| 1. |
- Andersson, Mikael, 1986, et al.
(författare)
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Control Rod Calculation in Axially-Heterogeneous Fast Reactors. Part I: Influence of the Absorber Environment
- 2017
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Ingår i: Nuclear Science and Engineering. - : Informa UK Limited. - 0029-5639 .- 1943-748X. ; 185:2, s. 263-276
-
Tidskriftsartikel (refereegranskat)abstract
- In axially heterogeneous fast reactor concepts, such as the ASTRID CFVcore, the accurate neutronic prediction of control rods is a challenge. In suchcores, the performance of the classical 2D equivalence procedure, used forcontrol rod homogenization in homogeneous fast reactors, is questionable.In this work (Part I of II), a number of axially heterogeneous environ-ments, representative of a CFV-type core are investigated using 2D (X-Z )models, with the objective to distinguish regions where the classical equiva-lence procedure is valid from those where it is not.It is found that the environments that affect the control rod absorber themost, and are likely to invalidate the procedure, are the internal control rodinterfaces, such as the absorber/follower interface and the interface betweenzones of different boron enrichments. The range of the main spectral impactcould be seen within 0-10 cm from the material interfaces studied.In a companion Paper (Part II), a full core investigation is performed,which builds upon the results of this paper.
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| 2. |
- Andersson, Mikael, 1986, et al.
(författare)
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Control rod calculation in axially-heterogeneous fast reactors. Part II: Impact of 3D homogenization on core parameters
- 2017
-
Ingår i: Nuclear Science and Engineering. - : Informa UK Limited. - 0029-5639 .- 1943-748X. ; 185:2, s. 277-293
-
Tidskriftsartikel (refereegranskat)abstract
- Advanced sodium-cooled fast reactors with improved safety features, such asthe French ASTRID CFV-core concept, is characterized by an axial heteroge-neous core, which will present a challenge on the homogenization proceduresused today, taking into account all the different axial material transitions.Reliable modeling of the control rod and accurate prediction of the controlrod worth are essential to determine the shutdown margins and to ensuresafe operation.In this work (Part II of II), two different homogenization schemes are com-pared. One is based on the traditional reactivity-equivalence procedure in 2D,and the other a newly implemented 3D version of the reactivity-equivalenceprocedure, with approximations based on the results in a companion pa-pers (Part I). The deterministic results are compared with a Monte Carloreference.Both of the cross section sets, from the two homogenization schemes, yielded results within the requested 5% error margin in reactivity. Thelargest discrepancy was found for the classical procedure for the case with aslightly inserted control rod (normal operating conditions).Both sets of cross sections yielded similar power profiles in the fuel sub-assembly neighboring the control rod within the 2 Monte Carlo standarddeviation. Neither of the cross section sets were able to predict the largegradients in capture rates close to the internal control rod interfaces.The study showed that the traditional 2D reactivity-equivalence proce-dure produces homogenized cross sections which yield reliable results in aCFV-type core. One exception from this was found for slightly inserted con-trol rods, where the effect of the follower/absorber interface could not be fullycaptured by the 2D scheme, and for such cases, 3D modeling is recommended.
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| 3. |
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| 4. |
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| 5. |
- Andersson, Mikael, 1986, et al.
(författare)
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Impact of Control Rod Position and Homogenization on Sodium Void Effect in CFV-type SFR
- 2016
-
Ingår i: PHYSOR 2016. - 9781510825734 ; 4, s. 2658-2667
-
Konferensbidrag (refereegranskat)abstract
- In complex innovative fast reactor concepts, fairly detailed core modeling is essential for reliable safety analysis during severe accident scenarios. The CFV core with its axially heterogeneous design, has a negative sodium void reactivity effect, a favorable feature wich increases the inherent system safety in case of sodium boiling. In this work, we studied the impact that the control rod homogenization model used, and the control rod position, have on the sodium void-reactivityeffect and the control rod worth, in the case of a voided CFV core. Three different control rodhomogenization models were studied, the traditional 2D equivalence procedure, and two models based on a 3D equivalence procedure, taking into account the axial heterogeneity of the CFV core.It was found that the impact of control rod homogenization has a negligible effect on the sodium void reactivity effect. However, between different control rod positions, a difference of up to 1$ in the sodium void reactivity effect was found, hence the control rod position has to be carefully considered when calculating the sodium void reactivity effect. For the control rod worth in a voidedCFV core, the traditional 2D procedure, could lead to discrepancies of up to 11% for control rod positions at the top of the core. These discrepancies could be much reduced by control rod homogenization with the 3D equivalence procedure. For the total control rod worth, all models andprocedures produced results within the desired error margin of 5%.
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| 6. |
- Andersson, Mikael, 1986, et al.
