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NORA: Non-Radioactive Waste Solidification Methods and Stability Assessment - WR0603

Treatment methods that effectively but economically prevent the release of non-destructible hazardous wastes into the environment are in increasing demand. Such technologies are referred to as either ‘solidification’ or ‘stabilisation’. Solidification refers to treatments that encapsulate a granular or sludge-like waste within a solid ‘matrix’ to form a single solid element known as a ‘wasteform’. Stabilisation involves a chemical reaction that renders the hazardous components of the waste less mobile. For many matrices, both solidification and stabilisation are achieved simultaneously. The wasteform can then be safely disposed of in long-term landfill.

Pioneered by the nuclear industry, a wide range of radioactive waste disposal methods, technologies and matrix materials for solidification and stabilisation of wastes have been developed. The effectiveness of the containment method is assessed by leaching tests. Techniques such as the Dutch NEN 7375 tank diffusion test have been adopted in the UK to characterise wasteforms in terms of the release of chemical species of environmental concern, to ensure that wasteforms satisfy acceptance and compliance criteria set by the Environment Agency.

However, at present, the issue of possible long-term physical deterioration of wasteforms is not covered by these criteria. Since physical stability will play a major role in ensuring long-term containment of hazardous constituents, there is a strong argument for including a means of characterising wasteforms to predict performance in this regard.

This project will review the predictive models, identify the most appropriate in terms of performance, and develop, validate and refine a procedure for characterising wasteforms for the prediction of long term physical stability. Validation and refinement will be carried out by conducting a series of leach tests on simulated wasteforms in parallel with characterisation of changes in physical integrity. These wasteforms will consist of either one of three types of simulated waste whose composition presents potential problems during solidification / stabilisation, encapsulated in matrices consisting either of a combination of cementitious materials, a thermoplastic material, or glass.

The outputs of the research will provide additional assurance during selection, implementation and performance assessment for solidification and stabilisation of a particular waste stream, whilst ensuring efficient use of matrix materials. Guidance documents will also be produced.

The overall aim of the proposed Project is to devise an effective method for characterising monolithic wasteforms derived from solidification / stabilisation treatments to establish their appropriateness in terms of long-term physical stability, thus enhancing the confidence with which such treatments can be employed.

The specific objectives are:

1. Conduct a review of international best practice and identify and analyse models of leaching and deterioration of wasteforms containing radioactive and non-radioactive wastes.

2. Evaluate the suitability of using existing models to predict long-term performance of non radioactive wasteforms, utilising results from the NEN 7375 tank test [1].

3. Develop a protocol for characterising wasteforms for predicting long-term performance in terms of physical stability.

4. Validate and refine the protocol by applying quantitative measures of goodness-of-fit to results of NEN 7375 tank tests and compressive strength measurements conducted on wasteforms containing synthetic wastes with compositions typical of UK major representatives of non-radioactive wastes suitable for solidification/stabilisation.

5. Develop guidance on carrying out characterisation and compliance testing to determine the physical stability of a given waste / matrix combination.
Project Documents
• Final Report : Non-radioactive waste solidification methods and stability assessment   (379k)
• Technical Report : Non-radioactive waste solidification methods andstability assessment   (2240k)
Time-Scale and Cost
From: 2006

To: 2008

Cost: £89,033
Contractor / Funded Organisations
University - Dundee
Environment and Health              
Environmental Protection              
Hazardous Waste              
Indicators and benchmarking              
Managing residual waste in landfill              
Waste Management              
Fields of Study
Waste Management