Nuclear power in the 21st century: Challenges and possibilities

Long-Service-Life Rigid Polyurethane Foam Fillings for Spent Fuel Transportation Casks

Soft materials bearing rigid, lightweight, and vibration-dampening properties offer distinct advantages over traditional wooden and metal-based fillings for spent fuel transport casks, due to their low density, tunable structure, excellent mechanical properties, and ease of processing. In this study, a novel type of rigid polyurethane foam is prepared using a conventional polycondensation reaction between isocyanate and hydroxy groups. Moreover, the density and size of the pores in these foams are precisely controlled through simultaneous gas generation. The as-prepared polyurethane exhibits high thermal stability exceeding 185 °C. Lifetime predictions based on thermal testing indicate that these polyurethane foams could last up to over 60 years, which is double the lifetime of conventional materials of about 30 years. Due to their occlusive structure, the mechanical properties of these polymeric materials meet the design standards for spent fuel transport casks, with maximum compression and tensile stresses of 6.89 and 1.37 MPa, respectively, at a testing temperature of -40 °C. In addition, these polymers exhibit effective flame retardancy; combustion ceased within 2 s after removal of the ignition source. All in all, this study provides a simple strategy for preparing rigid polymeric foams, presenting them as promising prospects for application in spent fuel transport casks.

Impact of microbial processes on the safety of deep geological repositories for radioactive waste

To date, the increasing production of radioactive waste due to the extensive use of nuclear power is becoming a global environmental concern for society. For this reason, many countries have been considering the use of deep geological repositories (DGRs) for the safe disposal of this waste in the near future. Several DGR designs have been chemically, physically, and geologically well characterized. However, less is known about the influence of microbial processes for the safety of these disposal systems. The existence of microorganisms in many materials selected for their use as barriers for DGRs, including clay, cementitious materials, or crystalline rocks (e.g., granites), has previously been reported. The role that microbial processes could play in the metal corrosion of canisters containing radioactive waste, the transformation of clay minerals, gas production, and the mobility of the radionuclides characteristic of such residues is well known. Among the radionuclides present in radioactive waste, selenium (Se), uranium (U), and curium (Cm) are of great interest. Se and Cm are common components of the spent nuclear fuel residues, mainly as 79Se isotope (half-life 3.27 × 105 years), 247Cm (half-life: 1.6 × 107 years) and 248Cm (half-life: 3.5 × 106 years) isotopes, respectively. This review presents an up-to-date overview about how microbes occurring in the surroundings of a DGR may influence their safety, with a particular focus on the radionuclide-microbial interactions. Consequently, this paper will provide an exhaustive understanding about the influence of microorganisms in the safety of planned radioactive waste repositories, which in turn might improve their implementation and efficiency.

Microscopic Insights and Optimization of the CH4-CO2 Replacement in Natural Gas Hydrates

Using the CO₂ replacement method to exploit natural gas hydrates and store CO₂ has great significance in energy access and environmental protection. Herein, the molecular dynamic method is utilized to analyze and evaluate the CH₄-CO₂ replacement at different constant temperatures and pressures. For optimization, various temperature oscillations are introduced in the CH₄-CO₂ replacement. It illustrates that increasing the temperature can improve the amounts of CH₄ escape and CO₂ capture but is unfavorable to the long-term CO₂ storage and hydrate stability. The effects of pressure are not as significant and definite as those of temperature. Appropriate temperature oscillations can achieve comprehensive improvements, which benefit from both the deep diffusion of CO₂ in the higher temperature stage and the rapid rebuilding of CO₂ hydrate within just nanoseconds caused by the memory effects in the lower temperature stage. The results also reveal that the optimal lower temperature duration and frequency should be moderate. Decreasing the lower temperature value can distinctly enhance CO₂ capture and hydrate stability. This study can help understand the mechanisms of CH₄-CO₂ replacement under different temperature and pressure conditions, especially at temperature transitions, and proposes a potentially effective method to achieve large-scale carbon sequestration in the hydrate.

Study of a Fiber Optic Fabry-Perot Strain Sensor for Fuel Assembly Strain Detection

This paper proposes a fiber optic Fabry-Perot (F-P) strain sensing system using non-scan correlation demodulation applied to the health monitoring of the pressurized water reactor's fuel assembly structures. The structural design and sensing mechanism analysis of the sensor were carried out, and the strain transfer model from the fuel sheet to the strain gauge was established. After the sensor fabrication and installation, the static tests have been conducted, and the results indicate that the sensing system can accurately measure the microstrain with a sensitivity of up to 12.6 nm/με at a high temperature (300 °C). The dynamic testing shows that the sensing system has a good frequency adaptation at 10-500 Hz. Thermal-hydraulic experiments show that the sensing system can run stably in a nuclear reactor, with high temperature, high pressure, and high-velocity flow flushing; additionally, the consistency deviation of the measured data is less than 1.5%.

