Long-term measurements of indoor Radon and its progeny in the presence of Thoron using nuclear track detectors : a novel approach /

Consultable des del TDXTítol obtingut de la portada digitalitzadaEn este trabajo, hemos establecido una nueva aproximación para determinar el factor de equilibrio de los descendientes de 222Rn, durante periodos largos de tiempo y en presencia de 220Rn, utilizando un sistema pasivo, integrador y multicomponente de detectores de trazas nucleares. El método se basa en el hecho de que los periodos de semidesintegración del 222Rn y del 220Rn son diferentes, de que ambos isótopos tienen el mismo coeficiente de difusión en un medio dado, y de que la respuesta de los detectores de trazas nucleares depende de las condiciones del revelado electroquímico utilizadas. El dosímetro puesto a punto consta de: i) dos detectores de Makrofol, designados como detectores A y B, que están situados en el interior de dos cámaras de difusión - cada una con un filtro diferente - para medir 222Rn+220Rn y 222Rn, además de ii) dos detectores de Makrofol (C y D) que están en contacto directo con el aire y a los cuales se les aplica diferentes condiciones de revelado electroquímico para obtener las concentraciones del 218Po y del 214Po. Las sensibilidades de cada detector de Makrofol con respecto al 222Rn, 220Rn y progenie se han calculado teóricamente utilizando la técnica de Monte Carlo, teniendo en cuenta: (1) la ecuación de Bethe-Bloch para determinar el poder de frenado de partículas cargadas pesadas en un medio material, (2) las propiedades y el comportamiento del 222Rn, 220Rn y descendientes en el aire libre y dentro de una cámara de difusión, y (3) el rango de energías de partículas a que registra cada detector. El código desarrollado para estos cálculos se ha validado reproduciendo la respuesta de un detector ideal, tanto en el aire libre como dentro de una cámara de difusión. Se ha llevado a cabo un estudio experimental detallado en el que se han determinado los filtros óptimos para la separación 222Rn/220Rn y las condiciones de revelado electroquímico apropiadas para cada detector. Asimismo, hemos calibrado los detectores A y B en atmósferas puras de 222Rn y hemos confirmado experimentalmente que los valores del factor de equilibrio determinados con nuestro dosímetro están en buen acuerdo con los obtenidos mediante sistemas activos. Finalmente, como experiencia piloto, varios dosímetros han sido expuestos en una casa unifamiliar habitada de Suecia. Los resultados de esta exposición indican la utilidad de nuestro método para llevar a cabo campañas de medida de los niveles de 222Rn, en lugares de trabajo y en casas privadas, a fin de estimar la dosis efectiva anual recibida por los trabajadores y por el público en general.In this work, we establish a novel approach for long-term determination of indoor 222Rn progeny equilibrium factor, even in the presence of 220Rn, using a passive, integrating and multi-component system of nuclear track detectors. The method is based on the fact that the half-lives of 222Rn and 220Rn are different, that both isotopes have the same diffusion coefficient in a given medium and that the response of the nuclear track detectors depends on the electrochemical etching conditions used. The new dosimeter set up for this purpose consists of: i) two Makrofol detectors, namely detectors A and B, which are enclosed within two diffusion chambers - each one with different filter membrane - to measure indoor 222Rn+220Rn and 222Rn, together with ii) two Makrofol detectors (C and D) that are kept in direct contact with air and that are electrochemically etched at different conditions to obtain the airborne 218Po and 214Po concentrations. The sensitivities of each Makrofol detector in front of 222Rn, 220Rn and their decay products have been theoretically obtained using Monte-Carlo technique, taking into account: (1) the Bethe-Bloch expression for the stopping power of heavily charged particles in a medium, (2) the behaviour of 222Rn, 220Rn and their progeny in the open air and within the diffusion chamber, and (3) the a-energy window response of each detector. The computer code used for the calculation has been validated by reproducing the response of an ideal detector, both in the free air and enclosed within a diffusion chamber. A detailed experimental study has been carried out in which we have determined the optimum filters for 222Rn/220Rn separation and the appropriate electrochemical etching conditions for each of the Makrofol detector used. Otherwise, we have calibrated the detectors A and B in pure 222Rn atmospheres and we have confirmed experimentally that the equilibrium factor values determined with our system agree with those obtained by active methods. Finally, as a pilot test, several dosimeters were exposed in an inhabited Swedish single-family house. The results of this exposure suggest the usefulness of this method to perform routine surveys for 222Rn level measurements in private homes and in workplaces in order to estimate the annual effective dose received by the general public and the workers