(författare)
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Influence of Local Spectral Variations on Control-Rod Homogenization in Fast Reactor Environments
- 2015
-
Ingår i: Nuclear Science and Engineering. - 0029-5639 .- 1943-748X. ; 181:2, s. 204-215
-
Tidskriftsartikel (refereegranskat)abstract
- Advanced fast reactor concepts, such as the CFV core (French acronym of "Coeur a Foible effet de Vide Sodium," meaning "low sodium void effect core"), are characterized by a heterogeneous axial core arrangement, with an inner fertile zone and a sodium plenum above the fuel. Such concepts represent a strong challenge for accurate predictions of the control-rod antireactivity effects, and the surrounding local fuel pin power. Classical equivalence procedures, which were developed for axially homogeneous cores, are put to the test when applied to such axially heterogeneous cores. In this work, we investigate the influence of variations in the local neutron spectra, for different control-rod environments, with the objective of understanding the impact of spectral variations in control-rod homogenization. This was conducted by considering a simple one-dimensional model of the equivalence procedure in which a transition zone between the fuel and control rod was introduced to represent different control-rod environments. Two types of situations were studied, one corresponding to softened neutron spectrum environments, for which the impact in the homogenized control-rod cross section was found to be smaller than 5%. The second situation was with wide elastic scattering resonances in the control-rod environment, which could locally lead to differences of up to 15% in the resulting equivalent cross sections. The reactivity effect of these changes was calculated to be less than 2%. In some cases, the numerical stability of the equivalence procedure was adversely affected, mainly in high-energy groups, due to the softening of the neutron spectra.
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| 7. |
- Csajbok, Ludvig Z, 1964, et al.
(författare)
-
Apolipoprotein E polymorphism in aneurysmal subarachnoid haemorrhage in West Sweden.
- 2016
-
Ingår i: Acta neurologica Scandinavica. - : Hindawi Limited. - 1600-0404 .- 0001-6314. ; 133:6, s. 466-474
-
Tidskriftsartikel (refereegranskat)abstract
- Aneurysmal subarachnoid haemorrhage (aSAH) is associated with high morbidity and mortality despite novel treatments. Genetic variability may explain outcome differences. Apolipoprotein E (ApoE) is a glycoprotein with a major role in brain lipoprotein metabolism. It has three isoforms encoded by distinct alleles: APOEε2, APOEε3 and APOEε4. The APOEε4 allele is associated with Alzheimer's disease and worse outcome after traumatic brain injury and ischaemic stroke. This prospective blinded study explored the influence of the APOEε4 polymorphism on the risk of aSAH, risk of cerebral vasospasm (CVS) and 1-year neurological outcome.
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| 8. |
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| 9. |
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| 10. |
- Dykin, Victor, 1985, et al.
(författare)
-
Ringhals Diagnostics and Monitoring, Annual Research Report 2015
- 2015
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report gives an account of the work performed by the Division of Subatomic and Plasma Physics (former Division of Nuclear Engineering), Chalmers, in the frame of a research collaboration with Ringhals, Vattenfall AB, contract No. 630217-031. The contract constitutes a 1-year co-operative research work concerning diagnostics and monitoring of the BWR and PWR units. The work in the contract has been performed between January 1st 2015, and December 31st, 2015. During this period, we have worked with five main items as follows: 1. Development of the mode separation model with an extension to describe 3-D core barrel vibrations; 2. Analysis of new ex-core measurements, taken in R-4 after power uprate; 3. Investigation of the correctness of the hypothesis that the reactivity component extracted from the ex-core detector signals can be due to fuel assembly vibrations with CORE SIM; 4. A basic study in neutron noise theory which could provide some indirect support for the determination of the void fraction from neutron noise measurements; 5. A preliminary study of the possibility of modelling 3-dimensional fuel assembly vibrations in a realistic PWR system with the CORE SIM simulator. This work was performed at the Nuclear Engineering Group of the Division of Subatomic and Plasma Physics, Chalmers University of Technology by Victor Dykin (project co-ordinator), Cristina Montalvo (visitor from the Technical University of Madrid), Hoai-Nam Tran (research collaborator from Duy Tan University), Imre Pázsit and Henrik Nylén, who was also the contact person at Ringhals.
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| 11. |
- Dykin, Victor, 1985, et al.
