Specific features of initial fuel load of the innovative power unit under AES-2006 project

Experience of initial fuel loading of VVER-type reactors was analyzed prior to initiation of the “first criticality” phase of Novovoronezh NPP-II unit no. 1 commissioning. The analysis demonstrated a number of negative factors which may develop during the commissioning phase under discussion, for instance those associated with fuel assembly stability. Special measures were undertaken to ensure safe initial fuel loading with simultaneous use of loaded and dummy assemblies. Monitoring of deformation, flushing and verification of dummy fuel assemblies were applied for ensuring safe first fuel loading with simultaneous loading of fuel and dummy assemblies in the reactor. Conventional method of nuclear fuel loading ensuring resistance of partially loaded reactor core against internal and external disturbances of natural and man-inflicted character (in particular, against seismic effects) was refined taking into account the revealed issues and the experience of start-up of new power units by the use in the implementation of initial loading of regular nuclear reactor core with fuel assembly imitators. Simultaneous loading of charged FAs and dummy FAs in the reactor core was used as applied to VVER reactors for the first time. A set of measures was suggested allowing formulating the conclusion about applicability of dummy FAs for joint use with regular FAs. Control of deformations, flushing and inspection of FA imitators for ensuring safe initial core load in the case of joint loading of FAs and dummy FAs in the reactor core were implemented. Additional equipment was implemented for controlling coolant level in the reactor core and concentration of boric acid in the process of initial loading of VVER-1200 reactor core, because low level and absence of coolant circulation in the core do not allow using standard control systems. Effects of calculation parameters and high sensitivity of detectors on the control of neutron flux in the course of implementation of nuclear fuel loading were investigated.