Pages 191-192
Natural circulation type boiling water reactors are expected as promising next generation nuclear reactors, because recirculation system is reduced and loss of coolant event is mitigated. Three-dimensional gas-liquid two-phase flow in the chimney above the core is important for developing natural circulation flow rate through void fraction profile and carry under bubbles into the downcomer. The experiments were carried out using the test section with double cylinders imitating the pressure vessel and the chimney of a natural circulation reactor. Numerical analysis of the experiments have been performed using the extended two-fluid model, which can treat large scale interface directly and small scale interface with the averaged parameters as conventional two-fluid model. Transient gas-liquid two-phase flow after air injection in the bottom cross-section of the inner cylinder are calculated. Predicted natural circulation velocity in the downcomer is overestimated by 10% compared with experimental data.
