Tests of bber-1000 maneuverability on the fifth unit of the zaporozh'e nuclear power plant

Abstract

All BBER-1000 reactors are currently operating in their base regime, which permits only single load changes which are isolated in time. However, experience in performing such individual power maneuvers as well as computational investigations show that reactors of this type can operate in a maneuvering regime, specifically, with power changes occurring daily [ 1 ]. In the period from March 29 to April 6, 1998 power maneuvers were performed on the fifth power generating unit of the Zaporozh'e nuclear power plant. In the course of these tests a typical daily-weekly cycle was conducted in which the grid load was followed by night-time load reduction to 80% nominal power (Nnom) on work days and shutdown on holidays. The purpose of the tests was to finish the control algorithms experimentally, to check the working capacity of the technological systems and equipment, and to assess the accuracy of the computational simulation of reactor operation.Control Algorithm. In contrast to the power manuever in the base regime, which consisted of switching the reactor from one stationary state into another, for daily power maneuvers the reactor is always in a nonstationary state on account of transient xenon processes. This requires continuous control of the reactivity and energy-release distribution in the core. This feature of the maneuver regime can lead to extreme accumulation of liquid radioactive wastes accompanying water exchange in the boron regulation system, In this connection a control algorithm with minimization of water exchange was optimized in the present tests.A power maneuver was performed using the following control actions: two groups of control rods -the working group and a control group with vertical distribution of energy release (controlling group) were moved; their position in the core is shown in Fig. 1; temperature regulation -variation of the water temperature at the reactor entrance (Tin) within the range of the corresponding variation of steam pressure in the second loop (P2) 6-6.2 MPa; introduction of distillate into the first loop in the quantities required to compensate burnup during the preceding days, together with spontaneous "reactivity overshoot" as a result of the burnup of xenon at the power increase stage.The control of the energy-release distribution reduced to preventing the development of xenon fluctuations of the axial offset. Since in the present tests power is lowered mainly as a result of the motion of groups, and under existing regulations this does not permit maintaining a constant offset, a different principle of offset stabilization, based on spatial localization of xenon processes, was used. According to this principle, to decrease the reactor power the vertical distribution of energy release is formed using groups in a manner so that the power of the bottom half of the core does not change and the entire change occurs in the top half-in this case the xenon transient processes occur in a small volume and cannot give rise to strong spatial xenon fluctuations. In addition, the requ...

Temperature regulation and maneuverability of VVER-1000

“…Soft temperature regulation with the power-generating unit operating on the daily load schedule was successfully tested at the Zaporozhie nuclear power plant [3], where at the end of a run the reactor was controlled by an optimal combination of movement of the regulation organs and variation of the steam pressure (±0.1 MPa) without using water exchange and correspondingly without accumulation of additional liquid wastes.…”

Testing of improved algorithms controlling energy release in VVÉR-1000 in maneuvering regimes at the Tianwan nuclear power plant (China)

“…Group 10 (working group) is always present in the core, and groups 9 and 8 are inserted into the core when the reactor is unloaded and when xenon fluctuations are suppressed. Xenon fluctuations are suppressed by maintaining a constant or equilibrium offset [4] or by spatially localizing the xenon processes [5].…”

“…Tests of VVÉR-1000 daily load schedule were performed first on the No. 5 unit of the Zaporozh'e nuclear power plant in 1998 [5] and then twice on the No. 2 unit of the Khmel'nitskaya nuclear power plant in 2006.…”