Analysis of nuclear reactions to determine the radionuclides generated and its activity in various devices

[EN] Nuclear reactions can generate radionuclides and it is necessary to know the activity produced in the reaction. Most of the activation reactions are induced by neutrons since the addition of one neutron produces normally an instability in the nucleus, but other particles like protons can also be used to produce radionuclides. Nuclear reactors and accelerators are some of the most used devices to host nuclear reactions to produce radionuclides for various applications. The MCNP5 code based on the Monte Carlo (MC) method can be used to estimate the activity generated in the reaction. A summary of the simulation of neutron reactions is presented in the paper. The comparison of simulation results with experimental measurements allows the validation of developed models.Ródenas Diago, J.; Verdú Martín, GJ. (2020). Analysis of nuclear reactions to determine the radionuclides generated and its activity in various devices. Radiation Physics and Chemistry. 167:1-6. https://doi.org/10.1016/j.radphyschem.2019.05.011S16167Ródenas, J., Gallardo, S., Abarca, A., & Juan, V. (2010). Estimation of the activity generated by neutron activation in control rods of a BWR. Applied Radiation and Isotopes, 68(4-5), 905-908. doi:10.1016/j.apradiso.2009.09.059Ródenas, J., Abarca, A., Gallardo, S., & Sollet, E. (2010). Validation of the Monte Carlo model developed to assess the activity generated in control rods of a BWR. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 619(1-3), 258-261. doi:10.1016/j.nima.2009.10.084Ródenas, J., Gallardo, S., Abarca, A., & Juan, V. (2010). Analysis of the dose rate produced by control rods discharged from a BWR into the irradiated fuel pool. Applied Radiation and Isotopes, 68(4-5), 909-912. doi:10.1016/j.apradiso.2009.09.060Ródenas, J., Gallardo, S., Weirich, F., & Hansen, W. (2014). Application of dosimetry measurements to analyze the neutron activation of a stainless steel sample in a training nuclear reactor. Radiation Physics and Chemistry, 104, 368-371. doi:10.1016/j.radphyschem.2014.05.01

Application case for phase III of UAM-LWR benchmark: Uncertainty propagation of thermal-hydraulic macroscopic parameters

[EN] This work covers an important point of the benchmark released by the expert group on Uncertainty Analysis in Modeling of Light Water Reactors. This ambitious benchmark aims to determine the uncertainty in light water reactors systems and processes in all stages of calculation, with emphasis on multi-physics (coupled) and multi-scale simulations. The Gesellschaft für Anlagen und Reaktorsicherheit methodology is used to propagate the thermal-hydraulic uncertainty of macroscopic parameters through TRACE5.0p3/PARCSv3.0 coupled code. The main innovative points achieved in this work are i) a new thermal-hydraulic model is developed with a highly-accurate 3D core discretization plus an iterative process is presented to adjust the 3D bypass flow, ii) a control rod insertion occurrence ¿which data is obtained from a real PWR test¿ is used as a transient simulation, iii) two approaches are used for the propagation process: maximum response where the uncertainty and sensitivity analysis is performed for the maximum absolute response and index dependent where the uncertainty and sensitivity analysis is performed at each time step, and iv) RESTING MATLAB code is developed to automate the model generation process and, then, propagate the thermal-hydraulic uncertainty. The input uncertainty information is found in related literature or, if not found, defined based on expert judgment. This paper, first, presents the Gesellschaft für Anlagen und Reaktorsicherheit methodology to propagate the uncertainty in thermal-hydraulic macroscopic parameters and, then, shows the results when the methodology is applied to a PWR reactor.The authors of this work thank the UAM-LWR benchmark organizers without whom this work would not have been possible. Besides, the authors sincerely thank to the Ministerio de Economia, Industria y Competitividad and the "Plan Nacional de I+D+i" for funding the projects NUC-MULTPHYS ENE2012-34585 and ENE2017-89029-P.Mesado, C.; Miró Herrero, R.; Verdú Martín, GJ. (2020). Application case for phase III of UAM-LWR benchmark: Uncertainty propagation of thermal-hydraulic macroscopic parameters. Nuclear Engineering and Technology. 52(8):1626-1637. https://doi.org/10.1016/j.net.2020.01.010S1626163752

