| 1. |
- Andersson, Peter, 1981-, et al.
(author)
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Coincidence spectroscopy for increased sensitivity in radionuclide monitoring
- 2022
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Conference paper (other academic/artistic)abstract
- The majority of the energy in a nuclear explosion is released in the immediate blast and the initial radiation accounts. The remaining fraction is released through radioactive decay of the explosion's fission products and neutron activation products over a longer time span. This allows for the detection of a nuclear explosion by detecting the presence of residual decay. Radionuclide monitoring stations for detection of radioactive emissions to the atmosphere is thereby an important tool in the verification of compliance with nuclear disarmament treaties. In particular, the globally spanning radionuclide station network of the International Monitoring System (IMS) has been implemented for verification of the Comprehensive Nuclear-Test-Ban Treaty.High Purity Germanium (HPGe) detectors are workhorses in radionuclide monitoring. The detection of characteristic gamma rays can be used to disclose the presence of signature nuclides produced innuclear weapon tests. A particular development that has potential to improve the sensitivity of radionuclide monitoring is the coincidence technique where decaying nuclides that emit several coincident gamma rays can be detected at much smaller activity concentrations than with conventional gamma spectroscopy.In this project, dedicated gamma-gamma coincidence detectors are being developed, utilizing electronically segmented HPGe detectors. These detectors are expected to be highly sensitive to low-activity samples of nuclides that present coincident emissions of gamma rays. In this paper we present the concept, define performance parameters, and explore the performance of such detectors to a subset of radionuclides of particular CTBT relevance. In addition, we discuss the path forward in developing a next generation gamma-gamma coincidence spectroscopy system of segmented HPGe.
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| 2. |
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| 3. |
- Grape, Sophie, 1982-, et al.
(author)
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Non-proliferation and safeguards activities within the Alva Myrdal Centre for nuclear disarmament
- 2022
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In: Proceedings of the Symposium on International Safeguards: Reflecting on the Past and Anticipating the Future.
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Conference paper (other academic/artistic)abstract
- In 2020, the Swedish government announced the intent to start up a national competence centre on nuclear disarmament in Sweden. The goal was to highlight the importance of nuclear disarmament issues, and to promote research, teaching and policy support on topics relevant to nuclear disarmament. During the spring semester 2021, the Alva Myrdal Centre (AMC) on nuclear disarmament was established at Uppsala University. The AMC combines competences from different disciplines such as peace and conflict research, applied nuclear physics, and international law, and organises the work into six different working groups. One of the working groups is focusing on technical aspects, while the remaining five working groups are focusing on policy aspects. The technical working group is led by the Division of Applied Nuclear Physics at Uppsala University, where research on nuclear safeguards has been performed for over 30 years, and where competence in addition exists on a number of applied physics applications ranging from nuclear reactions, nuclear power and detection of radionuclides.
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| 4. |
- Gustavsson, Cecilia, Dr, 1973-, et al.
(author)
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A technical view on Pakistan's nuclear weapons programme
- 2022
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Conference paper (other academic/artistic)abstract
- Pakistan performed at least two nuclear weapons tests in 1998 as a direct response to the Indian nuclear tests earlier the same year. With this act, Pakistan became the seventh country to successfully complete a nuclear weapons programme. The Pakistani nuclear weapons arsenal consists of both uranium and plutonium weapons and the country has an extensive nuclear industry with all facilities necessary for enrichment of uranium, production of plutonium and reprocessing of spent reactor fuel.Pakistan acquired a Canadian civil heavy water nuclear reactor in 1971; KANUPP-1. In 1976 however, the cooperation with Canada ended as Canada stopped supplying fuel for the reactor. At this point, Pakistan had acquired know-how and experience to manufacture its own fuel and also started building an independent nuclear industry with several unsafeguarded reactors at the Khushab site. With French assistance, a reprocessing plant was constructed and consequently, Pakistan is today in possession of all components necessary for developing and employing both uranium and plutonium nuclear devices. In this presentation, we will explore technical challenges associated with bringing a country such as Pakistan under the existing or proposed treaty verification following treaties such as the NPT, TPNW and FMCT. Using a simulation framework and estimates based on known physical quantities and derived abilities, we will discuss what conclusions can be drawn with regards to uranium and plutonium stockpiles.
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| 5. |
- Mishra, Vaibhav, Doktorand, 1989-, et al.
