Nuclear Plant Research Articles

A Quasi Time-Domain Method for Fatigue Analysis of Reactor Pressure Vessels in Floating Nuclear Power Plants in Marine Environments

The reactor pressure vessel (RPV) in onshore nuclear power plants is typically analysed for fatigue life by considering the temperature, internal pressure, and seismic effects using a simplified time-domain fatigue analysis. In contrast, the frequency-domain fatigue analysis method is commonly employed to assess the fatigue life of ship structures. The RPV of a floating nuclear power plant (FNPP) is subjected to a combination of temperature, internal pressure, and wave loads in the marine environment. Consequently, it is essential to effectively integrate the frequency-domain fatigue analysis method used for hull structures with the time-domain fatigue analysis method for RPVs in FNPPs or, alternatively, to develop a suitable method that effectively accounts for the temperature, internal pressure, and wave loads. In this study, a quasi-time-domain method is proposed for the fatigue analysis of RPVs in FNPPs. In this method, secondary components of marine environmental loads are filtered out using principal component analysis. Subsequently, the stress spectrum induced by waves is transformed into a stress time history. Fatigue stress under the combined influence of temperature, internal pressure, and wave loads is then obtained through a stress component superposition method. Finally, the accuracy of the quasi-time-domain method was validated through three numerical examples. The results indicate that the calculated values obtained by the quasi-time-domain method are slightly higher than those obtained by the traditional time-domain method, with a maximum deviation of no more than 24%. Additionally, the computation time of the quasi-time-domain method is reduced by 98.67% compared to the traditional time-domain method.

Development of ultrasonic phased array technique for inspection of fir-tree type turbine blade root and disc-rim in nuclear power plant

Development of ultrasonic phased array technique for inspection of fir-tree type turbine blade root and disc-rim in nuclear power plant

Contrasting pathogen prevalence between tick and dog populations at Chornobyl

Abstract Background The 1986 disaster at the Chornobyl Nuclear Power Plant released massive amounts of radioactive material into the local environment. In addition to radiation, remediation efforts and abandonment of military-industrial complexes contributed to contamination with heavy metals, organics, pesticides and other toxic chemicals. Numerous studies have evaluated the effects of this contamination on the local ecology. However, few studies have reported the effect of this contamination on vector-borne pathogens and their hosts. In this manuscript, we characterize tick-borne pathogen presence at two sample locations within the Chornobyl Exclusion Zone, one at the Nuclear Power Plant (NPP) and another 16 km away in Chornobyl City (CC). Methods Ticks and whole-blood samples were collected from free-breeding dogs captured at the NPP and CC. Endpoint PCR and quantitative PCR were used to identify tick species and to assess the presence of specific tick-borne pathogens, including Anaplasma phagocytophilum, Borrelia burgdorferi sensu lato, Babesia spp., Bartonella spp., Francisella tularensis and general Anaplasmataceae. A droplet digital PCR assay was developed for Babesia canis and A. phagocytophilum to evaluate their presence in dogs from the two populations. Pathogen prevalences between the two sample populations were compared by calculating Z-scores. Results Ticks were identified as Ixodes ricinus (n = 102) and Dermacentor reticulatus (n = 4). Overall, 56.9% of I. ricinus ticks were positive for at least one pathogen. A significantly higher prevalence of A. phagocytophilum and B. burgdorferi was found in ticks at the NPP (44.0% and 42.0%, respectively) compared to CC (23.1% and 19.2%, respectively). Babesia spp. (including B. canis and B. caballi) were detected in 8.8% ticks at similar proportions for both populations. Interestingly, we found a significantly lower level of A. phagocytophilum in dogs at the NPP (1.8%) than in dogs at CC (11.7%). In total, 24.3% of dogs were positive for B. canis, evenly distributed across the two populations. Conclusions The results of this study show contrasting pathogen prevalence in both ticks and dogs at the NPP and CC, which may reflect the differential exposures at the two locations. This work adds an important new component to our understanding of the consequences of prolonged exposure to environmental contamination on the wildlife and ecology within the Chornobyl Exclusion Zone. Graphical Abstract

