Development of Reference Materials and Evaluation of Decay Data in Support of Characterisation of Naturally Occurring Radioactive Material

"A number of industries generate by-products containing naturally occurring radioactive material (NORM). Such materials must be characterised prior to re-use, for example, in building materials or for sentencing as waste. In the UK, industries producing NORM are subject to the Environmental Permitting Regulations 2018 (EPR 2018). As a result, such industries have a duty to accurately characterise the radioactivity content of NORM to determine if they are within regulation. The work in this thesis supports this in a variety of ways.Firstly, this work supports accurate radionuclide measurement by increasing the number of reference materials available for NORM industries, by processing and characterising blast furnace slag for the steel industry and pipeline scale for the oil and gas industry. A global comparison exercise was undertaken for the characterisation of the blast furnace slag, resulting in two peer-reviewed publications, and plans have been put in place for an International comparison exercise of the pipeline scale led by NPL along with other National Measurement Institutes. Reference materials are a key requirement for validating radioanalytical methods for accurate measurement and to demonstrate compliance, and the variety of matrices and principal radionuclides encountered in NORM mean that having industry-specific reference standards is vital.Secondly, a method for total dissolution of solid samples by lithium borate fusion has been improved by increasing the sample size that can be processed. This allows for various complex sample matrices, such as those encountered in nuclear decommissioning or NORM, to be entirely dissolved. Dissolution of increased sample sizes provides confidence that quantitative recovery of low activity levels from complex matrices is routinely achievable. This work, the outcomes of which have been peer-reviewed and published, supports the accurate characterisation of the significant NORM and nuclear decommissioning activities now and in the future, as well as in the development of reference materials that provide the underpinning metrology to such programmes.Thirdly, the measurement of decay data which underpins all radioactive analysis has been reviewed and enhanced. A method has been developed for atom counting of long-lived radionuclides using tandem inductively coupled plasma mass spectrometry for the first time. In some cases, decay data are outdated and/or significant uncertainties remain. Half-life measurements of long-lived naturally occurring radionuclides in need of updating have been identified and measurement techniques compared, a summary of which has been peer-reviewed and published. The novel application of tandem inductively coupled plasma mass spectrometry in this field, which can be combined with primary counting to give a half-life measurement, has been investigated in this work. Initially applied to 238U and combined with defined solid angle counting measurement, this method is applicable to a range of long-lived radionuclides such as 151Sm, 93Zr, 237Np and 129I with the benefit of online separation.In summary, this work has contributed to the field of radiochemistry by improving the accuracy of measurements of naturally occurring radionuclides. This can be applied to characterisation of naturally occurring radioactive materials and environmental monitoring and can also be extended to nuclear decommissioning.

Production and characterisation of reference materials in support of naturally occurring radioactive material (NORM) industries

Naturally occurring radioactive material is a problematic by-product of a range of industries and needs to be handled, stored, processed and disposed of in a safe and economic manner. Accurate characterisation of such material should be underpinned by measurement of certified reference materials in order to validate the methods employed and ensure quality control. This work highlights the current shortage of suitable reference materials and the approach being followed to address this issue, initially for the steel and oil and gas industries

Complete dissolution of solid matrices using automated borate fusion in support of nuclear decommissioning and production of reference materials

Accurate measurement of natural and anthropogenic radionuclide concentrations is of critical importance to end users in the nuclear sector to ensure correct classification prior to storage, recycling, reprocessing or disposal. Uncertainties in the characterisation of solid matrices and materials could lead to safety, quality and financial implications. Robust sample preparation methods are vital, in particular effective sample digestion, as under-estimated chemical yield recovery results in a corresponding under-estimation of activity levels. Borate fusion has been proven to effectively digest a range of complex sample matrices in the geosciences but is not used routinely elsewhere. In this study, we describe an automated procedure for borate fusion of multiple matrices encountered in nuclear decommissioning, containing diverse radionuclides over a range of activity concentrations. The impact of digestion flux, sample mass and sample to flux ratios are described, as well as the subsequent separation and measurement techniques. The results contribute to accurate and precise measurement of radionuclides in various matrices, as well as to characterisation of reference materials, providing greater confidence in nuclear industry programmes worldwide