Multilevel matrix-free preconditioner to solve linear systems associated with a the time-dependent SPN equations

[EN] The evolution of the neutronic power inside of a nuclear reactor core can be approximated by means of the diffusive time-dependent simplified spherical harmonics equations (SPN). For the spatial discretization of these equations, a continuous Galerkin high order finite element method is applied to obtain a semi-discrete system of equations that is usually stiff. A semi-implicit time scheme is used for the time discretization and many linear systems are needed to be solved and previously, preconditioned. The aim of this work is to speed up the convergence of the linear systems solver with a multilevel preconditioner that uses different degrees of the polynomials used in the finite element method. Furthermore, as the matrices that appear in this type of system are very large and sparse, a matrix-free implementation of the preconditioner is developed to avoid the full assembly of the matrices. A benchmark transient tests this methodology. Numerical results show, in comparison with the block Gauss-Seidel preconditioner, an improvement in terms of number of iterations and the necessity of computational resources.This work has been partially supported by Spanish Ministerio de Economía y Competitividad under projects ENE2017-89029-P and MTM2017-85669-P. Furthermore, this work has been financed by the Generalitat Valenciana under the project PROMETEO/2018/035.Carreño, A.; Vidal-Ferràndiz, A.; Ginestar, D.; Verdú, G. (2022). Multilevel matrix-free preconditioner to solve linear systems associated with a the time-dependent SPN equations. En Proceedings of the YIC 2021 - VI ECCOMAS Young Investigators Conference. Editorial Universitat Politècnica de València. 68-77. https://doi.org/10.4995/YIC2021.2021.12510OCS687

Simulation studies on natural circulation phenomena during an SBO accident

[EN] Natural circulation flow capability for removing decay core power has been demonstrated, and several studies have focused on taking advantage of this fact. This work studies the sequence of events that occur during a station blackout accident, in which natural circulation is the dominant flow pattern in the primary system. To this end, the Test A1.1 carried out in ATLAS facility is analyzed and a TRACE5 model is developed paying special attention on the modeling of heat losses. This phenomenon is very influential in the flow capacity and this is demonstrated through the correlation G~(Q-qloss )m between the net power Q-qloss and the mass flow G, that has been established from simulations under steady-state conditions. The Test A1.1 reproduction shows the TRACE5 code adequacy to investigate natural circulation phenomena, which are difficult to control in a facility. In addition, the heat loss modeling technique using constant heat transfer coefficients is substantiated.The authors are grateful to the Management Board of the OECD-ATLAS Project for their consent to this publication, and thank the Spanish Nuclear Regulatory Body (CSN) for the technical and financial support under the agreement STN/4524/2015/640 and the Spanish Ministerio de Economia, Industria y Competitividad under the agreement ENE2017-89029-P. They also thank Ronald Harrington, from USNRC, for sharing the preliminary TRACE model used in this work.Lorduy, M.; Gallardo Bermell, S.; Verdú Martín, GJ. (2018). Simulation studies on natural circulation phenomena during an SBO accident. Applied Thermal Engineering. 139:514-523. https://doi.org/10.1016/j.applthermaleng.2018.04.130S51452313

Simulation of a SBLOCA in a hot leg. Scaling considerations andapplication to a nuclear power plant

