Almost all experimental studies of the characteristics of nuclear-excited plasma formed by excitation of gaseous media with nuclear reactions products are conducted at pulsed nuclear reactors that differ in the composition and design of the core, the duration, flux and fluence of the neutron pulse, the impulse repetition frequency, the volume and configuration of the irradiation space. This paper presents a description of the experimental (methodical and hardware) base of the National Nuclear Center of RK (Kurchatov) to conduct experiments on studying the threshold characteristics of laser action at the p-s-transition of noble gas atoms upon ⁶Li(n,α)³H nuclear reaction products excitation in conditions of a pulsed nuclear IGR reactor. To conduct in-pile reactor experiments, a special experimental facility was developed and constructed. The experimental facility functionally includes: in-pile experimental device, a gas–vacuum system, information and measurement system consisting of a system for registering and controlling the temperature of the device housing, and a system for registering optical radiation. The paper also briefly describes the methodology of in-pile reactor experiments on the pulsed nuclear reactor.

The luminescence of Kr-Xe, Ar-Kr, and Ar-Xe mixtures was studied in the spectral range 300–970 nm when excited by ⁶Li (n, α)³ H nuclear reaction products in the core of a nuclear reactor. Lithium was deposited on walls of experimental cell in the form of a capillary-porous structure, which made it possible to measure up to a temperature of 730 K. The temperature dependence of the radiation intensity of noble gas atoms, alkali metals, and heteronuclear ionic noble gas molecules was studied. Also, as in the case of single-component gases, the appearance of lithium lines and impurities of sodium and potassium is associated with vaporization during the release of nuclear reaction products from the lithium layer. The excitation of lithium atoms occurs mainly as a result of the Penning process of lithium atoms on noble gas atoms in the 1s states and subsequent ion-molecular reactions. Simultaneous radiation at transitions of atoms of noble gases and lithium, heteronuclear ion molecules of noble gases allows us to increase the efficiency of direct conversion of nuclear energy into light.

During the decommissioning of the BN-350 reactor, the spent nuclear fuel (SNF) was transferred to long-term dry storage in TUK-123 transport and storage cask systems designed for transportation and long-term storage with a design service life of approximately 50 years. The TUK-123 system consists of a UKKh-123 storage package, which is a sealed metal-concrete cask (MCC), and a protective-damping cover (PDC) used only during transportation. Radiation characteristics are a key quantitative criterion for assessing the safety of long-term storage in the absence of direct access to fuel and cask components. This paper presents the results of a computational study of the radiation characteristics of BN-350 SNF under dry storage conditions as of 1 January 2025. Spatial distributions of the ambient dose equivalent rate were determined for normal storage conditions and for accident scenarios involving partial failure of fuel assembly (FA) canisters and fuel redistribution. It was established that in the near-field region, the dose fields are formed predominantly by long-lived fission products and activation nuclides, whereas the neutron contribution is determined mainly by the spontaneous fission of actinides and (α, n) reactions. The results obtained provide a quantitative basis for assessing the radiation safety of long-term BN-350 SNF dry storage.

Long-term dry storage is a key stage in managing spent nuclear fuel (SNF) from sodium-cooled fast reactors, for which monitoring supports aging management and future fuel-cycle decisions. This study presents a monitoring-based condition assessment of BN-350 SNF stored in 60 UKKh-123 metal–concrete casks at the dedicated long-term container storage site of the «Baikal-1» research reactor complex. The casks were transported to and placed at this site in 2010, and their condition has been monitored annually. The assessment integrates dosimetric records, full-container campaigns from 2018 and 2023, and detailed inspection data for selected packages. The monitored indicators included external gamma dose equivalent rate, surface contamination, external surface temperature, visual condition, and leak-tightness of detachable sealing connections. For all 60 packages, the maximum gamma dose equivalent rates were 5.8–25.7 μSv/h in 2018 and 2.0–20.3 μSv/h in 2023, far below the nominal 500 μSv/h value specified for normal operation by the technical operating conditions. Surface contamination remained within applicable limits, and external surface temperatures were below the nominal 84 °C operating limit. A detailed inspection confirmed low gamma dose rates and satisfactory leak-tightness. The results support continued controlled storage with periodic monitoring and safety reassessment.

Legacy liquid radioactive waste (LRW) from the BN-350 sodium-cooled fast reactor is chemically heterogeneous and requires updated characterization for further management. This study investigated the physicochemical properties and gamma-emitting radionuclide composition of 13 LRW samples collected from four tanks (B-02/1, B-02/2, B-02/5, and B-02/6) at surface (“mirror”), middle, and lower levels. Five samples were analyzed as LRW and eight as evaporated LRW residues. Physicochemical analysis included pH, density, dry residue, alkalinity, and major inorganic components. Portable gamma spectrometry was applied to all samples, and laboratory HPGe measurements were performed for selected aqueous LRW samples. The saline LRW samples were strongly alkaline and highly mineralized, with dry residue values of 139.30–295.10 g/dm³. Tank B-02/6 contained distinct oil-containing, emulsion, and carbonate-rich alkaline aqueous phases. ¹³⁷Cs was the dominant identified gamma-emitting radionuclide, with specific activities ranging from (1.4 ± 0.3) × 10⁵ to (1.1 ± 0.2) × 10⁸ Bq/kg in liquid samples and up to (6.5 ± 1.3) × 10⁸ Bq/kg in evaporated residues. The results show that BN-350 LRW is not a homogeneous waste stream; therefore, future monitoring, retrieval, treatment, and conditioning should be planned according to matrix type, sampling depth, vertical phase heterogeneity, and ¹³⁷Cs-dominated radiological characteristics.

This paper presents the results of a comprehensive study of the desorption characteristics of expanded perlite grade M100 (LLP “UNION PERLITE”, Republic of Kazakhstan) impregnated with a liquid radioactive waste (LRW) simulant at a sorbent-to-solution mass ratio of 1:6. The investigations were performed by TGA/DSC-MS simultaneous technique using the “TiGrA” experimental complex under isothermal conditions at 40 and 70 °C with a holding time of 24 h in two modes: without gas purging and with a flow of dry air (50 mL/min). Desorption was found to be purely physical and associated with the evaporation of free water. The observed mass loss (~51% of the initial sample mass) is consistent with the water content of the LRW simulant used for impregnation. Increasing the temperature from 40 to 70 °C results in a 4.6-fold reduction in the time required to reach a steady state (from 9.2 to 2.0 h without purging; from 9.4 to 1.8 h with purging), whereas gas purging under laboratory conditions has only a minor effect on the process kinetics (<10% acceleration at 70 °C). Mass spectrometric analysis confirmed the absence of gaseous release of organic or inorganic volatile compounds other than water vapor (dominant signal at m/z = 18). No exothermic or endothermic effects were observed on the DSC curves. The obtained results confirm the chemical and thermal inertness of the investigated perlite and its potential applicability in technologies for low-temperature drying and interim storage of conditioned LRW.