Manufacturing and Erection of Mechanical Components
Sodium fast reactor (SFR) components, in general, are characterized as large-diameter thinwalled shell and slender structures. Tight manufacturing tolerances are specified to enhance their buckling strength as well as to have possibly minimum vessel dimensions. In the reactor assembly, the main vessel, thermal baffles, inner vessel, core support structure (CSS), and grid plate (GP) are to be positioned sequentially maintaining the coaxiality with the safety vessel, so that the core central line will be in line with the central lines of coaxial vessels: one of the requirements to facilitate smooth operation of control rods as well as facilitate accurate monitoring of sodium temperature emerging from the core subassemblies (CSAs). Further, they have to be erected accurately to maintain the annular gaps for uniform sodium flows and temperatures. During the manufacturing stage, single-side welds are unavoidable at some difficult locations particularly in the case of box-type structures. In-service inspection is difficult with the presence of sodium, and hence, stringent quality control is required in the preservice level itself. From the dimensional stability point of view, residual stresses should be kept at minimum value by adopting robust heat treatment processes and mock-up trials. It is preferable to use a minimum number of materials when considering economy and material data generation, also enhancing the reliability of performance of materials in the operation. Austenitic stainless steels, the main structural material in particular, call for careful considerations for welding without significant weld repairs and distortions. Construction experience of international fast reactors and prototype fast breeder reactor (PFBR) indicates that reactor assembly components decide the project time schedule, even though their cost is relatively small compared to civil, sodium circuits and balance of plant (BoP). There is only limited experience on manufacturing and erection of components. Apart from these, the design and manufacturing codes are still evolving. These are the major challenges in the manufacturing and erection of reactor assembly components. Figure 23.1 depicts the arrangement of reactor assembly components in a typical pool-type SFR.