The main factor of destruction of fuel rods in accidents with loss of coolant is associated with the vapor-zirconium reaction occurring between the fuel rod shell and the coolant (water). Improving the reliability of fuel cells can be obtained by modifying or replacing the fuel shell, materials that do not interact with the coolant during normal operation and in emergencies. The loss of coolant accident is a design-basis accident in light water reactors. The postulated accident requires an analysis of the double guillotine break in a main primary coolant pipe, which allows the coolant to freely discharge out of the primary system into the containment of the building. In the present work, the heat stored in the active zone of the reactor, the heat capacity of the fuel and the shell temperatures are determined for ATF materials U-10Mo and U3Si2. The calculated values are compared with the usually used fuel UO2. The results showed beneficial effect of using ATF materials. The above quantities are decreased dramatically for ATF, promising to replace UO2 with ATF fuels. This reduces the probabilities of accidents and oxidation in the nuclear reactors. The calculations are done for nuclear power plant, type VVER-1200.

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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.

The main factor of destruction of fuel rods in accidents with loss of coolant is associated with the vapor-zirconium reaction occurring between the fuel rod shell and the coolant (water). Improving the reliability of fuel cells can be obtained by modifying or replacing the fuel shell, materials that do not interact with the coolant during normal operation and in emergency situations. Increasing the reliability and economic characteristics of nuclear power plants is possible by replacing uranium dioxide with fissile compositions with a high content of fissile isotopes and with greater thermal conductivity. These two provisions form the concept of ATF (tolerant fuel). Variants of creation of tolerant fuel are considered., variants of modernization of shells and fissile compositions are studied for nuclear power plants with WWER reactors.

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.