Loading...

Hosseini, Abolfazl | 2013

494 Viewed
  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 44453 (46)
  4. University: Sharif University of Technology
  5. Department: Energy Engineering
  6. Advisor(s): Vosoughi, Naser
  7. Abstract:
  8. The present ph.D. thesis consists of three sections including the static calculation, neutron noise calculation and neutron noise source unfolding in VVER-1000 reactor core. The multi-group, two dimensional neutron diffusion equations and corresponding adjoint equations are solved in the static calculation. The spatial discretization of equations is based on Galerkin Finite Element Method (GFEM) using unstructured triangle elements generated by Gambit software. The static calculation is performed for both linear and quadratic approximations of shape function; baesd on which results are compared. Using power iteration method for the static calculation, the neutron and adjoint fluxes with the corresponding eigenvalues are obtained. Due to finite element method capability in modeling both of the rectangular and hexagonal geometries, the calculations are performed for both of the PWR and VVER benchmark problems. The results are benchmarked against the valid results for IAEA-2D, BIBLIS-2D and IAEA-PWR benchmark problems. A sensitivity analysis of the calculations to the number and arrangement of elements has been performed. This sensitivity analysis demonstrated the advantages of utilizing of unstructured triangle elements.In the second section, neutron noise calculations are performed for three types of noise sources, i.e. absorber of variable strength, vibrating absorber and Inadvertent Loading of a Fuel Assembly in an Improper Position (ILFAIP). The adjoint of noise equations are solved using a similar method used in forward calculation. Comparison of the calculated neutron noise at zero frequency with the results of static calculation, utilizing the results of adjoint noise calculations and qualitative comparison with the similar reported results are three different procedures to validate the neutron noise calculations. In the neutron noise calculations, the fluctuations are only considered in macroscopic absorption, fission and scattering cross sections and the fluctuations in the neutron diffusion coefficient are ignored. To investigate the effects of fluctuations in neutron diffusion coefficient on the results, the noise calculation is performed by considering these fluctuations as well.The last section of present thesis is the reconstruction of noise source using the detected neutron noise in the locations of detectors. To reconstruct noise source of type absorber of variable strength, three methods including inversion, zoning and scanning are applied and the location and strength of noise source are estimated. The proposed “improved scanning method” is applied to reconstruct noise source of type vibrating absorber. A sensitivity analysis of mentioned methods to different parameters like the location of noise source in the reactor core, number of triangle elements, number of available detectors and fuel burn up is performed. One of the purposes of the present work is the completely reconstruction of noise source which includes the all characteristics of noise source, i.e. strength, frequency and location. To this end, the multilayer perception neural network is developed and noise source is reconstructed with high accuracy. Also, the hybrid method which comprises scanning method and multilayer perception neural network is developed to reconstruct two coincidence noise sources with high accuracy. Finally, sensitivity analysis of the accuracy of reconstructed noise source to the number of detectors and their arrangement in the reactor core are done
  9. Keywords:
  10. Neutron Noise ; Steady State Calculation ; Neutron Calculation ; Neutron Noise Soure Unfolding ; Galerkin Finite Element Method

 Digital Object List

 Bookmark

No TOC