Analysis of Primary Side Feed and Bleed Operation at Armenian NPP Unit 2

Abstract

Analyses were performed for the primary side feed and bleed (F&B) procedures for Armenian Nuclear Power Plant (ANPP), using the RELAP5 code. ANPP is a six-loop WWER-440/270 model of Russian design. The purpose of the analyses was to demonstrate the core cooling capability of the plant using the high pressure injection (HPI) system (feed) and pressurizer safety valves (bleed), and to evaluate temperature changes in the Borated Water Supply Tank (BWST). The Mod3.2.2β version of RELAP5 was used for the analyses. The six loops of the plant were modeled by 4 loops; three loops represented three individual loops and one loop combined the other three loops. The input described the primary and secondary loops in detail, as well as all safety systems and most of control systems. The HPI system was connected to the cold leg of each loop. The Emergency Core Cooling (ECC) mixer component was applied in the connection of the HPI system to simulate the phenomena associated with the subcooled ECC injection into a reactor coolant system. Nominal operating parameters were used to establish the steady state conditions. Some of the initiating events and boundary conditions were based on the experience and information obtained from previous transients and incidents in the plant. The incident was assumed to be initiated by a loss of off-site power supply and simultaneous reactor scram. Diesel generators were assumed not to be available for 11,000 seconds. Thus, feedwater to the steam generators, main coolant pumps, and HPI pumps were not available during this period and the core was cooled by natural circulation in the primary loops supported by the remaining water in the steam generators. During this period the primary water temperature and pressure were near or slightly higher than the steady state values, but the water remained subcooled. At 11,000 seconds, upon starting of the diesel generators, the operator switched on two HPI pumps and opened one pressurizer safety valve. At this time, all six steam generators were found to be nearly empty. Once the F&B operation began, the pressure and temperature of the primary loops declined rapidly. The results of F&B analyses show that there is no violation of the core coolability conditions when two HPI pumps are available, and the temperature of BWST tank does not reach the saturation temperature when two heat exchanger pumps are available.