(författare)
-
Ringhals Diagnostics and Monitoring, Final Research Report 2012-2014
- 2014
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report gives an account of the work performed by the Department of Nuclear Engineering, Chalmers, in the frame of research collaboration with Ringhals, Vattenfall AB, contract No. 630217-031. The contract constitutes a 3-year co-operative research work concerning diagnostics and monitoring of the BWR and PWR units. The work in thecontract has been performed between January 1st 2012, and December 31st, 2014. During this period, we have worked with four main items as follows:1. Development and application of the analysis method of core barrel vibrations, developed in the previous Stages, to three ex-core measurements performed during several cycles in R2, R3 and R4. What regards R2, this was the first attempt to analyze ex-core measurements taken at BOC, MOC and EOC, with the new curve-fitting procedure;2. Investigation of the ultra-low frequency oscillations in reactor power in R4;3. Development of the theory and simulations in order to determine the void content in R1 from the analysis of in-core measurements;4. Evaluation of the measurements made in R1 with the use of 4 LPRMs and one TIP detector, for testing the velocity and void fraction profile reconstruction methods.This work was performed at the Department of Nuclear Engineering, Chalmers University of Technology by Victor Dykin, Cristina Montalvo (visitor from the TechnicalUniversity of Madrid), Imre Pázsit (project co-ordinator) and Henrik Nylén, who was also the contact person at Ringhals.
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| 12. |
- Hursin, Mathieu, et al.
(författare)
-
Measurement of the Gas Velocity in a Water-Air Mixture in CROCUS Using Neutron Noise Techniques
- 2020
-
Ingår i: Nuclear Technology. - : Informa UK Limited. - 0029-5450 .- 1943-7471. ; 206:10, s. 1566-1583
-
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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| 13. |
- Hursin, Mathieu, et al.
(författare)
-
Validation of axial void profile measured by neutron noise techniques in crocus
- 2020
-
Ingår i: International Conference on Physics of Reactors: Transition to a Scalable Nuclear Future, PHYSOR 2020. - : EDP Sciences. ; 2020-March, s. 1586-1593
-
Konferensbidrag (refereegranskat)abstract
- Recently a joint project has been carried out between the Paul Scherrer Institut, the Ecole Polytechnique Federale de Lausanne and swissnuclear, an industrial partner, in order to determine the axial void distribution in a channel installed in the reflector of the zero power research reactor CROCUS, using neutron noise techniques. The main objective of the present paper is to report on the validation of the results against an alternative measurement technique using gamma-ray attenuation and simulations with the TRACE code. For the gamma-ray attenuation experiments, the channel used in CROCUS is installed out of the core in a Plexiglass water tank. The source and detector are fixed and the channel is moved axially to keep the geometry of the source/detector arrangement untouched. This is key to measure the void effect by gamma attenuation due to the low contrast of this technique. The paper compares the experimental results obtained with both techniques, with the outcomes of simulations carried out with the TRACE code. Even though the quantitative void fraction estimations are not consistent, the trends obtained with the simulation and experimental techniques are the same. The discrepancies between the various experimental techniques and the simulation outcomes are related to the heterogeneous distribution of the water-air mixture in the radial sections of the channel.
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| 14. |
- Lau, Cheuk Wah, 1985, et al.
(författare)
-
Conceptual study of axial offset fluctuations upon stepwise power changes in a thorium-plutonium core to improve load-following conditions
- 2014
-
Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 72, s. 84-89
-
Tidskriftsartikel (refereegranskat)abstract
- The increased share of renewable energy, such as wind and solar power, will increase the demand for load-following power sources, and nuclear reactors could be one option. However, during rapid load-following events, traditional UOX cores could be restricted by the volatile oscillation of the power distribution. Therefore, a conceptual study on stability properties of Th-MOX PWR concerning axial offset power excursion during load-following events are investigated and discussed. The study is performed in SIMULATE-3 for a realistic PWR core (Ringhals-3) at the end of cycle, where the largest amplitude of the axial offset oscillations is expected. It is shown that the Th-MOX core possesses much better stability characteristics and shorter reactor dead time compared with a traditional UOX core, and the main reasons are the lower sensitivity to perturbations in the neutron spectrum, lower xenon poisoning and lower thermal neutron flux.
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| 15. |
- Lau, Cheuk Wah, 1985, et al.
(författare)
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Feasibility Study of 1/3 Thorium-Plutonium Mixed Oxide Core
- 2014
-
Ingår i: Science and Technology of Nuclear Installations. - : Hindawi Limited. - 1687-6075 .- 1687-6083. ; 2014:Art. no. 709415
-
Tidskriftsartikel (refereegranskat)abstract
- Thorium-plutonium mixed oxide (Th-MOX) fuel has become one of the most promising solutions to reduce a large and increasing plutonium stockpile. Compared with traditional uranium-plutonium mixed oxide (U-MOX) fuels, Th-MOX fuel has higher consumption rate of plutonium in LWRs. Besides, thorium based fuels have improved thermomechanical material properties compared with traditional U-MOX fuels. Previous studies on a full Th-MOX core have shown reduced efficiency in reactivity control mechanisms, stronger reactivity feedback, and a significantly lower fraction of delayed neutrons compared with a traditional uranium oxide (UOX) core. These problems complicate the implementation of a full Th-MOX core in a similar way as for a traditional U-MOX core. In order to reduce and avoid some of these issues, the introduction of a lower fraction of Th-MOX fuel in the core is proposed. In this study, one-third of the assemblies are Th-MOX fuel, and the rest are traditional UOX fuel. The feasibility study is based on the Swedish Ringhals-3 PWR. The results show that the core characteristics are more similar to a traditional UOX core, and the fraction of delayed neutrons is within acceptable limits. Moreover, the damping of axial xenon oscillations induced by control rod insertions is almost 5 times more effective for the 1/3 Th-MOX core compared with the standard core.
