Numerical analysis on flow instability of parallel channels in steam generator for sodium‐cooled fast reactor

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.