State-of-the-art and challenges of non-destructive techniques for in-situ radiological characterization of nuclear facilities to be dismantled

[EN]This paper reports on the state-of-the-art of the main non-destructive assay (NDA) techniques usually used for in-situ radiological characterization of nuclear facilities subject to a decommissioning programme. For the sake of clarity and coherence, they have been classified as environmental radiation monitoring, surface contamination measurements, gamma spectrometry, passive neutron counting and radiation cameras. Particular mention is also made here to the various challenges that each of these techniques must currently overcome, together with the formulation of some proposals for a potential evolution in the future.This study has been funded by the European INSIDER project, through the Euratom Research and Training Programme 2014-2018, under grant agreement No 755554

Recommendations for the selection of in situ measurement techniques for radiological characterization in nuclear/radiological installations under decommissioning and dismantling processes

[EN] In this paper, in-situ radiological characterisation by means of non-destructive techniques is studied and analysed in the context of the different constrained environments (identified as radioactivity, materials, accessibility and other hazards) that may be encountered in the nuclear facilities undergoing decommissioning and dismantling. As a complement to a previous paper (Aspe et al., 2020), the present one gives a global guidance to assist with the decision making process regarding the selection of in-situ measurement techniques that could be applied in such constrained environments. In addition, from the definition of the investigation objectives, and for each one of the most common in-situ measurement techniques, a brief description is given about the impact of the above constraints and how to integrate them onto the system definition, including the experimental design, the mechanical integration and the data management, to properly define the best radiological characterization methodology. Moreover, complementing this general view, all the phases – from initial to final – of a D&D programme were taken into account to provide basic recommendations, together with some particular dispositions, for the appropriate implementation of the chosen instruments. Strengths and weaknesses of the common detectors used for the different in-situ measurement techniques, as well as their recommended applications in nuclear facilities are also outlined.The research leading to these results has been carried out in the framework of the European INSIDER project and has received funding from the Euratom Research and Training Programme 2014–2018 under grant agreement no. 755554

Characterization of an 241AmBe neutron irradiation facility by different spectrometric techniques

An automated panoramic irradiator with a 3 Ci 241Am-Be neutron source is installed in a bunker-type large room at the Universidad Politécnica de Madrid (UPM). It was recently modified and a neutron spectrometry campaign was organized to characterize the neutron fields in different measurement points along the irradiation bench. Four research groups working with different Bonner Sphere Spectrometers (BSS) and using different spectral unfolding codes took part to this exercise. INFN-LNF used a BSS formed by 9 spheres plus bare detector, with cylindrical, almost point like, 6LiI(Eu) scintillator (4 mm x 4 mm, from Ludlum); UAZ-UPM employed a similar system but with only 6 spheres plus bare detector; UAB worked with a 3He filled proportional counter at 8kPa filling pressure, cylindrical 9 mm x 10 mm (05NH1 from Eurisys) with 11 spheres configuration; and CIEMAT used 12 spheres with an spherical 3He SP9 counter (Centronic Ltd., UK) with very high sensitivity due to the large diameter (3.2 cm) and the filling pressure of the order of 228 kPa. Each group applied a different spectral unfolding method: INFN and UAB worked with FRUIT ver. 3.0 with their own response matrixes; UAZ-UPM used the BUNKIUT unfolding code with the response matrix UTA4 and CIEMAT employed the GRAVEL-MAXED-IQU package with their own response matrix. The paper shows the main results obtained in terms of neutron spectra at fixed distances from the source as well as total neutron fluence rate and ambient dose equivalent rate H*(10) determined from the spectra. The latter are compared with the readings of a common active survey-meter (LB 6411). The small differences in the results of the various groups are discussed

