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

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 LaBr$_{3}$(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

O território paulista na iconografia oitocentista: mapas, desenhos e fotografias. análise de uma herança cotidiana

This paper presents a study about the cartography elaborated to represent São Paulos territory during the 19th century. The author seeks to show the permanence of cultural values related to the colonial period by analyzing some cartographical models, which are not necessarily linked to a cartographic school. In this context, the author seeks to identify the formative values of the regional territorial space, the cultural identity of the common Man and the specific needs of his or her daily life

Self-attenuation in the low-energy range: an experimental study on 210Pb

International audienceQuantitative analysis of environmental samples generally involves volume source with low radioactivity and an unknown composition of the sample matrix. Unless an efficiency calibration with the same geometry and matrix is available, it is necessary to correct the raw counting rates for self-attenuation effects in order to obtain the correct sample activity. This can be achieved either experimentally or by means of calculation based on mass attenuation coefficients that can be directly measured or taken from tabulated absorption data. The self-attenuation effect is more pronounced when the energy of the emitted photons is low. This is the case with 210Pb, which is a low-energy gamma emitting radionuclide (46.54 keV) suffering strong absorption in the sample matrix and whose concentration in the environment must be regularly monitored according to public health regulations. Within the framework of the GSWG, twelve laboratories agreed to carry out measurements with matrices containing 210Pb and to compare their approaches to the determination of self-attenuation correction factors in order to draft practical recommendations for users.With this aim, the Laboratoire National Henri Becquerel (LNHB) prepared two different sets of three samples, each packed in cylindrical containers with known activities of 210Pb and 137Cs, according to the preparation procedure using standard solutions. The sample filled with resin was meant to be considered as a standard source by the participants and could be used for the efficiency calibration of the detectors. The goal of the exercise was to determine the activity of the two radionuclides included in the other two samples, with unknown matrices. This required the participants to establish the self-attenuation correction factors between the calibration and the measurement matrices. Inactive matrices can be used to experimentally determine the attenuation coefficients for calculating self-absorption.The different approaches and results obtained by the participants are presented and general recommendations are proposed

Self-attenuation in the low-energy range: an experimental study on 210Pb

International audienceQuantitative analysis of environmental samples generally involves volume source with low radioactivity and an unknown composition of the sample matrix. Unless an efficiency calibration with the same geometry and matrix is available, it is necessary to correct the raw counting rates for self-attenuation effects in order to obtain the correct sample activity. This can be achieved either experimentally or by means of calculation based on mass attenuation coefficients that can be directly measured or taken from tabulated absorption data. The self-attenuation effect is more pronounced when the energy of the emitted photons is low. This is the case with 210Pb, which is a low-energy gamma emitting radionuclide (46.54 keV) suffering strong absorption in the sample matrix and whose concentration in the environment must be regularly monitored according to public health regulations. Within the framework of the GSWG, twelve laboratories agreed to carry out measurements with matrices containing 210Pb and to compare their approaches to the determination of self-attenuation correction factors in order to draft practical recommendations for users.With this aim, the Laboratoire National Henri Becquerel (LNHB) prepared two different sets of three samples, each packed in cylindrical containers with known activities of 210Pb and 137Cs, according to the preparation procedure using standard solutions. The sample filled with resin was meant to be considered as a standard source by the participants and could be used for the efficiency calibration of the detectors. The goal of the exercise was to determine the activity of the two radionuclides included in the other two samples, with unknown matrices. This required the participants to establish the self-attenuation correction factors between the calibration and the measurement matrices. Inactive matrices can be used to experimentally determine the attenuation coefficients for calculating self-absorption.The different approaches and results obtained by the participants are presented and general recommendations are proposed

Determining the probability of locating peaks using computerized peak-location methods in gamma-ray spectra as a function of the relative peak-area uncertainty

The probabilities of locating peaks with a high relative peak-area uncertainty were determined empirically with nine types of peak-location software used in laboratories engaged in gamma-ray spectrometry measurements. It was found that it is not possible to locate peaks with a probability of 0.95, when they have a relative peak-area uncertainty in excess of 50%. Locating peaks at these relatively high peak-area uncertainties with a probability greater than 0.95 is only possible in the library-driven mode, where the peak positions are supposed a-priori. The deficiencies of the library-driven mode and the possibilities to improve the probabilities of locating peaks are briefly discussed. © 2019 Elsevier Lt