Progress in Nuclear Energy最新文献

To ensure a reliable shutdown of the proposed advanced heavy water reactor (AHWR) of Indian origin during emergency conditions, it is imperative to use an increased concentration of liquid neutron poison for injection into the moderator system due to its higher reactivity. The sudden injection of this liquid poison may cause a surge in radiolytic product (H₂O₂ and H₂) yield, posing safety risks. If H₂/D₂ yield exceeds 4 % (v/v), a combustible mixture with oxygen can be formed and presence of oxidizing H₂O₂ can enhance corrosion. Hence, accurate estimation of H₂O₂ and H₂ is imperative from the reactor safety point of view. We investigated gadolinium and boron (two liquid neutron poisons) at varying concentrations through high energy electron beam and gamma radiolysis. The radiolytic yields from both the liquid neutron poisons of equivalent concentrations at a constant dose and operating moderator conditions in electron beam and gamma radiolysis were compared. The molecular product yield was observed to be concentration and dose-rate-dependent for both the neutron poisons. Electron radiolysis exhibited a higher yield of H₂O₂, whereas gamma radiolysis resulted in a greater H₂ yield. In electron radiolysis, the H₂O₂ yield decreased with increasing B concentration. These results give an overall estimation of radiolytic products for a particular dose rate, total dose and effect of head space volume over liquid irradiation zone from these two liquid poisons of a particular concentration. These insights will aid in selecting suitable poisons and managing their effects effectively to avoid hydrogen deflagrations after emergency shutdown.

The reactor Point Kinetics Equations (PKE) are simpler zero-dimensional approximation to space dependent dynamical models of nuclear reactor core, that are accurate enough to describe transients in small to medium size fast reactor cores. Even these simplified equations can be solved only by numerical methods, except in a very few restrictive cases, where they are amenable to analytical solution. Symmetry methods using Lie's point symmetry have been shown to be a systematic and powerful tool to solve any given ordinary or partial differential equation. An approximation of the PKE, known as Prompt Jump Approximation (PJA) converts the coupled system of first order ODEs with one delayed-neutron precursor group and power feedback, into a single first order nonlinear ordinary differential equation. In this study, we demonstrate an application of Lie symmetry method for solving the point kinetics equation under PJA. The analytical solution obtained is compared with benchmark numerical solution of PKE with PJA.

The nuclear criticality safety analysis is crucial for the nuclear safety of spent fuel reprocessing plants. Thus, a set of numerical tools with high accuracy and efficiency to predict the criticality and simulate the hypothetical accidents in the reprocessing procedure is of great importance. Among them, this paper focus on the analysis of the storage tank which is used for dissolution and storage of the spent fuel. According to the characteristics of spent fuel solution system, a parallel 3D critical safety analysis tool for fissile solution system, Hydra-TD, is developed. Generally, it contains the cross-section generation model, the three-dimensional space-time neutron kinetics model, and the R-Z two-dimensional heat conduction and radiolysis gas simulation model. The verifications based on the experiments of the SILENE and TRACY facility are conducted. The results show good accuracy of the prediction of the first fission power peak, multiplication time and total fission energy, indicating the reliability of these numerical models.

The control systems of small pressurized water reactors (SPWR) with complex structures, compact layouts, and variable operating environment may be involved in various types of signal and concurrent faults. Concurrent faults can be taken as two or more single faults occurring simultaneously, which usually cause much larger damage to the system and are more difficult to be diagnosed than single faults. However, their fault diagnosis methods are rarely studied because of the numerous fault types and tremendous diagnostic difficulty. This paper explores the concurrent fault diagnosis method for sensors and actuators in SPWR control systems. An intelligent current fault diagnosis model is developed using long short-term memory network with the training and test datasets generated based on a fault simulation platform of the target SPWR. The test results show that both single and concurrent faults of the SPWR can be diagnosed rapidly in an average of 1.06 s after their occurrence with the classification and diagnosis accuracies reaching up to 96.61% and 97.27%, respectively. Moreover, by injecting different noise signals on the faulty dataset for training and validation, it is shown that the proposed LSTM network has strong noise immunity. This demonstrate the excellent diagnosis accuracy and efficiency of the model under both single and concurrent fault conditions. This study provides valuable guidance for the accuracy diagnosis of complex concurrent faults of nuclear power plants.

Density wave oscillation (DWO) in parallel channels is an important problem that has been widely studied. The marginal stability boundary (MSB) is often found to be “L" shaped on the N_pch-N_sub plane, but some very different shapes were also reported. In this paper, the instability marsh region which could occur in the traditional instable region but having both instability and stability sections was presented and discussed, which is found to be an explanation of the distortion of MSB. The analysis of the instability marsh region showed that the evolution of instability marsh should be due to the stability change when operation condition changes, which can be estimated with the analysis of the two-phase and single phase pressure drop variation, as well as Ma's stability criterion for different heat flux profiles. Variation of instability marsh with different heat flux profile, inlet and outlet resistance coefficient, mass flow and pressure were obtained and analyzed, and the effects of these parameters on instability marsh variation were found to be well interpreted with stability change. The calculation and analysis of instability marsh showed a clear evolution figure of the distortion of MSB under different conditions, and related research could be helpful in better understanding the flow instability in parallel channels.

This study investigated the combined impact of temperature (from 25 to 80 °C) and dry density of bentonite (from 1.2 to 1.65 g·cm⁻³) on the apparent diffusion coefficient, D_a, of four radionuclides (HTO, ³⁶Cl, ⁸⁵Sr and ¹³³Ba) in a Ca-Mg bentonite. In this study, the different porewater chemistry, present under the specific experimental conditions -- a factor often overlooked in diffusion studies -- was explicitly considered. As a support to diffusion studies, batch sorption tests were carried out at different temperatures (25, 40, 60, and 80 °C) with the sorbing elements (⁸⁵Sr and ¹³³Ba).

