal Institute. “Countries without experience in dry storage may have a lot of questions about technical and regulatory issues, and meetings like this are great opportunities to help them answer these questions.”
Participants agreed that research reactor decommissioning can begin more quickly if dry storage is in place. They also shared other lessons learned, such as the importance of projecting future spent fuel inventories and securing public acceptance before deciding on introducing a new storage method. And they said an Agency publication providing technical guidance on dry storage, such as the drying process and ageing management of storage systems, would be beneficial.
The IAEA’s Back End Research Reactor Integrated Decision Making Evaluation (BRIDE) tool could potentially be adapted for this purpose, participants concluded. Periodic safety, licensing and regulatory reviews in dry storage planning would help streamline the process and avoid unnecessary implementation delays, participants said.