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| 16. |
- Lau, Cheuk Wah, 1985, et al.
(författare)
-
Improvement of LWR thermal margins by introducing thorium
- 2012
-
Ingår i: Progress in Nuclear Energy. - : Elsevier BV. - 0149-1970. ; 61, s. 48-56
-
Tidskriftsartikel (refereegranskat)abstract
- The use of thorium in pressurized water reactor fuel assemblies is investigated in this paper. The novelty of the reported work is to study a fuel design primarily intended to control the excess of reactivity at beginning of life, and flatten the intra-assembly power distribution rather than converting fertile Th-232 into fissile U-233. The fuel assembly is a traditional 17 x 17 pressurized water reactor fuel design. The majority of the fuel pins contain a mixture of uranium and thorium oxides, while a few fuel pins contain a mixture between uranium and gadolinium oxides. The calculation were performed by two-dimensional transport calculations with the Studsvik Scandpower CASMO-4E code in order to determine the main neutronic properties of the new fuel design, compared with the traditional uranium-based fuel assembly containing gadolinium used as reference. The majority of the neutronic properties of the uranium-thorium-based fuel assembly were similar to the reference fuel assembly. The Doppler and the moderator temperature coefficients of reactivity were found to be appreciably more negative in the uranium-thorium-based design, but still within acceptable limits. One advantage of this new uranium-thorium-based design is a reduction of the pin peak power at beginning of life, because of smaller amount of gadolinium being used. This is important from an operational and safety viewpoint, since the margin to departure from nucleate boiling becomes larger. Consequently, this new type of thorium-based fuel assembly shows advantageous properties for use in power-uprated cores.
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| 17. |
- Lau, Cheuk Wah, 1985, et al.
(författare)
-
Improvement of the thermal margins in the Swedish Ringhals-3 PWR by introducing new fuel assemblies with thorium
- 2012
-
Ingår i: Proc. Int. Conf. on Advances in Reactor Physics – Linking Research, Industry, and Education (PHYSOR 2012), Knoxville, TN, USA, April 15-20, 2012, American Nuclear Society. - 9781622763894 ; 5, s. 4041-4055
-
Konferensbidrag (refereegranskat)abstract
- Thorium is a fertile material and most of the past research has focused on breeding thorium to fissile material. In this paper, the focus is on using thorium to improve the thermal margins by homogeneously distributing thorium in the fuel pellets. A proposed uranium-thorium-based fuel assembly is simulated for the Swedish Ringhals-3 PWR core in a realistic demonstration. All the key safety parameters, such as isothermal temperature coefficient of reactivity, Doppler temperature of reactivity, boron worth, shutdown margins and fraction of delayed neutrons are studied in this paper, and are within safety limits for the new core design using the uranium- thorium-based fuel assemblies. The calculations were performed by the two-dimensional transport code CASMO-4E and the two group steady-state three dimensional nodal code SIMULATE-3 from Studsvik Scandpower. The results showed that the uranium-thorium-based fuel assembly improves the thermal margins, both in the pin peak power and the local power (Fq). The improved thermal margins would allow more flexible core designs with less neutron leakage or could be used in power uprates to offer efficient safety margins.
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| 18. |
- Lau, Cheuk Wah, 1985, et al.
(författare)
-
Innovative use of Thorium in LWR fuel assemblies
- 2011
-
Ingår i: International Congress on Advances in NPPs - Nice. ; , s. 2222-2231
-
Konferensbidrag (refereegranskat)abstract
- In this paper, the use of thorium in pressurized water reactor fuel assemblies is investigated. The novelty of the reported work is that the fuel design in this study is primarily intended to control the excess reactivity at beginning of life, and flatten the intra-assembly power distribution rather than converting fertile Th-232 into fissile U-233.The fuel assembly corresponds to the layout of a classical 17x17 pressurized water reactor assembly. Most of the fuel pins contain a mixture of uranium and thorium oxides, while a few additional fuel pins contain a mixture between uranium and gadolinium oxides. Two-dimensional transport calculations were performed with the Studsvik Scandpower CASMO-4E code in order to determine the main neutronic properties of the new fuel design, with a traditional uranium-based fuel assembly containing gadolinium used as a reference. The calculations demonstrated that most of the neutronic properties of the thorium-based fuel assembly were comparable to the properties of classical uranium-based fuel assemblies. The isothermal temperature coefficient of reactivity and the moderator temperature coefficient of reactivity were found to be appreciably more negative in the thorium-based design, while still remaining within acceptable limits. The main advantage of the thorium-based design is a significant reduction of the pin peak power at beginning of life. This special feature is of particular importance from an operational and safety viewpoint, since the margin to departure from nucleate boiling becomes larger. Consequently, this new type of fuel assembly could also be used in power-uprated cores.
