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Dubna’s IBR-2 periodic pulsed research reactors are the most effective source of slow neutrons in extracted beams for studying various structures by using diffraction, small-angle scattering, reflectometry, inelastic scattering, and neutronography, thanks to their short-pulse neutrons and high average flux (reaching 1014 cm–2 s–1). At the same time, due to the specificity of the kinetics, fluctuations in the power energy of pulses in such a reactor are tens of times higher than in stationary reactors and create problems when trying to control the apparatus. This paper proposes and substantiates a method to significantly reduce the level of fluctuations in the power pulses of such reactors using the NEPTUNE pulsed reactor project with the Np‑237 threshold isotope as a nuclear fuel as an example.

The IBR-2 (JINR) pulsed reactor is used in the field of solid state physics for experiments on extracted beams. It is predicted that the IBR-2 reactor will reach resource limits in 2032–2037. To keep and develop beam research at JINR, the development of a new pulsed neutron source has begun. According to estimates, the reactor will have average thermal power 12–15 MW, extracted by sodium coolant. At this power, the average flux density of thermal neutrons on the surface of the water moderator will reach 1014 sec–1·cm–2 and the peak density 5·1016 sec–1·cm–2, which is more than 10 times higher than the analogous parameters of the operating IBR-2 reactor. The new reactor is supposed to use neptunium-based fuel. The main characteristics and concept of the new reactor are presented.

A high-intensity pulsed neutron source can be constructed according to the principle of a superbooster, i.e., a neutron multiplying system of the neutron-generating target of the proton accelerator with proton energy of about 1 GeV in the subcritical reactivity modulation system. Usually, superboosters are considered to be safe and reliable nuclear facilities. However, as indicated in this paper, a powerful superbooster may prove to be less stable in operation than a pulsed reactor. Therefore, the problems of its safety call for close study.

The current trend in neutron-aided scientific research presupposes the development of new high-intensity pulsed sources. One variant of such an installation could be a pulsed reactor with a fissile-isotope core – 237Np. The present work is devoted to a study of the dynamics of power pulses of a neptunium reactor taking account of fast temperature feedback during pulse buildup. The problem is reduced to a simple model of a single frequency oscillator combined with the equation of single point kinetics of a reactor neglecting delayed neutrons. It is shown that on the basis of such an approximation, owing to feedback on the temperature of a fuel element the estimated energy of accidental power pulses decreases by almost a factor of 10 compared with a calculation neglecting fast feedback.

A consistent perturbation theory is formulated on the basis of a recently proposed method of reparameterization-invariant Hamiltonian reduction, and a linearized limit in the oscillator approximation of General Relativity is considered. Possible physical consequences of interpreting the nonzero local Hamiltonian as the gravitational field energy are discussed. The physical and geometrical meanings of reduced action variables are investigated. A qualitative conclusion is drawn about the dependence of the distribution of phases of relict gravitational waves at the current epoch on the initial conditions at the time of the Big Bang.