Predicting long-term performance of cement disposal systems for radionuclide-loaded zeolite and titanate ion exchangers

Lead Research Organisation: University of Sheffield
Department Name: Materials Science and Engineering

Abstract

One of the most important processes used to decontaminate nuclear waste streams, such as those resulting from cleanup operations at Fukushima, decommissioning at Sellafield, and other nuclear industry operations, is ion exchange. In this process, the radioactive contamination is removed from water by being bound onto (or into) a solid ion exchange material. Once the capacity of these ion exchange materials (which are used in the form of pellets of zeolites or titanates, in the cases of interest in this project) to take up radioactive contamination is filled ('becoming 'spent'), the pellets must somehow be converted into a solid form to ensure that they are stable for storage and final disposal. The cementation of ion exchangers into solid waste forms has been proposed and trialled in a number of locations, and using a variety of types of cements.

However, there is not yet a good fundamental understanding of how the ion exchangers and the cements will interact in the long term - and this is the core focus of the proposed project. This information is essential to developing a safety case for the use of cementation for the final treatment and disposal of ion exchange resins; we must be able to predict how the materials will behave in the long term, including knowledge of any possible release of radioactivity in the distant future, to enable this to be minimised or avoided. This project will generate the essential fundamental scientific insight related to the stability of ion exchange materials in cementitious environments, using both traditional and newly-developed bespoke cement types. We will characterise the cements and waste forms to an unprecedented level of precision using sorption, solubility and microstructural measurements. This fundamental knowledge will be used to generate a predictive model for the performance of the waste forms over the full timescale required for final disposal of nuclear wastes, tens to hundreds of thousands of years. This will also enable us to provide recommendations for which types of cements should be used, and in which way they should be applied, to give the best outcomes in keeping radioactive contamination away from the environment in the ultra-long term.

Planned Impact

The most important impact that will be gained from this project is the availability of a valid predictive model to support the safety case for long-term storage or disposal of conditioned wastes from the Fukushima Daiichi Nuclear Power Plant. The project team has the scope to communicate with leading Japanese government agencies, and report to them the advances made through our research, through the leading role of the Japanese side PI, Professor Sato, who has been involved in the Special Technical Committee at Radioactive Waste Management Funding and Research Center and the Expert Committee at International Research Institute for Nuclear Decommissioning (IRID). We will communicate our research outcomes, and their practical importance in a practical context, through direct interaction with key Japanese organisations such as the Nuclear Damage Compensation and Decommissioning Facilitation Corporation (NDF) and the recently-founded International Research Institute for Nuclear Decommissioning (IRID). These groups have, respectively, national and international focus, are supported by the Japanese government and industry, and are intimately involved in the Fukushima clean-up project. A central mission of NDF is to enable appropriate and progressive implementation of decommissioning through the provision of advice, guidance and recommendations to nuclear operators including those involved in decommissioning, and the current technological efforts in Japan for the restoration of Fukushima are being conducted in accordance with the 2015 NDF Road Map. The role of IRID is more technical, and they research and develop technologies for nuclear decommissioning, promote cooperation with international and domestic organizations on nuclear decommissioning, and develop human resources for research and development. These activities also link well to the broader aims of the proposed project, and will bring added impact.

The thermodynamic modelling of cemented wastes, in particular those containing zeolite ion exchangers which are used extensively in the UK, is also a key focus area of UK industry including the National Nuclear Laboratory. Ongoing work in the UK portfolio includes an NDA Bursary project (PI Provis) on thermodynamic modelling of cementitious wasteforms, co-supervised by National Nuclear Laboratory staff, and the proposed project will also make use of the methodologies and collaborations developed through those UK-funded interactions to bring national benefit on both sides of the partnership.

The position of this project within Phase 3 of the UK-Japan Civil Nuclear Research Programme enables direct impact generation through links to projects funded in previous phases. The most direct link will be to the Phase 2 project EP/N017684/1 (Development of solidification techniques with minimised water content for safe storage of secondary radioactive aqueous wastes in Fukushima), 2015-2018, which is led on the UK side by co-I Kinoshita of Sheffield, in partnership with Kyoto University and JAEA. That project is experimentally-focused, and will result in the development of novel phosphate cement matrices for solidification of aqueous radioactive wastes. This proposed project will connect directly to, and build impact from, the work conducted in EP/N017684/1 by providing validated thermodynamic data which will enable the ultra-long-term performance prediction of these novel cementing binders, among the other systems studied here. This connection will bring synergy between the projects, and will enable more extensive leverage of the funding invested in that project as well as the funds requested here.
 
