Development of an integrated neutronic/thermal-hydraulic tool for estimating fluctuations in PWRs
Doktorsavhandling, 2011

Monitoring and diagnostics of a reactor core at a given state is very important for detecting potential problems and anomalies at an early stage. Several methods exist for these purposes, but the majority of them require a disruption of the plant operation, e.g. by shut-down or by perturbation of the system. The knowledge of the noise, i.e. the fluctuations of a parameter around its time-averaged value, can be used for on-line/off-line core monitoring and diagnostics without any disruption of normal operation. Measurements of reactor parameters can be used for estimating dynamical parameters, as the Moderator Temperature Coefficient (MTC) in a Pressurized Water Reactor (PWR), or for detecting anomalies, as unseated fuel assemblies in Boiling Water Reactors (BWRs) or flow blockages. Since the interpretation of the neutron noise aims at finding the driving perturbation responsible for the observed noise in the system and the limited number of detectors makes this attempt difficult, it would be beneficial to be able to numerically estimate in-core noise for any arbitrary noise source so that the comparison between the measured and calculated noise would allow finding the root cause of the observed fluctuations. The intention of this work is thus to calculate the in-core noise for commercial systems using coupled thermal-hydraulic/neutronic models. This includes the determination of the neutron noise, as well as of fluctuations in fuel temperature, moderator density and flow velocity. The work is divided into two main parts, neutron kinetics and thermal-hydraulics. On the neutron kinetic side, P1 and diffusion theories were compared with the conclusion that diffusion theory was accurate enough for noise calculations. The spatial discretization was also tested through the finite difference method and the Analytical Nodal Method (ANM), where it was concluded that both could be used for calculating the neutron noise. The comparisons between those two methods revealed that finite differences seems to be accurate enough for most practical applications. Both methods were successfully validated against analytical solutions. The other part covered in this work was the development for PWRs of a thermal-hydraulic model coupled to the neutronic model. This model was validated against calculations by the commercial Computational Fluid Dynamics (CFD) code FLUENT. The integrated neutronic/thermal-hydraulic model was proven viable and was also benchmarked against a RELAP5/PARCS model of a commercial PWR with mostly good results.

Diffusion theory


Neutron noise

Coupled calculations

P1 theory Analytical Nodal Method

FB-salen, Fysikgården
Opponent: Assis Prof Tomasz Kozlowski


Viktor Larsson

Chalmers, Teknisk fysik, Nukleär teknik

Comparative study of 2-group P1 and diffusion theories for the calculation of the neutron noise in 1D 2-region systems

Annals of Nuclear Energy,; Vol. 36(2009)p. 1574-1587

Artikel i vetenskaplig tidskrift

Investigation of the MTC noise estimation with a coupled neutronic/thermal-hydraulic dedicated model – “Closing the loop”

Proc. Int. Conf. on Advances in Reactor Physics – Linking Research, Industry, and Education (PHYSOR 2012), Knoxville, TN, USA, April 15-20, 2012, American Nuclear Society,; Vol. 1(2012)p. 361-375

Paper i proceeding

Neutron Noise Calculations Using the Analytical Nodal Method

Proc of PHYSOR 2010 - Advances in Reactor Physics to Power the Nuclear Renaissance, Pittsburgh May 9-14 2010,; Vol. 2(2010)p. 939-950

Paper i proceeding

Neutron noise calculations using the Analytical Nodal Method and comparisons with analytical solutions

Annals of Nuclear Energy,; Vol. 38(2011)p. 808-816

Artikel i vetenskaplig tidskrift

A coupled neutronics/thermal–hydraulics tool for calculating fluctuations in Pressurized Water Reactors

Annals of Nuclear Energy,; Vol. 43(2012)p. 68-76

Artikel i vetenskaplig tidskrift

Comparison of the calculated neutron noise using finite differences and the Analytical Nodal Method

Annals of Nuclear Energy,; Vol. 43(2012)p. 176-182

Artikel i vetenskaplig tidskrift


Övrig annan teknik



CTH-NT - Chalmers University of Technology, Nuclear Engineering: 251

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 3257

FB-salen, Fysikgården

Opponent: Assis Prof Tomasz Kozlowski