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CAST Report Summary

Project ID: 604779
Country: United Kingdom

Periodic Report Summary 2 - CAST (CAST (CArbon-14 Source Term))

Project Context and Objectives:
Carbon-14 (14C, half-life 5,730 years) is a radionuclide of importance to safety assessments. The CAST project (CArbon-14 Source Term) develops understanding of the release of 14C from radioactive wastes under conditions relevant to geological disposal.

The main objectives of CAST are:
a) To gain scientific understanding of the rate of release of 14C from the corrosion of irradiated steels and Zircaloys and from the leaching of ion-exchange resins and irradiated graphites under geological disposal conditions, its speciation and how these relate to 14C inventory and aqueous conditions;
b) evaluate this understanding in the context of national safety assessments; and
c) disseminate this understanding and its relevance to safety assessments to a range of interested stakeholders and provide an opportunity for training of early career researchers.

These objectives are met through seven Work Packages:
• WP1 – Coordination (led by RWM, UK)
• WP2 – Steels (led by Nagra, Switzerland)
• WP3 – Zircaloy (led by Andra, France)
• WP4 – Ion-Exchange Resins (led by CEA, France)
• WP5 – Graphite (led by RWM, UK)
• WP6 – Relevance to Safety Cases (led by Ondraf/Niras, Belgium)
• WP7 – Dissemination (led by Covra, Netherlands)

WP1 - Coordination
The main objectives for WP1 Management are to:
• manage and coordinate the project;
• advise and support the work package leaders;
• assist WP7 with the CAST website;
• collect and compile project management information;
• distribute EC financial contributions;
• provide quality assurance and control of project results.

WP2 - Steels
The main objectives for WP2 Steels are to:
• develop analytical techniques to identify and quantify 14C species formed during corrosion of irradiated steels;
• validate activation models by measuring 14C inventories in irradiated steel;
• carry out experiments and modelling to further understand speciation and rate of 14C release from corrosion of irradiated steels under conditions relevant to deep geological repositories.

WP3 - Zircaloy
The objective of WP3 is to obtain a better understanding of 14C behaviour in waste Zr fuel claddings under disposal conditions by:
• assessing 14C inventories in zirconium alloy metals and oxides;
• characterising 14C release from Zr corrosion and Zr oxide dissolution;
• determining 14C speciation under simulated disposal conditions.

WP4 – Ion Exchange Resins
The aim of WP4 is to obtain a better understanding of the 14C source term from spent ion-exchange resins (SIERs) of different origins (BWR or PWR) and release and chemical species under disposal conditions by:
• reviewing the current status of understanding;
• characterising the 14C inventory and its speciation;
• undertaking experiments to measure 14C release to gas and solution.

WP5 - Graphite
The objective of this work package is to understand the factors determining release of 14C from
irradiated graphite (i-graphite) under geological disposal conditions by:
• determining the 14C inventory and concentration distribution in i-graphites and factors that may control these;
• measuring the rate and speciation of 14C release to solution and gas from i-graphites in contact with aqueous solutions;
• determining the impact of selected waste treatment options on 14C release and relating this to the nature of 14C in i-graphite.

WP6 – Relevance to Safety Cases
WP6 integrates results with the aim of:
• combining the results of WP 2 to 5 to deliver sound scientific basis and safety relevant information;
• considering the results in the context of safety cases;
• identifying commonalities and differences between national programmes;
• providing conclusions and recommendations over possible future studies.

WP7 – Dissemination
The objective of WP7 is to disseminate information about CAST and its results to target groups. This is provided via a public project website and newsletters and scientific publications. Two training courses will be held to train early career researchers and two workshops to engage key stakeholders.

Project Results:

WP1 – Coordination
Four General Assembly Meetings have been held: London, 2013; Brussels, 2014; Bucharest, 2015; and Lucerne (October 2016).

WP2 – Steels
The corrosion rates and speciation of 14C release from irradiated steels has been reviewed.

Analytical methods for speciation of 14C in aqueous and gaseous samples at extremely low concentrations and a methodology to remove radionuclides other than 14C from solution have been developed. Compound-specific 14C accelerator mass spectrometry (AMS) has been applied to detect 14C-acetate and formate in solution at low concentrations.

Leaching studies on irradiated stainless steels and carbon steel and acidic dissolution of irradiated stainless steel are underway. Early results have shown 14C release to solution and gas.

The corrosion rates of unirradiated stainless steel in sodium hydroxide solution at pH12.5 and in deionised water are less than 1 nm y-1. Hydrocarbons and oxygen–containing organic compounds have been detected from the anoxic alkaline corrosion of unirradiated iron powders.

WP3 -Zircaloy
A review of the current status of knowledge on 14C release from Zircaloy has been published.

The development of analytical methodology for measuring 14C speciation from Zircaloy is complete. Liquid scintillation counting is too insensitive to measure speciation and the use of AMS is foreseen.

Measurement of 14C in irradiated Zircaloy-4 cladding by acid dissolution agrees with calculation. Almost all the 14C is released to gas as hydrocarbons/organic compounds.

