- Email: [email protected]
Radionuclide metrology research for nuclear site decommissioning
Radiation Physics and Chemistry xxx (xxxx) xxx–xxx
Contents lists available at ScienceDirect
Radiation Physics and Chemistry journal homepage: www.elsevier.com/locate/radphyschem
Radionuclide metrology research for nuclear site decommissioning ⁎
S.M. Judgea,b, , P.H. Regana,b a b
National Physical Laboratory, Hampton Road, Teddington, Middlesex TW11 0LW United Kingdom University of Surrey, Guildford, Surrey GU2 7XH, United Kingdom
A R T I C L E I N F O
A BS T RAC T
Keywords: Radioactivity Metrology Nuclear decommissioning
The safe and cost-effective decommissioning of legacy nuclear sites relies on accurate measurement of the radioactivity content of the waste materials, so that the waste can be assigned to the most appropriate disposal route. Such measurements are a new challenge for the science of radionuclide metrology which was established largely to support routine measurements on operating nuclear sites and other applications such as nuclear medicine. In this paper, we provide a brief summary of the international measurement system that is established to enable nuclear site operators to demonstrate that measurements are accurate, independent and fit for purpose, and highlight some of the projects that are underway to adapt the measurement system to meet the changing demands from the industry.
1. Introduction The first generation nuclear power plants and reprocessing facilities are coming to the end of their working lives. The average age of a nuclear power plant in Europe is 29 years and the approved operating life is 30–50 years, depending on the design. There are currently 91 power plants already shut down and being decommissioned in the EU; the majority of the remaining 129 reactors plus fuel cycle facilities will also be in decommissioning by 2030 (European Commission, 2016; NEA OECD, 2014). The aim of the decommissioning process is to clear the site so that it can be used for other purposes, while minimising the risk to the public, the environment and the workforce from the process and the waste arising. All of the nuclear sites contain large quantities of hazardous materials such as spent nuclear fuel and contaminated plant and buildings (for example, the Sellafield fuel reprocessing site in the UK has 2 million m3 of concrete, 2200 buildings and 170 large plants to decommission, plus 10 million m3 of contaminated soil); the cost of decommissioning and waste management in the EU is estimated to be in excess of 150 billion Euro. The long term radiation dose from the waste to members of the public has to be controlled to minimise the risk to health. In practice, this means measuring the specific activity concentrations (determined in Bq/g) of materials, and then choosing the best disposal route for that particular material. The ‘out of scope’ limit (ie, the quantity that is deemed as ‘not radioactive’) depends on the radionuclide (DEFRA, 2011) - the limits are determined based on models of the impact on health. These limits are close to the minimum detectable activity ⁎
(MDA) and measurements at this level challenge the sensitivity and accuracy of existing measurement techniques. This problem is exacerbated as nuclear sites have been operating for many decades, so the disposition and level of radioactivity are not well known. As inaccuracies in measurements could result in unsafe disposal with serious long term environmental effects, nuclear site operators are routinely conservative and select waste disposal options that are costly but have little environmental benefit. To date, only 13 nuclear power plants have been completely decommissioned worldwide and therefore technical experience in the measurement of radioactivity for decommissioning is somewhat limited. Regulatory bodies, site owners or operators and international organisations have carried out detailed studies of the needs (Emptage et al., 2016; NEA OECD, 2014). The common themes that have been raised are: (1) improvements in capability (technology, measurement methods and sampling strategies), (2) harmonisation and quality assurance, and (3) sharing knowledge. Although accurate measurement for decommissioning legacy nuclear sites may seem to be an intractable problem, this particular research field can build on the existing international measurement system to ensure that measurements are accurate, harmonised and scientifically rigorous. Such work can also take advantage of national and international research projects that seek to develop new capability. 2. The international measurement system The International Measurement System is the technical and administrative infrastructure that aims to ensure that measurements
Corresponding author. E-mail address: [email protected] (S.M. Judge).
http://dx.doi.org/10.1016/j.radphyschem.2017.02.027 Received 26 October 2016; Received in revised form 8 February 2017; Accepted 10 February 2017 0969-806X/ Crown Copyright © 2017 Published by Elsevier Ltd. All rights reserved.
