Experimental and Theoretical Investigations on Steady State Behavior of Natural Circulation Systems Operating with Supercritical Carbon-Dioxide

ABSTRACT

Supercritical water (SCW) exhibits excellent heat transfer characteristics and high volumetric expansion coefficient (hence high mass flow rates in natural circulation systems) near critical temperature. SCW is being considered as a coolant in some advanced nuclear reactor designs on account of its potential to offer high thermal efficiency, compact size, elimination of steam generator, separator & dryer, making it economically competitive. The elimination of phase change results in elimination of the Critical Heat Flux (CHF) phenomenon. Cooling a reactor at full power with natural instead of forced circulation is generally considered as enhancement of passive safety. In view of this, it is essential to study natural circulation behavior at supercritical conditions. Carbon-dioxide can be considered to be a good simulant of water for natural circulation at supercritical conditions since the density and viscosity variation of carbon-dioxide follows a parallel curve as that of water at supercritical conditions. Hence, experiments were conducted in a closed supercritical natural circulation loop (SCNCL) with supercritical carbon-dioxide as working fluid. A computer code NOLSTA has been developed to carry out steady state analysis of open and closed loop natural circulation at supercritical conditions. The code has been validated with experimental data available in open literature and experiments conducted in SCNCL.

Keywords: Supercritical, Natural circulation, Orientation, Steady-state.

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