IMPROVED NEUTRON KINETICS FOR COUPLED THREE-DIMENSIONAL BOILING WATER REACTOR ANALYSIS

Open Access
Author:
Akdeniz, Bedirhan
Graduate Program:
Nuclear Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
July 09, 2007
Committee Members:
  • Kostadin Nikolov Ivanov, Committee Chair
  • Lawrence E Hochreiter, Committee Member
  • Yousry Y Azmy, Committee Member
  • Cengiz Camci, Committee Member
  • Erwin Müller, Committee Member
  • Dobromir Panayotov, Committee Member
Keywords:
  • Neutron Kinetics
  • Delayed Neutron
  • Importance Factor
  • Parameterization Technique
  • BWR
Abstract:
The need for a more accurate method of modeling cross section variations for off-nominal core conditions is becoming an important issue with the increased use of coupled three-dimensional (3-D) thermal-hydraulics/neutronics simulations. In traditional reactor core analysis, thermal reactor core calculations are customarily performed with 3-D two-group nodal diffusion methods. Steady-state multi-group transport theory calculations on heterogeneous single assembly domains subject to reflective boundary conditions are normally used to prepare the equivalent two-group spatially homogenized nodal parameters. For steady-state applications, the equivalent nodal parameters are theoretically well-defined; but, for transient applications, the definition of the nodal kinetics parameters, in particular, delayed neutron precursor data is somewhat unclear. The fact that delayed neutrons are emitted at considerably lower energies than prompt neutrons and that this difference cannot be accounted for in a two-group representation is of particular concern. To compensate for this inherent deficiency of the two-group model a correction is applied to the nodal values of the delayed neutron fractions; however, the adequacy of this correction has never been tested thoroughly for Boiling Water Reactor (BWR) applications, especially where the instantaneous thermal-hydraulic conditions play an important role on the core neutron kinetics calculations. This thesis proposes a systematic approach to improve the 3-D neutron kinetics modeling in coupled BWR transient calculations by developing, implementing and validating methods for consistent generation of neutron kinetics and delayed neutron data for such coupled thermal-hydraulics/neutronics simulations.