Startup instability in natural circulation driven nuclear reactors

Abstract

Natural circulation driven nuclear reactors are prone to flow instability during the startup transients. This paper intends to provide the state-of-the-art reviews on the theoretical analysis and experimental studies on flow instability in three types of natural circulation driven reactors, ranging from conventional nuclear reactors to small modular reactors. Brief overviews of three categories of startup flow instability, i.e., density wave oscillations, flashing instability, and Geysering instability, are provided. A critical review is conducted for the scaling analysis and design of small scaled test facility. The review of obtaining quasi-steady state stability maps in the dimensionless stability plane through frequency domain analysis and experimental tests provides the state-of-the-art methodology of analyzing the flow instability. Experimental startup instability during different initial startup procedures is reviewed. Although extensive efforts have been made to study the flow instability, further work is required to improve the scaling ability of experimental investigation and the accuracy of code analysis. Some discussions for future research directions are given.

Modeling of flashing-induced flow instabilities for a natural circulation driven novel modular reactor

“…The basic method used in this research to study the flashing instability is called linear frequency domain stability analysis, which can be used to obtain stability boundaries for a flow system. This method is a conventional way to analyze other flow instabilities such as the density wave oscillations (DWO) [1] and Ledinegg instability (flow excursion) etc. The frequency domain analysis in this research was based on the drift-flux model and its constitutive equations [18] for a two-phase flow system.…”

“…The flashing induced stability problem, simplified as flashing instability, in two-phase flow system is of great importance to the safe operation of naturally driven nuclear reactors and passively safe engineering safety system in nuclear industry. The designs of naturally driven nuclear reactors, ranging from conventional nuclear reactors to small modular reactors [1], feature a relative long chimney section above the reactor core to increase the driving force of natural circulation. In addition, the design of the reactor cavity cooling system for the generation IV reactors characterizes a long riser above the cooling panel [2].…”

Effect of Upstream and Downstream Pressure Losses on Flow Reversals in Low-Pressure Natural Circulation Loops

“…On the opposite if P in is large enough, boiling occurs in the heated section and nonlinear phenomena happen. Past works [2][3][4][5][6][7][8][9][10][11][12] have shown that natural circulation exchanger are stable at low P in and high subcooling T sat − T in (with T sat the saturation temperature), and exhibit strong flow reversals at high P in and low T sat − T in . These works included theoretical, experimental and numerical studies.…”

Dynamic mode decomposition of numerical data in natural circulation

“…More recently the occurrence of the natural circulation in nuclear research reactors has been described in the literature by studies focusing mainly: the prevention of a severe accident [8], the effect of an unprotected reactivity insertion on the dynamic response of Materials Testing Reactor -MTR research reactors under natural circulation regime [9], the investigation of flow reversal from downward forced to upward natural circulation [10], the stability of the natural circulation and its suppression due to the presence of oscillations [11], [12].…”