(author)
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Assessments of radiation emission from molten salt reactor spent fuel: Implications for future nuclear safeguards verification
- 2023
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Conference paper (other academic/artistic)abstract
- Safeguards verification using non-destructive assay (NDA) techniques is an important pillar of the safeguards regime to ensuring that nuclear technology is not used for non-peaceful purposes. The methods and approaches for safeguards verification for conventional spent nuclear fuel (SNF) originating from the global fleet of water-cooled reactors are well-established. However, for reactors such as molten salt reactors (MSR), accountancy verification method of irradiated fuel salts is not quite well-established. This is primarily since the irradiated salt is in “bulk form” whereas more conventional LWR SNF encountered by the safeguards inspectors is in “item form”. Moreover, much about the nature of such SNF still remains unknown due to the lack of operational MSRs and equipment adequate to further study, develop and test NDA verification methods.As MSRs could play a complementary role with the existing fleet of reactors in the near future, verification methods concerning the nature of emissions from irradiated fuel salts is timely. Therefore, in this current study we aim to quantify and study the nature of gamma and neutron emissions as well as decay heat production in irradiated fuel salt from the Compact Molten Salt Reactor (CMSR) developed by Seaborg Technologies in Denmark. Simulations were carried out using the Monte-Carlo particle transport code Serpent as well as the code SOURCES 4C to compute nuclide inventories and the associated emission rates of gamma and neutron (from spontaneousfissions, or SF and from (α, n) reactions) emissions and decay heat calculations. These results willshed more light on the implications for nuclear safeguards verification for irradiated fuel salts andalso highlight some of the challenges and opportunities associated with detecting and characterizingthe emissions using NDA methods in the future for SNF of such unique nature.
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| 6. |
- Preston, Markus, 1989-, et al.
(author)
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Neptunium: time for nuclear safeguards?
- 2022
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Conference paper (other academic/artistic)abstract
- Plutonium and uranium are well known weapons-usable nuclear materials which are currently placed under international safeguards. Examples of nuclear-safeguards methods are surveillance of nuclear facilities, inspections of spent nuclear fuel and process monitoring at fuel reprocessing facilities. Once material comes under safeguards, records of the amount of material are kept throughout its life cycle, and material accountancy verification is regularly performed. Deviations from the expected material balances could indicate diversion of nuclear material.It has been known for many years that there exist materials which are currently not under full international safeguards, but which could at least theoretically be used to manufacture a nuclear explosive device. One material that has attracted particular attention in this context is neptunium, which can be found in spent nuclear fuel. Although it is unclear if neptunium has ever been used in a nuclear explosive device, measures for preventing un-declared separation of neptunium have been implemented since 20 years by the International Atomic Energy Agency. However, it has never been placed under safeguards to the same extent as uranium and plutonium. In part, this decision was motivated by the relatively limited amount of neptunium available 20 years ago. Many things have happened in the nuclear industry since then, and there might be a need for re-visiting the issue. In this paper, the relationship between neptunium and international safeguards will be discussed in the context of recent trends in the nuclear energy sector and efforts to close the nuclear fuel cycle.
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| 7. |
- Branger, Erik, 1988-, et al.
(author)
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Effects of modelling assumptions on Cherenkov light intensity predictions
- 2022
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Conference paper (other academic/artistic)abstract
- The Digital Cherenkov Viewing Device (DCVD) is one of the instruments available to IAEA inspectors to verify spent nuclear fuel in wet storage. The DCVD can be used for partial defect verification, verifying that 50% or more of a fuel assembly has not been diverted. The partial defect verification relies on a comparison between measured and predicted intensities, based on operator fuel declarations. Recently, IAEA inspectors have encountered spent fuels with short cooling times where there were systematic differences between predictions and measurements. Through the Swedish support program, this deviation was investigated, by studying various modelling assumptions that could cause the discrepancy.The predominant cause of the discrepancy was beta-decay electrons, passing through the fuel cladding and entering the water with sufficient energy to directly produce Cherenkov light. Analysis of measurement data for a set of fuels where the discrepancy was found to be pronounced revealed that for modern fuel designs with thin claddings the beta contribution is enhanced, and for short-cooled fuels additional beta-decaying isotopes are abundant and must be considered. Furthermore, the data showed that for nuclear fuels that had not reached the discharge burnup, the fuel irradiation history may cause a relative enhancement of the abundance of beta-decaying isotopes relative to other isotopes causing Cherenkov light. Other studied modelling assumptions, such as void, burnable absorbers and using binned gamma spectra, showed that they only introduced a modest bias, and proper default values and data handling can mitigate it. A method to predict the direct beta contribution to the Cherenkov light intensity was developed, which can ensure that the observed biases will be eliminated from future verification campaigns. It is advised that this enhanced prediction method be included in the DCVD software, and made available to inspectors.
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| 8. |
- Branger, Erik, 1988-, et al.
(author)
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Image analysis to support DCVD verification
- 2023
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In: Proceedings of the INMM & ESARDA Joint Annual Meeting, May 22-26, 2023. - : Institute of Nuclear Materials Management (INMM).