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| 19. |
- Lau, Cheuk Wah, 1985, et al.
(författare)
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Investigation of the Equilibrium Core Characteristics for the Ringhals-3 PWR with Improved Thermal Margins Using Uranium-thorium Fuel
- 2013
-
Ingår i: Proceedings of ICAPP 2013. ; , s. 8-
-
Konferensbidrag (refereegranskat)abstract
- Nowadays, PWR core thermal margins have decreased because of higher enrichment of U-235 in the fuel assemblies to achieve higher discharge burnup, higher core power to improve economical competiveness, and reduction of fast neutron leakage to prevent rapid ageing of the pressure vessel. Thus, a new uranium-thorium-based fuel assembly is proposed for improving the thermal margins. The proposed fuel is simulated for the Swedish Ringhals-3 PWR equilibrium core in a realistic demonstration. The difference between the uranium-thorium and traditional fuel assemblies is the fuel pellets composition. In the uranium-thorium fuel assembly, 7 weight percentage of thorium oxide is added to some of the fuel pellets. In those fuel pellets, the enrichment is kept below 5 % enrichment of U-235 in order to avoid extra certification on transport, management and storage.The two most significant results showed in this paper are the improved pin peak power, and the axial offset in the core. The pin peak power margin could be improved by 75 % by using the uranium-thorium-based fuel compared with the reference core containing traditional fuel assemblies. The maximum axial offset was decreased by 33 % using the uranium-thorium-based fuel compared with the reference core. The improved thermal margins in the core would allow more flexible core designs with less neutron leakage, or could be used for power uprates while guaranteeing sufficient safety margins.
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| 20. |
- Lau, Cheuk Wah, 1985, et al.
(författare)
-
Reducing axial offset and improving stability in PWRs by using uranium-thorium fuel
- 2014
-
Ingår i: Progress in Nuclear Energy. - : Elsevier BV. - 0149-1970. ; 76, s. 137-147
-
Tidskriftsartikel (refereegranskat)abstract
- The axial offset (AO) is a parameter used to monitor the core axial power distribution, and is important for safe reactor operation. Previous works have showed that a new type uranium-thorium (U-Th) based fuel assembly could be used to achieve a more homogenous radial power distribution, and thereby improve the thermal margins in the core. In this paper, it is shown that a core containing U-Th fuel assemblies also reduces the AO and improves the core stability. For an equilibrium U-Th core, the maximum AO could be reduced by 33%, and the minimum AO could be reduced by 8% compared with a standard uranium core. In the U-Th core, the maximum AO was influenced by the more negative moderator temperature coefficient of reactivity, while the minimum AO is mainly affected by the more homogenous radial power distribution. These findings conclude that the U-Th core displays a more homogenous power distribution both axially and radially, thus offering better thermal margins for power uprates and flexible power operation. Moreover, xenon oscillations in the core due to perturbations induced by the control rods are 30% more effectively damped for the U-Th core compared with the standard core, improving the stability in AO. © 2014 Elsevier Ltd. All rights reserved.
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| 21. |
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| 22. |
- Pazsit, Imre, 1948, et al.
(författare)
-
Development of a new method to determine the axial void velocity profile in BWRs from measurements of the in-core neutron noise
- 2021
-
Ingår i: Progress in Nuclear Energy. - : Elsevier BV. - 0149-1970. ; 138
-
Tidskriftsartikel (refereegranskat)abstract
- Determination of the local void fraction in BWRs from in-core neutron noise measurements requires the knowledge of the axial velocity of the void. The purpose of this paper is to revisit the problem of determining the axial void velocity profile from the transit times of the void between axially placed detectors, determined from in-core neutron noise measurements. In order to determine a realistic velocity profile which shows an inflection point and hence has to be at least a third order polynomial, one needs four transit times and hence five in-core detectors at various axial elevations, whereas the standard instrumentation usually consists only of four in-core detectors. Attempts to determine a fourth transit time by adding a TIP detector to the existing four LPRMs and cross-correlate it with any of the LPRMs have been unsuccessful so far. In this paper we thus propose another approach, where the TIP detector is only used for the determination of the axial position of the onset of boiling. By this approach it is sufficient to use only three transit times. Moreover, with another parametrisation of the velocity profile, it is possible to reconstruct the velocity profile even without knowing the onset point of boiling, in which case the TIP is not needed, although at the expense of a less flexible modelling of the velocity profile. In the paper the principles are presented, and the strategy is demonstrated by concrete examples, with a comparison of the performance of the two different ways of modelling the velocity profile. The method is tested also on velocity profiles supplied by system codes, as well as on transit times from neutron noise measurements.