Radiological characterisation in view of nuclear reactor decommissioning: On-site benchmarking exercise of a biological shield

[EN] Nearly all decommissioning and dismantling (D&D) projects are steered by the characterisation of the plant being dismantled. This radiological characterisation is a complex process that is updated and modified during the course of the D&D. One of the tools for carrying out this characterisation is the performance of in-situ measurements. There is a wide variety of equipment and methodologies used to carry out on-site measurements, depending on the environment in which they are to be carried out and also on the specific objectives of the measurements and the financial and personnel resources available. The extent to which measurements carried out with different types of equipment or methodologies providing comparable results can be crucial in view of the D&D strategy development and the decision-making process. This paper concerns an on-site benchmarking exercise carried out at the activated biological shield of Belgian Reactor 3 (BR3). This activity allows comparison and validation of characterisation methodologies and different equipment used as well as future interpretation of final results in terms of uncertainties and sensitivities. This paper describes the measurements and results from the analysis of this exercise. Other aspects of this exercise will be reported in separate papers. This paper provides an overview of the on-site benchmarking exercise, outlines the participating organisations and the measurement equipment used for total gamma, dose rate and gamma spectrometry measurements and finally, results obtained and their interpretations are discussed for each type of measurement as a function of detector type. Regarding the dose measurements, results obtained by using a large variety of equipment are very consistent. In view of mapping the inner surface of the biological shield the most appropriate equipment tested might be the organic scintillator, the BGO or even the ionisation chamber. In addition, for mapping this surface, the most appropriate total gamma equipment tested might be the LaBr3(Ce), the thick organic scintillator or the BGO. These measurements can only be used as a secondary parameter in a relative way. Results for the gamma spectrometry are very consistent for all the equipment used and the main parameters to be determined.INSIDER is a EU Horizon 2020 project and received funding from the Euratom Research and Training Programme 2014–2018 under grant agreement No 755554

Monte Carlo simulations of a microstructured silicon detector with high efficiency for thermal neutrons

In this work we present a design optimization of a high efficiency neutron detector with MCNPX simulations. The detector is based on a silicon structure incorporating a boron-based converter to detect thermal neutrons by means of the 10B(n,α)7Li nuclear reaction. In order to improve the efficiency of planar detectors, limited to 5%, we have designed a perforated detector based on microstructures etched inside the silicon bulk, which would considerably increase this value. Each one of these microstructures is a micro-channel filled with the converter that provides a high surface-volume contact ratio between the converter and the sensitive silicon bulk. The main parameters optimized with the simulations are micro-channel width and depth, width of the silicon wall between micro-channels, and converter density, all comprised within technologically viable ranges. The results show that the detector could achieve up to 50% thermal neutron efficiency for a realistic prototype that can be produced with MEMS fabrication techniques. © 2012 IOP Publishing Ltd and Sissa Medialab srl.Peer reviewe

INSIDER WP5 (in situ measurements): developed activities, main results and conclusions

Within the INSIDER project, the WP5 (in situ measurements) has been tasked with analysing the existing systems and methodologies for carrying out these types of measurements in constrained environments, aiming to classify and categorise these environments. An additional task is to organise the participation in in situ intercomparison exercises in real situations, defining the most suitable equipment to carry these out. This paper presents the activities of the WP5 and a summary of the main results obtained in these activities after the first two years of work

