Release of safety relevant radionuclides from spent nuclear fuel under deep disposal conditions (SAREC)

Objectives

Improved quantification and mechanistic understanding of the release of safety relevant radionuclides covering most representative types of spent nuclear fuel (SNF) and of the fuel evolution both prior and posterior to contact with ground water to better predict the radionuclide source term for post-closure safety assessment.

Major highlights (March 2025 - March 2026)

• The Work Package is on-going and all tasks are in full stride: The experimental tasks (Task 3,4,5) have all initiated their laboratory work. The modelling task (Task 6) have had an online workshop to discuss and define input parameters, and modelling work has been initiated.  With regards to knowledge management (Task 2), the structure for the data base for spent fuel leaching data is already set up. 
• In October we met in Madrid for the first Annual meeting - se summary below. Most partners were there in person, as well as End Users, and it was concluded it was good to meet in person and to enjoy the social interactions. We are grateful to CIEMAT for hosting us! 
• There have been fruitful interactions with Work Packages DITUSC and CSFD, resulting in input to 2^nd wave proposal from DITUSC and information exchange regarding spent fuel leaching with CSFD. 

Forward look

• In April 2026, Task 2 leader Olga Riba together with colleagues from Amphos 21 are arranging a training event in Barcelona, Spain. This training concerns modelling using iCP: Interface Comsol-PhreeqC. 
• In May, an online workshop is planned with the focus on establishing connections and conveying needs between the different experimental tasks and the modelling task. 
• Planning is ongoing for the 2^nd Annual WP Meeting or the week 19-23 October, and it will be held in conjunction with the 33^rd Spent Fuel Workshop. More details will come soon! 

Description of the WP

The aim of this WP is to close knowledge gaps outlined in for example the EURAD State of Knowledge Report Spent Nuclear Fuel Domain 3.1.1 (K. Spahiu 2021) and the WP is built on the experiences gained in the FIRST Nuclides and DisCo projects.

The aim is to provide data that allows re-evaluation of the current approaches to release of safety relevant radionuclides in post closure safety assessments. This will clarify what approaches are overly pessimistic and what approaches need to be adjusted to better represent expected radionuclide release in the repository environment.

In order to do this an improved mechanistic understanding is required, as well as quantification of the radionuclide source term for different fuel types. Carefully designed experiments with advanced experimental set-ups and improved analytical methods for activation- and fission products will increase the system understanding and give confidence in the proposed release values and models.

The studies shall be focused on representative fuel, operated at representative reactor conditions, relevant for WMOs at a European level. 

Efforts shall be made to adapt the experimental protocols to allow for comparison between studies performed at different laboratories whilst still utilizing the strengths at the individual laboratories. 

For Knowledge Management there is a need to synthesize information from past projects.

Outcomes

• Implementing Safety: Radionuclide release data that allows the needed re-evaluation of the current approaches to release of safety relevant radionuclides in post closure safety assessments. 
• Scientific Insight: Data for deriving an updated and improved mechanistic understanding of radionuclide release processes.
• Knowledge management: Completion of SNF dissolution database, thus enhancing knowledge management and transfer between the participating organisations (and beyond).