Ionising radiation metrology for the metallurgical industry

Every year millions tons of steel are produced worldwide from recycled scrap loads. Although the detection systems in the steelworks prevent most orphan radioactive sources from entering the furnace, there is still the possibility of accidentally melting a radioactive source. The MetroMetal project, carried out in the frame of the European Metrology Research Programme (EMRP), addresses this problem by studying the existing measurement systems, developing sets of reference sources in various matrices (cast steel, slag, fume dust) and proposing new detection instruments. This paper presents the key lines of the project and describes the preparation of radioactive sources as well as the intercomparison exercises used to test the calibration and correction methods proposed within the project.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard

Detection Efficiency Calculation for Photons, Electrons and Positrons in a Well Detector - Part II: Analytical Model versus Simulations

A comparison is made between the results of Monte Carlo simulations and a new analytical model (cf. part I) for the detection efficiency of a well-type NaI detector for photons, electrons and positrons in the energy range of 0.01-10 MeV. Using MCNP 5.1.40, GEANT3 and PENELOPE simulation results as benchmark, it was found that the analytical model was quite successful at reproducing the total detection efficiency for photons and positrons, and at giving rough indications on the photon peak-to-total ratio and the electron detection efficiency.JRC.D.5-Neutron physic

Assessment of the uncertainty budget associated with 4pi-gamma counting

The 4pig-counting technique is recognized as a powerful primary method for the standardization of radionuclides decaying with abundant gamma emissions. Based on the use of a gamma detector in quasi 4pi-geometry, a detection efficiency close to 100% and a low uncertainty can be achieved thanks to the summing effect of subsequent gamma transitions. Uncertainties have to be assigned to the realistic modelling of the source-detector geometry with respect to dimensions, density and material composition, the calculation of the total counting efficiency of the detector for the various emitted radiation and the effect of possible flaws in the decay scheme of a radionuclide on the calculated total efficiency. Other uncertainty factors pertain to typical metrological sources of uncertainty, such as weighing, nuclear counting with pulse pile-up and system dead-time effects, impurity corrections, decay corrections, timing and frequency, etc. In order to ensure good metrological practices at NMIs, the uncertainties particular to the method are discussed.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard

Measurement of absolute γ-ray emission probabilities in the decay of 235U

Accurate measurements were performed of the photon emission probabilities following the α decay of 235U to 231Th. Sources of highly enriched 235U were characterised in terms of isotopic composition by mass spectrometry and their activities were standardised by means of alpha-particle counting at a low defined solid angle. The standardised sources were subsequently measured by high-resolution γ-ray spectrometry with calibrated high-purity germanium detectors to determine the photon emission probabilities. Four laboratories participated in this work and reported emission probabilities for 33 γ-ray lines. Most of them agree with previously published evaluated data. In addition, new values are proposed for γ-lines which have been measured only once in the past.JRC.G.2-Standards for Nuclear Safety, Security and Safeguard

Interlaboratory comparison on 137Cs activity concentration in fume dust

A comparison was conducted, between 11 European National Metrology Institutes and EC-JRC, on measurement of 137Cs activity concentration in fume dust. As comparison material an activity standard produced from real contaminated fume dust was used. The standard material consisted of 13 samples of compressed fume dust, each of 50 g mass and of well-defined cylindrical geometry (diameter 69.5 mm and height 18.7 mm). The material contained 137Cs and 60Co of reference activity concentrations of (9.72 ± 0.10) Bq/g and (0.450 ± 0.018) Bq/g, respectively, determined using the comparison results. The organisation and results of the intercomparison, as well as the process of obtaining reliable reference values are presented.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard

Characterisation of a radionuclide specific laboratory detector system for the metallurgical industry by Monte Carlo simulations

One of the outputs of the European Metrology Research Programme project “Ionising radiation metrology for the metallurgical industry” (MetroMetal) was a recommendation on a novel radionuclide specific detector system optimized for the measurement of radioactivity in metallurgical samples. The detection efficiency of the recommended system for the standards of cast steel, slag and fume dust developed within the project was characterized by Monte Carlo (MC) simulations performed using different MC codes. Capabilities of MC codes were also tested for simulation of true coincidence summing (TCS) effects for several radionuclides of interest in the metallurgical industry. The TCS correction factors reached up to 32 % showing that the TCS effects are of high importance in close measurement geometries met in routine analyses of metallurgical samples.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard

