Neutron Coincidence Measurements and Monte Carlo Modelling of Waste Drums Containing Reference Nuclear Material

Within the EC-funded CHANCE project several non-destructive techniques are being considered for the assay of waste bearing drums. Such techniques include calorimetry, gamma-ray spectrometry and neutron coincidence counting. The aim is to quantify uncertainties on the inventory of radionuclides, and...

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Autores principales:	Borella A., Rossa R., Boden S., Bruggeman C., Rogiers B., Smets S., Valcke E.
Formato:	article
Lenguaje:	EN
Publicado:	EDP Sciences 2021
Materias:	neutron coincidence counting reference nuclear material waste characterization Physics QC1-999
Acceso en línea:	https://doaj.org/article/4b8091956a5148c9812ac948d9134b63
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spelling	oai:doaj.org-article:4b8091956a5148c9812ac948d9134b632021-12-02T17:12:46ZNeutron Coincidence Measurements and Monte Carlo Modelling of Waste Drums Containing Reference Nuclear Material2100-014X10.1051/epjconf/202125307001https://doaj.org/article/4b8091956a5148c9812ac948d9134b632021-01-01T00:00:00Zhttps://www.epj-conferences.org/articles/epjconf/pdf/2021/07/epjconf_animma2021_07001.pdfhttps://doaj.org/toc/2100-014XWithin the EC-funded CHANCE project several non-destructive techniques are being considered for the assay of waste bearing drums. Such techniques include calorimetry, gamma-ray spectrometry and neutron coincidence counting. The aim is to quantify uncertainties on the inventory of radionuclides, and how these are potentially reduced by combining the signatures from different techniques in the data analysis. In this framework, neutron coincidence measurements were carried out with two slab counters based on 3He detectors coupled to shift register electronics. Such a system consists of two identical slabs with 6 detectors each, and is transportable, rather compact and flexible in terms of sizes and geometries that can be measured. With this system three 200 L drums containing certified reference nuclear material and different filling materials were measured. The certified nuclear material was in the form of 21 pellets of mixed oxide of U and Pu with a total mass of about 10.5 g; in addition, a single pellet of about 10.05 g was also available. The pellets could be placed in predefined positions within the drum in a reproducible way. The geometry and composition of the three drums was well characterized and consisted of Ethafoam, a mixture of Ethafoam, stainless steel and PVC, and mortar with an inner core of extruded polystyrene. The measurement setup was arranged such that the drum was placed between the two slab counters. The positions of the slab counters relative to the drum were accurately measured before each measurement, and a dedicated system was used to minimize the uncertainty on the detector positioning. The measurement data were first analysed by applying the point model of Hage and the mass of nuclear material in the drum was determined from the rate of totals and reals and the radionuclide composition. Due to the fact that not all the point model conditions were met, we found that the point model overestimates the mass up to about 50%. In addition, a Monte Carlo model of the measurement geometry was developed using the MCNP code. The model was used to determine a calibration factor between the reals rate and the mass of the sample. Measurements with a calibrated 252Cf source were used to verify the model. With a Monte Carlo based approach the mass of the mixed oxide pellets is within a few percent from the nominal values, except for strongly asymmetrical configurations where the deviation is up to about 20%. The results reveal the importance of an accurate background correction and of accounting for surrounding materials of the building such as walls, floor and ceiling in the Monte Carlo model.Borella A.Rossa R.Boden S.Bruggeman C.Rogiers B.Smets S.Valcke E.EDP Sciencesarticleneutron coincidence countingreference nuclear materialwaste characterizationPhysicsQC1-999ENEPJ Web of Conferences, Vol 253, p 07001 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	neutron coincidence counting reference nuclear material waste characterization Physics QC1-999
spellingShingle	neutron coincidence counting reference nuclear material waste characterization Physics QC1-999 Borella A. Rossa R. Boden S. Bruggeman C. Rogiers B. Smets S. Valcke E. Neutron Coincidence Measurements and Monte Carlo Modelling of Waste Drums Containing Reference Nuclear Material
description	Within the EC-funded CHANCE project several non-destructive techniques are being considered for the assay of waste bearing drums. Such techniques include calorimetry, gamma-ray spectrometry and neutron coincidence counting. The aim is to quantify uncertainties on the inventory of radionuclides, and how these are potentially reduced by combining the signatures from different techniques in the data analysis. In this framework, neutron coincidence measurements were carried out with two slab counters based on 3He detectors coupled to shift register electronics. Such a system consists of two identical slabs with 6 detectors each, and is transportable, rather compact and flexible in terms of sizes and geometries that can be measured. With this system three 200 L drums containing certified reference nuclear material and different filling materials were measured. The certified nuclear material was in the form of 21 pellets of mixed oxide of U and Pu with a total mass of about 10.5 g; in addition, a single pellet of about 10.05 g was also available. The pellets could be placed in predefined positions within the drum in a reproducible way. The geometry and composition of the three drums was well characterized and consisted of Ethafoam, a mixture of Ethafoam, stainless steel and PVC, and mortar with an inner core of extruded polystyrene. The measurement setup was arranged such that the drum was placed between the two slab counters. The positions of the slab counters relative to the drum were accurately measured before each measurement, and a dedicated system was used to minimize the uncertainty on the detector positioning. The measurement data were first analysed by applying the point model of Hage and the mass of nuclear material in the drum was determined from the rate of totals and reals and the radionuclide composition. Due to the fact that not all the point model conditions were met, we found that the point model overestimates the mass up to about 50%. In addition, a Monte Carlo model of the measurement geometry was developed using the MCNP code. The model was used to determine a calibration factor between the reals rate and the mass of the sample. Measurements with a calibrated 252Cf source were used to verify the model. With a Monte Carlo based approach the mass of the mixed oxide pellets is within a few percent from the nominal values, except for strongly asymmetrical configurations where the deviation is up to about 20%. The results reveal the importance of an accurate background correction and of accounting for surrounding materials of the building such as walls, floor and ceiling in the Monte Carlo model.
format	article
author	Borella A. Rossa R. Boden S. Bruggeman C. Rogiers B. Smets S. Valcke E.
author_facet	Borella A. Rossa R. Boden S. Bruggeman C. Rogiers B. Smets S. Valcke E.
author_sort	Borella A.
title	Neutron Coincidence Measurements and Monte Carlo Modelling of Waste Drums Containing Reference Nuclear Material
title_short	Neutron Coincidence Measurements and Monte Carlo Modelling of Waste Drums Containing Reference Nuclear Material
title_full	Neutron Coincidence Measurements and Monte Carlo Modelling of Waste Drums Containing Reference Nuclear Material
title_fullStr	Neutron Coincidence Measurements and Monte Carlo Modelling of Waste Drums Containing Reference Nuclear Material
title_full_unstemmed	Neutron Coincidence Measurements and Monte Carlo Modelling of Waste Drums Containing Reference Nuclear Material
title_sort	neutron coincidence measurements and monte carlo modelling of waste drums containing reference nuclear material
publisher	EDP Sciences
publishDate	2021
url	https://doaj.org/article/4b8091956a5148c9812ac948d9134b63
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Neutron Coincidence Measurements and Monte Carlo Modelling of Waste Drums Containing Reference Nuclear Material

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