Description We are developing new cement types, and proving that they can perform for very extended periods of time in service, to give excellent performance in the safe and long-lasting solidification treatment of wastes that have been generated during the clean-up of the Fukushima accident, in partnership with Japanese colleagues. Geopolymer cements (if designed appropriately) have been demonstrated to be highly effective in conditioning these wastes, which offers a new route to their safe disposal. We have also made fundamental advances in understanding the chemistry, nanostructure and geochemical interactions of geopolymer and related cement types, through the fundamental characterisation and modelling work conducted in the UK and Japan, and have gained new insight into transport processes in the cements used for waste immobilisation in both countries.
Exploitation Route Other national nuclear facilities and operations may also be interested to use the cements we are developing, as there are several facilities around the world with complex waste treatment needs that could be met by our materials.
Sectors Energy,Environment

 
Description Resulting from our joint project team symposium in Sapporo in February 2018, and a further event in November 2018 both UK and Japan-side participants have observed a strongly increased degree of interest from Japanese industry in the use of our proposed geopolymer technology for key applications in the safe treatment of wastes resulting from the Fukushima accident cleanup process. We are continuing to engage with industry representatives to build impact from these initial steps. The project team also met with the President of Hokkaido University and a Sheffield University Vice-President when a top-level Hokkaido team visited Sheffield in June 2018, with discussion of how to formalise the collaboration into something ongoing beyond the project term.
First Year Of Impact 2018
Sector Construction,Energy,Environment
Impact Types Economic,Policy & public services

 
Description Dissemination of findings to Fortum (titanate manufacturer)
Geographic Reach Asia 
Policy Influence Type Influenced training of practitioners or researchers
Impact Producer of titanate ion exchange material, which is one of the key focus points of this proposal, now has access to a safe and effective means of its cementation to prevent release of any contamination to the environment from spent exchanger media (if it were not treated appropriately e.g. by the new technique we have developed), and to condition it for final disposal in a GDF
 
Description Development of low-cement concretes
Amount £200,000 (GBP)
Organisation Sumitomo Corporation 
Start 12/2018 
End 12/2020
 
Description DuRSAAM
Amount € 3,397,847 (EUR)
Funding ID 813596 
Organisation European Commission H2020 
Sector Public
Country Belgium
Start 11/2018 
End 10/2022
 
Description NDA ICASE
Amount £113,200 (GBP)
Organisation Nuclear Decommissioning Authority NDA 
Sector Public
Country United Kingdom
Start 10/2018 
End 09/2022
 
Description Project team UK-JP Phase 3 
Organisation Hokkaido University
Country Japan 
Sector Academic/University 
PI Contribution We are the UK branch of this collaborative project; we are conducting thermodynamic and solubility analysis of the alkali aluminosilicate 'geopolymer' materials and other cements that are proposed as candidate cements for the immobilisation of Fukushima ion exchanger wastes, and contributing to their performance prediction.
Collaborator Contribution The Hokkaido University team is investigating leaching, sorption, tomographic analysis, and performance prediction of the candidate cements, interlinking closely with the Sheffield work.
Impact Collaborative outputs have been presented at conferences; journal papers have been submitted.
Start Year 2017
 
Description Hosting visitors from National Institute of Technology, Fukushima College 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Undergraduate students
Results and Impact The representatives from Fukushima College (3 undergraduate students and 2 academic staff) visited the Department of Materials Science and Engineering at The University of Sheffield, to see the research activities in the decommissioning of nuclear power plants and environmental recovery, currently undertaken at Sheffield. This was a part of the training of the next generation of engineers commissioned by the Nuclear Regulatory Agency in Japan.
Year(s) Of Engagement Activity 2018
URL https://www.sheffield.ac.uk/materials/news/fukushima0703-1.767398
 
Description Symposium, Hokkaido University, Feb 2018 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Industry/Business
Results and Impact Symposium on geopolymer cements and their use in the nuclear sector - attended by ~200 delegates, the majority from Japanese industry and government/policy organisations, and a large number of graduate students. Keynote lectures were presented by J Provis and T Sato (UK-side and Japan-side PIs, respectively), with further presentations from project team members from both sides.
Year(s) Of Engagement Activity 2018
 
Description Symposium, Hokkaido University, Nov 2018 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Research symposium targeting Japanese nuclear waste cementation practitioners & policymakers to disseminate findings on suitability of geopolymer cements for waste immobilisation. Project work was featured as the core of the day's activities.
Year(s) Of Engagement Activity 2018