Ringhals Diagnostics and Monitoring, Final Research Report 2012-2014

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 P\ue1zsit (project co-ordinator) and Henrik Nyl\ue9n, who was also the contact person at Ringhals

Development of a new method to determine the axial void velocity profile in BWRs from measurements of the in-core neutron noise

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

Ringhals Diagnostics and Monitoring, Annual Research Report 2015

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 P\ue1zsit and Henrik Nyl\ue9n, who was also the contact person at Ringhals

Ringhals Diagnostics and Monitoring, Annual Research Report 2016-17

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 P\ue1zsit (project co-ordinator), CristinaMontalvo (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 Nyl\ue9n, 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

Ringhals Diagnostics and Monitoring, Annual Research Report 2018-19

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

Ringhals Diagnostics and Monitoring, Annual Research Report 2022-2023

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 P\ue1zsit (project leader at Chalmers), Victor Dykin and Henrik Nyl\ue9n, the latter being the contact person at Ringhals

Innovative use of Thorium in LWR fuel assemblies

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

Innovative use of Thorium in LWR fuel assemblies

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

Impact of 3D Modeling and Homogenization of Control Rod on Reactivity in CFV-type SFR Cores

International audienc

Control Rod Calculation in Axially-Heterogeneous Fast Reactors. Part I: Influence of the Absorber Environment

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