The paper considers some possible input data of NPP power unit model for solving the problem of model state matching with prototype state. In the course of work on matching the state of NPP model with the prototype, a numerical experiment using full-scale modeling complex PROSTOR was conducted. Its essence was to obtain steady states of the model with capacity from 94% to 104% with a step of 0,05%. For modeling we used data of Kalinin NPP unit 3 loading 4 on 248 effective days. When analyzing the results of the numerical experiment, two effects were found. One of them, expressed in the bend of the derivative of the obtained graph, is connected with reaching the upper limit of the possibility to regulate the pressure in the main steam collector. The regulating valves on the turbine generator are the executing mechanism of pressure regulator in main steam collector. At the break of the graph they open at 100%, which causes further inability to regulate pressure. The pressure in the main steam collector starts to increase. This effect corresponds to the real processes occurring at the NPP. In this case, as one of the model tuning parameters, it is proposed to use the adaptive coefficient to the concentration of boric acid in the reactor, for the control of which, it is proposed to use a mathematical boric regulator. It was also shown that it is impossible to accurately control the pressure in the reactor due to the peculiarities of operation of the volume compensator electric heaters automatics. In this regard, it was proposed to use an additional mathematical volume compensator electric heaters regulator to match the state of the model with the prototype. These regulators have been successfully tested as part of the PROSTOR software package to match the states of the model and the prototype.

In order to solve the problem of water exchange minimization in the primary loop of VVER-1200 reactor operating in load-following mode, we chose the dynamic programming method (DPM). However, this method is very expensive in terms of RAM and computing time. A heuristic is introduced for the DPM to decrease the computational costs. The introduction of the heuristics makes it possible to cut the inefficient branches of the DPM algorithm and to increase its speed without loss of precision. In the proposed algorithm, the use of temperature regulation control reduces the amount of coolant removed from the reactor primary loop, the movement of control rods is limited, which keeps the current axial offset (AO) in the recommended area, makes it possible to equalize the energy release in the reactor core volume. The simulation results obtained confirm the improvement of reactor power control in terms of load following: deviation of core power from the load schedule is reduced, water exchange is decreased by more than 50%, which is useful from the point of view of liquid waste management and treatment.

Startup to minimum controllable power level (criticality approach) is one of the most hazardous nuclear operations during operation. In particular, the spontaneous and unauthorized startup to minimum controllable power is very dangerous, and it occurs as a result of some technological operations or changes in technological regimes. Currently, there are codes for neutron-physical calculations at NPPs with VVER, such as reactor simulator (IR) and BIPR-7A. These codes calculate the boric acid critical concentration without relying on excore ionization detectors data, which may result in inaccuracies in determining the critical concentration. In addition, feeding the primary circuit with clean condensate must be stopped at least 15 minutes before is reached, and these codes do not calculate the time to reach the critical state. As a result, the idea arose to develop a code that would predict the time to reach the critical state and the critical concentration of boric acid only using the measuring equipment readings without reliance on additional calculations.