Acoustic sensing and autoencoder approach for abnormal gas detection in a spent nuclear fuel canister mock-up

Currently, spent nuclear fuel (SNF) from commercial nuclear power plants is stored in stainless-steel canisters for interim dry storage. To provide an inert environment, these canisters are backfilled with helium after vacuum drying. However, the helium environment may be contaminated during extended storage because of the material degradation. For example, the heavier fission gas xenon may be released from the fuel rods into the canister cavity should the fuel cladding be breached. Other gases such as air and water vapor may also be present as a result of leakage caused by chloride-induced stress corrosion cracking on the canister walls or by insufficient vacuum drying. Therefore, monitoring the gas composition can provide critical information about the health of SNF canisters. In this study, noninvasive testing was conducted on a 2/3-scaled SNF canister mock-up using acoustic sensing. Ultrasonic transducers were placed on the exterior surface of the canister to probe the gas composition. A dataset was collected by sealing the canister mock-up and introducing up to 1.53% argon or 1.29% air into the helium background gas. Three methods were used to detect changes in the gas composition: the time-of-flight (TOF) method, the differential method, and the autoencoder method. Results showed that the TOF method had sufficient resolution to detect abnormal gas concentrations of less than 1.0%. The differential method demonstrated a periodic in-phase and out-of-phase behavior between the benchmark (i.e., pure helium) and abnormal (i.e., with argon or air) state signals. The variational autoencoder (VAE) and the Wasserstein autoencoder (WAE) were trained on the benchmark data and were applied directly to the abnormal state data. It was found that both the unsupervised VAE and the WAE were able to distinguish the benchmark and abnormal states of the canister mock-up based on the reconstruction error.

Glaciation of liquid clouds, snowfall, and reduced cloud cover at industrial aerosol hot spots.

The ability of anthropogenic aerosols to freeze supercooled cloud droplets remains debated. In this work, we present observational evidence for the glaciation of supercooled liquid-water clouds at industrial aerosol hot spots at temperatures between -10° and -24°C. Compared with the nearby liquid-water clouds, shortwave reflectance was reduced by 14% and longwave radiance was increased by 4% in the glaciation-affected regions. There was an 8% reduction in cloud cover and an 18% reduction in cloud optical thickness. Additionally, daily glaciation-induced snowfall accumulations reached 15 millimeters. Glaciation events downwind of industrial aerosol hot spots indicate that anthropogenic aerosols likely serve as ice-nucleating particles. However, rare glaciation events downwind of nuclear power plants indicate that factors other than aerosol emissions may also play a role in the observed glaciation events.

Fukushima Daiichi Nuclear Power Station Accident and Monitoring Post Data —The Role of Monitoring Posts in the Early Stages of a Nuclear Power Plant Accident

Fukushima Daiichi Nuclear Power Station Accident and Monitoring Post Data —The Role of Monitoring Posts in the Early Stages of a Nuclear Power Plant Accident

The development of international civil liability legal regime for nuclear damage and their inspiration for domestic law-making