Please cite this article as: Judge, S.M., Radiation Physics and Chemistry (2017), http://dx.doi.org/10.1016/j.radphyschem.2017.02.027
Radiation Physics and Chemistry xxx (xxxx) xxx–xxx
S.M. Judge, P.H. Regan
of any physical quantity are accurate, consistent and fit-for-purpose worldwide. In principle, the system is very simple: all measurements are ratios of the fundamental or ‘primary’ standards, and this has to be demonstrated by a documented chain of calibrations back to the primary standard, ie, all measurements of any physical quantity should be traceable to a primary standard. To be traceable, the chain must be unbroken and measurement uncertainties must be calculated at each stage in order to demonstrate that the final measurement is fit for purpose. The primary standards themselves are developed and maintained by National Measurement Institutes (NMIs) such as NPL in the UK, NIST in the USA and PTB in Germany. The NMIs check the accuracy of the primary standards by comparing the primary standards against those held at other NMIs; any discrepancies are investigated and corrective actions are taken. This international measurement system is overseen by the Bureau International des Poids and Mesures (BIPM) in Paris. Under the auspices of the BIPM, NMIs have signed a Mutual Recognition Arrangement (MRA) which requires NMIs to participate in the comparison exercises and to publish their capabilities (further details are given on www.bipm.org). The international measurement system for radioactivity dates back to just after the discovery of radioactivity in 1896 by Henri Becquerel (further details of the historical background are given in Judge et al., 2014 and references therein). In 1906, a Röntgen Society meeting in London proposed that a radium standard be used as a basis for checking the rather erratic doses from X-ray machines. At the meeting, Soddy proposed that the standard be kept at NPL and the Society set up a committee to establish a base unit of radioactivity. In 1910, the International Radium Standards Commission, with Ernest Rutherford as its President, asked Marie Skłodowska Curie to prepare a standard which consisted of a weighed quantity of radium salt in a sealed ampoule. This first international primary standard was delivered to the BIPM; copies of the standard were prepared by Stefan Meyer and sold to countries that wanted them. The UK standard was delivered to NPL, and was certificated by Curie, Rutherford and Meyer dated 2nd June 1913. (Note that this refers to the particular isotope 226Ra). By 1925, primary standards had been established in Paris, Brussels, London, Washington, Vienna and Berlin. Demand grew rapidly for measurements comparing samples to the national primary standards, largely to support the trade in radium, which was a very valuable material at that time. The radium primary standard was, by definition, only valid for radium; over time, standards were needed for different radionuclides to support measurements in the nuclear power generation industry and nuclear medicine. A wide range of different methods were developed, and indeed continue to be developed, to realise these primary standards, depending on the details of the decay schemes of the radionuclides. An overview of the different methods is given by Simpson and Judge (2007). Today, NMIs have developed methods to realise primary standards for many and varied chemical species of radionuclides – these methods continue to be developed and refined to meet the demand from new applications. For example, the recent focus on the increased use of alpha-emitting radionuclides for metastasised bone tumour treatment has resulted in the development of a new isotopic primary radioactivity standard for 223Ra (Keightley et al., 2015). NMIs use a range of techniques to support laboratories in demonstrating traceability to these standards – supplying standardised solutions and reference materials, publishing papers on measurement techniques, writing Good Practice Guides, offering consultancy and also measuring and evaluating the nuclear decay data (e.g., half lives, emission probabilities, decay energies) which underpin most metrological applications.
