[en] Based on the comprehensive evaluation in the feasibility study on F/S (commercialized fast reactor cycle systems), straight double-wall tube SG (steam generator) was recommended as reference design from the view point of reliability and property protection. But straight double-wall tube SG has many technical issues. Alternative SG must be designed with less technical issues. Alternative SG was designed by the objects as shown bellow. Safety performance (reactor core protection) is equal to reference design. Property protection performance is equal to reference design. Economically acceptable. Based on common technology with reference design. Alternative SG was designed by the applicability study of design options in return for long and double wall tube as technical issues of reference design with high difficulty. To design alternative SG with prevention of tube failure propagation, design options to resist the wastage by sodium-water reaction were evaluated from the point of view of property protection performance. And, candidates for alternative SG were proposed with combination of design options. By comparative evaluation of alternative SG by view of technical issues and adoption time, 'Protective wall tube SG', 'Coated wall tube SG' with resistance to tube wastage, and 'Short length double wall tube SG' with low difficulty were elected. (author)