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.

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Новый код Монте-Карло под названием OpenMC был разработан Массачусетским технологическим институтом. В данной работе рассматривается проверка детерминированного транспортного кода решетки реактора OpenMC для различных типов тепловыделяющих сборок ВВЭР 1200. Трехмерная полная модель с обогащением по 3 урана 4,95%, 4,0% и 1,3% построена с использованием кода Монте-Карло для переноса частиц OpenMC. Значения эффективного коэффициента умножения () для свежего топлива с двумя конфигурациями топлива и конца жизненного цикла (EOL) выполнены для трех типов ТВС с разным обогащением и выполнены для каждого из девяти случаев; результаты показывают согласование с двумя другими кодами (Serpent и UNK). Значения интегральных параметров, рассчитанные OpenMC, сравнивались с кодом UNK, результат коэффициента диффузии показывает большое относительное отличие от UNK, поскольку метод кумулятивной миграции не реализован в коде OpenMC.