Table 1 Changes in requirements for radioactivity measurement as nuclear sites transition from operations to decommissioning. Operating nuclear plants
Decommissioning nuclear site
Regular, routine, measurements Known radionuclide composition of samples Narrow range of activity content of samples Mostly aqueous samples Longer turnaround times
Project based Unknown composition
Reproducibility important – activity levels usually well below regulatory limits
Wide range of activity content Mostly solid samples Rapid results needed – on the critical path of expensive projects High accuracy and traceability important – activity levels can be near regulatory limits
aqueous and other discharges from the nuclear industry into the environment, and also for monitoring radioactive materials in the food chain and wider environment. Decommissioning, however represents a new phase for the nuclear industry. Table 1 summarises how the measurement requirements are changing in response to these decommissioning needs; similar issues apply following nuclear accidents. In response, NMIs and other organisations within and related to the nuclear industry are working together to develop new standards and capabilities to meet the changing metrological landscape. Examples of related projects in the field include: 3.1. Development of new reference materials The existing international measurement system has relied largely on standardised solutions, since most of the measurements were of aqueous waste, or could be made traceable to solution standards using techniques from analytical chemistry. The next phase is the development of reference materials based on solid materials with a certificated activity content. These may be synthetic or based on samples of waste materials from the nuclear industry. Producing the reference materials can be complex. One recent example is the development of large-volume reference standards, intended for calibrating waste package measurement systems. The standard comprises cast-iron tubes with certificated concentrations of 60 Co and 110mAg, produced by centrifugal casting from a smelt into which 60Co was added and neutron-irradiated silver wire was diluted. The total mass of the new standard was 250 kg (Tzika et al., 2016). New reference materials are also being developed for verifying laboratory-scale measurements. Dean et al. (2015, 2016) have used a synthetic glass reference material and material from the nuclear industry in laboratory proficiency test exercises. The development of reference materials is continuing under international research programmes such as MetroDECOM (2016), in parallel with developments for other applications of such materials (Inn et al., 2013, 2016; Jerome et al., 2015). 3.2. New laboratory-based measurement techniques Inductively Coupled Plasma Mass Spectrometry (ICPMS) may replace some traditional radioactivity measurement techniques in the long term. Measurements are much faster for some radionuclides with long half-lives – for example, long-lived alpha emitters can be measured in a few minutes by ICPMS compared to many days of data acquisition by alpha spectrometry. Once set up the instruments are easy to run and automate, require less laboratory space overall, and sample preparation is simpler (Russell et al., 2014, 2015). However, there is a need to develop the measurement protocols to meet the requirements for nuclear decommissioning. The accuracy and the achievable detection limits depend on removing or correcting for isobaric interferences and reducing the background under peaks from
3. Research projects for nuclear decommissioning The international measurement system for radioactivity is well established. It is used to determine the activity content of permitted 2
Radiation Physics and Chemistry xxx (xxxx) xxx–xxx
S.M. Judge, P.H. Regan
tailing from stable isotopes – these are particularly important for measuring radionuclides with relatively short half lives (in the tens of years). Some of the issues can be addressed using a triple-quadrupole ICPMS which enables a reaction cell to be used to reduce isobaric interferences, and work is underway at NPL and other organisations to make best use of this new technology.
Acknowledgements
3.3. New in-situ approaches to measurement
References
In practice, determining the radioactivity content of samples of plant, building materials and land on a decommissioning site can be very time consuming. Most measurement laboratories are off-site, and there can be a time-consuming permitting and administrative process to follow before the samples can be despatched for analysis. As measurement results lie on the critical path for decommissioning projects this can lead to long delays, with the project team waiting for the results from the analysis before work can start on demolition or disposal. NPL, in collaboration with the University of Surrey has developed a solution to this problem – carrying out radiochemical analyses in a mobile laboratory. The vehicle was designed by the British Geological Society; it is reconfigurable and has its own independent power supply and utilities. Equipment needed for a particular analysis campaign can be rapidly installed, and removed or replaced as required. It has become a realistic proposition only during the last few years – robust detectors that are less susceptible to variations in temperature and new radiochemistry techniques such as lithium-borate fusion and automated radiochemical separation devices show promise. The mobile laboratory has been trialled on a nuclear site and used to determine the activity of gamma emitting radionuclides in samples; the results showed that a high resolution gamma spectrometer gave reliable, repeatable, results and it was possible to reach minimum detectable activities an order of magnitude below the ‘out of scope’ limits within reasonable counting times.