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| 23. |
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| 24. |
- Pazsit, Imre, 1948, et al.
(författare)
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Reconstructing the axial void velocity profile in BWRS from measurements of the in-core neutron noise
- 2020
-
Ingår i: International Conference on Physics of Reactors: Transition to a Scalable Nuclear Future, PHYSOR 2020. - : EDP Sciences. ; 2020-March, s. 211-218
-
Konferensbidrag (refereegranskat)abstract
- The problem of determining the axial velocity profile from the in-core neutron noise measurements is revisited, with the purpose of developing an objective method for the determination of the void fraction. Until now it was assumed that in order to determine a realistic velocity profile which shows an inflection point and hence has to be at least a third order polynomial, one needs four transit times and hence five in-core detectors at various axial elevations. However, attempts to determine a fourth transit time by adding a TIP detector to the existing four LPRMs and cross-correlate it with any of the LPRMs were unsuccessful so far. In this paper we thus propose another approach, where the TIP detector is only used for the determination of the axial position of the onset of boiling. By this approach it is sufficient to use only three transit times. Moreover, with another parametrisation of the velocity profile, it is possible to reconstruct the velocity profile even without knowing the onset point of boiling, in which case the TIP is not needed. In the paper the principles are explained and the strategy is demonstrated by concrete examples.
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| 25. |
- Pazsit, Imre, 1948, et al.
(författare)
-
REFINED METHOD FOR SURVEILLANCE AND DIAGNOSTICS OF THE CORE BARREL VIBRATIONS OF THE RINGHALS PWRs
- 2014
-
Ingår i: Proceedings of the International Conference on Physics of Reactors, PHYSOR 2014.
-
Konferensbidrag (refereegranskat)abstract
- Surveillance and diagnostics of core barrel vibrations has been performed in the Swedish Ringhals PWRs for several years, with main focus on the pendular motion (beam mode). The monitoring of the beam mode showed that the amplitude of the corresponding peak in the ex-core neutron spectra increases along the cycle, and decreases after refueling. Previous investigations on the reason of this behaviour, i.e. whether it is due to the increase of the core barrel vibration amplitude or to the increase of the neutron physics coupling between vibrations and neutron noise, were not decisive. The objective of the work reported here is to clarify this question. From frequency analysis, two modes of vibration have been identi-fied in the frequency range of the beam mode. Several results coming from the trend analysis performed during recent years indicate that one of the modes is due to the core barrel motion itself and remains constant during cycle, and the other is due to the indi-vidual flow induced vibrations of the fuel elements, showing an increasing trend during the cycle. In this work, the method to separate the contributions from the two modes has been refined, and the results of this approach to the latest measurements are presented. The results confirm the origin of the two vibration modes and show constant amplitude of the core barrel motion throughout the cycle.
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| 26. |
- Pazsit, Imre, 1948, et al.
(författare)
-
Ringhals Diagnostics and Monitoring, Annual Research Report 2016-17
- 2017
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report gives an account of the work performed by the Division of Subatomic and Plasma Physics (formerly, Division of Nuclear Engineering), Chalmers, in the frame of a research collaboration with Ringhals, Vattenfall AB, contract No. 663628-054. The contract constitutes a 1-year co-operative research work concerning diagnostics and monitoring of the BWR and PWR units. The work in the contract has been performed between July 1st 2016, and December 31st, 2017. During this period, we have worked with six main items as follows: 1. Further development and improvement of the coupled coarse-fine mesh CORE SIM-based model; 2. Further investigation of the point-kinetic component of the noise induced by fuel assembly vibrations; 3. Analysis of new ex-core measurements, taken in R-4 after power increase; 4. Further development and test of the mode separation model as applied to 3-D “wobbling” type or “tilting” type core-barrel vibrations; 5. A basic study in neutron noise theory which could provide some indirect support for the determination of the void fraction from neutron noise measurements; 6. A pilot study of the possibility of using fission chambers for zero power noise experiments. The work was performed at the Nuclear Engineering Group of the Division of Subatomic and Plasma Physics, Chalmers University of Technology by Imre Pázsit (project co-ordinator), Cristina Montalvo (visitor from the Technical University of Madrid), Hoai-Nam Tran (research collaborator from Duy Tan University, Vietnam), Omar Alejandro Olvera Guerrero (visitor, PhD student at UAM/Autonomus Metropolitan University, Mexico City, Mexico) and Henrik Nylén, the contact person at Ringhals. The measurements reported in Chapter 6 were designed and executed by our collaborating partners in EPFL/PSI, Mathieu Hursin, Oskari Pakari and Vincent Lamirand.
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| 27. |
- Pazsit, Imre, 1948, et al.