As International Atomic Energy Agency has stated in its Handbook on Nuclear Law, “Even in situations for which the highest standard of safety has been achieved, the occurrence of nuclear accidents cannot be completely excluded.” Therefore, the international legal framework for nuclear damage compensation liability has been evolving since the establishment of Nuclear Energy Agency of Organization for Economic Co-operation and Development (OECD NEA) and International Atomic Energy Agency (IAEA). Over the years, various international treaties have been enacted to address the compensation of nuclear damage and to establish liability regimes for nuclear incidents. To date, these treaties have established a series of legal principles of nuclear damage liability, such as the sole liability principle, the strict liability principle, the financial guarantee principle etc., which have been developing since establishment. This paper offers an overview of the historical development of the principles of these international treaties for nuclear damage liability and thus draws upon both primary and secondary sources, including treaties, official documents, academic literature, and reports by international organizations. Including the legislation study methodology, comparative methodology is also adopted in this paper to analyze the changes and trend of these principles. The paper reveals that the Paris Convention, which was established in 1960, was the first attempt to establish a comprehensive legal regime for nuclear damage liability. Most of the principles of this Convention have been inherited by subsequent international treaties and domestic legislations. With the awareness of protecting public’s rights having been significantly strengthened, the range of compensation has been broader, the matters of immunity from liability for operators of nuclear power plants have been reduced, the limitation of the compensation amount has been higher etc. In conclusion, the international legal regime for nuclear damage liability has been showing a shift from protecting the development of the nuclear industry to a joint protection of both public health and rights and the nuclear industry, which should be paid attention to and deeply learnt by domestic legislators of all states for the establishment and perfection of their domestic legislation in this field.

A mapping-free natural language processing-based technique for sequence search in nanopore long-reads.

In unforeseen situations, such as nuclear power plant's or civilian radiation accidents, there is a need for effective and computationally inexpensive methods to determine the expression level of a selected gene panel, allowing for rough dose estimates in thousands of donors. The new generation in-situ mapper, fast and of low energy consumption, working at the level of single nanopore output, is in demand. We aim to create a sequence identification tool that utilizes natural language processing techniques and ensures a high level of negative predictive value (NPV) compared to the classical approach. The training dataset consisted of RNA sequencing data from 6 samples. Multiple natural language processing models were examined, differing in the type of dictionary components (word length, step, context) as well as the encoding length and number of sequences required for algorithm training. The best configuration analyses the entire sequence and uses a word length of 3 base pairs with one-word neighbor on each side. For the considered FDXR gene, the achieved mean balanced accuracy (BACC) was 98.29% and NPV was 99.25%, compared to minimap2's performance in a cross-validation scenario. The next stage focused on exploring the dictionary components and attempting to optimize it, employing statistical techniques as well as those relying on the explainability of the decisions made. Reducing the dictionary from 1024 to 145 changed BACC to 96.49% and the NPV to 98.15%. Obtained model, validated on an external independent genome sequencing dataset, gave NPV of 99.64% for complete and 95.87% for reduced dictionary. The salmon-estimated read counts differed from the classical approach on average by 3.48% for the complete dictionary and by 5.82% for the reduced one. We conclude that for long Oxford nanopore reads, a natural language processing-based approach can reliably replace classical mapping when there is a need for fast, reliable and energy and computationally efficient targeted mapping of a pre-defined subset of transcripts. The developed model can be easily retrained to identify selected transcripts and/or work with various long-read sequencing techniques. Our results of the study clearly demonstrate the potential of applying techniques known from classical text processing to nucleotide sequences.

Overview of High-Performance Timing and Position-Sensitive MCP Detectors Utilizing Secondary Electron Emission for Mass Measurements of Exotic Nuclei at Nuclear Physics Facilities

Timing and/or position-sensitive MCP detectors, which detect secondary electrons (SEs) emitted from a conversion foil during ion passage, are widely utilized in nuclear physics and nuclear astrophysics experiments. This review covers high-performance timing and/or position-sensitive MCP detectors that use SE emission for mass measurements of exotic nuclei at nuclear physics facilities, along with their applications in new measurement schemes. The design, principles, performance, and applications of these detectors with different arrangements of electromagnetic fields are summarized. To achieve high precision and accuracy in mass measurements of exotic nuclei using time-of-flight (TOF) and/or position (imaging) measurement methods, such as high-resolution beam-line magnetic-rigidity time-of-flight (Bρ-TOF) and in-ring isochronous mass spectrometry (IMS), foil-MCP detectors with high position and timing resolution have been introduced and simulated. Beyond TOF mass measurements, these new detector systems are also described for use in heavy ion beam trajectory monitoring and momentum measurements for both beam-line and in-ring applications. Additionally, the use of position-sensitive timing foil-MCP detectors for Penning trap mass spectrometers and multi-reflection time-of-flight (MR-TOF) mass spectrometers is proposed and discussed to improve efficiency and enhance precision.

