The integral and spatial xenon transient processes in the No. 1 unit of the Tianwan nuclear power plant (China) have been studied experimentally. A measurement method which is unconventional for VVER-1000 was tested in the investigations of the integral processes: the course of the xenon process was recorded according to the variation of the critical concentration of boric acid in the reactor at the same time as the concentration was calculated in real-time. The spatial transient processes were studied for the diametric and axial free xenon oscillations of the energy release in the core. It was confirmed experimentally that axial deformations of the energy release affect the power of the reactor as well as the associated operational particularities of the automatic power regulator.Processes which are associated with a change of the 135 Xe concentration in the core have a large effect on VVER-1000 operation [1]. Xenon transient processes can be conventionally divided into integral -those involving a change of the average concentration of xenon in the core, and spatial -those involving a redistribution of the concentration within the interior volume of the core.Integral xenon processes result from a change of the power of the reactor. Their effect on the operation of the reactor is characterized by a reactivity increase or decrease and, correspondingly, a decrease or an increase of the xenon concentration. The following stages of the integral xenon processes are distinguished according to the character of the dominant effects: poisoning -xenon concentration increasing as a result of 135 I decay; unpoisoning -xenon concentration decreasing as a result of xenon decay; and xenon burnup -xenon concentration decrease as a result of neutron absorption by xenon.Calculations and experiments show that in the absence of control the xenon processes can be accompanied by power oscillations, which can be divergent and can result in reactor shutdown or power increasing above the admissible level [2]. In practice, ordinarily, the reactor power is kept at a prescribed level; the change of the xenon concentration is compensated by changing the 10 B concentration by moving the absorbing control rods and changing the boric acid concentration in the first-loop water.When the reactor shuts down, poisoning and subsequent unpoisoning occur in the core. In the process, correspondingly, the degree of subcriticality increases and then decreases. When the initial boric acid concentration in the first loop is

The salient features of improved algorithms adopted at the Tianwan nuclear power plant for controlling the energy released in a VVÉR-1000 core are examined. The optimal configuration of the controlling groups is chosen in the first two power-generating units, the reactor power can be varied automatically under the control of an automatic power regulator, the boron regulation system makes it possible to determine the first-loop makeup automatically, and a modern version of the Imitator Reactora program has been installed. The results of testing the algorithms in the No. 1 unit in regimes with single and cyclic (daily) power maneuvers are presented. The tests of single power maneuvers were combined with dynamic tests of equipment. The operation of the power-generating unit in a daily load schedule was tested separately. Five daily load-change cycles were conducted during these tests.Improved algorithms consist of a complex of modern means adopted in new power-generating units at nuclear power plants for controlling the energy release in a VVÉR-1000 reactor. This complex includes a new arrangement of groups of control rods and methods for moving them inside the core, a procedure for monitoring energy release, means for providing information to the operator, and the control algorithms themselves (the sequence of actions taken by the operator). Such algorithms have been partially adopted in the No. 1 unit of the Volgodonsk (2001) nuclear power plant and completely adopted in the Nos. 2 and 3 units of the Khmel'nitskaya (2004) and Kalinin (2005) nuclear power plants, respectively, and the first two units in the Tianwan nuclear power plant (2007).Fundamental Features of the Algorithms. By definition, an increase of the axial offset corresponds to a redistribution of the power release into the top half of the core. The concepts of instantaneous (AO) and equilibrium (AO*) offsets, offset-offset, and offset-power phase diagrams are used [1,2]. The information provided to the operator is based on the use of the Imitator Reaktora computational program [3]. Free controlling groups of regulation rods with numbers 10, 9, and 8 ( Fig. 1a) are used to control the energy released in the core under normal conditions. These rods can be moved in manual or automatic regimes, individually, or with motion transferred from group to group downward or outward by 50 and 100% of the core height, respectively. 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].

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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...

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