Leaching studies of irradiated Zircaloy-2, -4 and M5 are underway. Early results for the Zircaloy-M5 have found inorganic and organic 14C in solution. Analyses of gas and solution from leaching of irradiated Zircaloy-2 found low concentrations of 14C in gas and in solution.

WP4 – Ion-exchange resins

The current status of knowledge of 14C in spent ion-exchange resins (SIERs) was reviewed.

Measurements of total 14C by combustion under oxygen have been compared to measurements of inorganic and organic 14C by acidification and wet oxidation. For one PWR SIER sample the results for total 14C were in close agreement. A similar analytical approach is being applied to spent BWR ion exchange resins.

Some release of 14C from spent ion exchange resins in sodium hydroxide solution or synthetic groundwater has been measured. No 14C leached into solution from laboratory samples of resin loaded with 14C- carbonate and immobilised in cement.

WP5 - Graphite

The current understanding of the inventory and release of 14C from irradiated graphite has been reviewed.

The behaviour of 14C during reactor operation is simulated by examining the effect of irradiation and high temperature on 13C implanted in unirradiated graphite. Implanted 13C is not released from the graphite matrix.

Leaching of irradiated graphite from the thermal column of the TRIGA reactor, from the Rossendorf research reactor and from Vandellós I NPP (for comparison with leaching of impermeable graphite matrix) is underway. The 14C inventory of irradiated graphite from the thermal column of the VVR-S reactor has been characterised.

Exfoliation of irradiated graphite in polar organic solvents has been applied to samples from the Latina NPP but 14C removal efficiencies are relatively low.

WP6 – Relevance to safety cases

WP6 has published an overview of the current treatment of 14C in safety assessments of geological disposal.

Two WP6 technical meetings have been held. The first discussed knowledge supporting safety assessment hypotheses and different concepts. The second meeting in March 2016 focused on sensitivity and uncertainty analysis.

WP7 - Dissemination
Covra manage the CAST public website. There have been 9635 individual visitors to the site. The first CAST training course was held in July 2016 and the first CAST workshop in October 2016. A CAST overview was given at the Nuclear 2015 conference (Carbon-14 Source Term in Geological Disposal: The EC Project CAST, J Nucl Res Dev 10, 8-12, 2015).

Potential Impact:
The results from CAST will be captured in an overall synthesis report summarising the results and achievements of the whole project. WPs 2 to 5 will each produce a final work package synthesis report for public dissemination describing: a) the key results from the work package; b) the relevance of the scientific issues addressed for the repository concepts of the countries involved; c) how the results improve the understanding of the evolution of the repository concepts and wastes; and d) the implications for data input in PA calculations and for safety case arguments for the concepts considered (with WP6). Items b) to d) will be provided as Annexes in the final work package synthesis reports. WP6 will deliver a final report for public dissemination.

The results are expected to fill gaps in the understanding of, and data for, the release of 14C from irradiated steels, irradiated Zircaloys, spent ion exchange resins and irradiated graphites under geological disposal conditions. They may underpin existing assumptions used in performance assessments, demonstrate that some of these assumptions are overly cautious, or that some need revision. The state of the art reviews for CAST have highlighted the general lack of data for the release of 14C and the results from CAST will allow a more quantitative treatment.

CAST will ensure robust and efficient cross-fertilisation of knowledge, understanding, information and experience amongst many countries and organisations, both within and outside Europe. It will allow opportunities for international progress on the integral issue of 14C generation to be reflected in national programmes, and for the partners’ progress to be highlighted internationally. CAST will provide invaluable experimental data that can then be applied by the national WMOs to their programmes. In addition CAST will put these experimental results into the context of national safety assessments.

WP 2, 3 and 4 will have similar impact in providing significant data and understanding on 14C generation from steels, Zircaloys and ion-exchange resins respectively. WP 5 will consolidate and further the current understanding of 14C release from irradiated graphite. WP 6 will have perhaps the largest and most significant impact for the end users of the data as, drawing on the results from WPs 2 to 5, it will lead to a greater understanding for WMOs of the impact of 14C in safety assessments for disposal facilities. WP7 has been established with a specific dissemination objective and significant effort is being made to disseminate the project results most effectively and widely. This will include presentations at international conferences and other meetings, publication in journals and conference proceedings, and through two workshops to be held over the duration of CAST. The first workshop outlined the initial findings from CAST, and allow interested parties to familiarise themselves with the proposed research, and to ask questions of WP representatives. The second workshop will present the overall results and findings of CAST and discuss these with the target groups.

Training is a key aspect of CAST by the engagement of PhD students, post-doctoral scientists and the ongoing development of existing staff. Two training courses will be provided for junior participants. The first provided experience in radioanalytical techniques and sample handling; the second will provide understanding of 14C generation and wastes, and experience in transport modelling. It is also be possible for early–career researchers to exchange with other partners.

List of Websites:

Reported by

United Kingdom


Nuclear Fission
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