Analysis of Tyre Tread for Metal Tracers with Applications in Environmental Monitoring

The purpose of this study was to identify a characteristic elemental tyre fingerprint that can be utilised in atmospheric source apportionment calculations. Currently zinc is widely used as a single element tracer to quantify tyre wear, however several authors have highlighted issues with this approach. To overcome this, tyre rubber tread was digested and has been analysed for 25 elements by ICP-MS to generate a multielement profile. Additionally, to estimate the percentage of the tyre made up of inert fillers, thermogravimetric analysis was performed on a subset. Comparisons were made between passenger car and heavy goods vehicle tyre composition, and a subset of tyres had both tread and sidewall sampled for further comparison. Finds showed 19 of the 25 elements were detected in the analysis. The mean mass fraction of zinc detected was 11.17 g/kg, consistent with previous estimates of 1% of the tyre mass. Aluminium, iron, and magnesium were found to be the next most abundant elements, and barium, magnesium and tin were all detected at higher concentrations than have been reported previously. The analysis found significant differences in elemental composition of goods vehicle and passenger car tyres, which could potentially allow for separate source profiles for each type. Only one source profile for tyre wear exists in both the US and EU air pollution species profile databases, highlighting the need for more recent data with better coverage of tyre makes and models. This study provides data on new tyres which are currently operating on-road in Europe and is therefore relevant for ongoing atmospheric studies assessing the levels of tyre wear particles in urban areas

Multi-element analysis of tyre rubber for metal tracers

The purpose of this study was to identify a characteristic elemental tyre fingerprint that can be utilised in atmospheric source apportionment calculations. Currently zinc is widely used as a single element tracer to quantify tyre wear, however several authors have highlighted issues with this approach. To overcome this, tyre rubber tread was digested and has been analysed for 25 elements by ICP-MS to generate a multielement profile. Additionally, to estimate the percentage of the tyre made up of inert fillers, thermogravimetric analysis was performed on a subset. Comparisons were made between passenger car and heavy goods vehicle tyre composition, and a subset of tyres had both tread and sidewall sampled for further comparison. 19 of the 25 elements were detected in the analysis. The mean mass fraction of zinc detected was 11.17 g/kg, consistent with previous estimates of 1% of the tyre mass. Aluminium, iron, and magnesium were found to be the next most abundant elements. Only one source profile for tyre wear exists in both the US and EU air pollution species profile databases, highlighting the need for more recent data with better coverage of tyre makes and models. This study provides data on new tyres which are currently operating on-road in Europe and is therefore relevant for ongoing atmospheric studies assessing the levels of tyre wear particles in urban areas

Multi-element analysis of tyre rubber for metal tracers

The purpose of this study was to identify a characteristic elemental tyre fingerprint that can be utilised in atmospheric source apportionment calculations. Currently zinc is widely used as a single element tracer to quantify tyre wear, however several authors have highlighted issues with this approach. To overcome this, tyre rubber tread was digested and has been analysed for 25 elements by ICP-MS to generate a multielement profile. Additionally, to estimate the percentage of the tyre made up of inert fillers, thermogravimetric analysis was performed on a subset. Comparisons were made between passenger car and heavy goods vehicle tyre composition, and a subset of tyres had both tread and sidewall sampled for further comparison. 19 of the 25 elements were detected in the analysis. The mean mass fraction of zinc detected was 11.17 g/kg, consistent with previous estimates of 1% of the tyre mass. Aluminium, iron, and magnesium were found to be the next most abundant elements. Only one source profile for tyre wear exists in both the US and EU air pollution species profile databases, highlighting the need for more recent data with better coverage of tyre makes and models. This study provides data on new tyres which are currently operating on-road in Europe and is therefore relevant for ongoing atmospheric studies assessing the levels of tyre wear particles in urban areas.NIH