Vol 82, No 8 (2019)

This paper is devoted to the algorithm of the linear Cauchy problem solution for large systems of first-order ordinary differential equations using parallel calculations. The proof of the convergence of the iteration process using the solution as expansion over orthogonal polynomials for the interval [0,1] is presented. The features of this algorithm are its simplicity, the opportunity to get a solution by parallel calculations, and also the possibility to get a solution for nonlinear problems by changing the operator using the solution from the iteration process.

The experiments on recording the radiation decay signal of the GIR2 reactor core in the range from 0 to 40 µs when exposed to an external intense neutron pulse with a duration of ∼1 µs are performed. The reactivity interval from subcritical (−7.5 β) to critical (+0.28 β) states of the reactor is studied. It is found that the signal of the detector with a plastic scintillator depends on the reactivity and is proportional to the change in the density of thermalized neutrons in the reactor converter. The results show that the reactivity of the GIR2 reactor can be determined on the basis of measurement of the signal decay of a scintillation detector and the well-known expression \({\alpha _\infty } = {\beta \over \Lambda }(\rho - 1)\) to calculate the reactivity values only for states with a reactivity greater than ∼−3 β.

The procedure of measurement of the brightness distribution of the hard X-ray source of the MIB-7.5 betatron with a penumbral aperture is detailed (i.e., a measurement algorithm and a calculation model are proposed). This measurement method involves reconstructing the brightness distribution of a source based on the radiation distribution in the penumbral region of a large circular collimator. The influence of the penumbral aperture diameter on the signal-to-noise ratio in the distribution of the source brightness is estimated. A parametric model of formation of the source X-ray pattern is presented. This model is based on a priori information on the measurement setting and the brightness distribution of the radiation source.

A procedure for determining the linear heat generation rate in a fuel assembly of VVER reactor at the location of a rhodium self-powered neutron detector (SPND) and verification of this procedure are discussed. A method of measurements of the VVER thermal power based on SPND readings is described.

The use of ²³²Th instead of ²³⁸U as a fertile isotope, ²³³U instead of ²³⁹Pu as the main fissile isotope, heavy water instead of light water as a coolant, and its dilution with light water in the VVER reactor campaign make possible self-enrichment of fuel with fissile isotopes, including the time upon achieving the balanced isotopic abundance ratio of actinides, and also provide conditions for closing the Th-U-Pu fuel cycle. This allows increasing the fuel lifetime by around two orders of magnitude, making it much easier to handle radioactive waste, reducing the nuclear hazard of PWE reactors, and providing a technological barrier to prevent the distribution of fissile materials and nuclear technologies.

A schematic of a low-power nuclear power unit with circulating fuel based on molten metal fluoride salts is considered. The possibility of creating a virtually maintenance-free reactor facility with a thermoelectric generator with a power of 1 to 500 kW e and a lifetime of 5–10 years or more is discussed.

The problems arising at creation and calculation of the space kinetics benchmarks are considered by three tasks. The connection between the nonstationary diffusion equation and the inverse solution of the kinetics equation (ISKE) is considered with the different methods of preparation and presentation of kinetic parameters. The following benchmarks are considered: the nondiffusion Small LWR benchmark from the series of Takeda’s tasks, complemented by modeling the motion of control rods; Ferguson’s benchmark, enlarged by calculation of the reactivity change with ISKE; TWIGL benchmark—2D LWR model with insertion of positive reactivity.

The problems associated with the physics of heterogeneous pool boiling at a low pressure on a flat horizontal surface are considered. The examples of parametric mismatch between the trends are connected with the thermophysical properties and wall surface microgeometry, with the size of the working area, with the affected zone of a growing bubble, and with the contact angle at the interface between the liquid, solid, and vapor phases. A conclusion is drawn concerning the possible causes of ambiguity in the results of the simulation of nucleate pool boiling modes under calculation of the individual contribution of each of the heat transfer mechanisms (convection, liquid microlayer evaporation, and rearrangement of the thermal boundary layer after bubble detachment). It is emphasized that the problem should be solved in the 3D conjugate formulation.

A modification of the FP Kinetics code [1] has been performed to calculate the fission product release from HTGR microfuel particles, allowing for chemical binding, limited solubility effects, and component concentration jumps at the interfaces of the coating layers. A comparison is made of the release curves of Cs from microfuel particles calculated using the FP Kinetics and PARFUME codes [2]. It is shown that taking into account the concentration jumps at the interfaces of the silicon carbide layer makes it possible to give a noncontradictory explanation of the experimental data obtained for Cs release in post-reactor thermal testing. The need for performing experiments to determine the limits of solubility in coating materials is noted.