28th Symposium of AER on VVER Reactor Physics and Reactor Safety (2018, Olomouc, Czechia)
Reactor dynamics and safety analysis
A.I. Sinegribova, M.A. Uvakin (JSC GIDROPRESS)
The report provides a brief description of the fuel assembly pin-by-pin model developed earlier with the KORSAR/GP code. The nodalization of the developed model consists of parallel 1D hydraulic elements (channels). Each fuel rod is modeled as a individual structural element. Two special calculation elements of KORSAR/GP are used in the pin-by-pin model for coolant mixing simulation. They are cross-junction and turbulent mixing element. The first one calculates the convection of the coolant. The second one simulates the interchange of coolant between two channels through some surface. Such a model consists of large number of elements (nodes), that increases time calculation. So the the pin-by-pin model application for calculations is not always justified and necessary.
The purpose of this paper is application field assessment of FA pin-by-pin model. The paper presents the results of the “Control rod ejection” transient simulation. This accident is interesting by power redistributions in the accident FA. The safety margins are calculated with use of «hot channel» model for NPP safety analyses. Only the fuel rods of the core with the highest power are taking into account. The absence of pin power distribution change for FA during transient is compensated by increased conservatism. In this paper the maximum fuel rod power assessment was obtained using of pin-by-pin model.