Search

Summary: Steam generator is the heat transfer component of sodium‐cooled fast reactor (SFR). It is possible to happen flow instability in the tubes of sodium heated once‐through steam generator (OTSG). In order to investigate the flow instability of parallel channels in sodium heated OTSG, a numerical analysis code called COSFIAS has been developed in Fortran language based on time‐domain method. The experimental data of parallel channels flow instability with uniform heating power condition and sodium heated condition have been applied to validate the code. The relative errors between calculation results and experimental data of uniform heating power condition are within 10%. The relative errors between calculation results and experimental data of sodium heated conditions are within 7%. The comparison results indicate that the COSFIAS program is reasonable and accurate for practical engineering application. In addition, the effects of important parameters on flow instability of parallel channels have been analyzed. From the calculation results some conclusions could be drawn: the decrease of water pressure would cause the increase of heat transfer power and destabilize the parallel channels system; in high subcooling region, the increase of inlet subcooling would stabilize the system; in low subcooling region, with the decrease of inlet subcooling, the parallel channels system would turn to be unstable and then return to be stable again; the increase of water mass flow rate could stabilize the parallel channels system.; the sodium heated condition is more stable than uniform heat flux condition in the same heat transfer power; the increase of sodium inlet temperature could destabilize the parallel channels system; the increase of sodium mass flow rate could destabilize the parallel channels system. In addition, the code could be applied to support the design work of sodium heated OTSG. [ABSTRACT FROM AUTHOR]

Summary: In this study, two‐phase density wave instability in parallel‐twin rectangular channels was investigated with axially nonuniform heat profiles in the reactor core combined with static and rolling conditions. A parallel‐channel thermal‐hydraulic model was built using the method of two‐phase homogeneous flow developed in previous work, while the drift‐flux approach for void fraction and profile‐fit model for subcooled boiling were implemented. Although the rolling condition was chosen as the typical motion in this work, the additional force caused by the motion with six degrees of freedom was derived. The theoretical analysis was performed based on the method of small power perturbation for parallel‐twin rectangular channels. The flow oscillation caused by rolling was studied for different system parameters, including inlet resistance, exit resistance, pressure, and axial heating profile. The influence on flow instability of rolling parameters such as period, amplitude, and distance between channels was analyzed. The results showed that it would destabilize the system if a larger additional force was generated by rolling parameters. The influence of different axial heat profiles on flow instability was also studied under inlet‐peaked, cosine‐shape, and outlet‐peaked heat fluxes. The coupling effect of rolling motion and axial nonuniform heating was finally studied. The stability boundaries under different conditions were compared to the inherent boundary under the static condition with uniform heating. The results indicated that the influence of nonuniform heating was more evident and should be paid more attention to. [ABSTRACT FROM AUTHOR]