The main goal of this work is to study the physical phenomena observed during a Small Break Loss-Of-Coolant Accident transient performed in a small-scale Integral Test Facility and to determine the capabilityof the thermal hydraulic code TRACE5 to reproduce these phenomena in a scale-up model. The accidentscenario analyzed is based on Test 1.2 in the frame of the OECD/NEA ROSA Project, which simulatesa 1% hot leg Small Break Loss-Of-Coolant Accident in the Large Scale Test Facility of the Japan AtomicEnergy Agency. During this test, natural circulation in primary loops occurs, cooling the core during someminutes. This is an important phenomenon, which needs to be checked by means of different TRACE5models. With this aim, Test 1 2 has been simulated using a TRACE5 model reproducing the geometricaland thermal hydraulic features of Large Scale Test Facility. In order to determine if this phenomenon canbe reliably extrapolated to a scale-up plant, a new TRACE5 model has been developed. The geometricalfeatures of this scale-up model are determined using a fixed scaling ratio respect to the original LSTFfeatures. On the other hand, 4 and 3-loop standard Westinghouse PWR models are used in order tosimulate the same transient and compare the behaviour of the main thermal hydraulic variables withthose obtained in the Large Scale Test Facility model and in the Large Scale Test Facility scale-up model.Results show that both Large Scale Test Facility and the scale-up models present the same behaviourduring the whole transient. Important discrepancies are found in the results corresponding to 4 and3-loop PWR TRACE5 models. In both models, natural circulation is not properly reproduced. Trying toimprove the simulation results, the nodalizations of U-tubes and pressure vessel were tested. Resultsstate that the nodalization of U-tubes clearly affects the natural circulation simulation. However, thevessel nodalization effect is not as important.This work contains findings produced within the OECD-NEA ROSA Project. This work is partially supported by the Grant-in-Aid for Scientific Research of the Spanish Ministerio de Educacion (Grant number: AP2009-2600), the Spanish Ministerio de Ciencia e Innovacion under Projects ENE2011-22823 and ENE2012-34585 and the Generalitat Valenciana under Projects PROMETEO/2010/039 and ACOMP/2013/237.Querol Vives, A.; Gallardo Bermell, S.; Verdú Martín, GJ. (2015). Simulation of a SBLOCA in a hot leg. Scaling considerations andapplication to a nuclear power plant. Nuclear Engineering and Design. 283:81-99. https://doi.org/10.1016/j.nucengdes.2014.10.006S819928

Unfolding X-ray spectra using a flat panel detector. Determination of the accuracy of the method with the Monte Carlo method

[EN] The primary X-ray spectrum depends on different parameters such as high voltage, filament current, high voltage ripple, anode angle and thickness of filter material. The objective of this work is to determine whether the unfolding technique based on the Tikhonov regularization method is accurate enough to estimate the X-ray spectrum when slight changes in the operation variables are considered. In this frame, several X-ray spectra are considered (extracted from the IPEM78 Catalogue Report) varying the main operation variables of the X-ray tube (high voltage, voltage ripple, filter thickness and filter material). With those spectra, the corresponding absorbed dose curves are obtained by simulation with a MCNP5 model reproducing a flat panel detector and a PMMA wedge. Once the absorbed dose curves are simulated and applying the unfolding Tikhonov regularization method, the unfolded spectrum is obtained, which is finally compared with the theoretical one (IPEM78 Catalogue Report). Discrepancies between unfolded and primary X-ray spectra can be attributed to the fact that this is an ill-posed problem, and the unfolding of the spectrum is strongly affected by the method used to improve the conditioning of the response function (response matrix).Gallardo Bermell, S.; Ródenas Diago, J.; Verdú Martín, GJ. (2019). Unfolding X-ray spectra using a flat panel detector. Determination of the accuracy of the method with the Monte Carlo method. Radiation Physics and Chemistry. 155:233-238. https://doi.org/10.1016/j.radphyschem.2018.09.014S23323815

Block strategies to compute the lambda modes associated with the neutron diffusion equation

