Static and Dynamic Modelling of 1D Heterogeneous Molten Salt Reactors
Typ
Examensarbete för masterexamen
Program
Publicerad
2021
Författare
Andersson, Erik
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Molten salt reactors represent one of the so called Generation IV concepts. In this
design the fuel is dissolved in a molten salt, which also acts as a coolant. The
moving fuel introduces a new physical phenomenon not present in reactor designs
with stationary fuel. Delayed neutrons, emitted through the decay of certain fission
fragment nuclei, called precursors, will in this case be emitted down-stream from
where the original fission event occurred. Since the precursor nuclei have mean lives
comparable to the temporal scale of the velocity, this will affect the neutron flux
in the reactor. There is also the possibility of precursors reentering the core since
the molten salt is circulating in the system. This thesis describes the process of
developing a novel numerical simulation tool, using the diffusion approximation for
neutron flux, for the calculation of the neutron flux and precursor concentration of
a one dimensional heterogeneous reactor core. The tool solves the diffusion equations
with two energy groups and one group of precursors in the stationary case
and for a monochromatic perturbation in the frequency domain, respectively. The
eigenvalue problem arising in the stationary case with no external sources is solved
using the power iteration method with a Wielandt’s shift technique and the inversion
of matrices is done using an LUPQ factorization. For the purpose of testing
the implementation, a scaled down solver for one energy group and one group of
precursors was developed in the same way as the full solver. When tested, the full
solver reproduces the results of a previously developed similar solver for the case
of zero fuel velocity and the scaled down version reproduces the results of a previously
developed one-group solver as well as the analytical solution to the special
case of infinite fuel velocity. A condition on the mesh resolution was found that
greatly impacted the dynamic solution for the precursor concentration as its spatial
distribution exhibits an oscillatory behaviour.
Beskrivning
Ämne/nyckelord
Molten Salt Reactors , two-group neutron diffusion theory , neutron noise , numerical reactor modelling