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Description
The IBR-2M reactor located in Dubna (Russia), which has been in operation since 2012 with power of 2 MW and a pulse repetition rate of 5 1/s [1]. The power pulse is generated by two movable reflectors rotating near to reactor core. The movable reflectors for a short time transfer the reactor from a deeply subcritical condition into supercritical condition. The reactor core uses plutonium dioxide fuel and it is cooled by sodium with flow rate of 100 m3/h.
The reactor operates continuously for a 10-18 days cycle followed by a shutdown for 7 days to prepare for the next experiments. It is known experimentally that by the end of each cycle the reactor experiences a significant increase in resonant oscillations at a frequency close to 0.1 Hz, and during the reactor shutdown at the beginning of the next cycle, oscillations are restored to almost the previous level in accordance with the fuel burnout during the cycle [2]. In such conditions, it is necessary to select the optimal reactor operating mode. Optimality in this case is understood as a condition for safe reactor operation with the maximum possible energy release and, accordingly, neutron fluence on the physical experiment.
The study was carried out. Using the reactor dynamics model [3-5], two effects observed during reactor operation: slow process - amplification of low-frequency oscillations from the beginning of one reactor cycle to the beginning of the next one and the second process - amplification of instability directly in the cycle [2]. This stage of the research included determining the dependence of the change in the amplitude of low-frequency oscillations of pulse energy with a change in power and energy release. Then, using the dynamics model, the reactor's stability to changes in the amplitude of low-frequency oscillations was estimated. This made it possible to select the optimal reactor operating mode.
The following conclusions were reached from the studies. Take into consideration the strong weakening of the power feedback, causing an increase in resonant power oscillations with energy release above 1800 MW·day, and optimal power level for reliable and safe reactor operation was chosen 1.25 MW. At such a power, the duration of the reactor cycle can be 14 days, and the total time of reactor operation in this mode 3.2 years. In the future, after this period has expired, it is necessary to reduce resonance phenomena in the reactor, for example, by changing the sodium flow rate through the reactor core, as well as by optimizing the parameters of the automatic power regulation system [6-7].
References
1. Dragunov Yu.G., Tretiyakov I.T., Lopatkin A.V. et al. Modernization of the IBR-2 Pulsed Research Reactor // Atomic Energy, 2012, vol. 113 No. 1, p. 29-34.
2. Pepelyshev Yu.N, Sumkhuu D. On the cyclic change in the dynamics of the IBR-2M pulsed reactor // Nuclear Engineering and Technology, 2023, vol. 55, No. 5, p. 1665-1670. DOI: 10.1016/j.net.2023.01.004
3. Pepelyshev Yu.N., Popov A.K., Sumkhuu D. Model of the IBR-2M pulsed reactor dynamics for investigating transition processes in a wide range of power variation // Annals of Nuclear Energy, 2015, vol. 85, p. 488-493. DOI: 10.1016/j.anucene.2015.06.002
4. Pepelyshev Yu.N, Popov A.K, Sumkhuu D., Sangaa D. Dynamics model of the IBR-2M pulsed reactor for analysis of fast transition processes // Physics of Particles and Nuclei Letters, 2015, vol. 12, No. 3, p. 435-438. DOI: 10.1134/s1547477115030188
5. Pepelyshev Yu.N., Popov A.K., Sumkhuu D. IBR-2M reactor power feedback parameters evaluation using square reactivity oscillations // Atomic Energy, 2017, vol. 122, No. 2, p. 75-80. DOI: 10.1007/s10512-017-0238-8
6. Pepelyshev Yu.N, Sumkhuu D. Optimization of automatic power control of pulsed reactor IBR-2M in the presence of instability // Nuclear Engineering and Technology, 2022, vol. 54, No. 8, p. 2877-2882. DOI: 10.1016/j.net.2022.03.017
7. Pepelyshev Yu. N., Sumkhuu D. Influence of an Automatic Power Control System of the IBR-2M Pulsed Reactor on Its Dynamics. Preprint JINR Р13-2023-64. Dubna, 2023.
