Thesis Open Access

A neutron noise solver based on a discrete ordinates method.

Huaiqian YI

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  "publisher": "Zenodo", 
  "DOI": "10.5281/zenodo.3813173", 
  "language": "eng", 
  "title": "A neutron noise solver based on a discrete ordinates method.", 
  "issued": {
    "date-parts": [
  "abstract": "<p>A neutron noise transport modelling tool is presented in this thesis. The simulator allows to<br>\ndetermine the static solution of a critical system and the neutron noise induced by a prescribed<br>\nperturbation of the critical system. The simulator is based on the neutron balance equations in<br>\nthe frequency domain and for two-dimensional systems. The discrete ordinates method is used<br>\nfor the angular discretization and the diamond finite difference method for the treatment of the<br>\nspatial variable. The energy dependence is modelled with two neutron energy groups. The<br>\nconventional inner-outer iterative scheme is employed for solving the discretized neutron<br>\ntransport equations. For the acceleration of the iterative scheme, the diffusion synthetic<br>\nacceleration is implemented.<br>\nThe convergence rate of the accelerated and unaccelerated versions of the simulator is studied<br>\nfor the case of a perturbed infinite homogeneous system. The theoretical behavior predicted by<br>\nthe Fourier convergence analysis agrees well with the numerical performance of the simulator.<br>\nThe diffusion synthetic acceleration decreases significantly the number of numerical iterations,<br>\nbut its convergence rate is still slow, especially for perturbations at low frequencies.<br>\nThe simulator is further tested on neutron noise problems in more realistic, heterogeneous<br>\nsystems and compared with the diffusion-based solver. The diffusion synthetic acceleration<br>\nleads to a reduction of the computational burden by a factor of 20. In addition, the simulator<br>\nshows results that are consistent with the diffusion-based approximation. However,<br>\ndiscrepancies are found because of the local effects of the neutron noise source and the strong<br>\nvariations of material properties in the system, which are expected to be better reproduced by a<br>\nhigher-order transport method such as the one used in the new solver.</p>", 
  "author": [
      "family": "Huaiqian YI"
  "type": "thesis", 
  "id": "3813173"
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