The planar source method was used for the determination of apparent diffusion coefficients, D_a, which demonstrated its efficacy for both conservative (HTO and Cl) and sorbing elements. For all the investigated radionuclides, D_a values decreased with increasing the clay dry density and increased with increasing temperature. Notably, the highest D_a value (1·10⁻⁹ m² s⁻¹) was attained for HTO diffusion in the clay at 1.2 g cm⁻³ and 80 °C, while the lowest D_a (3.6·10⁻¹² m² s⁻¹) value was determined for Ba diffusion at 1.65 g cm⁻³ and 25 °C.

The experimental D_a values were analysed employing the Arrhenius law and the Stokes-Einstein equations. Results revealed that diffusion data are in a reasonable agreement with Arrhenius behaviour, but deviations from the Stokes-Einstein equation were observed for compaction densities higher than 1.4 g cm⁻³.

The reasons for the occurrence of exothermic processes of oxidation of nitric acid solutions with reducing agents are analyzed. The main condition is heating the mixtures to temperatures (T_st), above which the release of heat as a result of a chemical reaction begins to exceed its removal from the system. An analysis of the characteristics of exothermic processes obtained experimentally for solutions with reducing agents has been carried out. The effect of irradiation of solutions on the T_st value is small, while other parameters of exothermic processes decrease - heat release, the self-heating value, and the volume of released gases. Necessary and sufficient parameters have been identified to assess the explosion hazard of heating operations of these solutions. Conditions have been established to ensure safety during the evaporation of nitric acid solutions with reducing agents.

In the present work, a group of four glass samples that have chemical composition of [(35-x) B₂O₃-20TeO₂-10GeO₂-35MgO-xLa₂O₃] were x values varies from 2.5 to 10 all in mol percentage, which fabricated using ordinary melting then quenching technique. Many physical and mechanical have been measured and calculated like: density, packing density, internuclear distance (r_i), oxygen packing density (OPD), oxygen molar volume (OMV), dissociation energy (G_t), packing density (V_t), Poisson ratio (σ), fractal bond connectivity (d), elastic modulus. The behavior of the La10 was examined using XRD in the range of 10–80°. The UV–visible spectrum of absorption of the La2.5, La5, La7.5, and La10 glasses were measured. Several optical parameters have been calculated and extracted including the cutoff wavelength, Urbach's energy (E_U), dielectric constant (ε), refractive index (n), molar refraction (R_M), reflection loss (R_L), molar electron polarizability (α_M), Optical transmission (T), Optical basicity (Λ), and Metallization criteria (M). Various noticeable bands vibration of boron units structural besides the modes of vibration of that effected by adding metal cations were studied using FTIR to analyze different structure groups like: BO₃ triangles, BO₄ pyramids, tetragonal TeO₄ pyramids, and trigonal TeO₃ pyramids. Using Monte Carlo simulation, the MAC of glass materials was evaluated in the current work. Various radiation shielding parameters were investigated at low and high energies.

Accurate and reliable predictions are fundamental for the condition monitoring and maintenance of components and systems in nuclear power plants (NPPs). In this work, we propose a hybrid condition prediction approach based on the combination of complementary ensemble empirical mode decomposition (CEEMD), sample entropy (SampEn) and optimized long short-term memory (LSTM) neural network. Firstly, the CEEMD decomposes the time series signals into multiple subsequences called intrinsic mode functions (IMFs), by doing so, the complexity of the time series signals can be reduced, and this facilitates the accurate prediction of the original signals. Then, in order to reduce the calculation cost of prediction models for subsequences, SampEn is used to measure the complexities of the IMFs, and the IMFs whose values of SampEn are lower than the average are aggregated into a new component. Finally, the LSTM with the hyperparameters optimized by the Bayesian optimization algorithm (BOA) is used to perform the prediction of each component. The prediction results of the original signals are reconstructed by synthesizing the predictions of all components. The proposed hybrid prediction model is utilized on the time series signals collected from an NPP. The results obtained show that the proposed approach can capture the characteristics of the signals and has better performance in prediction accuracy than other models.

This paper introduces a¹⁶N monitoring system designed for the real-time detection of minor coolant leaks in nuclear reactors. Conventional coolant leak detection methods in nuclear power plants rely on observing changes in sump tank water levels, as guided by Nuclear Regulatory Commission standards. However, these methods are slow and often inaccurate, particularly for detecting small leakages of less than 0.5 gallons per minute (gpm). Such delays pose risks of corrosion from boric acid and potential safety hazards due to mechanical or thermal fatigue at critical junctions. To address these challenges, we have developed a Reactor Coolant System (RCS) leakage detection system that can swiftly identify small coolant leaks. This system employs beta-ray emissions from ¹⁶N, a nuclide predominantly produced during reactor operation and accounting for 90.4% of the total radioactivity in the APR1400 RCS coolant. High-energy beta-rays emitted by ¹⁶N are ideal for monitoring due to their significant energy levels, which distinguish them from other nuclides. This system is specifically designed for installation within the annulus zone of the reactor containment, where it captures air near reactor pipes to measure ¹⁶N beta-rays. Given the short half-life of ¹⁶N (7.13 s), direct measurement is challenging; hence, we use an indirect method to determine calibration factors between dose rate with count rate and estimate radioactivity concentrations based on simulation data and experimental measurements with a surrogate ⁹⁰Sr/Y source. This system can enhance the safety protocols of nuclear plants by enabling early detection of leaks. Our findings demonstrate that this system can detect leaks as small as 0.01 gpm within seconds, significantly improving response times compared to conventional methods.