Dean J.C.J., Aitken-Smith P., Collins S.M., Garcia-Miranda M., Woods S., 2016. Environmental Radioactivity Proficiency Test Exercise 2015. NPL Report IR 36. Dean J.C.J., Collins S.M., Woods S., 2015. Environmental Radioactivity Proficiency Test Exercise 2014, NPL Report IR 34. DEFRA, 2011. Guidance on the Scope of and Exemptions from the Radioactive Substances Legislation in the UK, 〈https://www.gov.uk/government/publications/ guidance-on-the-scope-of-and-exemptions-from-the-radioactive-substanceslegislation-in-the-uk〉 (Accessed 8 February 2016). Emptage M., Loudon D., McLeod R., Milburn H., 2016. Characterisation: Challenges and Opportunities - A UK Perspective 〈https://www.oecd-nea.org/rwm/wpdd/ predec2016/docs/S-5-1_FP_EMPATGE_.pdf〉 (Accessed 21 October 2016). European Commission, 2016. Nuclear Illustrative Programme Presented Under Article 40 of the Euratom Treaty for the opinion of the European Economic and Social Committee {COM(2016) 177}. Inn, K.G.W., Jerome, S.M., Griggs, J., Johnson, C.M., Jones, R., LaMont, S., MacKill, P., Mackney, D., Oldham, W., Palmer, B., Schaaff, T., Smith, D., Tandon, L., 2013. The urgent requirement for new radioanalytical certified reference materials for nuclear safeguards, forensics, and consequence management. J. Radioanal. Nucl. Chem. 296, 5–22. Inn, K.G.W., LaMont, S., Jerome, S.M., Essex, R., Johnson, C.M., Morrison, J., Frechou, C., Branger, T., Dion, H., 2016. Roadmap for radioanalytical reference and performance evaluation materials for current and emerging issues. J. Radioanal. Nucl. Chem. 307, 2529–2538, 2016. Jerome, S.M., Inn, K.G.W., Lin, Z., Wätjen, U., 2015. Certified Reference, Intercomparison, Performance Evaluation and Emergency Preparedness Exercise Materials for Radionuclides in Food. J. Radioanal. Nucl. Chem. 303, 1771–1777. Judge, S.M., Arnold, D., Chauvenet, B., Collé, R., De Felice, P., García-Toraño, E., Wätjen, U., 2014. 100 years of radionuclide metrology. Appl. Radiat. Isot. 87, 27–31. Keightley, J., Pearce, A., Fenwick, A., Collins, S., Ferreira, K., Johansson, L., 2015. Standardisation of 223Ra by liquid scintillation counting techniques and comparison with secondary measurements. Appl. Radiat. Isot. 95, 114–121. MetroDECOM 〈http://www.decommissioning-emrp.eu/〉 (Accessed 25 October 2016). NEA OECD, 2014. R & D and Innovation needs for decommissioning of nuclear facilitie, Report no 7191. Russell, B.C., Croudace, I.W., Warwick, P.E., Milton, J.A., 2014. Determination of Precise 135 Cs/137Cs Ratio in Environmental Samples Using Sector Field Inductively Coupled Plasma Mass Spectrometry. Anal. Chem. 86, 8719–8726. Russell, B.C., Croudace, I.W., Warwick, P.E., 2015. Determination of 135Cs and 137Cs in environmental samples: a review. Anal. Chim. Acta 890, 7–20. Simpson, B.R.S., Judge, S.M. (Eds.), 2007. Special issue on radionuclide metrology, Metrologia, 44, 4. Tzika, F., Hult, M., Stroh, H., Marissens, G., Arnold, D., Burda, O., Kovář, P., Suran, J., Listkowska, A., Tyminski, Z., 2016. A new large-volume metal reference standard for radioactive waste management. Radiat. Prot. Dosim. 168, 293–299.
This work was supported by the UK government's Department for Business, Energy and Industrial Strategy. PHR also acknowledges partial support from the UK Science and Technology Facilities Council grant ST/L005743/1.
4. Conclusions Much of the nuclear industry is going through a period of significant change, as routine operations are replaced by site decommissioning. This is bringing new challenges for the science of radionuclide metrology but these are not insurmountable, as the foundations of a new international measurement infrastructure are already in place. Building on this with new standards, instruments and methods will enable the decommissioning process to be safe and cost effective.