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Conference paper (other academic/artistic)abstract
- The Digital Cherenkov Viewing Device (DCVD) is one instrument available to authority inspectors for verifying spent fuel assemblies in wet storage. The measurements result in images of the Cherenkov light emissions from the fuel assembly under study. This work presents research on applying image analysis and statistical methods to improve data quality and to extract more information from the measurements, extending the use of these methods beyond what is currently implemented in the DCVD software. The goal of this project is to apply template matching and statistical analysis to the images. However, before such techniques can be applied, effort is needed to ensure that the measurements are directly comparable. Two main issues are investigated here, the first being the positioning of the Region-Of-Interest. By developing an automated Region-Of-Interest placer, a consistent and reproducible Region-Of-Interest placement can be achieved. The second is automatic identification of fuel type, to support a later comparison with a template. We demonstrate that a method based on Principal Component Analysis can be used to determine the fuel type. Finally, we present the first results regarding template matching, comparing a measured image to a template, aiming to identify regions in the image where the two differ. Such differences could be due to a partial defect located in that region, but also due to other reasons such as debris covering the fuel top. Automatically identification of such regions can in the future be used to focus inspector attention to features requiring expert judgement, supporting efficient use of the measurement data and inspector effort. The first results demonstrate the feasibility of the method, but also that more work is required before the method is robust.
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| 9. |
- Branger, Erik, 1988-, et al.
(author)
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Investigating the sensitivity to irradiation history when predicting fuel parameters using random forest regression
- 2021
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In: ESARDA Bulletin. - : European Commission Joint Research Centre. - 1977-5296. ; 62, s. 2-10
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Journal article (peer-reviewed)abstract
- Safeguards verification of spent nuclear fuel assemblies is frequently done by performing non-destructive measurements, which are used to verify the completeness and correctness of operator declarations such as initial enrichment (IE), burnup (BU) and cooling time (CT) of the fuel. However, different irradiation histories may result in the same combination of CT, BU and IE, and such fuels may behave differently despite identically declared values. The goal of this work is to investigate what effect the irradiation history has on the ability to predict the fuel parameters using random forest regression. Random forest regression models were trained to predict the fuel parameters IE, BU and CT based on combinations of radiation signatures calculated from a previously modelled Pressurised Water Reactor (PWR) spent nuclear fuel library. The radiation signatures studied were the relative gamma-ray activities of Cs137, Cs134 and Eu154, their total gamma-ray activity, the total neutron emission rate and the parametrized early die-away time ? from the Differential Die-away Self Interrogation (DDSI) instrument. The performance of the models were tested on simulations of 2192 PWR fuel assemblies from the Ringhals 3 and 4 nuclear power plants in Sweden, which were simulated based on their documented irradiation histories. Despite significant differences in irradiation history between the training and testing data sets, the Ringhals assembly parameters could be predicted with similar accuracy as for assemblies in the training set. The relative gamma-ray activities were sufficient to predict the CT with an RMSE of 2 years, and adding a total gamma or total neutron signature allowed the BU to be predicted with an RMSE of 1.4 MWd/kgU. The DDSI early die-away time ? enabled an accurate IE prediction, with an RMSE of 0.16 w%. The differences between irradiation histories introduced a systematic bias where CT was overestimated by about 1 year and the BU by about 1.5 MWd/kgU.
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| 10. |
- Branger, Erik, 1988-, et al.
(author)
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Studies of the impact of beta contributions on Cherenkov light emission by spent nuclear fuel
- 2022
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In: ESARDA Bulletin. - : ESARDA. - 1977-5296. ; 64:1, s. 2-9
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Journal article (peer-reviewed)abstract
- The Digital Cherenkov Viewing Device (DCVD) is one of the instruments used by safeguards inspectors to verify spent nuclear fuel in wet storage. The DCVD can be used for partial defect verification, where the inspectors verify that 50% or more of an assembly has not been diverted. The methodology is based on comparing the measured Cherenkov light intensity with a predicted intensity, calculated with operator information.Recently, IAEA inspectors have encountered fuel assemblies for which systematic deviations between predictions and measurements could be observed, indicating that the prediction model did not take into account all sources of Cherenkov light production. One contribution to the Cherenkov light intensity that is frequently omitted is the contribution from beta decays, where energetic electrons exit the fuel material and enter the water with sufficient energy to directly produce Cherenkov light. The objective with this work was hence to study beta contributions and evaluate whether that could be the cause of discrepancy between predictions and experimental data.By simulating the beta contribution for fuel assemblies where the discrepancy was experimentally observed, it was determined that beta decays were the cause. The fuel assemblies had fuel rods with relatively small radii, thin cladding, a short cooling time and an irradiation history that resulted in a relatively large beta contribution for assemblies that had a comparatively low burnup. Therefore, the beta contribution was significant, and caused 10-40% of the total Cherenkov light intensity. By including the beta contributions in the predictions, the RMSE of the deviation between prediction and measurement could be reduced from 20.7% to 11.6% for the available measurement data. The results highlight that the beta contribution can be significant and should be taken into account for accurate predictions.
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