Pulsed reactors, or ‘pulsed periodic reactors’, have been operating at the Frank Laboratory of Neutron Physics for 65 years: IBR, IBR+microtron, IBR-30 with an injector, IBR-2, IBR-2M. At present, the design of the future NEPTUN reactor with neptunium-based nuclear fuel is underway. Reactors of this type are unique in the world, and special. However, not all of their features are well studied, and not all are still known. For example, the so-called ‘stochastic’ instability was discovered only ‘at the tip of the pen’ 26 years after the startup of the first IBR in 1960.

The speaker will acquaint the audience with the phenomenon of dynamic bending, which was noticed only when developing the conceptual design of NEPTUN. The effects of dynamic bending are not obvious and not easy to understand, but they play a significant role in evaluating the stable operation of pulsed reactors.