Integration Group for the Safety Case (IGSC): Scientific Basis

    The Scientific Basis activities of the Integration Group for the Safety Case (IGSC) examine important scientific and technical issues for the development and integration of safety cases. Activities in this field are designed to address the question: "What do we know?"

    Sorption project phase III report: Guideline on thermodynamic sorption modelling

    Radionuclide (RN) sorption is one of the most important processes with regard to the prevention or retardation of RN migration to the biosphere. Sorption is generally characterised by equilibrium distribution coefficients (Kd). Nearly all waste management organisations use Kd in their PA calculations, and there is a general desire by these organisations to have scientifically robust arguments for showing selected Kd values and associated uncertainty management are based on a demonstrable and credible knowledge base.

    The first workshop on this topic was organised in Oxford in May 1997 and included researchers, both modellers and experimentalists, investigating performance assessment and sorption. In parallel with this activity, a comprehensive status report was commissioned to summarise the current knowledge in the field of sorption modelling.

    The Sorption Project, Phase II, was a "benchmarking" exercise to interpret selected well-characterised datasets for sorption onto complex materials of interest to safety assessments of radioactive waste disposal systems using several different modelling approaches in use at various organisations.

    The third phase of the project was launched in November 2007 to address the needs identified during Phase II. A report with information on thermodynamic sorption models (TSM) applications for systems relevant to radioactive waste disposal concepts has been published in 2012. To this end, a workshop to present and discuss the draft guidance document will be held.

    Publications and Reports

    • Status report on sorption modeling
    • NEA Sorption Project Phase II
    • Thermodynamic Sorption Modelling in Support of Radioactive Waste Disposal Safety Cases

    Cementitous material

    The disposal of long-lived radioactive wastes requires the evolution and interactions of cementitious materials with other repository components, host rocks and ground water to be well understood. In 2009, the NEA IGSC organized a workshop to assess current understanding on the use of cementitious materials in radioactive waste disposal. The workshop was designed to consider issues relevant to the post-closure safety of radioactive waste disposal, but also to address some related operational issues such as cementitious barrier emplacement. Proceedings of the workshop are published in a report

    Publications and Reports

    • Cementitous Materials in Safety Cases for Geological Repositories for Radioactive Waste: Role, Evolution and Interactions (2012)

    Gas migration

    In a geological repository, both radioactive and non-radioactive gases can be produced from processes such as metal corrosion, radiolysis of water, radioactive decay and degradation of waste. Gas production and migration through the geosphere may affect the performance of the repository, in particular the engineered barriers and excavated disturbed zone in the host rock, by creating pathways for groundwater and gas flows. Understanding the gas evolution processes as well as gas migration is important in the assessing the safety and performance of a repository. To better understand the various aspects of gas evolution and gas transport through the geosphere, a Topical Session was organized at the 2011 IGSC Annual Meeting (IGSC-13). The Topical Session discussed the impact of gases on (i) the integrity of the host rock and engineered barriers, solute transport; and (iii) the release and migration of volatile radionuclides in three major host rock formations (i.e. clay, granite and rock salt).

    The IGSC will also participate in the EC FORGE (Fate of Repository Gases) Symposium in 2013. For more information of the symposium, visit the FORGE web site.

    Salt Club

    Rock salt is a candidate rock to host a repository for high-level radioactive waste (HLW) because of its favourable characteristics. Specifically, rock salt provides isolation of the waste from groundwater due to its low hydraulic conductivity. Visit the Salt Club web page for more information.

    The most important positive attributes of rock salt for use as a repository host rock are:

    • Extremely low permeability/hydraulic conductivity that isolates the waste from any near surface groundwaters;
    • Dry environment;
    • Thermal conductivity;
    • Viscoplastic behaviour that increases with temperature and pressure, which closes all void spaces;
    • Predictable geology.

    To further develop a repository in rock salt, a working group, comprised of scientists and experts in developing disposal in geological rock salt formations, has been formed in 2011.

    Clay Club

    The Clay Club examines those various argillaceous rocks that are being considered for the deep disposal of radioactive waste, ranging from soft clays to indurated shales. These rocks exhibit a wide spectrum of characteristics which make them useful as barriers to the movement of water and solutes and as repository construction materials. Studies include clay media characterisation and modelling.

    For more information, click on:

    Publications and Reports

    Uncertainty/Sensitivity Analysis

    In conducting a safety assessment, assessment results are often associated with uncertainties. Mathematical methods to quantitatively assess the influence of uncertainties on the calculated results have been developed. Understanding of the advantages and drawbacks of specific methods has also increased considerably in recent years. Many national radioactive waste management programmes have also used other probabilistic or statistical methods to gain further insight into the effect of uncertainty on system performance. The Topical Session at the IGSC 2012 Annual Meeting will further explore how uncertainties shall be handled.

    Geosphere stability

    In order to provide assurance of the long-term safety of an underground repository, it is necessary to argue persuasively that the long-term containment capability of the geosphere and underground environment are stable and able to provide a firm buffer against natural pertubations. To this end, an international forum on Clays in natural and engineered barriers for radioactive waste confinement was held in 2005, co-sponsored by the NEA. A workshop on Stability and Buffering Capacity of the Geosphere for Long-Term Isolation of Radioactive Waste: Application to Argillaceous Media took place on 9-11 December 2003 in Braunshweig, Germany. A workshop on the Management of Uncertainty in Safety Cases and the Role of Risk took place on 2-4 February 2004 in Stockholm, Sweden. A workshop on crystalline (strong, fractured) rocks was held on 13-15 November 2007 in Manchester, UK.

    Publications and Reports

    Using Natural and Engineered Clay-based Barriers for the Containment of Radioactive Waste 
    Tours, 14-18 March 2005
    Stability and Buffering Capacity of the Geosphere for Long-Term Isolation of Radioactive Waste: Application to Argillaceous Media
    Proceedings of a Workshop held in Braunshweig, Germany on 9-11 December 2003
    Management of Uncertainty in Safety Cases and the Role of Risk
    Proceedings of a Workshop held in Stockholm, Sweden on 2-4 February 2004
    Gas Generation and Migration in Radioactive Waste Disposal : Safety-relevant Issues
    Workshop Proceedings, Reims, France, 26-28 June 2000

    Thermodynamic data base

    The Thermochemical Data Base (TDB) project, under the guidance of the NEA Data Bank, aims to make available a comprehensive, internally consistent, internationally recognised and quality-assured chemical thermodynamic database. A new phase of the project is now under way to develop a guidance document on the application of sorption models in safety assessments for the deep disposal of radioactive waste. For more information, visit the TDB Project web site.


    This technical activity addressed the scientific basis for the modelling of radionuclide transport in actual geologic media and was organised as a series of five workshops. The last in the series, GEOTRAP 5, took place on 7-9 June 2001. A synthesis of all GEOTRAP workshops held to date is also available.

    Publications and Reports

    The Role of Biosphere

    A Topical Session on the “Role of the Biosphere in a Safety Case” was organized in October 2001, in Paris. The Topical Session focused on the recent scientific developments in international programmes such as the IAEA BIOMASS, EC BIOCLIM, the views of regulators and the strategies used by implementers in incorporating the biosphere in the safety assessments. A synthesis report based on the proceedings of the Topical Session has been published.

    Publications and Reports

    Last reviewed: 26 June 2013