| 1. |
- Bengtsson, Martin, et al.
(författare)
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Experimental method for verification of calculated Cs-137 content in nuclear fuel assemblies
- 2022
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Ingår i: Nuclear Technology. - : Informa UK Limited. - 0029-5450 .- 1943-7471. ; 208:2, s. 295-302
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Tidskriftsartikel (refereegranskat)abstract
- A method to determine the absolute activity of 137Cs in irradiated nuclear fuel is presented. Using a well-known point-like calibration source in combination with measurements of the gamma-ray intensity from the nuclear fuel and Monte Carlo calculations based on the nominal measurement geometry, the activity content can be determined without prior knowledge of the intrinsic detection efficiency of the gamma-ray detector. The presented method is tested using measurements of the 137Cs intensity from spent nuclear fuel of the pressurized water type at the central interim storage in Sweden. Using an assumption of homogeneous distribution of 137Cs throughout the fuel, we demonstrate a linear relationship between measured activity and the activity calculated by a state-of-the-art simulation code. For future studies, we suggest some factors that potentially can decrease the uncertainty in the correlation between measured and calculated activity.
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| 2. |
- Hursin, Mathieu, et al.
(författare)
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Measurement of the Gas Velocity in a Water-Air Mixture in CROCUS Using Neutron Noise Techniques
- 2020
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Ingår i: Nuclear Technology. - : Informa UK Limited. - 0029-5450 .- 1943-7471. ; 206:10, s. 1566-1583
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Tidskriftsartikel (refereegranskat)abstract
- The possibility of measuring the gas-phase velocity in a two-phase mixture through the use of neutron noise techniques is demonstrated in the zero-power reactor CROCUS of the Ecole Polytechnique Federale de Lausanne. It is the first step toward the experimental validation of an existing theoretical model whose objective is the reconstruction of the void profile in a channel. The use of zero-power research reactors is advantageous due to their clean environment in terms of signal fluctuations. To this end, a channel was installed in the reflector of CROCUS. A two-component mixture is generated inside the channel through the injection of compressed air. The signal fluctuations of neutron detectors located at various axial locations next to the channel are processed to determine the transit time of the gas phase between detectors. Four methods are presented based on the detector signal time series either in the time domain (time correlations between signals) or in the frequency domain (phase of the cross-power spectral density. All four methods returned consistent transit times and similar experimental uncertainty. The largest possible gas injection rates as well as the highest possible neutron flux level improve the visibility of the traveling perturbation and reduce the experimental uncertainty on the transit time for a given acquisition time. © 2020, © 2020 American Nuclear Society.
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| 3. |
- Kaiserfeld, Thomas, et al.
(författare)
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Changing the System Culture : Mobilizing the Social Sciences in the Swedish Nuclear Waste System
- 2021
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Ingår i: Nuclear Technology. - : Informa UK Limited. - 0029-5450 .- 1943-7471. ; 207:9, s. 1456-1468
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this paper is to analyze how competence in the humanities and social sciences has been introduced into the system culture of the Swedish nuclear waste system (SNWS) traditionally dominated by scientists and engineers. In the spring of 1980, fierce local protests were directed against drilling teams sent out to investigate the geology of potential locations for a repository of spent nuclear fuel. This demonstrated the political and ethical dimensions of the waste issue and the limitations of the technocratic approach that had hitherto dominated the system culture of the SNWS. In order to counter this tendency, the government established an advisory board, Samrådsnämnden för kärnavfall (abbreviated KASAM), in 1985 with the task to widen the perspectives on the nuclear waste issue. KASAM engaged social scientists and humanists and started organizing annual workshops inviting engineers and scientists working with the waste issue to discuss its ethical and political dimensions. In the early 1990s, SKB, the Swedish implementer organization responsible for the management of nuclear waste, changed its strategy for finding suitable locations for a repository of spent nuclear fuel. Approval from the local population became a key condition. In the early 2000s, only two municipalities remained, both of them already housing nuclear power plants. After careful investigations and many deliberations, one of them was eventually chosen. The combination of KASAM’s activities to broaden the discussion and the local protests in many communities initiated a gradual change of the system culture within the SNWS. The initial technocratic approach was broadened to encompass ethical, social, and political aspects, and the main organizations now acknowledge that not only technical and scientific skills but also competence from social science and the humanities were of essence.
