• nuclear waste
• dry storage
• melcor

The management of highly radioactive spent nuclear fuel (SNF) has always been a key topic in nuclear field. It is not possible to talk about the future of nuclear energy without dealing with the back-end of the nuclear fuel cycle. Dry storage, as an alternative to wet storage, has been proposed as an interim step before permanent deep underground disposal.

In this master thesis work, concrete dry casks have been studied in order to have a deep understanding of how the system works and the challenges it is supposed to face. In this perspective, the main objective of this work was to assess the MELCOR capability to predict the performance of a concrete dry cask under steady conditions.
Since no MELCOR application on dry cask systems has been found on literature, the first challenge in the creation of the input desk was making approximations and hypotheses that allowed to maintain the real cask characteristics. Parametric and sensitivity analyses have been useful to refine the initial input deck and to reach the final one. This last model has showed results that can be considered consistent with the real behavior of the cask.
In addition, MELCOR results have been compared with those derived from a FLUENT calculation, previously set by the Unit of Nuclear Safety Research of CIEMAT. The comparison has revealed that MELCOR is able to simulate the general performance of the dry cask and to reasonably estimate the peak cladding temperature, that is the one under regulatory surveillance.

In order to test MELCOR capabilities even more, calculations have been carried out trying to analyze another typology of dry storage: the vault system. A conceptual model of the Spanish Centralized Temporary Storage (CTS) was created and implemented on MELCOR, in the attempt of conducting both thermal and retention analyses on a scaled model. The obtained results have indicated that the code has the ability to capture the behavior of the system, even in accidental conditions.
It is, however, necessary to underline that, even if the results are consistent with what expected, they are not completely representative of the real vault system, being them affected by the scaling process.