Vol 124, No 5 (2018)

The results of verification of the IBRAE-developed SAFR/V1 module, describing in the EVKLID/V2 integral code the thermal breakdown of fuel pins, on the basis of data obtained using experimental facilities. The experiments performed on the TREAT and DEH facilities at the Argonne National Laboratory and on a bench at the Nizhny Novgorod State Technical University were picked for the verification process. The computational error was evaluated for individual parameters on the basis of the verification results. The impact of the uncertainties in the initial data on the computational results was analyzed.

A validation of the hydrodynamic characteristics of the coolant loop of a high-temperature gas-cooled reactor at low power in a power-generating facility using a turbo-machine conversion in a Brayton cycle is given. The validation is accomplished using diagnostics of models of a coolant loop, numerical modeling of the hydrodynamics, heat-and-mass transfer in models with more accurate three-dimensional CFD codes. Relations for ensuring tangential uniformity of the coolant velocity distribution near the core shell and at the entry into the distributing manifold are obtained. A distributing manifold geometry securing a uniform coolant flow distribution over core cooling tracts at low hydraulic resistance is proposed. Data are obtained on the velocity and temperature distributions in fuel pins spaced by a wire winding.

In the system UO₂(NO₃)₂–PuO₂(NO₃)₂–HNO₃–H₂O with the ratio Pu/(U + Pu) = 0.3–0.5 and stabilization of the pair U(VI)–Pu(VI), the crystallization of (U, Pu)O₂(NO₃)₂·6H₂O occurs in accordance with the metric of the phase diagram of the system UO₂(NO₃)₂–HNO₃–H₂O with coefficient of cocrystallization of plutonium 0.804 ± 0.028. This condition holds in the sector of the working lines of the crystallization process that correspond to the minimum content of uranium in the mother solution. The degree of enrichment of the mother solution is determined by the crystallization temperature, i.e., the mass fraction of the mother solution in the total mass of the system. The constancy of the coefficient of cocrystallization with the technologically important parameters of the process makes it possible to use the metric of the solubility diagram of the system UO₂(NO₃)₂–HNO₃–H₂O to calculate the crystallization of (U, Pu)O₂(NO₃)₂·6H₂O with the crystalline phase with the required composition being obtained.

A method of managing one type of radwaste forming during BREST-300 reactor operation – the structural materials of FA – is described. In the module developed for reprocessing, the fissile materials losses together with all forms of waste must not exceed 0.1% of the initial amount, in connection with which the maximum admissible content of facade materials and structural materials sent into long-term storage must not exceed 0.001% by weight. Only the plutonium content may reach 0.015% by weight, which makes it necessary to perform additional purification and return fissile materials into the nuclear fuel cycle. A method of reprocessing the structural materials of irradiated fuel elements is proposed on the basis of induction-slag remelting in a cold crucible, which makes it possible to conduct purification to the desired index value. The operating regime of the melting unit and the qualitative composition of the employed flux that make it possible to reach the required level of purification by removal of fissile materials are described.

The energy spectra of 14 MeV neutron generators of different types were measured using spectrometers with organic scintillators. Additional neutron peaks with energy less than 14 MeV, which are due to the neutrons produced in the ancillary reaction ²H + ²H = ³H + p, and neutrons generated in the material of the target blocks and the scintillation crystals of the spectrometers were identified in the neutron spectra of the generators. Specifically, a peak at 3.6 MeV was found in the resulting neutrons spectra; this peak is produced when carbon nuclei present in the scintillators of the spectrometers decay under the action of 14 MeV neutrons.

The physical principles of passive and active methods of remote-sensing monitoring of radioactive substances and toxic chemicals in accidental emissions (leaks) at nuclear fuel cycle objects are examined. The analytical possibilities of the most sensitive methods of remote-sensing monitoring, which are based on the advances made in UV and microwave range radiometry, laser IR-absorption spectroscopy, laser-induced fluorescence, and laser spark emission spectrometry, are discussed. The prospects for the development of spectral methods of remote-sensing monitoring in different ranges are analyzed.