(författare)
-
Ringhals Diagnostics and Monitoring, Annual Research Report 2018-19
- 2019
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report gives an account of the work performed by the Division of Subatomic and Plasma Physics (formerly, Division of Nuclear Engineering), Chalmers, in the frame of a research collaboration with Ringhals, Vattenfall AB, contract No. 677353-003. The contract constitutes a 1-year co-operative research work concerning diagnostics and monitoring of the BWR and PWR units. The work in the contract has been performed between 1 July 2018 – 30 June 2019. During this period, we have worked with five main items as follows: 1. Investigation of possible baffle jetting in R3 with noise analysis of in-core and ex-core detector signals; 2. Analysis of the vibrations of thimble tubes with axially dependent in-core measurements in various radial positions; 3. Evaluation of new ex-core measurements for beam mode and tilting mode vibrations in R3; 4. Development of a method to use the Eigenvalue Separation in noise analysis for characterising regional power oscillations and understanding the role of loosely coupled cores in the development of regional instabilities; 5. Further investigations of the possibilities of using fission chamber signals for measurement of subcritical reactivity, such as elaboration of the equivalent of the Feynman-alpha method of pulse counting, and accounting for delayed neutrons. The work was performed at the Nuclear Engineering Group of the Division of Subatomic and Plasma Physics, Chalmers University of Technology, by Imre Pázsit (project co-ordinator), Luis Alejandro Torres (visitor from UPM, Madrid, Spain), Cristina Montalvo (research collaborator from UPM), Yasunori Kitamura (research collaborator from KURNS, Kyoto, Japan), Lajos Nagy (double degree PhD student) and Henrik Nylén, the contact person at Ringhals.
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| 28. |
- Pazsit, Imre, 1948, et al.
(författare)
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Ringhals Diagnostics and Monitoring, Annual Research Report 2019-2020
- 2020
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report gives an account of the work performed by the Division of Subatomic, High Energy and Plasma Physics (formerly, Division of Nuclear Engineering), Chalmers, in the frame of a research collaboration with Ringhals, Vattenfall AB, contract No. 686103-003. The contract constitutes a 1-year co-operative research work concerning diagnostics and monitoring of the BWR and PWR units. The work in the contract has been performed between July 1st 2019, and June 30th, 2020. Originally, we planned to work with five items as follows: 1. Continued investigation of possible baffle jetting in R3 with noise analysis of in-core and ex-core detector signals; 2. Further analysis of the vibrations of thimble tubes with axially dependent in-core measurements in various radial positions; 3. Evaluation of new ex-core measurements for beam mode and tilting mode vibrations in R3; 4. Experimental work and simulations in support of the use of fission chambers in the current mode for reactor diagnostics, as an alternative of pulse counting methods; 5. Development of a new method to determine the axial velocity profile of the void in the core of a BWR by using four permanent in-core LPRMs and a TIP detector. Due to changed circumstances, mostly related to the Covid-19 pandemics, some changes were made in the project. Item #1 was reduced, whereas the work planned in item #2 was postponed to the next Stage. The work was performed by Imre Pázsit (project co-ordinator), Luis Alejandro Torres and Cristina Montalvo (research collaborators from UPM, Madrid), Lajos Nagy (double degree PhD student jointly with BME Budapest), Gergely Klujber and Máté Szieberth (research collaborators from BME), Tsuyoshi Misawa and Yasunori Kitamura (research collaborators from KURNS, Kyoto, Japan) and Henrik Nylén, the contact person at Ringhals.
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| 29. |
- Pazsit, Imre, 1948, et al.
(författare)
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Ringhals Diagnostics and Monitoring, Annual Research Report 2020-2021
- 2021
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report gives an account of the work performed by the Division of Subatomic, High Energy and Plasma Physics (formerly, Division of Nuclear Engineering), Chalmers, in the frame of a research collaboration with Ringhals, Vattenfall AB, contract No. 4501737229-003. The contract constitutes a one-year co-operative research work concerning diagnostics and monitoring of the BWR and PWR units. The work in the contract has been performed between 1 July 2020 and 30 June 2021.
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| 30. |
- Pazsit, Imre, 1948, et al.
(författare)
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Ringhals Diagnostics and Monitoring, Annual Research Report 2021-2022
- 2022
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report gives an account of the work performed by the Division of Subatomic, High Energy and Plasma Physics (formerly, Division of Nuclear Engineering), Chalmers, in the frame of a research collaboration with Ringhals, Vattenfall AB, contract No. 4501747546-003. The contract constitutes a one-year co-operative research work concerning diagnostics and monitoring of the PWR units. The work in the contract has been performed between 1 July 2021 and 30 June 2022.
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| 31. |
- Pazsit, Imre, 1948, et al.
