Supercritical water reactor (SCWR), a possible generation IV nuclear reactor, is expected to be more efficient and economical than the existing reactors. However, the possibility of thermal-hydraulic (TH) instabilities poses a challenge to its development. A generic pressure vessel (PV) SCWR concept, similar to the US SCWR design, is investigated at present for density wave oscillations (DWOs). An existing TH model, which was used earlier for the single-channel analysis, is extended here for the analysis of parallel channels. The TH model accounts for the regional heterogeneity in power distribution. The TH model is validated with the existing numerical results to access its capability to simulate the parallel-channel density wave instabilities (DWIs) in a supercritical water (SCW) system. Then, the TH model is used to capture the core-wide as well as regional modes of parallel-channel DWIs in the PV SCWR. The marginal stability thresholds are obtained for both the modes of DWOs and are compared. Subsequently, the aforementioned stability thresholds are compared with those obtained from the single-channel model as well, with the purpose to quantify the difference in stability thresholds obtained from the single-and parallel-channel analysis.
A numerical model for a supercritical natural circulation loop is developed to examine the flow instabilities by nonlinear stability analysis. The supercritical natural circulation loop is a loop geometry, which is driven by natural circulation with supercritical fluids as a coolant. A mathematical formulation is developed to study the steady-state and transient solution procedure for supercritical natural circulation loop. This mathematical model is then used to perform various parametric studies with different supercritical fluids (water, [Formula: see text], R134a, ammonia, R22, propane, and isobutane). The behavior of all the fluids is analyzed on identical geometrical and operating conditions. A comprehensive numerical study of the nonlinear stability analysis is presented with particular emphasis on the feasibility of various fluids in a natural circulation loop environment. The 50% increment in loop diameter and height increased the stable operating zones and shifted the marginal stability boundary upward respectively by approximately three times and 25–40% of the previous value. However, further increase in diameter and height reduces the increment of stable operating zones; hence the marginal stability boundary shifts upward marginally than the previous value. Furthermore, the marginal stability boundaries are generated to identify the stable and unstable zones for the available geometrical and operating conditions.
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