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Investigating the Propagation Noise in PWRs via Coupled Neutronic and Thermal-Hydraulic Noise Calculations

Malmir, Hessam | 2015

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 47277 (46)
  4. University: Sharif University of Technology
  5. Department: Energy Engineering
  6. Advisor(s): Vosoughi, Naser
  7. Abstract:
  8. In operating nuclear reactor core, fluctuations (deviations from normal operating conditions) are usually produced and propagated. These fluctuations can be due to control rod vibrations, inlet coolant temperature fluctuations, inlet coolant velocity fluctuations and so on. The induced neutron noise can be detected by in-core neutron detectors. Noise source identifications (such as the type, location and propagating velocity) as well as the calculation of the dynamical parameters (such as moderator temperature coefficient in PWRs and Decay Ratio in BWRs) are of the main applications of the neutron noise analysis in power reactors.
    Investigating the propagation noise in PWRs (specifically in VVER-1000 reactors) via closed-loop neutronic and thermal-hydraulic noise calculations is the main contribution of this thesis. For this aim, the different types of the propagation noise in PWRs are firstly presented and then the different models for the simulation of these fluctuations are studied in detail.
    The main propagating noise sources in PWR core are the inlet coolant temperature fluctuations, the inlet coolant velocity fluctuations and the reactivity fluctuations (caused by the boron concentration fluctuations). However, these fluctuations must be small enough to be considered as the noise sources.
    In order to simulate the different types of the propagation noise in PWRs, three different computational tools for the neutronics, thermal-hydraulics and nuclear macroscopic cross-sections are required. In other words, one needs to have a computational module for the thermal-hydraulic noise calculations and another one for the neutron noise calculations. Then, with coupling of them via a model for the nuclear macroscopic cross-sections, one obtains the distributed dynamic transfer function for a PWR core.
    In this dissertation, first the 3-D 2-group neutron noise equations are solved numerically using the box-scheme finite difference method in different possible geometries. Then, the thermal-hydraulic noise equations (in the frequency domain) are derived based on the mass, momentum and energy conservation laws (for the coolant, fuel, gap and cladding), without any simplifying assumptions. These equations are numerically solved, using the finite volume method, for different channels of the reactor core. Next, the neutronic and thermal-hydraulic noise calculation modules are coupled based on the point-kinetic and spatial-kinetic models and results are studied comparatively.
    After the simulation of the different propagating noise sources in PWRs, an intelligent system is proposed (using multi-layer artificial neural networks) for the noise source identification in this kind of reactor core. Furthermore, the moderator temperature coefficient of reactivity has been estimated (in all the frequencies) based on both the point-kinetic and spatial-kinetic models.
    The different computational modules have been examined in different benchmark problems (both single and coupled modes). Although the BNPP-1 VVER-1000 reactor core has been considered as the main benchmark problem in almost all the chapters of this dissertation, the discretization of the equations and their final forms are presented for all the possible geometries and fuel assemblies of pressurized water reactors (rectangular-z and hexagonal-z)
  9. Keywords:
  10. Neutron Noise ; Dynamic Parameters ; Pressurized Water Reactor (PWR,WWER) ; Vodo-Vodyanoi Energetichesky (VVER)1000 ; Propagation Noise ; Thermal-Hydraulic Noise ; Reactor Dynamic Transfer Function ; Noise Source Identification

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