[EN] Given a configuration of a nuclear reactor core, the neutronic distribution of the power can beapproximated by means of the multigroup neutron diffusion equation. This is an approximationof the neutron transport equation that assumes that the neutron current is proportional to thegradient of the scalar neutron ux with a diffusion coeffcient [1]. This approximation is known asthe Fick's first law. To define the steady-state problem, the criticality of the system must be forced.In this work, the -modes problem is used. That yields a generalized eigenvalue problem whoseeigenvector associated with the dominant eigenvalue represents the distribution of the neutron uxin steady-state.The spatial discretization of the equation is made by a continuous Galerkin high order finite elementmethod is applied [2] to obtain an algebraic eigenvalue problem. Usually, the matrices obtainedfrom the discretization are huge and sparse. Moreover, they have a block structure given by the different number of energy groups. In this work, block strategies are developed to optimize thecomputation of the associated eigenvalue problems.First, different block eigenvalue solvers are studied. On the other hand, the convergence of theseiterative methods mainly depends on the initial guess and the preconditioner used. In this sense,different multilevel techniques to accelerate the rate of convergence are proposed. Finally, the sizeof the problems can be suffciently large to be unfeasible to be solved in personal computers. Thus,a matrix-free methodology that avoids the allocation of the matrices in memory is applied [3].Three-dimensional benchmarks are used to show the effciency of the methodology proposed.This work has been partially supported by Spanish Ministerio de Economía y Competitividad under projects ENE2017-89029-P and MTM2017-85669-P. Furthermore, this work has been financed by the Generalitat Valenciana under the project PROMETEO/2018/035.Carreño, A.; Vidal Ferrándiz, A.; Ginestar Peiró, D.; Verdú, G. (2022). Block strategies to compute the lambda modes associated with the neutron diffusion equation. En Proceedings of the YIC 2021 - VI ECCOMAS Young Investigators Conference. Editorial Universitat Politècnica de València. 423-430. https://doi.org/10.4995/YIC2021.2021.13470OCS42343

Modified Block Newton method for the lambda modes problem

[EN] To study the behaviour of nuclear power reactors it is necessary to solve the time dependent neutron diffusion equation using either a rectangular mesh for PWR and BWR reactors or a hexagonal mesh for VVER reactors. This problem can be solved by means of a modal method, which uses a set of dominant modes to expand the neutron flux. For the transient calculations using the modal method with a moderate number of modes, these modes must be updated each time step to maintain the accuracy of the solution. The updating modes process is also interesting to study perturbed configurations of a reactor. A Modified Block Newton method is studied to update the modes. The performance of the Newton method has been tested for a steady state perturbation analysis of two 2D hexagonal reactors, a perturbed configuration of the IAEA PWR 3D reactor and two configurations associated with a boron dilution transient in a BWR reactor.This work has been partially supported by the Spanish Ministerio de Educación y Ciencia under projects ENE2008-02669 and MTM2007-64477-AR07, the Generalitat Valenciana under project ACOMP/2009/058, and the Universidad Politécnica de Valencia under project PAID-05-09-4285.González Pintor, S.; Ginestar Peiro, D.; Verdú Martín, GJ. (2013). Modified Block Newton method for the lambda modes problem. Nuclear Engineering and Design. 259:230-239. https://doi.org/10.1016/j.nucengdes.2011.06.045S23023925

Evaluation of image filters for their integration with LSQR computerized tomography reconstruction method

