Design, fabrication and installation of reactor internals for prototype FBR

Monju, a 280 MWe prototype fast breeder reactor, completed its construction in April 1991, and is now under preoperational tests for the forthcoming initial criticality. The design study of reactor internals (R/I), for 300 MWe class FBR based on the design experience of Monju R/I, and the fabrication and the installation of Monju R/I are described herein. The Reactor Structure is made up of a reactor vessel (RV), a core, R/I, and a shield plug. The RV forms coolant boundary and supports R/I. The shield plug is mounted on the RV pedestal and serves as a lid of RV and loads fuel handling machine and control rod driving mechanisms. R/I is composed of core support plates (CSP) and a core barrel and their supporting structures to RV, and supports core elements (C/E), such as fuel subassemblies, blanket fuel subassemblies, control rods and neutron shielding subassemblies. It also provides a coolant path from the inlet Plenum to each of C/E. R/I has various functions, such as distribution of a coolant, the hydraulic hold-down for C/E and prevention of fuel subassembly misloading. The core barrel is a cylindrical structure surrounding C/E and prevents C/E from deforming either by thermal expansion or by a seismic load, At first , some features of a R/I design are described, and then the fabrication and the installation of Monju R/I are described