Carbon accumulation model for simulating 14C radioactivity in Chinese yam grown from a seed bulbil.

Modeling carbon accumulation in crop plants is key to evaluating the transfer of atmospheric 14C into the edible parts of the plants growing near nuclear facilities. Chinese yam 'Nagaimo' (Dioscorea polystachya Turcz.) is a major crop cultivated near a spent nuclear fuel reprocessing plant in Rokkasho, Aomori, Japan. We developed a dynamic compartment model for assessing carbon and 14C accumulation in Chinese yam grown from a seed bulbil in the field. Light and temperature dependence of leaf photosynthesis and temperature dependence of respiration in leaves, stems and belowground parts (tuber and root) were incorporated into the model. Estimated amounts of carbon in the leaves, stems and belowground parts were good agreement with the measured data from the field. Simulation results of 14C accumulation using this model indicated that the accumulation of 14C in belowground parts at the harvest depends on the rate of photosynthesis on the day of exposure.

Effect of sampling face velocity on the ultrafine particle surface collection efficiency of a cellulose membrane filter and a cellulose-glass fiber filter for environmental airborne radioactivity monitoring.

Surface collection efficiency (SCE) of a cellulose membrane filter (CMF) and a cellulose-glass fiber filter used in environmental monitoring for alpha-emitting radionuclides from nuclear facilities and natural radioactivity sources was evaluated for particles in the size range of 0.03-0.1μm at different levels of face velocity. The SCE of the CMF was higher than that of the cellulose-glass fiber filter, and only the membrane filter showed the dependence of SCE on the particle size at higher face velocity. The use of the CMF at higher face velocity in environmental radioactivity monitoring leads to measurements of the background alpha spectrum with more degradation under the changing particle size condition in the atmosphere. Consequently, that fact needs to be taken into account, along with the expected particle size distribution and concentration of the airborne radioactivity being sampled, when selecting a face velocity to achieve the best possible detection limit.

Investigating the association between dry deposition of cesium and different growth stages of aboveground parts of Chinese yam.

Radiocesium released into the atmosphere from accidents at nuclear facilities, can be deposited on the surface of the surrounding crop fields as dry and wet deposits. Radiocesium deposition can occur at any time during the growth season. In this study, we used stable cesium (Cs) to investigate the changes in dry Cs deposits on surfaces of aboveground parts of Chinese yam (Dioscorea polystachya) during different growth stages. Chinese yam seedlings were grown for eight different lengths of time and were then simultaneously exposed to aerosol particles containing stable Cs in an aerosol exposure chamber for 5h. The deposition density of Cs on the aboveground parts of the seedlings decreased from 29 to 72d after transplantation (DAT) and did not change significantly after 72 DAT. The Cs deposition density on the seedlings on different DAT correlated with the leaf area available for the deposition of aerosol Cs particles.

Parametric dependencies of ion temperature profile peaking in ASDEX Upgrade high-beta scenarios

