Stability and bifurcation analysis of Oskarshamn-2 event with nuclear data and kinetic parameter uncertainties

Abstract

The primary aim of the current research is to investigate the impact of nuclear data and kinetic parameters uncertainties on the stability and bifurcation behaviour of the Oskarshamn-2 core under unstable conditions. Utilizing the SHARK-X platform, nuclear data and kinetic parameter uncertainties are propagated in 2-D lattice calculations with CASMO5 and downstream to static and dynamic calculations using SIMULATE3 and SIMULATE-3 K. Results show that, the nuclear data uncertainties have a drastic effect on the stability behaviour of the core when the instability is triggered because the system become highly nonlinear at such conditions. However, more interesting is the qualitative effect on the stability behaviour where the nature of solution changes, i.e. occurrence of bifurcation, from a highly unstable state (diverging oscillation amplitudes) to a highly stable state (rapidly decreasing oscillation amplitudes). This change in the nature of behaviour, i.e. solution, is found to be due to the fact that the stability event occurs very close to the stability boundary of the system and therefore any change in any parameter could be enough to swing the system to the other side of the stability boundary. Concerning kinetic parameters, results show a clearly smaller impact compared to that of nuclear data, leading to uncertainties in the decay ratio and resonance frequency around 2.5 % and 0.2 % respectively. The main effect is variations in oscillation amplitude without altering the nature of the solution.