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| 4. |
- Neretnieks, Ivars
(författare)
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Radionuclide Transport in Channel Networks with Radial Diffusion in the Porous Rock Matrix
- 2023
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Ingår i: Nuclear Technology. - : Informa UK Limited. - 0029-5450 .- 1943-7471. ; 209:4, s. 604-621
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Tidskriftsartikel (refereegranskat)abstract
- Water flows in only a small fraction of the total area of the fractures in fractured rocks. The width of the “channels” is often in the range of centimeters to tens of centimeters. Nuclides can diffuse into and out of the porous rock matrix, which causes them to be significantly retarded compared to the water velocity. In discrete facture networks, diffusion is modeled to be linear and perpendicular to the fracture surface. From a narrow channel, the diffusion cloud would then be as wide as the channel. When the nuclide has propagated farther than the channel width, the diffusion will become essentially radial, which allows the nuclide flux to increase enormously. For the times of interest for a repository for high-level nuclide waste, this will increase nuclide flux into the matrix by tens to thousands of times, and consequently, the nuclide retardation in the flowing water. Radial diffusion was not invoked in the performance assessment of the Forsmark site, which in January 2022 was chosen by the government to locate Sweden’s high-level waste repository. It is shown, using data from this site, that the effect of radial diffusion from the narrow channels considerably increases the retardation of any escaping radionuclides, potentially allowing for the use of thinner copper canisters.
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| 5. |
- Pasi, Anna-Elina, 1993, et al.
(författare)
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Organic Telluride Formation from Paint Solvents Under Gamma Irradiation
- 2022
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Ingår i: Nuclear Technology. - : Informa UK Limited. - 0029-5450 .- 1943-7471. ; 208:11, s. 1734-1744
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Tidskriftsartikel (refereegranskat)abstract
- The interactions between tellurium and organic material during a nuclear reactor accident are critical to source term estimations because of the possible formation of volatile species. Reactions taking place in the containment sump are of interest since these can lead to re-volatilization and increase the fission product source term. This paper presents results from experiments investigating the interaction of tellurium dioxide with three paint solvents-texanol ester, methyl isobutyl ketone, and toluene-under containment sump conditions. The experiments were performed by irradiating a mixed solution of tellurium dioxide and paint solvents at a dose rate of 4 kGy/h up to 300 kGy. The resulting samples were analyzed for tellurium concentration and speciation. Tellurium(IV) was found to reduce to metallic tellurium under irradiation when paint solvents were present. More importantly, several volatile organic tellurides were identified in the irradiated samples, which suggests that tellurium can form volatile species in sump conditions when in contact with dissolved paint solvents. This paper provides novel evidence of organic telluride formation in the sump and raises further interest in tellurium chemistry during a severe nuclear reactor accident.
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| 6. |
- Pasi, Anna-Elina, 1993, et al.
(författare)
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Tellurium Behavior in the Containment Sump: Dissolution, Redox, and Radiolysis Effects
- 2020
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Ingår i: Nuclear Technology. - : Informa UK Limited. - 0029-5450 .- 1943-7471. ; , s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- In the event of a severe nuclear accident, one major concern is the release of radioactive material into the environment causing potential exposure of the general public to radiation. Among the volatile radionuclides are a range of tellurium isotopes. Due to the radioactivity and the volatility of tellurium, it has to be taken into account when assessing the overall effects of an accident. The interest in tellurium is not limited only to its release but also to the fact that some tellurium isotopes decay to iodine, and thus affect the iodine release behavior. The release and transport behavior of tellurium has been investigated over the past decades, however, the aqueous chemistry of tellurium in the complex containment sump system is still unclear. This study presents the behavior of tellurium dioxide in simplified containment sump conditions in relation to dissolution, redox reactions, and interactions with water radiolysis products. The results indicate that radiolysis products have a significant effect on tellurium chemistry in both a reducing and oxidizing manner depending on the solution composition. The redox reactions also affect the solubility of tellurium. The results show that the current information used to assess tellurium source term needs to be reevaluated for both severe accident management and for code validation purposes.
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| 7. |
- Preston, Markus, et al.
