uu.seUppsala University Publications
Change search
Link to record
Permanent link

Direct link
BETA
Publications (10 of 65) Show all publications
Zsolt, E., Mishra, V., Grape, S., Branger, E., Jansson, P. & Caldeira Balkeståhl, L. (2019). Investigating the gamma and neutron radiation around quivers for verification purposes. In: : . Paper presented at ESARDA Symposium 2019.
Open this publication in new window or tab >>Investigating the gamma and neutron radiation around quivers for verification purposes
Show others...
2019 (English)Conference paper, Oral presentation with published abstract (Other academic)
Abstract [en]

Before encapsulation of spent nuclear fuel in a geological repository, the fuels need to be verified fors afeguards purposes. This requirement applies to all spent fuel assemblies, including those with properties or designs that are especially challenging to verify. One such example are quivers, a new type of containers used to hold damaged spent fuel rods. After placing damaged rods inside the quivers, they are sealed with a thick lid and the water is removed. The lid is thick enough to significantly reduce the amount of the gamma radiation penetrating through it, which can make safeguards verification from the top using gamma techniques difficult.

In this paper we make a first feasibility study related to safeguards verification of quivers, aimed at investigating the gamma and neutron radiation field around a quiver using a simplified quiver geometry. The nuclide inventory of the rods placed in the quiver is calculated with Serpent and Origen-Arp, and the radiation transport is modeled with Serpent. The objective is to assess the capability of existing non-destructive assay instruments, measuring the gamma and/or neutron radiation from the object, to verify the content for nuclear safeguards purposes. The results show that the thick quiver lid attenuates the gamma radiation, thereby making gamma-radiation based verification from above the quiver difficult. Verification using neutron instruments above the quiver, or gamma and/or neutron instruments on the side may be possible. These results are in agreement with measurements of a BWR quiver using a DCVD, performed by the authors.

Keywords
quiver, safeguards verification, gamma radiation, neutron radiation, spent fuel, PWR, modeling
National Category
Subatomic Physics
Research subject
Physics with specialization in Applied Nuclear Physics
Identifiers
urn:nbn:se:uu:diva-389765 (URN)
Conference
ESARDA Symposium 2019
Available from: 2019-07-24 Created: 2019-07-24 Last updated: 2019-07-24
Grape, S., Branger, E., Elter, Z., Jansson, P. & Mishra, V. (2019). Machine learning in nuclear safeguards. In: : . Paper presented at Swedish Workshop on Data Science.
Open this publication in new window or tab >>Machine learning in nuclear safeguards
Show others...
2019 (English)Conference paper, Poster (with or without abstract) (Other academic)
Abstract [en]

•Before placing spent nuclear fuel in in a geological repository, they will be characterized and their declared properties will be verified.

•We have created large library of modelled spent nuclear fuel (SNF) assemblies and estimated their activity of gamma-ray emitting fission products, the early die-away time τ and the Cherenkov light intensity.

•We have used Random Forest regression to evaluate the capability to determine the fuel parameters initial enrichment (IE), burnup (BU) and cooling time (CT) using data from non-destructive assay (NDA) techniques

National Category
Other Physics Topics
Identifiers
urn:nbn:se:uu:diva-394881 (URN)
Conference
Swedish Workshop on Data Science
Funder
Swedish Radiation Safety Authority
Available from: 2019-10-10 Created: 2019-10-10 Last updated: 2019-10-10
Branger, E., Grape, S., Jansson, P. & Jacobsson Svärd, S. (2019). On the inclusion of light transport in prediction tools for Cherenkov light intensity assessment of irradiated nuclear fuel assemblies. Journal of Instrumentation, 14, Article ID T01010.
Open this publication in new window or tab >>On the inclusion of light transport in prediction tools for Cherenkov light intensity assessment of irradiated nuclear fuel assemblies
2019 (English)In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 14, article id T01010Article in journal (Refereed) Published
Abstract [en]

The Digital Cherenkov Viewing Device (DCVD) is a tool used to verify irradiated nuclear fuel assemblies in wet storage by imaging the Cherenkov light produced by the radiation emitted from the assemblies. It is frequently used for partial defect verification, verifying that part of an assembly has not been removed and/or replaced. In one of the verification procedures used, the detected total Cherenkov light intensities from a set of assemblies are compared to predicted intensities, which are calculated using operator declarations for the assemblies.

