Study of core stability during load follow with ROM methods

Research Project, 2020 – 2025

With the decreasing share of electricity produced by nuclear power in Sweden in the years to come and the corresponding increasing share of electricity produced by wind and solar power systems, an increasing reliance on intermittent energy sources in the Swedish grid is expected. Correspondingly, the Swedish nuclear fleet will have to move from a base load production mode to a load-follow production mode.
 
It is well known in classical reactor physics that adjusting the reactor power might result in Xenon oscillations under unfavourable core conditions. Such oscillations have a period of ca. 15-30 hours. Because of their relatively long time period, the oscillations might remain unnoticed before they develop significantly, then requiring operator action in form of partial control rod insertion. In addition to detect these oscillations when they develop, it is of utmost importance to detect whether a core configuration is stable or unstable with respect to Xenon oscillations.
 
In this PhD thesis, a Reduced-Order Model (ROM) to study the stability properties of nuclear reactors during load follow conditions is developed, capitalizing on some earlier ROM work carried out at Chalmers. In a ROM, the time-dependent neutron kinetic equations are projected onto a few eigenmodes of the neutron diffusion operator. The main advantage of a ROM is to replace a set of many Partial Differential Equations (PDEs) describing the space-time dependence of the neutron flux through the core into a set of very few Ordinary Differential Equations (ODEs). These few ODEs still catch the main features of the space-time response of the system to perturbations.