[EN] In CT (computerized tomography) imaging reconstruction, the acquired sinograms are usually noisy, so artifacts will appear on the resulting images. Thus, it is necessary to find the adequate filters to combine with reconstruction methods that eliminate the greater amount of noise possible without altering in excess the information that the image contains. The present work is focused on the evaluation of several filtering techniques applied in the elimination of artifacts present in CT sinograms. In particular, we analyze the elimination of Gaussian and Speckle noise. The chosen filtering techniques have been studied using four functions designed to measure the quality of the filtered image and compare it with a reference image. In this way, we determine the ideal parameters to carry out the filtering process on the sinograms, prior to the process of reconstruction of the images. Moreover, we study their application on reconstructed noisy images when using noisy sinograms and finally we select the best filter to combine with an iterative reconstruction method in order to test if it improves the quality of the images. With this, we can determine the feasibility of using the selected filtering method for our CT reconstructions with projections reduction, concluding that the bilateral filter is the filter that behaves best with our images. We will test it when combined with our iterative reconstruction method, which consists on the Least Squares QR method in combination with a regularization technique and an acceleration step, showing how integrating this filter with our reconstruction method improves the quality of the CT images.This research has been supported by "Universitat Politecnica de Valencia", "Generalitat Valenciana" under PROMETEO/2018/035 as well as ACIF/2017/075 predoctoral grant co-financed by FEDER and FSE funds, and "Spanish Ministry of Science, Innovation and Universities" under Grant RTI2018-098156-B-C54 co-financed by FEDER funds.Chillarón-Pérez, M.; Vidal-Gimeno, V.; Verdú Martín, GJ. (2020). Evaluation of image filters for their integration with LSQR computerized tomography reconstruction method. PLoS ONE. 15(3):1-14. https://doi.org/10.1371/journal.pone.0229113114153Managing patient dose in computed tomography. (2000). Annals of the ICRP, 30(4), 7-7. doi:10.1016/s0146-6453(01)00049-5Chillarón, M., Vidal, V., Segrelles, D., Blanquer, I., & Verdú, G. (2017). Combining Grid Computing and Docker Containers for the Study and Parametrization of CT Image Reconstruction Methods. Procedia Computer Science, 108, 1195-1204. doi:10.1016/j.procs.2017.05.065Flores, L., Vidal, V., & Verdú, G. (2015). Iterative Reconstruction from Few-view Projections. Procedia Computer Science, 51, 703-712. doi:10.1016/j.procs.2015.05.188Flores, L. A., Vidal, V., Mayo, P., Rodenas, F., & Verdú, G. (2014). Parallel CT image reconstruction based on GPUs. Radiation Physics and Chemistry, 95, 247-250. doi:10.1016/j.radphyschem.2013.03.011Parcero, E., Flores, L., Sánchez, M. G., Vidal, V., & Verdú, G. (2017). Impact of view reduction in CT on radiation dose for patients. Radiation Physics and Chemistry, 137, 173-175. doi:10.1016/j.radphyschem.2016.01.038I. Kumar, H. Bhadauria, J. Virmani, and J. Rawat, “Reduction of speckle noise from medical images using principal component analysis image fusion,” in Industrial and Information Systems, 2014 9th International Conference on. IEEE, 2014, pp. 1–6.Barrett, J. F., & Keat, N. (2004). Artifacts in CT: Recognition and Avoidance. RadioGraphics, 24(6), 1679-1691. doi:10.1148/rg.246045065Chillarón, M., Vidal, V., Verdú, G., & Arnal, J. (2018). CT Medical Imaging Reconstruction Using Direct Algebraic Methods with Few Projections. Computational Science – ICCS 2018, 334-346. doi:10.1007/978-3-319-93701-4_25Joseph, P. M. (1982). An Improved Algorithm for Reprojecting Rays through Pixel Images. IEEE Transactions on Medical Imaging, 1(3), 192-196. doi:10.1109/tmi.1982.4307572F. P. Group. FORBILD head phantom. [Online]. Available: http://www.imp.uni-erlangen.de/forbild/english/results/index.htm.Paige, C. C., & Saunders, M. A. (1982). LSQR: An Algorithm for Sparse Linear Equations and Sparse Least Squares. ACM Transactions on Mathematical Software, 8(1), 43-71. doi:10.1145/355984.355989Yu, H., & Wang, G. (2010). A soft-threshold filtering approach for reconstruction from a limited number of projections. Physics in Medicine and Biology, 55(13), 3905-3916. doi:10.1088/0031-9155/55/13/022Beck, A., & Teboulle, M. (2009). A Fast Iterative Shrinkage-Thresholding Algorithm for Linear Inverse Problems. SIAM Journal on Imaging Sciences, 2(1), 183-202. doi:10.1137/080716542C. Tomasi and R. Manduchi, “Bilateral filtering for gray and color images,” in Sixth International Conference on Computer Vision. IEEE, 1998, pp. 839–846.A. Hore and D. Ziou, “Image Quality Metrics: PSNR vs. SSIM,” in 2010 20th International Conference on Pattern Recognition. IEEE, aug 2010, pp. 2366–2369