(författare)
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Methodology for Multiparameter Evaluation of Barriers Against Proliferation of Minor Actinides
- 2024
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Ingår i: Nuclear Technology. - 0029-5450 .- 1943-7471.
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Tidskriftsartikel (refereegranskat)abstract
- There exist elements apart from uranium and plutonium that could potentially be used to construct the core of a nuclear explosive device. These belong to the so-called minor actinides (MAs), which exist in nonnegligible amounts in spent nuclear fuel (SNF) and are in nearly all cases not covered by international safeguards. Future reprocessing of SNF could result in significant separation of these elements, potentially leading to new proliferation concerns. In this work, a methodology for a transparent assessment of the barriers against proliferation of MAs has been developed and applied to the case of neptunium, americium, and curium separated from spent fuel from pressurized water reactors. In this methodology, openly available data and Monte Carlo simulations have been used to assess the barriers posed by a number of parameters relevant to the production of a nuclear explosive device from SNF. The evaluation shows that the properties of neptunium present low barriers to proliferation and that it should be discussed within the context of future nonproliferation treaties and possibly be placed under international safeguards. The properties of americium and curium present higher barriers to proliferation, meaning that these elements require less focus in the nonproliferation context.
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| 8. |
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| 9. |
- Rathore, Vikram, et al.
(författare)
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First experimental demonstration of the use of a novel planar segmented HPGe detector for gamma emission tomography of mockup fuel rods
- 2023
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Ingår i: Nuclear Technology. - 0029-5450 .- 1943-7471.
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Tidskriftsartikel (refereegranskat)abstract
- Post-irradiation examination of nuclear fuel is routinely performed to characterize the important properties of the current and the future fuel. Gamma emission tomography is a proven non-invasive technique for this purpose. Among various measurement elements of the technique, a gamma-ray detector is an important element whose spectroscopic abilities and detection efficiency affect the overall results. Finding a combination of high detection efficiency and excellent energy resolution in a single detector is often a challenge. We have designed a novel planar segmented HPGe detector which offers simultaneous measurement in six lines of sight with excellent energy resolution. The simultaneous detection ability enables faster data acquisition in a tomographic measurement which may facilitate achieving higher spatial resolution. In this work, we have demonstrated the first use of the detector by performing a full tomographic measurement of mockup fuel rods. Two methods of detector data analysis were used to make spectra and the images (tomograms) were reconstructed using the filtered back projection algorithm. The reconstructed images validate the successful use of the detector for tomographic measurement. The use of the detector for real fuel measurement is being planned and will be performed in the near future.
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| 10. |
- Soler, Josep M., et al.
(författare)
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Predictive and Inverse Modeling of a Radionuclide Diffusion Experiment in Crystalline Rock at ONKALO (Finland)
- 2023
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Ingår i: Nuclear Technology. - : Informa UK Limited. - 0029-5450 .- 1943-7471. ; 209:11, s. 1765-1784
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Tidskriftsartikel (refereegranskat)abstract
- The REPRO-TDE test was performed at a depth of about 400 m in the ONKALO underground research facility in Finland. Synthetic groundwater containing radionuclide tracers [tritiated water tracer (HTO), 36Cl, 22Na, 133Ba, and 134Cs] was circulated for about 4 years in a packed-off interval of the injection borehole. Tracer activities were additionally monitored in two observation boreholes. The test was the subject of a modeling exercise by the SKB GroundWater Flow and Transport of Solutes Task Force. Eleven teams participated in the exercise, using different model concepts and approaches. Predictive model calculations were based on laboratory-based information concerning porosities, diffusion coefficients, and sorption partition coefficients. After the experimental results were made available, the teams were able to revise their models to reproduce the observations. General conclusions from these back-analysis calculations include the need for reduced effective diffusion coefficients for 36Cl compared to those applicable to HTO (anion exclusion), the need to implement weaker sorption for 22Na compared to results from laboratory batch sorption experiments, and the observation of large differences between the theoretical initial concentrations for the strongly sorbing 133Ba and 134Cs, and the first measured values a few hours after tracer injection. Different teams applied different concepts, concerning mainly the implementation of isotropic versus anisotropic diffusion, or the possible existence of borehole disturbed zones around the different boreholes. The role of microstructure was also addressed in two of the models.
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