This work presents a new, time-efficient method to simulate DCVD images of fuel assemblies, allowing for estimations of the Cherenkov light production, transport and detection. Qualitatively, good agreement between simulated and measured images is demonstrated. Quantitatively, it is shown that relative intensity predictions based on simulated images are within 0.5% of corresponding predictions based solely on the production of Cherenkov light, neglecting light transport and detection. Consequently, in most cases it is sufficient to use predictions based on produced Cherenkov light, neglecting transport and detection, thus substantially reducing the time needed for simulations.

In a verification campaign, assemblies are grouped according to their type, and the relative measured and predicted intensities are compared in a group. By determining transparency factors, describing the fraction of Cherenkov light that is blocked by the top plate of an assembly, it is possible to adjust predictions based on the production of Cherenkov light to take the effect of the top plate into account. This procedure allows assemblies of the same type bit with different top plates to be compared with increased accuracy. The effect of using predictions adjusted with transparency factors were assessed experimentally on a set of Pressurized Water Reactor 17x17 assemblies having five different top plate designs. As a result of the adjustment, the agreement between measured and predicted relative intensities for the whole data set was enhanced, resulting in a reduction of an RMSE from 14.1% to 10.7%. It is expected that further enhancements may be achieved by introducing more detailed top-plate and spacer descriptions.

Keywords
Nuclear safeguards, Geant4, Cherenkov light, DCVD, Nuclear fuel
National Category
Subatomic Physics
Research subject
Physics with specialization in Applied Nuclear Physics
Identifiers
urn:nbn:se:uu:diva-357151 (URN)10.1088/1748-0221/14/01/T01010 (DOI)000457930800001 ()
Funder
Swedish Radiation Safety Authority, SSM2012-2750Swedish National Infrastructure for Computing (SNIC), p2007011
Available from: 2018-08-13 Created: 2018-08-13 Last updated: 2019-03-05Bibliographically approved
Pöder Balkeståhl, L., Elter, Z. & Grape, S. (2019). Parametrization of the differential die-away self-interrogation early die-away time for PWR spent fuel assemblies. In: : . Paper presented at 41st ESARDA Annual Meeting Symposium.
Open this publication in new window or tab >>Parametrization of the differential die-away self-interrogation early die-away time for PWR spent fuel assemblies
2019 (English)Conference paper, Oral presentation with published abstract (Other academic)
Abstract [en]

The differential die-away self-interrogation (DDSI) instrument developed and built in Los Alamos National Laboratory (LANL) is being considered for verification before final disposal. One of the signals from this instrument, the early die-away time, has been shown to be proportional to the multiplication of the spent fuel assembly. Full-scale simulations of the instrument response using MCNP are time consuming. This may become a problem in cases when the instrument response to a large number of fuel assemblies is required, such as in the case of training machine learning models.

 

In this paper, we propose a parametrization of the early die-away time as a function of initial enrichment (IE), burn-up (BU) and cooling time (CT), for intact PWR spent fuel assemblies. The parametrization is calculated from a dataset of 1040 simulated PWR spent fuel assemblies with fuel parameters in the range of IE=2-5%, BU=15-60 GWd/tU and CT=5-70 years. The simulations are done using Serpent2 for the depletion calculation and MCNP6 for the neutron transport and detection in the DDSI.

 

It was found that the CT dependence can be decoupled from the BU and IE dependence, and that it follows an exponential decay. The BU and IE dependences have been fitted with several different functions, and the best fit was chosen based on the chi-square value. The determination of the die-away time using the parametrization has been tested on a separate dataset, resulting in a root mean square error (RMSE) of 0.6 µs (the early die-away time ranges from 28 µs to 84 µs). A description of this work is given in the paper together with details on the choice of parametrizing function, and qualitative arguments for that choice.

