Том 81, № 8 (2018)

The article presents the main trends in the development of nuclear physics research conducted at the Kurchatov Institute after commissioning of the first pool-type water-water research reactor in 1957 in the Soviet Union.

The current state of neutron research at the IR-8 reactor is considered and it is shown that the research is focused on two main avenues: comprehensive radiation diagnostics for the sake of those knowledge domains which have not used it before and research of the structure of material under extreme conditions (high pressures, strong magnetic fields, and irradiation). Case studies are given in the areas of materials technology, geology, paleontology, archaeology, and medicine, as well as studies of materials under thermobaric impact and self-radiation. The possibilities of a combination of different experimental techniques are discussed.

The goals of construction of the BIGR reactor, which was commissioned in 1977 at the All-Russian Scientific Research Institute of Experimental Physics, are reviewed. The primary avenues of research at BIGR are outlined. A brief description of the neutron-physics parameters of the reactor and the characteristic shapes of generated fission pulses is given. The possible sites for installation of objects to be irradiated are specified. Devices enhancing the irradiation capacity of the reactor are characterized. Current data on various research applications of the reactor are summarized.

A physical model of a high-flux neutron source based on a deep subcritical (k_eff = 0.96) two-stage booster driven by a proton accelerator with the energy of 600 MeV and beam power of 0.3 MW is proposed. It is shown that the thermal neutron flux density will be comparable to the flux density at the European Spallation Source (ESS) with the proton beam power of 5 MW. Owing to a shorter pulse, neutron diffraction experiments at the proposed source will be almost an order of magnitude more efficient than at the ESS.

In the paper, algorithms of the surface harmonics method (SHM) for deriving finite difference (algebraic) equations to describe the neutron field in a heterogeneous reactor are developed. The neutron transport equation is used as the initial equation. The step of deriving the diffusion equation in the differential form is omitted. The paper contains no assumptions on the symmetry of the reactor unit cells (unstructured mesh is accepted) or on the possibility to describe the neutron distribution at the cell boundaries in the diffusion approximation for deriving the equations. It is computationally shown that rejection of the diffusion approximation at the cell boundaries considerably improves the accuracy of solutions of the test problems.

The DAREUS software package designed for modeling dynamic processes in the cores of experimental solution reactors is described. The KIR program based on the Monte Carlo method is used in the package to compute the necessary kinetic parameters. The results of the calculations of some test cases are given.

The main aspects of the technique implemented in the LUCKY-A computer code for solving the transport equation with the use of parallel computations are presented. The basic characteristics and specific features of the program are discussed. The parallel algorithm implemented in the LUCKY-A is developed for application on supercomputers with the use of the MPI standard for data exchange between parallel processes.

An option of high-density neutron flux generation locally, at a distance from the source, is considered in this paper. The energy dependence of the cross sections of neutron scattering by nuclei of some isotopes displays resonance behavior. Below the resonance level by energy, there is a deep drop of the scattering cross section dictated by the effect of resonance and potential scattering interference. When a slowing-down neutron gets the energy corresponding to a very small scattering cross section, it is capable of flying for several meters without interaction with nuclei of the medium. The possibilities of creating conditions for selection of high-energy neutrons emitted by a reactor or other source and moving in the required direction are investigated in the paper. The research described in the paper is focused on various factors (material composition, geometry) influencing the neutron radiation density and achievable neutron flux limits.

The value of the positive scram effect on the control rods is discussed, which, in the authors’ opinion, was the trigger for the accident. The results of the calculation by a new STEPAN reactor code version, which uses the surface harmonics method for description of the neutron transport, are presented. The magnitude of the neutron burst during the accident is estimated and its relation to high graphite temperatures of more than 1000°C observed after the destruction of the reactor is established. The influence of the neutron burst on the radiation characteristics and the decay heat of the fuel during the first hours after the destruction of the reactor is considered.