Spent Fuel characterisation and evolution until disposal (SFC)

‘What’

This WP will develop and document an experimentally verified procedure to accurately determine the source term of irradiated spent fuels. It will also develop characterisation techniques that will allow us to more fully understand the physiochemical evolution of irradiated spent fuels (pellets and cladding) under normal and credible accident scenarios following reactor discharge (i.e. during interim storage (wet and dry), transport to and emplacement in a GDF). 

'Why'

Accurately determining the source term (see “…management of inventory data and uncertainty treatment”) and evolving condition (see “Improved understanding of the impacts of extended storage…”) of spent fuel is fundamental to safety assessment. This is reflected in the fact that both of these Roadmap theme 2 activities are shared high priorities. Parameters such as decay heat and nuclear reactivity (fissile content) need to be known to decide how much fuel can be safely loaded into a disposal container and how closely disposal containers can be emplaced at disposal. In the absence of accurate knowledge there is a risk that these parameters could be too conservatively estimated. Conservatisms would then percolate through container loadings and facility layouts, potentially resulting in substantially more containers than necessary, more transport operations and ultimately a larger facility footprint. This scenario has safety and cost ramifications. Conversely, the alternative is also possible (i.e. optimistic parameters are estimated), which could then be detrimental to safety, i.e. inadvertently breach a thermal or criticality safety limit.
WMOs are particularly interested in the possibility of an NDA technique that could allow swift and accurate corroboration of spent fuel records, prior to fuel containerisation (i.e. potential waste acceptance criteria (WAC), such as a fuel burn-up measurement or a thermal limit acceptance check). WAC is a key thematic area under theme 2of the EURAD Roadmap and is typically of most interest to more advanced stage programmes (Phase 2 onwards). 
This has potential to effectively integrate with the parallel HITEC RD&D WP (i.e. scrutinise actual thermal output and also the validity of currently applied thermal limits).
 

Major highlights (June - Nov 2022)

- In Task 2, work has focused on two papers that are/has been in preparation summarizing the main activities in progress and the experimental work in Task 2.3.
- In Task 3, three-point bending tests with a newly developed device were performed with fresh and pre-hydrided samples, with and without ceramic inserts, simulating fuel pellets at room temperature, 135 and 300 °C.
- In Task 4, CIEMAT has selected two SNF dry casks (PWR and BWR) for its criticality analysis during normal, abnormal, and accidental conditions. These analyses have been carried out with spent and fresh fuel for a series of selected scenarios, so the codes MCNP6 and EVOLCODE have been used for the activities.
 

Forward look

- In Task 2 there will be a workshop in May 2023 at KIT, after the finalisation of the summary report - a paper that is close to be published in EPJN.
- In Task 3, an analysis of failure mechanisms in ring compression and three-point bending tests as a function of zirconium hydride morphology and temperature is planned.
- In Task 4, the contribution to deliverable 8.13 will be submitted soon, the drafts are under internal review at CIEMAT.