(författare)
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Ringhals Diagnostics and Monitoring, Annual Research Report 2022-2023
- 2023
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report gives an account of the work performed by the Division of Subatomic, High Energy and Plasma Physics (formerly, Division of Nuclear Engineering), Chalmers, in the frame of a research collaboration with Ringhals, Vattenfall AB, contract No. 4501756928-062. The contract constitutes a one-year co-operative research work concerning diagnostics and monitoring of the PWR units. The work in the contract has been performed between 1 July 2022 and 30 June 2023. During this period, we worked with one single item, namely with the analysis of in-core measurements with wavelet techniques, to detect and quantify thimble tube vibrations. The work was performed by Imre Pázsit (project leader at Chalmers), Victor Dykin and Henrik Nylén, the latter being the contact person at Ringhals.
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| 32. |
- Persson, Leif, et al.
(författare)
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Application of a Monte Carlo method to the uncertainty assessment in in situ gamma-ray spectrometry
- 2018
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Ingår i: Journal of Environmental Radioactivity. - : Elsevier BV. - 0265-931X .- 1879-1700. ; 187, s. 1-7
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Tidskriftsartikel (refereegranskat)abstract
- In situ gamma-ray spectrometry has since the introduction of portable germanium detectors been a widely used method for the assessment of radionuclide ground deposition activity levels. It is, however, a method that is most often associated with fairly large and, more important, poorly known combined measurement uncertainties. In this work an uncertainty analysis of in situ gamma ray spectrometry in accordance with the Guide to the Expression of Uncertainty in Measurements is presented. The uncertainty analysis takes into account uncertainty contributions from the calibration of the detector system, the assumed activity distribution in soil, soil density, detector height and air density. As a result, measurement results from in situ gamma spectrometry will serve as a better basis for decision-making in e.g. radiological emergencies.
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| 33. |
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| 34. |
- Tran, Hoai Nam, 1981, et al.
(författare)
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Investigation of the ex-core noise induced by fuel assembly vibrations in the Ringhals-3 PWR
- 2015
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Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 80, s. 434-446
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Tidskriftsartikel (refereegranskat)abstract
- © 2015 Elsevier Ltd. The effect of cycle burnup on the ex-core detector noise at the frequency of the pendular core barrel vibrations in the Ringhals-3 PWR core was investigated using a neutron noise simulator. The purpose of the investigations was to confirm or disprove a hypothesis raised by Sweeney et al. (1985) that fuel assembly vibrations could affect the ex-core detector noise and cause the corresponding peak in the auto power spectral density (APSD) to increase during the cycle due to the effects of fuel burnup, the change of boron concentration, flux redistribution etc. Numerical calculations were performed by modelling the vibrations of fuel assemblies at different locations in the core and calculating the induced neutron noise at three burnup steps. The APSD of the ex-core detector noise was evaluated with the assumption of vibrations either along a straight-line or along a random two-dimensional trajectory, with two different representations of the cross section perturbations caused by the vibrations. The results show the obvious effect of in-core fuel vibrations on the ex-core detector noise, but the monotonic increase of the APSD does not occur for all fuel elements, vibration types and cross section perturbation models. Such an increase of the of APSD occurs predominantly for peripheral assemblies with one of the perturbation models. However, assuming simultaneous vibrations of a number of fuel assemblies uniformly distributed over the core with random vibrations and the more realistic perturbation model, the effect of the peripheral assemblies will dominate and hence the surmised monotonic increase of the amplitude of the ex-core neutron noise during the cycle can be confirmed.
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| 35. |
- Zylbersztejn, Florian, et al.
(författare)
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On the dependence of the noise amplitude on the correlation length of inlet temperature fluctuations in PWRs
- 2013
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Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 57, s. 134-141
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Tidskriftsartikel (refereegranskat)abstract
- The dependence of the amplitude of the neutron noise in PWRs on the radial correlation length of the noise source, that is the inlet temperature fluctuations, is investigated. The motivation for this work comes from the recent observation that the noise amplitude has increased significantly in certain Spanish PWRs. The reason of this increase has not yet been satisfactorily identified, although there are a few assumptions. One new hypothesis, put forward in this paper, is that a coolant ow with more coherent characteristics, which has actually been observed, could explain the increase of the noise amplitude. A more coherent ow leads to a longer spatial (radial) correlation length of the inlet temperature fluctuations, which in turn, in case the APSD of the temperature noise is unchanged, will lead to the increase of the neutron noise APSD. The mechanism behind this phenomenon is the same as the reason of the failure of the traditional noise based method for the determination of the Moderator Temperature Coeficient (MTC), and is related to the characteristics of the spatially randomly distributed noise sources. In this paper the relationship between the radial correlation length of the inlet temperature fluctuations and the neutron noise amplitude is investigated quantitatively and the increase of the noise amplitude with the increased spatial correlation of the inlet temperature fluctuations is demonstrated.
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