National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-394882 (URN)
Conference
41st ESARDA Annual Meeting Symposium
Funder
Swedish Radiation Safety Authority
Available from: 2019-10-10 Created: 2019-10-10 Last updated: 2019-10-10
Branger, E., Grape, S. & Jansson, P. (2019). Verifying PWR assemblies with rod cluster control assembly inserts using a DCVD. ESARDA Bulletin (58), 35-40
Open this publication in new window or tab >>Verifying PWR assemblies with rod cluster control assembly inserts using a DCVD
2019 (English)In: ESARDA Bulletin, ISSN 1977-5296, no 58, p. 35-40Article in journal (Refereed) Published
Abstract [en]

One of the instruments available to authority inspectors to measure and characterize the Cherenkov light emissions from irradiated nuclear fuel assemblies in wet storage is the Digital Cherenkov Viewing Device (DCVD). Based on the presence, characteristics and intensity of the Cherenkov light, the inspectors can verify that an assembly under study is not a dummy object, as well as perform partial defect verification of the assembly.

PWR assemblies are sometimes stored with a rod cluster control assembly (RCCA) inserted, which affects the Cherenkov light production and transport in the assembly. Such an insert will also block light from exiting the top of the fuel assembly, which will affect the light distribution and intensity of the Cherenkov light emissions. Whether or not this constitutes a problem when verifying the assemblies for gross or partial defects with a DCVD has not previously been investigated thoroughly.

In this work, the Cherenkov light intensity of a PWR 17x17 assembly with two different RCCA inserts were simulated and analysed, and compared to the Cherenkov light intensity from an assembly without an insert. For the studied assembly and insert types, the DCVD was found to be able to detect partial defects on the level of 50% in all studied cases with similar performance, though with a higher measurement uncertainty due to the reduced intensity when an RCCA insert is present. Consequently, for the studied assembly and insert types, assemblies with inserts can be verified with the same methodology as used for assemblies without inserts, with similar partial defect detection performance.

The simulation approach used also made it possible to investigate the minimum Cherenkov light intensity reduction resulting from partial defects of other levels than 50%, in the PWR 17x17 fuel assembly with and without RCCA inserts. The results for the simulations without an insert were in agreement with previous results, despite differences in substitution patterns, substitution materials, modeling software and analysis approach.

Keywords
DCVD, partial defect verification, Rod cluster control assembly, Cherenkov light, Geant4, nuclear fuel
National Category
Subatomic Physics
Research subject
Physics with specialization in Applied Nuclear Physics
Identifiers
urn:nbn:se:uu:diva-388553 (URN)
Available from: 2019-07-01 Created: 2019-07-01 Last updated: 2019-07-01
Caldeira Balkeståhl, L., Elter, Z., Grape, S. & Hellesen, C. (2018). Application of Multivariate Analysis to Gamma and Neutron Signatures from Spent Nuclear Fuel. In: : . Paper presented at 59th Annual Meeting of the Institute of Nuclear Materials Management (INMM), July 22-26 2018, Baltimore, USA.
Open this publication in new window or tab >>Application of Multivariate Analysis to Gamma and Neutron Signatures from Spent Nuclear Fuel
2018 (English)Conference paper, Oral presentation with published abstract (Other academic)
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-380882 (URN)
Conference
59th Annual Meeting of the Institute of Nuclear Materials Management (INMM), July 22-26 2018, Baltimore, USA
Available from: 2019-04-02 Created: 2019-04-02 Last updated: 2019-10-02Bibliographically approved
Åberg Lindell, M., Andersson, P., Grape, S., Hellesen, C., Håkansson, A. & Eriksson, M. (2018). Discrimination of irradiated MOX fuel from UOX fuel by multivariate statistical analysis of simulated activities of gamma-emitting isotopes. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 885, 67-78
Open this publication in new window or tab >>Discrimination of irradiated MOX fuel from UOX fuel by multivariate statistical analysis of simulated activities of gamma-emitting isotopes
Show others...
2018 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 885, p. 67-78Article in journal (Refereed) Published
Abstract [en]

