Performance Analysis and Tube Inlet Orifice Length Evaluation of a Once-Through Steam Generator

A numerical study is conducted for performance analysis and secondary side screw-type tube inlet orifice design of a once-through steam generator (OTSG). Various tube plugging conditions and power levels are considered, and the secondary coolant flow rate is adjusted to maintain a constant thermal power. Comprehensive numerical solutions are acquired to evaluate the OTSG thermal-hydraulic performance and minimum orifice length under various operating conditions. The OTSG performance is analyzed according to the tube plugging condition in terms of the OTSG thermal power, steam outlet superheat degree, and secondary coolant pressure drop. The results obtained show that a constant thermal power can be maintained by properly adjusting the secondary coolant flow rate with a variation of the steam outlet superheat degree and secondary coolant pressure drop when the OTSG operates at high power level. The required minimum orifice length to suppress the flow oscillation below the allowable level is evaluated. The lowest power level results in the highest minimum orifice length, and non-plugging condition provides a limiting case for the orifice length criterion.