State-of-the-art progress for the selective crystallization of actinides, synthesis of actinide compounds and their functionalization

Crystallization and immobilization of actinides to form actinide compounds are of significant importance for the extraction and reutilization of nuclear waste in the nuclear industry. In this paper, the state-of-art progress in the crystallization of actinides are summarized, as well as the main functionalization of the actinide compounds, i.e., as adsorbents for heavy metal ions and organic pollutant in waste management, as (photo)catalysts for organic degradation and conversion, including degradation of organic dyes and antibiotics, dehydrogenation of N-heterocycles, CO₂ cycloaddition, selective alcohol oxidation and selective oxidation of sulfides. This review will give a comprehensive summary about the synthesis and application exploration of solid actinide crystalline salts and actinide-based metal organic frameworks in the past decades. Finally, the future perspectives and challenges are proposed in the end to give a promising direction for future investigation.

Evaporation behavior of 233Pa in FLiBeZr molten salt

In thorium molten salt reactors (TMSR), ²³³Pa is an important intermediate nuclide in the conversion chain of ²³²Th to ²³³U, its timely separation from the fuel salt is critically important for both the thorium–uranium (Th–U) fuel cycle and the neutron economy of the reactor. In this study, the evaporation behavior of ²³³Pa in the FLiBeZr molten salt was investigated during a vacuum distillation process. The separation characteristics between ²³³Pa and the major components of the fuel (salt and fission products) were evaluated in a calculation of the separation factors between these components. It was found that ²³³Pa⁵⁺ evaporated more readily than ²³³Pa⁴⁺ and the other components of the fuel, the relatively low temperature and medium pressure were much more beneficial to the separation of ²³³Pa⁵⁺ from FLiBeZr salt in the evaporation process, with the maximum value of the separation factor achieving more than 10². Results of distillation experiments also show that increasing the temperature and decreasing the ambient pressure enhances the separation between ²³³Pa⁵⁺ and most of the fission product nuclides due to the ²³³Pa⁵⁺ volatility more strongly depending on the process conditions. These results will be utilized to design a concept for a process for ²³³Pa separation from the fuel of a molten salt reactor.

The evaporation behavior of ²³³Pa in the FLiBeZr molten salt was investigated during a vacuum distillation process.

Global and regional probabilities of major nuclear reactor accidents

The continued and extended use of nuclear power is often considered and discussed as a viable energy policy option to meet energy demands while also meeting national CO₂ emission reduction goals. A central issue in energy policy for sustainability is the question of nuclear reactor safety. However, studies on nuclear reactor safety often run up against the problem of estimating the probability of a major accident from patchy and limited empirical data. Here, we describe a simple probabilistic model of catastrophic nuclear reactor accidents based on a set of four assumptions. The model treats the accident probability in each of n reactors as a variable and returns the probability of a major accident in the reactor fleet. We find that, at 99.5% reactor safety, the probability of another Chernobyl- or Fukushima-sized event is 49% for the global fleet, and that safety would have to be 99.96% in order to bring that probability below 5%. We discuss our findings in light of the debate on energy policy for sustainability.

Response to "Regarding nuclear energy: Between global electricity demand, worldwide decarbonisation imperativeness, and planetary environmental implications"

In their critical comments, Davies et al. (2019) claim that our paper (Prăvălie and Bandoc, 2018) features a series of shortcomings, such as the lack of quantitative or qualitative weighting of the nuclear energy trilemma, the insufficient analysis of specialized scientific literature or the presence of certain inconsistencies and inaccuracies throughout the paper. Starting from the idea that debate in the nuclear energy sector, in this particular instance, or in science, in general, is constructive, as long as based on credible arguments, we acknowledge these comments and wish to provide pertinent responses for each critical observation. Given this context, this scientific communication is meant to provide explanations and justify the fact that the findings of the original review-type paper (Prăvălie and Bandoc, 2018) are real and supported by various relevant scientific data and papers, and that our vision on the global nuclear energy trilemma is sufficiently substantiated.

Advanced Modelling of 238U(n,f) in a Fast Reactor Application

Fast neutron reactors, as a possible future solution on energy demand of human society, based on fission process of 238U, request new and reliable nuclear data necessary for new generation reactors design. Fission process induced by fast neutrons on 238U was investigated. Fission observables like cross sections and their uncertainties, fission fragment mass distribution, prompt neutrons emission, isomer ratios and other parameters were obtained by using Talys computer code or programs realized by authors. Then the production of isotopes like 135,133Xe, 99Mo, 131I, 89Y as well as yields of fissile nuclei were evaluated. Obtained theoretical evaluations are compared with existing experimental data.

Nuclear energy: Between global electricity demand, worldwide decarbonisation imperativeness, and planetary environmental implications

For decades, nuclear energy has been considered an important option for ensuring global energy security, and it has recently started being promoted as a solution for climate change mitigation. However, nuclear power remains highly controversial due to its associated risks - nuclear accidents and problematic radioactive waste management. This review aims to assess the viability of global nuclear energy economically (energy-wise), climatically and environmentally. To this end, the nuclear sector's energy- and climate-related advantages were explored alongside the downsides that mainly relate to radioactive pollution. Economically, it was found that nuclear energy is still an important power source in many countries around the world. Climatically, nuclear power is a low-carbon technology and can therefore be a viable option for the decarbonization of the world's major economies over the following decades, if coupled with other large-scale strategies such as renewable energies. These benefits are however outweighed by the radioactive danger associated to nuclear power plants, either in the context of the nuclear accidents that have already occurred or in that of the large amounts of long-lived nuclear waste that have been growing for decades and that represent a significant environmental and societal threat.