Abstract Advanced Tokamak (AT) scenarios are attractive candidates for future nuclear fusion power plants. These scenarios often feature peaked temperature profiles, suggesting a local reduction of turbulent transport. The mechanisms behind this are, as yet, not fully understood. Parameters that are thought to be connected to these transport reductions include the q-profile and the ExB-shear ωExB. Another parameter considered to be important is the fast ion content, which can reduce transport in multiple different ways.
This work presents AT experiments performed at the ASDEX Upgrade tokamak (AUG) in which these three parameters are varied to investigate their respective effect on the observed peaked ion temperature profiles. To disentangle potentially competing effects, simulations using the codes GENE and TGLF have been performed. It is found that the ExB-shear does not play a role in the AT scenarios performed at AUG, which have relatively low rotation, with vtor=100-250km/h. Experimentally, a significant dependence of R/LTi on the electron cyclotron current drive (ECCD) settings was found, indicating that either the current profile (and, therefore, the q-profile) or Te/Ti has a significant impact on the observed suppression of turbulent transport. In support of the first option, both GENE and TGLF show a q-profile dependence of R/LTi. Furthermore, according to GENE, electromagnetic (EM) fast ion effects are essential in reproducing the experimental results. Scans with TGLF (which does not include such effects), suggest that these fast ion effects become relevant above a threshold of R/LTi= 4-5. In the presence of ICRF, additional electrostatic (ES) fast ion effects seem to come into effect, according to GENE, albeit to a smaller degree than the EM effects.

VERIFICATION OF THE PROPERTIES OF AN INDUSTRIAL ROBOT FOR THE NUCLEAR INDUSTRY

The article deals with the issue of verification of selected geometric characteristics of a special robot intended for the nuclear industry. The design of the robot is specific in that the robot works in both semi-automatic and manual mode. This leads to frequent collisions of some parts of the robot with fragmented equipment. Therefore, it was necessary to ensure the accuracy and repeatability of the robot after its production and during its operation. Verification of the parameters of the robot after one year of operation was carried out in the controlled zone of the nuclear power plant, which was specific due to the presence of ionizing radiation. The methodology, technique and method of verification had to be adapted to this.

Adaptive Forecasting of Nuclear Power Plant Operational Status Under Sensor Concept Drift Using a Bridging Distribution Adaptive Network

A large number of sensors are required to collect information during the operation of nuclear power plants to ensure their absolutely safe operation. However, because of the unique nature of nuclear reactions, the physical environment of nuclear power production is prone to changes, leading to concept drift in the data collected by the sensors. Concept drift describes the phenomenon of sample distribution changing over time, which typically negatively impacts the model’s training and inference processes. We found that nongradual distribution changes could be guided by generating transitional intermediary distributions within the distribution, thereby achieving a gradual change process. Based on this, we designed a bridging distribution adaptive network (BDAN), which consisted of identical-depth TDoA (time difference of arrival) homomorphic backbone neural networks on both sides with a latent adaptive bridging module in the middle. By calculating the distribution differences over multiple timesteps, a series of bridge distributions were generated to guide the gradients in the latent space, updating the parameters of the latent adaptive guiding module in a directional manner and enabling the model to perceive nongradual distribution changes in the time domain. Experimental results showed that the BDAN outperformed the previous state-of-the-art benchmark methods by 5.6% in terms of mean squared error in the nuclear power data prediction task under concept drift, achieving the best fault prediction performance.

Risks associated with evacuation and disaster-related death after a radiation disaster: summary of research results from Hamadori region, Fukushima.

Radiation disasters can lead to a myriad of direct and indirect health effects. The term 'disaster-related deaths' is commonly used in Japan; however, comprehensive studies in regions severely impacted by nuclear accidents are scarce. Our research primarily focuses on Minamisoma City, situated north of the Fukushima Daiichi Nuclear Power Plant (FDNPP), and aimed to study the risks associated with evacuation and disaster-related death. We introduce the following studies: (1) risks from evacuation in elderly care facilities after the FDNPP accident; (2) detailed case reports on hospital evacuation and (3) detailed reports on disaster-related deaths. A critical lesson from the FDNPP accident is the significant risk to life posed by evacuation actions taken to avoid radiation exposure. Despite evacuation being an effective measure to reduce exposure, our preparation and knowledge are insufficient for safe execution. This paper ensures that the lessons from Fukushima are leveraged in future radiation protection measures.

