Temperature regulation and maneuverability of VVER-1000

Abstract

The possibility of using coolant temperature changes (temperature regulation) as an additional control on energy release in the core of VVER-1000 reactors is examined. It is shown that it is desirable to use temperature regulation in maneuvering regimes of a power-generating unit of a nuclear power plant. Possible control algorithms using temperature regulation are presented.The power-generating units currently being designed for nuclear power plants with VVER-1000 reactors are being developed taking account of operation in a maneuvering regime, providing repeated cyclic power changes. In this connection, the present article examines temperature regulation -a change of the coolant (water) temperature as the control on energy release in the core with a variable load.Operational control of the energy release of a reactor is mainly accomplished by changing in the core the concentration of nuclei which absorb neutrons -boron ( 10 B). For this, the control organs (bundles of rods containing boron) are moved or the boron concentration in the first-loop coolant is changed by water exchange -introducing boric acid or pure water (distillate). Thus, the power of the reactor is lowered by inserting the control organs and introducing boric acid and raised by extracting the control organs and introducing a distillate. The distribution of the intensity of energy release in the core is also controlled by moving the regulation organs together with water exchange. Since the movement of the control organs gives rise to deformation of the power distribution in the core, undesirable from the standpoint of possible damage to the fuel, while water exchange is accompanied by the accumulation of liquid radwastes, one of the main problems of optimizing reactor control is decreasing the amplitude of the indicated control actions, specifically, by means of optimal temperature regulation.A change of the coolant temperature T in the core affects the neutron moderation process and correspondingly the power W of the reactor. When temperature increases or decreases, negative or positive, respectively, reactivity is introduced. As a result the amplitude of the control actions required to change the power increases in the case where there is a direct relation between the change of power and temperature and decreases in the opposite case. Thus, temperature regulation can play a negative as well as a positive role in reactor control.The particulars of the temperature regulation are determined by the conditions for balance of reactor power and turbines as well as maintaining the required steam pressure P in the steam generator. The turbine power is changed by varying the steam flow rate, and to maintain the require steam pressure the coolant temperature and therefore the reactor power must change at a corresponding rate. For a serially produced VVER-1000 power-generating unit, when a constant (nominal) steam pressure is maintained the change of power and temperature are related as T = 280 + 0.22W (here and below the coolant temperature is taken to b...

Investigation of algorithms for suppressing xenon oscillations in a VVER-1200 reactor

“…For the second method, temperature and boron regulation served not just to keep the axial offset near the equilibrium value but also to retain the control rod assembly position in the scheduled limits. Simulation was undertaken for not less than 160 hours (Filimonov et al 1998, Averyanova et al 2010.…”