Flow Particulars of Some Transient Regimes with Load Shedding on VVER-1000

The results of an investigation of the operating regime of a nuclear power plant with VVER-1000 with actuation of accelerated preventative protection at power 100% Nnom with one of two turbo pumps switched off are presented. The modeling was performed using the improved accuracy RELAPSCDAPSIM/Mod3.4 code and a corresponding model for the No. 2 unit of the Khmelnitsky NPP. It is shown that the actuation of emergency protection based on the fact that the three main circulation pumps are switched off because of a drop in the feed water in the steam generators cannot be avoided. On the basis of the results obtained, it is proposed that for the second half of the fuel run an emergency protection signal instead of an accelerated preventative protection be immediate generated when one of the turbo pumps is switched off at power level >95% Nnom; this will make it possible to secure more forgiving temperature regimes for fuel and equipment, avoid additional thermal cycling loads, and prevent violation of the safe operating limits on the basis of the feed water level in the steam generators.