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DISCO: Modern Spent Fuel Dissolution and Chemistry in Failed Containers

DISCO aims to fill the gap of knowledge on spent fuel dissolution arising from the development and use of novel types of fuel (Cr-doped and MOX). The project aims to enhance understanding of spent fuel matrix dissolution under conditions representative of failed containers in reducing repository environments and to assess whether novel types of fuel behave like the conventional ones.

Overview

Project Dates: 1/06/2017 – 31/05/2021

Project Status: Ongoing

Project Website: www.disco-h2020.eu

The development of robust safety cases for geological disposal of spent nuclear fuel requires a solid understanding of its dissolution over very long timescales (up to a million years).  The spent fuel dissolution is the main source term for the release of radionuclides under repository conditions, and it will control the release of radioactivity in the environment surrounding the engineered barriers (the near field) of a disposal facility once the engineered barrier system has degraded and groundwater comes into contact with the spent fuel.

The DISCO project represents a logical follow-up of earlier Euratom projects (such as SFS, NF-PRO, MICADO, REDUPP and FIRST-Nuclides) which focused on dissolution and radionuclide release from conventional UO2 spent fuels.  In this sense, this project aims to fill the gap of knowledge on spent fuel dissolution arising from the development and use of novel types of fuel (Cr-doped and MOX).

Specific objectives of DISCO can be summarised as follows:

  • to enhance our understanding of spent fuel matrix dissolution under conditions representative of failed containers in reducing repository environments; and
  • to assess whether novel types of fuel (MOX, doped) behave like the conventional ones.

The expected gain in knowledge is essential for waste management organisations, but is also of interest for a wider range of potential users (e.g. research organisations).  Therefore, the project also aims to disseminate the new knowledge through different channels in order to reach a wider community.

DISCO is a collaborative project funded by the European Commission under the Horizon 2020 Research and Training Programme.  The project is implemented by a consortium with 16 beneficiaries.  The consortium will be advised by an End User Group (EUG), consisting of waste management organisations in seven countries (Belgium, Finland, France, Spain, Sweden, Switzerland, and the UK) as well as regulatory authorities in five countries (Belgium, Germany, Spain, Sweden, and Switzerland).

Objective

While the scientific understanding of the dissolution of standard spent uranium oxide fuel has reached a certain mature state, new types of fuels with additives (“doped fuels”) have been developed.  These fuels are already in use in some reactors and their use is foreseen to be expanded.  Dissolution data is now required to confirm that the dissolution behaviour of such fuels in a geological repository environment is similar to that of standard fuel.  Similarly, there is a dearth of dissolution data from mixed oxide (MOX) fuels, which are also currently in use in several reactors.  Therefore, this project is targeting oxide fuels containing additives, including Cr, Gd and Pu, in order to ensure that relevant characteristics are understood to a level commensurate with standard fuels.  This project aims to expand the database on spent fuel dissolution with results from dissolution studies performed in truly reducing conditions, with hydrogen present.  The effects of dopants will be investigated through experiments using both spent nuclear fuel and synthetic materials specifically designed for the project.  In addition, chemical modelling will be employed to improve the understanding and description of the dissolution process relevant to the expected chemical conditions inside a failed waste container in a deep geological repository environment.