This paper investigates how concentrations of certain fission products and their related gamma-ray emissions can be used to discriminate between uranium oxide (UOX) and mixed oxide (MOX) type fuel. Discrimination of irradiated MOX fuel from irradiated UOX fuel is important in nuclear facilities and for transport of nuclear fuel, for purposes of both criticality safety and nuclear safeguards. Although facility operators keep records on the identity and properties of each fuel, tools for nuclear safeguards inspectors that enable independent verification of the fuel are critical in the recovery of continuity of knowledge, should it be lost. A discrimination methodology for classification of UOX and MOX fuel, based on passive gamma-ray spectroscopy data and multivariate analysis methods, is presented. Nuclear fuels and their gamma-ray emissions were simulated in the Monte Carlo code Serpent, and the resulting data was used as input to train seven different multivariate classification techniques. The trained classifiers were subsequently implemented and evaluated with respect to their capabilities to correctly predict the classes of unknown fuel items. The best results concerning successful discrimination of UOX and MOX-fuel were acquired when using non-linear classification techniques, such as the k nearest neighbors method and the Gaussian kernel support vector machine. For fuel with cooling times up to 20 years, when it is considered that gamma-rays from the isotope  134Cs can still be efficiently measured, success rates of 100% were obtained. A sensitivity analysis indicated that these methods were also robust.

Keywords
Spent nuclear fuel, MOX, Gamma spectroscopy, Multivariate analysis, Classification
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-337676 (URN)10.1016/j.nima.2017.12.020 (DOI)000424740800009 ()
Funder
Swedish Research Council, VR 621-2009-3991Swedish Radiation Safety Authority, SSM2016-661
Available from: 2018-01-03 Created: 2018-01-03 Last updated: 2018-04-19Bibliographically approved
Åberg Lindell, M., Andersson, P., Grape, S., Håkansson, A. & Eriksson, M. (2018). Estimating irradiated nuclear fuel characteristics by nonlinear multivariate regression of simulated gamma-ray emissions. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 897, 85-91
Open this publication in new window or tab >>Estimating irradiated nuclear fuel characteristics by nonlinear multivariate regression of simulated gamma-ray emissions
Show others...
2018 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 897, p. 85-91Article in journal (Refereed) Published
Abstract [en]

In addition to verifying operator declared parameters of spent nuclear fuel, the ability to experimentally infer such parameters with a minimum of intrusiveness is of great interest and has been long-sought after in the nuclear safeguards community. It can also be anticipated that such ability would be of interest for quality assurance in e.g. recycling facilities in future Generation IV nuclear fuel cycles. One way to obtain information regarding spent nuclear fuel is to measure various gamma-ray intensities using high-resolution gamma-ray spectroscopy. While intensities from a few isotopes obtained from such measurements have traditionally been used pairwise, the approach in this work is to simultaneously analyze correlations between all available isotopes, using multivariate analysis techniques. Based on this approach, a methodology for inferring burnup, cooling time, and initial fissile content of PWR fuels using passive gamma-ray spectroscopy data has been investigated. PWR nuclear fuels, of UOX and MOX type, and their gamma-ray emissions, were simulated using the Monte Carlo code Serpent. Data comprising relative isotope activities was analyzed with decision trees and support vector machines, for predicting fuel parameters and their associated uncertainties. From this work it may be concluded that up to a cooling time of twenty years, the 95% prediction intervals of burnup, cooling time and initial fissile content could be inferred to within approximately 7 MWd/kgHM, 8 months, and 1.4 percentage points, respectively. An attempt aiming to estimate the plutonium content in spent UOX fuel, using the developed multivariate analysis model, is also presented. The results for Pu mass estimation are promising and call for further studies.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2018
Keywords
Nuclear safeguards, Spent nuclear fuel, Gamma-ray, Multivariate analysis, Nonlinear regression
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-357374 (URN)10.1016/j.nima.2018.04.034 (DOI)000433206800014 ()
Available from: 2018-08-24 Created: 2018-08-24 Last updated: 2018-08-24Bibliographically approved
Branger, E., Grape, S., Jansson, P. & Jacobsson Svärd, S. (2018). Experimental evaluation of models for predicting Cherenkov light intensities from short-cooled nuclear fuel assemblies. Journal of Instrumentation, 13, Article ID P02022.
Open this publication in new window or tab >>Experimental evaluation of models for predicting Cherenkov light intensities from short-cooled nuclear fuel assemblies
2018 (English)In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 13, article id P02022Article in journal (Refereed) Published
Abstract [en]

The Digital Cherenkov Viewing Device (DCVD) is a tool used by nuclear safeguards inspectors to verify irradiated nuclear fuel assemblies in wet storage based on the recording of Cherenkov light produced by the assemblies. One type of verification involves comparing the measured light intensity from an assembly with a predicted intensity, based on assembly declarations. Crucial for such analyses is the performance of the prediction model used, and recently new modelling methods have been introduced to allow for enhanced prediction capabilities by taking the irradiation history into account, and by including the cross-talk radiation from neighbouring assemblies in the predictions.