3
Contents lists available at ScienceDirect
Radiation Physics and Chemistry journal homepage: www.elsevier.com/locate/radphyschem
Radionuclide metrology research for nuclear site decommissioning ⁎
S.M. Judgea,b, , P.H. Regana,b a b
National Physical Laboratory, Hampton Road, Teddington, Middlesex TW11 0LW United Kingdom University of Surrey, Guildford, Surrey GU2 7XH, United Kingdom
A R T I C L E I N F O
A BS T RAC T
Keywords: Radioactivity Metrology Nuclear decommissioning
The safe and cost-effective decommissioning of legacy nuclear sites relies on accurate measurement of the radioactivity content of the waste materials, so that the waste can be assigned to the most appropriate disposal route. Such measurements are a new challenge for the science of radionuclide metrology which was established largely to support routine measurements on operating nuclear sites and other applications such as nuclear medicine. In this paper, we provide a brief summary of the international measurement system that is established to enable nuclear site operators to demonstrate that measurements are accurate, independent and fit for purpose, and highlight some of the projects that are underway to adapt the measurement system to meet the changing demands from the industry.
1. Introduction The first generation nuclear power plants and reprocessing facilities are coming to the end of their working lives. The average age of a nuclear power plant in Europe is 29 years and the approved operating life is 30–50 years, depending on the design. There are currently 91 power plants already shut down and being decommissioned in the EU; the majority of the remaining 129 reactors plus fuel cycle facilities will also be in decommissioning by 2030 (European Commission, 2016; NEA OECD, 2014). The aim of the decommissioning process is to clear the site so that it can be used for other purposes, while minimising the risk to the public, the environment and the workforce from the process and the waste arising. All of the nuclear sites contain large quantities of hazardous materials such as spent nuclear fuel and contaminated plant and buildings (for example, the Sellafield fuel reprocessing site in the UK has 2 million m3 of concrete, 2200 buildings and 170 large plants to decommission, plus 10 million m3 of contaminated soil); the cost of decommissioning and waste management in the EU is estimated to be in excess of 150 billion Euro. The long term radiation dose from the waste to members of the public has to be controlled to minimise the risk to health. In practice, this means measuring the specific activity concentrations (determined in Bq/g) of materials, and then choosing the best disposal route for that particular material. The ‘out of scope’ limit (ie, the quantity that is deemed as ‘not radioactive’) depends on the radionuclide (DEFRA, 2011) - the limits are determined based on models of the impact on health. These limits are close to the minimum detectable activity ⁎
(MDA) and measurements at this level challenge the sensitivity and accuracy of existing measurement techniques. This problem is exacerbated as nuclear sites have been operating for many decades, so the disposition and level of radioactivity are not well known. As inaccuracies in measurements could result in unsafe disposal with serious long term environmental effects, nuclear site operators are routinely conservative and select waste disposal options that are costly but have little environmental benefit. To date, only 13 nuclear power plants have been completely decommissioned worldwide and therefore technical experience in the measurement of radioactivity for decommissioning is somewhat limited. Regulatory bodies, site owners or operators and international organisations have carried out detailed studies of the needs (Emptage et al., 2016; NEA OECD, 2014). The common themes that have been raised are: (1) improvements in capability (technology, measurement methods and sampling strategies), (2) harmonisation and quality assurance, and (3) sharing knowledge. Although accurate measurement for decommissioning legacy nuclear sites may seem to be an intractable problem, this particular research field can build on the existing international measurement system to ensure that measurements are accurate, harmonised and scientifically rigorous. Such work can also take advantage of national and international research projects that seek to develop new capability. 2. The international measurement system The International Measurement System is the technical and administrative infrastructure that aims to ensure that measurements
Corresponding author. E-mail address: [email protected] (S.M. Judge).
http://dx.doi.org/10.1016/j.radphyschem.2017.02.027 Received 26 October 2016; Received in revised form 8 February 2017; Accepted 10 February 2017 0969-806X/ Crown Copyright © 2017 Published by Elsevier Ltd. All rights reserved.
