Thermal hydraulic modeling of a natural circulation loop

The experiment was carried out on the test loop HRTL-5, which simulates the geometry and system design of a 5 MW nuclear heating reactor. The analysis was based on a one-dimensional two-phase flow drift model with conservatio n equations for mass, steam, energy and momentum. Clausius-Clapeyron equati on was used for the calculation of flashing front in the riser. A set of or dinary equations, which describes the behavior of two-phase flow in the nat ural circulation system, was derived through integration of the above conse rvation equations for the subcooled boiling region, bulk boiling region in the heated section and for the riser. The method of time-domain was used fo r the calculation. Both static and dynamic results are presented. System pr essure, inlet subcooling and heat flux are varied as input parameters. The results show that subcooled boiling in the heated section and void flashing in the riser have significant influence on the distribution of the void fr action, mass flow rate and flow instability of the system, especially at lo w pressure. The response of mass flow rate, after a small disturbance in th e heat flux is shown, and based on it the instability map of the system is given through experiment and calculation. There exists three regions in the instability map of the investigate natural circulation system, namely, the stable two-phase flow region, the unstable bulk and subcooled boiling flow region and the stable subcooled boiling and single phase flow region. The mechanism of two-phase flow oscillation is interpreted.