WELDING AND FABRICATION OF STAINLESS STEEL EQUIPMENT FOR 500MWe PROTOTYPE FAST BREEDER REACTOR

摘要

Austenitic stainless steel is the major structural material for the primary and secondary sodium systems (except for the steam generators) for the currently operating and planned fast reactors all over the world. The boundaries of sodium systems of Prototype Fast Breeder Reactor (PFBR) is designed so as to have an extremely low probability of leakage, rapidly propagating failure and gross rupture under the static & dynamic loads expected during various operating conditions.The degradation of material properties (e.g. effect of sodium, temperature and irradiation), transients, residual stresses, flaw size etc. are the important considerations, which shall be taken into account. The principal material of construction for PFBR is austenitic stainless steel of grade 316LN/304LN. The scope of welding and fabrication of PFBR components is too large due to versatile types of systems with varieties of components with complex constructional features. High operating temperature of various systems causing high stresses are to be minimized by designing thin walled structure. Most of the Nuclear Steam Supply System (NSSS) components are thin walled and require manufacturing in separate nuclear clean hall conditions to assure the quality.The welding with stringent tolerances along with high distortion in stainless steels due to high thermal expansion and low thermal conductivity makes the fabrication extremely challenging.The welding standards and acceptance criteria of PFBR equipment is stringent compared to other industrial specification.