| 1. |
- Yi, Huaiqian, 1993, et al.
(författare)
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A discrete ordinates solver with diffusion synthetic acceleration for simulations of 2-D and 2-energy group neutron noise problems
- 2019
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Ingår i: International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering, M and C 2019. ; , s. 2023-2032
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Konferensbidrag (refereegranskat)abstract
- A neutron transport solver for 2-D, 2-energy-group neutron noise problems is presented. The simulator allows to determine: 1) the static neutron flux associated with a critical system; 2) the neutron noise in the frequency domain, according to a prescribed perturbation of the critical system. The perturbation is modeled as stationary fluctuations of the macroscopic nuclear cross-sections. The solution algorithm is based on a diamond finite difference scheme, discrete ordinates method, and it is accelerated using a diffusion synthetic acceleration technique. The solver is tested on 2-D homogeneous and heterogeneous systems with a localized neutron noise source. Its convergence is analyzed and compared to the case without acceleration.
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| 2. |
- Yi, Huaiqian, 1993, et al.
(författare)
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Development and test of a hybrid probabilistic-deterministic framework based on the interface current method
- 2019
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Ingår i: International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering, M and C 2019. ; , s. 2166-2177
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Konferensbidrag (refereegranskat)abstract
- This paper investigates the feasibility of performing reactor physics calculations using a hybrid neutron transport methodology. In the presented implementation, the interface current method is used as the deterministic framework, for which the necessary probabilities appearing in the method are estimated in advance using the probabilistic Monte Carlo code Serpent2. Two grids are used: one fine grid for estimating the scalar neutron flux and a coarse grid for computing the neutron currents on this grid. Once the probabilities have been estimated, the solutions on both grids are computed deterministically and simultaneously. The main advantage of this implementation lies with the fact that the modelling of possible complex geometries is left to the Monte Carlo solver. In addition, since only within cells probabilities are required, the estimation of such probabilities represents a task having an acceptable computing cost. Several two-dimensional test cases were developed for benchmarking the framework in two energy groups. For single assembly calculations in an infinite lattice, the deviation of the dominant eigenvalue is smaller than typically 50 pcm. Concerning the spatial distribution of the flux, some acceptable agreement was also obtained, with relative deviations generally smaller than 6%. In some other cases considering a checkerboard pattern of fuel assemblies, though, higher discrepancies were noticed. It is believed that such discrepancies could be alleviated by implementing a finer resolution in space, angle and energy of the framework. This feasibility study demonstrates the viability of the proposed computational route.
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| 3. |
- Demaziere, Christophe, 1973, et al.
(författare)
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JFNK preconditioning for coupled BWR calculations
- 2018
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Ingår i: International Conference on Physics of Reactors, PHYSOR 2018: Reactor Physics Paving the Way Towards More Efficient Systems. ; Part F168384-2, s. 1365-1376
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Konferensbidrag (refereegranskat)abstract
- In this paper, a one-dimensional Boiling Water Reactor (BWR) model in steady-state conditions is developed. The model accounts for neutron transport, fluid dynamics, heat transfer and the interdependences between the various physics. The modelling assumptions were chosen so that the physics of BWRs could be properly accounted for with an as simple as possible model. The model is thereafter used to study the effect of preconditioning when a Jacobian-Free Newton Krylov (JFNK) method is used to solve the system of equations. Preconditioning is a key aspect in any JFNK method. By clustering the eigenvalues of the system of equations, a preconditioner is expected to drastically reduce the number of iterations. Nevertheless, the design of an efficient preconditioner is a far from trivial task. Using the developed model, different preconditioning alternatives are tested. It is demonstrated that an efficient preconditioner is found to have the following characteristics: separate preconditioning of the neutron transport problem, no preconditioning of the heat transfer problem, preconditioning of the fluid dynamics problem where the cross-dependencies between the void fraction and the phasic velocities are resolved and where the pressure field is treated independently. This paper thus provides guidelines about how to develop an efficient preconditioner for coupled BWR physics.
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| 4. |
- Demaziere, Christophe, 1973, et al.
(författare)
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Overview of the CORTEX project
- 2018
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Ingår i: International Conference on Physics of Reactors, PHYSOR 2018: Reactor Physics Paving the Way Towards More Efficient Systems. ; Part F168384-5, s. 2971-2980
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Konferensbidrag (refereegranskat)abstract
- This paper gives an overview of the CORTEX project, which is a Research and Innovation Action funded by the European Union in the Euratom 2016-2017 work program, under the Horizon 2020 framework. CORTEX, which stands for CORe monitoring Techniques and Experimental validation and demonstration, aims at developing an innovative core monitoring technique that allows detecting anomalies in nuclear reactors, such as excessive vibrations of core internals, flow blockage, coolant inlet perturbations, etc. The technique is based on primarily using the inherent fluctuations in neutron flux recorded by in-core and ex-core instrumentation (often referred to as neutron noise), from which the anomalies will be differentiated depending on their type, location and characteristics. In addition to be non-intrusive and not requiring any external perturbation of the system, the method allows the detection of operational problems at a very early stage. Proper actions could thus be taken by utilities before such problems have any adverse effect on plant safety and reliability. In order to develop a method that can reach a high Technology Readiness Level, the consortium, made of 20 partners, was strategically structured around the required core expertise from all the necessary actors of the nuclear industry, both within Europe and outside. The broad expertise of the consortium members ensures the successful development of new in-situ monitoring techniques.
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| 5. |
- Mylonakis, Antonios, 1987, et al.
(författare)
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CORE SIM+ simulations of COLIBRI fuel rods oscillation experiments and comparison with measurements
- 2020
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Ingår i: International Conference on Physics of Reactors: Transition to a Scalable Nuclear Future, PHYSOR 2020. - : EDP Sciences. ; 2020-March, s. 2930-2938
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Konferensbidrag (refereegranskat)abstract
- At EPFL, the CROCUS reactor has been used to carry out experiments with vibrating fuel rods. The paper presents a first attempt to employ the measured data to validate CORE SIM+, a neutron noise solver developed at Chalmers University of Technology. For this purpose, the original experimental data are processed in order to extract the necessary information. In particular, detector recordings are scrutinized and detrended, and used to estimate CPSDs of detector pairs. These values are then compared with the ones derived from the CORE SIM+ simulations of the experiments. The main trend of the experimental data along with the values for some detectors are successfully reproduced by CORE SIM+. Further work is necessary on both the experimental and computational sides in order to improve the validation process.
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| 6. |
- Yi, Huaiqian, 1993, et al.
(författare)
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Acceleration of a 2-dimensional, 2-energy group neutron noise solver based on a discrete ordinates method in the frequency domain
- 2020
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Ingår i: International Conference on Physics of Reactors: Transition to a Scalable Nuclear Future, PHYSOR 2020. - : EDP Sciences. ; 2020-March, s. 2922-2929
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Konferensbidrag (refereegranskat)abstract
- The acceleration of the convergence rate is studied for a neutron transport solver to simulate 2-D, 2-energy-group neutron noise problems in the frequency domain. The Coarse Mesh Finite Difference (CMFD) method is compared to the Diffusion Synthetic Acceleration (DSA) method. Numerical tests are performed using heterogeneous system configurations with different boundary conditions. The CMFD scheme leads to a better convergence rate. The results also show that CMFD can accelerate neutron noise problems in a wide range of perturbation frequencies with almost equal efficiency. An unstable convergence behavior is nevertheless observed in problems with purely reflective boundary conditions. Stabilization techniques such as performing multiple transport sweeps, underrelaxing the flux update, and using the lpCMFD method are investigated and improvements can be obtained.
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