Prediction method of critical power by film flow rate measurement and subchannel analysis

This paper presents a new experiment-simulation combined method that can estimate the critical power of boiling water reactors, BWRs, regarding to spacer geometry. Current experimental method for estimating critical power for BWRs design, require many trained experts and much expensive flow facilities to conduct the experiments. In the present method, a measurement of liquid film flow rate of adiabatic gas-liquid two-phase flow and a subchannel analysis of actual BWRs flow condition are conducted in experimentally and analytically, coincidently. In the experiment, deposition enhancement coefficients of three spacer geometies, a ferrule, an egg-crate, and a ferrule spacer with twisted tape (CYCLONE spacer) were estimated by measuring liquid film flow rate of air-water two-phase flow flowing up in a vertical square (4 × 4) rod bundle that simulated BWRs 8 × 8 rod bundle. Using these coefficients, critical powers under each spacer geometry condition were calculated in the subchannel analysis. A validation of this method was conducted using previous data of critical power in actual BWRs flow condition. The critical powers predicted by this method agreed well with those of the experimental data. The result confirmed the effectiveness of this experiment-simulation combined method as well as the advantage over current experimental method in human and facility costs.