A decision helping tool for D&D activities

As a result of the INSIDER European project (Improved Nuclear SIte characterisation for waste minimisation in Decommissioning and Dismantling operations under constrained EnviRonment), two D&D tools were developed: INSPECT (IN Situ Probe SelECtion Tool, see INSPECT V1.0.zip) and STRATEGIST (Sampling Toolbox for Radiological Assessment to Enable Geostatistical and statistical Implementation with a Smart Tactic, at https://strategist.sckcen.be/).INSPECT is a decision making tool for the selection of the suitable in-situ equipment/detector to be used in a nuclear facility for the different decommissioning and dismantling (D&D) phases, depending on the constrained environment. STRATEGIST intends to guide experts in handling the characterization problem definition and applies a strategy based on proper data analysis and sampling design for the application of an integrated characterization methodology and strategy in view of or during nuclear decommissioning and various types of dismantling operations.The INSPECT software was developed by A. Houzelot, F. Aspe and G. Auge from ONET Technologies, K. Amgarou from CEA and from M. Herranz and R. Idoeta from the University of the Basque Country UPV/EHU. It is based on project results that can be found in the following papers: K. Amgarou and M. Herranz (2021): State-of-the-art and challenges of non-destructive techniques for in-situ radiological characterization of nuclear facilities to be dismantled, Nuclear Engineering and Technology 53 (2021); F. Aspe et al.: Classification and categorization of the constrained environments in nuclear/radiological installations under decommissioning and dismantling processes, Progress in Nuclear Energy 124 (2020); K. Amgarou at al.: Recommendations for the selection of in situ measurement techniques for radiological characterization in nuclear/radiological installations under decommissioning and dismantling processes, Progress in Nuclear Energy 137 (2021).The STRATEGIST web tool was developed by S. Boden and B. Rogiers from SCK CEN, Y. Desnoyers from Geovariances, N. Pérot from CEA, G. von Oertzen from Brenk Systemplanung, O. Sevbo from Energorisk and S. Demeyer from laboratoire LNE. More information can be found in B. Rogiers et al.: Statistical approach guide. EC H2020 INSIDER project, http://insider-h2020.eu/, Deliverable D3.7 (2021); directly available at: https://strategist.sckcen.be/docs/INSIDER_D3.7.pdf.A short video explaining the functioning of both tools can be seen in INSIDER D&D tools.European Commissio

Geant4 and MCNPX simulations of thermal neutron detection with planar silicon detectors

We used Geant4 and MCNPX codes to evaluate the detection efficiency of planar silicon detectors coupled to different Boron-based converters with varied compositions and thicknesses that detect thermal neutrons via the 10B(n,α)7Li nuclear reaction. Few studies about the thermal neutron transport in Geant4 have been reported so far and it is becoming increasingly difficult to ignore its discrepancies with MCNPX in this neutron energy range. In the thermal energy range, Geant4 shows high discrepancies with MCNPX giving a maximum efficiency of about 3.3% in the 10B case whereas that obtained with MCNPX was 5%. Disagreements obtained between both codes in this energy range are analyzed and discussed. © 2011 IOP Publishing Ltd and SISSA.Peer reviewe

TS2f.5 Characterization of an 241AmBe neutron irradiation facility by different spectrometrictechniques

An automated panoramic irradiator with a 3 Ci 241Am-Be neutron source is installed in a bunker-type large room at the Universidad Politécnica de Madrid (UPM). It was recently modified and a neutron spectrometry campaign was organized to characterize the neutron fields in different measurement points along the irradiation bench. Four research groups working with different Bonner Sphere Spectrometers (BSS) and using different spectral unfolding codes took part to this exercise. INFN–LNF used a BSS formed by 9 spheres plus bare detector, with cylindrical, almost point like, 6LiI(Eu) scintillator (4 mm x 4 mm, from Ludlum); UAZ-UPM employed a similar system but with only 6 spheres plus bare detector; UAB worked with a 3He filled proportional counter at 8kPa filling pressure, cylindrical 9 mm x 10 mm (05NH1 from Eurisys) with 11 spheres configuration; and CIEMAT used 12 spheres with an spherical 3He SP9 counter (Centronic Ltd., UK) with very high sensitivity due to the large diameter (3.2 cm) and the filling pressure of the order of 228 kPa. Each group applied a different spectral unfolding method: INFN and UAB worked with FRUIT ver. 3.0 with their own response matrixes; UAZ-UPM used the BUNKIUT unfolding code with the response matrix UTA4 and CIEMAT employed the GRAVEL-MAXED-IQU package with their own response matrix. The paper shows the main results obtained in terms of neutron spectra at fixed distances from the source as well as total neutron fluence rate and ambient dose equivalent rate H*(10) determined from the spectra. The latter are compared with the readings of a common active survey-meter (LB 6411). The small differences in the results of the various groups are discussed