Please cite this article as: Judge, S.M., Radiation Physics and Chemistry (2017), http://dx.doi.org/10.1016/j.radphyschem.2017.02.027
Radiation Physics and Chemistry xxx (xxxx) xxx–xxx
S.M. Judge, P.H. Regan
of any physical quantity are accurate, consistent and fit-for-purpose worldwide. In principle, the system is very simple: all measurements are ratios of the fundamental or ‘primary’ standards, and this has to be demonstrated by a documented chain of calibrations back to the primary standard, ie, all measurements of any physical quantity should be traceable to a primary standard. To be traceable, the chain must be unbroken and measurement uncertainties must be calculated at each stage in order to demonstrate that the final measurement is fit for purpose. The primary standards themselves are developed and maintained by National Measurement Institutes (NMIs) such as NPL in the UK, NIST in the USA and PTB in Germany. The NMIs check the accuracy of the primary standards by comparing the primary standards against those held at other NMIs; any discrepancies are investigated and corrective actions are taken. This international measurement system is overseen by the Bureau International des Poids and Mesures (BIPM) in Paris. Under the auspices of the BIPM, NMIs have signed a Mutual Recognition Arrangement (MRA) which requires NMIs to participate in the comparison exercises and to publish their capabilities (further details are given on www.bipm.org). The international measurement system for radioactivity dates back to just after the discovery of radioactivity in 1896 by Henri Becquerel (further details of the historical background are given in Judge et al., 2014 and references therein). In 1906, a Röntgen Society meeting in London proposed that a radium standard be used as a basis for checking the rather erratic doses from X-ray machines. At the meeting, Soddy proposed that the standard be kept at NPL and the Society set up a committee to establish a base unit of radioactivity. In 1910, the International Radium Standards Commission, with Ernest Rutherford as its President, asked Marie Skłodowska Curie to prepare a standard which consisted of a weighed quantity of radium salt in a sealed ampoule. This first international primary standard was delivered to the BIPM; copies of the standard were prepared by Stefan Meyer and sold to countries that wanted them. The UK standard was delivered to NPL, and was certificated by Curie, Rutherford and Meyer dated 2nd June 1913. (Note that this refers to the particular isotope 226Ra). By 1925, primary standards had been established in Paris, Brussels, London, Washington, Vienna and Berlin. Demand grew rapidly for measurements comparing samples to the national primary standards, largely to support the trade in radium, which was a very valuable material at that time. The radium primary standard was, by definition, only valid for radium; over time, standards were needed for different radionuclides to support measurements in the nuclear power generation industry and nuclear medicine. A wide range of different methods were developed, and indeed continue to be developed, to realise these primary standards, depending on the details of the decay schemes of the radionuclides. An overview of the different methods is given by Simpson and Judge (2007). Today, NMIs have developed methods to realise primary standards for many and varied chemical species of radionuclides – these methods continue to be developed and refined to meet the demand from new applications. For example, the recent focus on the increased use of alpha-emitting radionuclides for metastasised bone tumour treatment has resulted in the development of a new isotopic primary radioactivity standard for 223Ra (Keightley et al., 2015). NMIs use a range of techniques to support laboratories in demonstrating traceability to these standards – supplying standardised solutions and reference materials, publishing papers on measurement techniques, writing Good Practice Guides, offering consultancy and also measuring and evaluating the nuclear decay data (e.g., half lives, emission probabilities, decay energies) which underpin most metrological applications.