Non-returning factors from an interview survey of 16 residents of Katsurao village 12years after the Fukushima nuclear power plant accident.

People generally wish to return home after being evacuated due to disaster situations. Evacuation orders have now been lifted in the Fukushima region following the nuclear accident in 2011, and the Japanese government is promoting a return policy. However, many residents who wish to return home remain unable to and continue living in evacuation sites or other areas. Sixteen residents of Katsurao village were interviewed after evacuation orders were lifted in 2016 who have not yet returned. Concerns were cited regarding radiation, prolonged evacuation, health problems, buying a house in the evacuation area and schooling. The problems identified were primarily due to the rapid ageing and decline of the regional population, reflecting similar issues throughout Japan. In particular, health problems and intention to return were thought to be closely related. Over 10 y have passed since the evacuation, and many residents have experienced familial separation and divided living situations.

Behavior of radioactive cesium concentration for 13 years after FDNPP accident at Koriyama campus of Nihon University, Fukushima, Japan.

The concentration of the radioactive cesium (134Cs and 137Cs) in soils and in atmospheric fallouts has been measured at the Koriyama campus, Nihon University, after the Fukushima Dai-ichi Nuclear Power Plant accident for 13y, from October 2011 till September 2023 and now ongoing. The concentration of them decreased very rapidly due to decontamination activities and weathering effects, with an environmental half-life of 1.21 and 2.82y in soils, with those of 1.58 and 2.08y in atmospheric fallouts for 134Cs and 137Cs, respectively. The behavior of the decrease was not simple, due to particles raised from the surface soil in wooded areas that had not been thoroughly decontaminated or that had been accumulated due to the re-release of radioactive cesium by trees after decontaminated activity.

Tritium determination in natural water samples in Fukushima from 2022 to 2023 using an ultra-low-level tritium counting system.

The Fukushima Daiichi Nuclear Power Plant (FDNPP) accident created large stockpiles of tritium containing cooling water, which is to be gradually released into the Pacific Ocean, gaining attention from surrounding countries, environmental groups, and local residents concerned with the possibility of increasing tritium concentrations in the water and food cycle. Establishing baseline concentration levels and monitoring tritium immission values are important for assuring public safety, providing data for scientific research and risk communication. Tritium concentrations in the environment are very low; therefore, tritium measurements require enrichment in order to estimate the radiation exposure from drinking water intake and provide information on the water cycle. Natural water samples were collected at Tomioka Town located south of the FDNPP. Samples were distilled, enriched by electrolysis, and re-distilled using an improved SPE method to preconcentrate tritium to measureable levels. Tritium concentrations were determined by a low-background liquid scintillation counter. The observed tritium concentrations were relatively low, rainwater had a mean and SD value of 0.40±0.13Bq/L, and freshwater samples showed similar concentrations, while brackish coastal water samples were below 0.13±0.02Bq/L. The observed tritium concentrations in this study are considered safe as effective doses based on annual drinking water intake; however, continous monitoring is necessary to assure public safety.

A pilot study to directly estimate radiation-induced mutation in large Japanese field mouse duo sample, mother and offspring, excluding unknown father, using ddRAD sequencing.

DNA mutations are one of the effects of radiation exposure. A large amount of radioactive materials was released into the environment from the Fukushima Daiichi Nuclear Power Plant after a major earthquake and tsunami. Wild animals and plants living in highly radiation-contaminated areas are constantly exposed to high doses of radiation, and concerns occur about its effects on their health and the next generations. As a pilot study, double-digest restriction site-associated DNA (ddRAD) sequencing was conducted to assess the incidence of mutations in wild large Japanese field mice collected from the evacuation area. The optimal combination of restriction enzymes, encompassing the functionally important coding regions, was selected using in silico analysis. These enzymes were used for ddRAD sequence analysis of females and their fetuses to evaluate mutation rates. The results indicated that no significant differences were observed in mutation rates between mothers and fetuses in the study areas.