Power reactor noise deals with neutron fluctuations that are induced by fluctuations or oscillations of the reactor properties, i.e. displacement of core components, temperature or density variations and so on. It is clear that any temporal changes in the reactor composition manifests itself as changes of the corresponding cross-sections. These changes are called “perturbations”. The cross sections are, in turn, coefficients of the pertinent transport or diffusion equations. Time-dependence of the cross-sections will naturally lead to the time-dependence of the neutron flux, which is in addition space-dependent. The origin of neutron noise theory can be traced back to the reactor oscillator experiments performed at the “Clinton Pile” in Oak Ridge in 1942. [1]

A vast research program for power reactor noise development was commenced in Department of Energy Engineering (DOEE) in SHARIF University of Technology from 2008. Development of a neutron noise simulator for hexagonal-structured reactor cores was performed in DOEE at 2010. The spatial discretization of both 2-D 2-group static and dynamic equations was based on a developed box-scheme finite difference method for hexagonal mesh boxes in this work. [2]

After that the Galerkin Finite Element Method (GFEM) was used to solve the 2-D 2-group and 3-D 2-group neutron noise equation based on Galerkin-type scheme by considering the linear approximation of a shape function. Unstructured triangle elements were used to discretize the equations. The main advantage of the unstructured triangular elements was their superiority in mapping the curved boundaries or material interfaces. [3,4,5]

Development of a neutron noise simulator, DYN-ACNEM, using the Average Current Nodal Expansion Method (ACNEM) in 2-D 2-group hexagonal geometries was reported in 2017. Thus one could enjoy the benefit of using the coarse mesh for power noise analysis. The Inadvertent Loading and Operation of a Fuel Assembly in an Improper Position (ILOFAIP) as an important neutron noise source was investigated using ACNEM in this study. [6]

Neutron noise based on transport theory was calculated in 2018. Comparing the accuracy of Green’s function based on transport and diffusion theory in order to survey the differences between these theories were performed in this study. [7]

Investigating the propagation noise (inlet coolant temperature fluctuations, inlet coolant velocity fluctuations and the reactivity fluctuations caused by the boron concentration fluctuations) in PWRs (specifically in VVER-1000 reactors) via closed loop were investigated in 2015. Coupling of neutronic and thermal-hydraulic noise calculations was the main contribution of this study. [8,9,10]

Neutron noise source reconstruction was performed using three different unfolding techniques in a typical VVER-1000 reactor core in 2013. The inversion, zoning and scanning methods were applied for reconstruction of the noise source of type absorber of variable strength. Improved Scanning Method (ISM) was also used to reconstruct the noise source of type vibrating absorber. [11] Neutron noise source reconstruction using Artificial Neural Network (ANN) in a typical VVER-1000 reactor core was performed in 2014. The multilayer perception neural network was developed for reconstruction of the noise source. Noise source characteristics including strength, frequency and the location (X and Y coordinates) were identified with high accuracy. [12]

A power reactor noise simulator for investigation of neutronic and thermo hydraulic perturbations with the capability of noise source characteristic reconstruction in pressurized water reactors (either PWR or VVER) is elaborated during our  last decade research activities.

Keywords: Power Reactor Noise, Neutron noise, Propagation noise, noise source reconstruction.

REFERENCES

[1] Imre Pazsit, Transport Theory and Stochastic Theory, Lecture Note 2006. 

[2] Hessam Malmir, Naser Vosoughi, Ehsan Zahedinejad , “Development of a 2-D 2-group neutron noise simulator for hexagonal geometries”, Ann. Nucl. Energy, Vol. 37, pp. 1089-1100, 2010.

[3] Seyed Abolfazl Hosseini, Naser Vosoughi , “Development of two-dimensional, multigroup neutron diffusion computer code based on GFEM with unstructured triangle elements”, Ann. Nucl. Energy, Vol. 51, pp. 213-226, 2013.

[4] Seyed Abolfazl Hosseini, Naser Vosoughi , “Neutron noise simulation by GFEM and unstructured triangle elements”, Nuclear Engineering and Design, Vol. 253, pp. 238-258, 2012.

[5]  Seyed Abolfazl Hosseini, Naser Vosoughi , “Development of 3D neutron noise simulator based on GFEM with unstructured tetrahedron elements”, Annals of Nuclear Energy, Volume 97, 2016, Pages 132-142.

[6] Seyed Abolfazl Hosseini, Naser Vosoughi, Javad Vosoughi ,”Neutron noise simulation using ACNEM in the hexagonal geometry”, Annals of Nuclear Energy, Volume 113, 2018, Pages 246-255. 

[7] Mona Bahrami, Naser Vosoughi, “SN Transport Method for neutronic noise calculation in nuclear reactor system: comparative study between transport theory and diffusion theory”, Annals of Nuclear Energy, Volume 114, 2018, Pages 236-244.

[8] Hessam Malmir, Naser Vosoughi,“Calculation and analysis of thermal -hydraulics fluctuations in pressurized water reactor”, Annals of Nuclear Energy, Volume 76, 2015, Pages 75-84.

[9] Hessam Malmir, Naser Vosoughi ,“Propagation noise calculation in VVER-type reactor core”, Progress in Nuclear Energy, Volume 78, 2016, Pages 10-18.

[10] Hessam Malmir, Naser Vosoughi, “Investigating the propagation noise in PWR's via closed loop Neutron-kinetic thermal-hydraulic noise calculation”, Annals of Nuclear Energy, Volume 80, 2015, Pages 101-113.

[11] Seyed Abolfazl Hosseini, Naser Vosoughi, “On a various noise source reconstruction algorithms in VVER-1000 reactor core”, Nuclear Engineering and Design, Vol. 261, pp. 132-143, 2013.

[12] Seyed Abolfazl Hosseini, Naser Vosoughi, “Noise source reconstruction using ANN and hybrid methods in VVER-100 reactor core”, Progress in Nuclear Energy, Vol. 71, pp. 232-247, 2014. 

Dr. Naser Vosoughi is a professor in Nuclear Energy Engineering at Department of Energy Engineering, SHARIF University of Technology in Tehran, IRAN.

He has acquired about 2 years international work experience in a capacity of academic visitor in Trieste University (Italy), Chalmers University (Sweden) and International Center for Theoretical Physics (ICTP). He has been the author and/or co-author of 2 books and more than 90 ISI journal papers. he is currently the chair of Department of Energy Engineering, SHARIF University of Technology. He has supervised more than 100 M.Sc. students and more than 20 Ph.D. students and postdoctoral researcher.