Characterisation of activity content of 226Ra in spiked metallurgical slag using an interlaboratory comparison

More than half of yearly steel production in EU comes from recycling. The metal foundries pass the metal scrap through radiation portal monitors at the entrance of the foundry; nevertheless an orphan radioactive source may still remain undetected e.g. due to the shielding from the scrap load itself. In such case the source may enter the smelting route ending in contaminated steel products and by-products of the process. The European metal foundries are aware of the problem and increasingly apply radioactivity monitoring of the steel products. It is of outmost importance to perform accurate measurements, in order to prove compliance with respect to legal radioactivity limits, and metrologically challenging to ensure the quality of such measurements. In the light of a global steel market it is obvious that harmonisation of the analytical methodologies is critical. In the EURAMET's EMRP joint research project, 'MetroMetal' (Ionising radiation metrology for the metallurgical industry), existing radioactivity measurement methods were studied and new optimized methods, systems and standards were proposed for the radioactivity control of steel and by-products in steel mills. In this context, reference activity standards, including the most frequently occurring radionuclides in melting incidents in suitable geometries and matrices, have been developed. Amongst these standards were two series of sources of 60Co in cast steel, one of 137Cs in fume dust and one of 226Ra in furnace slag. The common feature in all four standards was that Interlaboratory comparisons (ILCs) were used to characterise the activity concentrations. In the particular case of 226Ra in slag the material was prepared by spiking and an ILC was conducted amongst 9 European National Metrology Laboratories and JRC, with the aim to verify the activity concentration of the spiked material and to validate the calibration and correction methods proposed by MetroMetal. In the present work, the organization and the results of the ILC on 226Ra activity concentration in metallurgical slag standards are presented.JRC.G.2-Standards for Nuclear Safety, Security and Safeguar

Radioactive waste management: Review on clearance levels and acceptance criteria legislation, requirements and standards

In 2011 the joint research project Metrology for Radioactive Waste Management (MetroRWM) of the European Metrology Research and Development Program (EMRP) started with a total duration of three years. Within this project, new metrological resources for the assessment of radioactive waste, including their calibration with new reference materials traceable to national standards will be developed. This paper gives a review on national, European and international strategies as basis for science-based metrological requirements in clearance and acceptance of radioactive waste.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard

The half-life of 129I

The radionuclide 129I is a long-lived fission product that decays to 129Xe by beta-particle emission. It is an important tracer in geological and biological processes and is considered one of the most important radionuclides to be assessed in studies of global circulation. It is also one of the major contributors to radiation dose from nuclear waste in a deep geological repository. Its half-life has been obtained by a combination of activity and mass concentration measurements in the frame of a cooperation of 6 European metrology institutes. The value obtained for the half-life of 129I is 16.14 (12) × 106 a, in good agreement with recommended data but with a significant improvement in the uncertainty.JRC.G.2-Standards for Nuclear Safety, Security and Safeguard

Results of the EURAMET.RI(II)-K2.Ho-166m activity comparison

In 2013, five laboratories took part in the EURAMET.RI(II)-K2.Ho-166m comparison of activity concentration measurements of 166mHo. The activity measurements of this comparison are part of the joint research project “Metrology for Radioactive Waste Management” of the European Metrology Research Programme (EMRP). One aim of this project is a new determination of the 166mHo half-life.The results were found to be in good agreement and no outlier could be identified. A comparison reference value (CRV) has been calculated as the power-moderated mean (PMM) of all final laboratory results and was found to be 119.27(10) kBq g–1. Preliminary degrees of equivalence based on the Comparison Reference Value were also calculated for each reporting laboratory. The Key Comparison Reference Value and final degrees of equivalence will be calculated by the BIPM from the data contained herein and data from measurements made in the International Reference System (SIR).JRC.D.4-Standards for Nuclear Safety, Security and Safeguard