In this work, the performance of three models for Cherenkov-light intensity prediction is evaluated by applying them to a set of short-cooled PWR 17x17 assemblies for which experimental DCVD measurements and operator-declared irradiation data was available; (1) a two-parameter model, based on total burnup and cooling time, previously used by the safeguards inspectors, (2) a newly introduced gamma-spectrum-based model, which incorporates cycle-wise burnup histories, and (3) the latter gamma-spectrum-based model with the addition to account for contributions from neighbouring assemblies.

The results show that the two gamma-spectrum-based models provide significantly higher precision for the measured inventory compared to the two-parameter model, lowering the standard deviation between relative measured and predicted intensities from 15.2% to 8.1% respectively 7.8%.

The results show some systematic differences between assemblies of different designs (produced by different manufacturers) in spite of their similar PWR 17x17 geometries, and possible ways are discussed to address such differences, which may allow for even higher prediction capabilities. Still, it is concluded that the gamma-spectrum-based models enable confident verification of the fuel assembly inventory at the currently used detection limit for partial defects, being a 30% discrepancy between measured and predicted intensities, while some false detection occurs with the two-parameter model. The results also indicate that the gamma-spectrum-based prediction methods are accurate enough that the 30% discrepancy limit could potentially be lowered.

Keywords
Cherenkov detectors; Search for radioactive and fissile materials; Simulation methods and programs; Radiation calculation
National Category
Subatomic Physics
Research subject
Physics
Identifiers
urn:nbn:se:uu:diva-346692 (URN)10.1088/1748-0221/13/02/P02022 (DOI)000425937900001 ()
Funder
Swedish Radiation Safety Authority, SSM2012-2750Swedish National Infrastructure for Computing (SNIC), p2007011
Available from: 2018-03-20 Created: 2018-03-20 Last updated: 2018-08-17Bibliographically approved
Branger, E., Grape, S., Jansson, P. & Jacobsson Svärd, S. (2018). Experimental study of background subtraction in Digital Cherenkov Viewing Device measurements. Journal of Instrumentation, 13(8), Article ID T08008.
Open this publication in new window or tab >>Experimental study of background subtraction in Digital Cherenkov Viewing Device measurements
2018 (English)In: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 13, no 8, article id T08008Article in journal (Refereed) Published
Abstract [en]

The Digital Cherenkov Viewing Device (DCVD) is an imaging tool used by authority inspectors for partial defect verification of nuclear fuel assemblies in wet storage, i.e. to verify that part of an assembly has not been diverted. One of the currently adopted verification procedures is based on quantitative measurements of the assembly's Cherenkov light emissions, and comparisons to an expected intensity, calculated based on operator declarations. A background subtraction of the intensity data in the recorded images is necessary for accurate quantitative measurements. The currently used background subtraction is aimed at removing an electronics-induced image-wide offset, but it is argued here that the currently adopted procedure may be insufficient.

It is recommended that a standard dark-frame subtraction should be used, to remove systematic pixel-wise background due to the electronics, replacing the currently used offset procedure. Experimental analyses show that a dark-frame subtraction would further enhance the accuracy and reliability of DCVD measurements. Furthermore, should ageing of the CCD chip result in larger systematic pixel-wise deviations over time, a dark-frame subtraction can ensure reliable measurements regardless of the age of the CCD chip. It can also help in eliminating any adverse effects of malfunctioning pixels. In addition to the background from electronic noise, ways to compensate for background from neighbouring fuel assemblies and ambient light are also discussed.

Keywords
Nuclear safeguards, Cherenkov light, DCVD, Nuclear fuel
National Category
Subatomic Physics
Research subject
Physics with specialization in Nuclear Physics
Identifiers
urn:nbn:se:uu:diva-357150 (URN)10.1088/1748-0221/13/08/T08008 (DOI)000442556100001 ()
Funder
Swedish Radiation Safety Authority, SSM2012-2750Swedish National Infrastructure for Computing (SNIC), p2007011
Available from: 2018-08-13 Created: 2018-08-13 Last updated: 2019-08-01Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-5133-6829

Search in DiVA

Show all publications