Steam Generators for Future Fast Breeder Reactors

Abstract

Abstract The operating experience of fast reactors worldwide has highlighted the need for reliable performance of Steam Generator (SG) as it is one of the most critical components deciding the plant availability. Based on design, development and manufacture of steam generator for 500 MWe Prototype Fast Breeder Reactor (PFBR) and also the reassuring operational feedback from experimental Steam Generator Test Facility (SGTF), the concept of integral once through SG with mod. 9Cr 1Mo as principle material of construction is retained for future FBRs. SG is a vertical counter flow shell & tube heat exchanger with sodium on shell side and water / steam in tubes. For future FBRs, the present design of SG for PFBR is reassessed and optimised based on manufacturing experiences with focus on improved economics and enhanced safety. Various key aspects like selection of number of SG modules per secondary sodium loop, tube length, heat transfer area margin and optimization of tube size are discussed in the paper. The results of CFD studies carried out with a 30 sector model coupled with an in-house code (DESOPT) to investigate on thermal and flow distribution of such longer steam generators at different operating conditions are also highlighted. Through detailed optimisation studies, it is concluded that 3 SG per loop with each having 433 tubes of 30 m long, 12.6 mm ID and 2.4 mm wall thickness for a design life of 60 years provides economical configuration leading to a saving of ∼25% in total cost. Further, enhanced safety is ensured by reduction of ∼40% tube to tube-sheet joints as compared with PFBR SG.