Stability analysis of parallel-channel systems under supercritical pressure with heat exchanging

The flow in the core of supercritical water reactors (SCWRs) experiences drastic change in its thermodynamic properties and transport properties near the pseudo-critical temperature, thus the core flow may be susceptible to density wave oscillation instability, which is a challenge to the system safety and must be studied carefully. This work studies the stability characteristics of parallel-channel systems with heat exchanging, the prototype of which is originated from the thermal-spectrum zone assemblies of a newly designed mixed-spectrum SCWR (SCWR-M). A frequency-domain model has been developed for linear stability analysis, and marginal stability boundaries under several conditions are generated, which indicate that the system normal operational condition is in an absolute stable region. Decreasing the wall thermal conductivity can improve system stability while increasing mass flow is beneficial for the system stability. The system is not very sensitive to the axial power distributions. A one-dimensional time-domain model has also been developed for nonlinear analysis, and several transients with mass flow perturbations are calculated. The system marginal stability boundaries calculated by using frequency-domain and time-domain methods are in good agreement with each other. The existence of transitional stable region has been observed. A special case of parallel-channel systems with heat exchanging has been studied and achieved the conclusion that the second eigenvalue should be considered when studying the stability characteristics of complicated systems by using frequency-domain methods.