Table 1 Changes in requirements for radioactivity measurement as nuclear sites transition from operations to decommissioning. Operating nuclear plants
Decommissioning nuclear site
Regular, routine, measurements Known radionuclide composition of samples Narrow range of activity content of samples Mostly aqueous samples Longer turnaround times
Project based Unknown composition
Reproducibility important – activity levels usually well below regulatory limits
Wide range of activity content Mostly solid samples Rapid results needed – on the critical path of expensive projects High accuracy and traceability important – activity levels can be near regulatory limits
aqueous and other discharges from the nuclear industry into the environment, and also for monitoring radioactive materials in the food chain and wider environment. Decommissioning, however represents a new phase for the nuclear industry. Table 1 summarises how the measurement requirements are changing in response to these decommissioning needs; similar issues apply following nuclear accidents. In response, NMIs and other organisations within and related to the nuclear industry are working together to develop new standards and capabilities to meet the changing metrological landscape. Examples of related projects in the field include: 3.1. Development of new reference materials The existing international measurement system has relied largely on standardised solutions, since most of the measurements were of aqueous waste, or could be made traceable to solution standards using techniques from analytical chemistry. The next phase is the development of reference materials based on solid materials with a certificated activity content. These may be synthetic or based on samples of waste materials from the nuclear industry. Producing the reference materials can be complex. One recent example is the development of large-volume reference standards, intended for calibrating waste package measurement systems. The standard comprises cast-iron tubes with certificated concentrations of 60 Co and 110mAg, produced by centrifugal casting from a smelt into which 60Co was added and neutron-irradiated silver wire was diluted. The total mass of the new standard was 250 kg (Tzika et al., 2016). New reference materials are also being developed for verifying laboratory-scale measurements. Dean et al. (2015, 2016) have used a synthetic glass reference material and material from the nuclear industry in laboratory proficiency test exercises. The development of reference materials is continuing under international research programmes such as MetroDECOM (2016), in parallel with developments for other applications of such materials (Inn et al., 2013, 2016; Jerome et al., 2015). 3.2. New laboratory-based measurement techniques Inductively Coupled Plasma Mass Spectrometry (ICPMS) may replace some traditional radioactivity measurement techniques in the long term. Measurements are much faster for some radionuclides with long half-lives – for example, long-lived alpha emitters can be measured in a few minutes by ICPMS compared to many days of data acquisition by alpha spectrometry. Once set up the instruments are easy to run and automate, require less laboratory space overall, and sample preparation is simpler (Russell et al., 2014, 2015). However, there is a need to develop the measurement protocols to meet the requirements for nuclear decommissioning. The accuracy and the achievable detection limits depend on removing or correcting for isobaric interferences and reducing the background under peaks from
3. Research projects for nuclear decommissioning The international measurement system for radioactivity is well established. It is used to determine the activity content of permitted 2
Radiation Physics and Chemistry xxx (xxxx) xxx–xxx
S.M. Judge, P.H. Regan
tailing from stable isotopes – these are particularly important for measuring radionuclides with relatively short half lives (in the tens of years). Some of the issues can be addressed using a triple-quadrupole ICPMS which enables a reaction cell to be used to reduce isobaric interferences, and work is underway at NPL and other organisations to make best use of this new technology.
Acknowledgements
3.3. New in-situ approaches to measurement
References
In practice, determining the radioactivity content of samples of plant, building materials and land on a decommissioning site can be very time consuming. Most measurement laboratories are off-site, and there can be a time-consuming permitting and administrative process to follow before the samples can be despatched for analysis. As measurement results lie on the critical path for decommissioning projects this can lead to long delays, with the project team waiting for the results from the analysis before work can start on demolition or disposal. NPL, in collaboration with the University of Surrey has developed a solution to this problem – carrying out radiochemical analyses in a mobile laboratory. The vehicle was designed by the British Geological Society; it is reconfigurable and has its own independent power supply and utilities. Equipment needed for a particular analysis campaign can be rapidly installed, and removed or replaced as required. It has become a realistic proposition only during the last few years – robust detectors that are less susceptible to variations in temperature and new radiochemistry techniques such as lithium-borate fusion and automated radiochemical separation devices show promise. The mobile laboratory has been trialled on a nuclear site and used to determine the activity of gamma emitting radionuclides in samples; the results showed that a high resolution gamma spectrometer gave reliable, repeatable, results and it was possible to reach minimum detectable activities an order of magnitude below the ‘out of scope’ limits within reasonable counting times.
