Analysis of criticality achievement process and obtained experience
28th Symposium of AER on VVER Reactor Physics and Reactor Safety (2018, Olomouc, Czechia)
Reactor physics experiments and code validation (benchmarks)
The implementation of the Low Leakge Loading Pattern (L3P) in Dukovany NPP (VVER-440) led to high differences between expected undercriticality during criticality achievement process and measured one. There was formulated a new approach to the undercriticality inspection during criticality achievement process in previous paper in 2014. This method has been used during start-up in Dukovany NPP since 2012.
Non-uniform distributions of spontaneous fission sources in different loading patterns are described in this paper. The influence of this non-uniformity to core power and ionisation chamber (IC) signal behaviour during criticality achievement process is demonstrated. The improvement of the calculation of start-up parameters and the information about the comparison of calculated and measured parameters are described. Results obtained from both criticality reaching methods (boron dilution, control rods withdrawal) are discussed for different situations during fuel cycle.