Dean J.C.J., Aitken-Smith P., Collins S.M., Garcia-Miranda M., Woods S., 2016. Environmental Radioactivity Proficiency Test Exercise 2015. NPL Report IR 36. Dean J.C.J., Collins S.M., Woods S., 2015. Environmental Radioactivity Proficiency Test Exercise 2014, NPL Report IR 34. DEFRA, 2011. Guidance on the Scope of and Exemptions from the Radioactive Substances Legislation in the UK, 〈https://www.gov.uk/government/publications/ guidance-on-the-scope-of-and-exemptions-from-the-radioactive-substanceslegislation-in-the-uk〉 (Accessed 8 February 2016). Emptage M., Loudon D., McLeod R., Milburn H., 2016. Characterisation: Challenges and Opportunities - A UK Perspective 〈https://www.oecd-nea.org/rwm/wpdd/ predec2016/docs/S-5-1_FP_EMPATGE_.pdf〉 (Accessed 21 October 2016). European Commission, 2016. Nuclear Illustrative Programme Presented Under Article 40 of the Euratom Treaty for the opinion of the European Economic and Social Committee {COM(2016) 177}. Inn, K.G.W., Jerome, S.M., Griggs, J., Johnson, C.M., Jones, R., LaMont, S., MacKill, P., Mackney, D., Oldham, W., Palmer, B., Schaaff, T., Smith, D., Tandon, L., 2013. The urgent requirement for new radioanalytical certified reference materials for nuclear safeguards, forensics, and consequence management. J. Radioanal. Nucl. Chem. 296, 5–22. Inn, K.G.W., LaMont, S., Jerome, S.M., Essex, R., Johnson, C.M., Morrison, J., Frechou, C., Branger, T., Dion, H., 2016. Roadmap for radioanalytical reference and performance evaluation materials for current and emerging issues. J. Radioanal. Nucl. Chem. 307, 2529–2538, 2016. Jerome, S.M., Inn, K.G.W., Lin, Z., Wätjen, U., 2015. Certified Reference, Intercomparison, Performance Evaluation and Emergency Preparedness Exercise Materials for Radionuclides in Food. J. Radioanal. Nucl. Chem. 303, 1771–1777. Judge, S.M., Arnold, D., Chauvenet, B., Collé, R., De Felice, P., García-Toraño, E., Wätjen, U., 2014. 100 years of radionuclide metrology. Appl. Radiat. Isot. 87, 27–31. Keightley, J., Pearce, A., Fenwick, A., Collins, S., Ferreira, K., Johansson, L., 2015. Standardisation of 223Ra by liquid scintillation counting techniques and comparison with secondary measurements. Appl. Radiat. Isot. 95, 114–121. MetroDECOM 〈http://www.decommissioning-emrp.eu/〉 (Accessed 25 October 2016). NEA OECD, 2014. R & D and Innovation needs for decommissioning of nuclear facilitie, Report no 7191. Russell, B.C., Croudace, I.W., Warwick, P.E., Milton, J.A., 2014. Determination of Precise 135 Cs/137Cs Ratio in Environmental Samples Using Sector Field Inductively Coupled Plasma Mass Spectrometry. Anal. Chem. 86, 8719–8726. Russell, B.C., Croudace, I.W., Warwick, P.E., 2015. Determination of 135Cs and 137Cs in environmental samples: a review. Anal. Chim. Acta 890, 7–20. Simpson, B.R.S., Judge, S.M. (Eds.), 2007. Special issue on radionuclide metrology, Metrologia, 44, 4. Tzika, F., Hult, M., Stroh, H., Marissens, G., Arnold, D., Burda, O., Kovář, P., Suran, J., Listkowska, A., Tyminski, Z., 2016. A new large-volume metal reference standard for radioactive waste management. Radiat. Prot. Dosim. 168, 293–299.
This work was supported by the UK government's Department for Business, Energy and Industrial Strategy. PHR also acknowledges partial support from the UK Science and Technology Facilities Council grant ST/L005743/1.
4. Conclusions Much of the nuclear industry is going through a period of significant change, as routine operations are replaced by site decommissioning. This is bringing new challenges for the science of radionuclide metrology but these are not insurmountable, as the foundations of a new international measurement infrastructure are already in place. Building on this with new standards, instruments and methods will enable the decommissioning process to be safe and cost effective.
3