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The formation of a stress corrosion crack (SCC) in the canister wall of a dry cask storage system (DCSS) has been identified as a potential issue for the long-term storage of spent nuclear fuel. The presence of a SCC in a storage system could represent a through-wall flow path from the canister interior to the environment. Modern, vertical DCSSs are of particular interest due to the commercial practice of using relatively high helium backfill pressures (up to approximately 800 kPa) in the canister to enhance internal natural convection. This pressure differential offers a comparatively high driving potential for blowdown of any particulates that might be present in the canister in the event of a through-wall SCC. In this study, the rates of gas flow and aerosol transmission of a spent fuel surrogate through an engineered microchannel with dimensions representative of a SCC were evaluated experimentally using coupled mass flow and aerosol analyzers. The microchannel was formed by mating two gauge blocks with a linearly tapering slot orifice nominally 13 μm (0.0005 in.) tall on the upstream side and 25 μm (0.001 in.) tall on the downstream side. The orifice is 12.7 mm (0.500 in.) wide by 8.89 mm (0.350 in.) long (flow length). Surrogate aerosols of cerium oxide (CeO2) were seeded and mixed with either helium or air inside a pressurized tank. The aerosol characteristics were measured immediately upstream and downstream of the simulated SCC at elevated and ambient pressures, respectively. The next iteration of testing involves replacing the engineered microchannel with lab-grown SCCs. Preliminary clean flow testing has been conducted on SCC samples provided by the Electric Power Research Institute. These data sets demonstrate a new capability to characterize SCCs under well-controlled boundary conditions. Preliminary testing efforts are focused on understanding the evolution in both the size and quantity of a hypothetical release of aerosolized spent fuel particles from failed fuel cladding into the canister interior, and ultimately, through a SCC. [ABSTRACT FROM AUTHOR]

A recently revised American Society for Testing and Materials consensus standard guide for drying of spent nuclear fuel (SNF) provides considerations and guidance for preparing SNF for its safe storage in a sealed dry storage system. The standard discusses (1) needs for drying, (2) techniques to dry, and (3) demonstration of adequate dryness. No specific approach is prescribed since the effective techniques and needs for drying depend on the specifics of the fuel and dry storage system. This paper discusses these topics using examples for both Zr-alloy-clad commercial SNF and for aluminum-alloy-clad research reactor SNF. Residual water can include free water (liquid and/or vapor), physisorbed water bound to internal surfaces, and chemisorbed water incorporated into surface films, such as (oxy)hydroxides. The potential impacts of these residual waters are corrosion/oxidation, radiolytic breakdown into gaseous and/or reactive species, and canister pressurization. For commercial SNF, inadvertent free water, even up to large amounts (e.g., 10+ mol), is not predicted to cause adverse corrosion degradation, except possible fuel oxidation for breached SNF. For aluminum-clad SNF, the production of radiolytic hydrogen with contribution from the chemisorbed water in its hydrated oxides is a primary consideration. For both SNF systems, canister pressurization is predicted to be well within the canister design, and flammability would not pose a safety concern using an oxygen limit of 5 vol % criterion. (Flammability control can be achieved by limiting either hydrogen or oxygen, and an oxygen limit is expected to be easier to meet in the presence of radiolytic H2 generation.) The two primary technologies for SNF drying, vacuum drying and forced-gas dehydration, are described herein, and drying tests and campaigns using these methods are cited. Dryness criteria and the methods used to detect and measure residual (free) water are also discussed. [ABSTRACT FROM AUTHOR]

CANDU spent fuels in the Wolsung site have been stored in dry storage systems, such as concrete canisters and modular air-cooled storage system. The primary role of the canister is to ensure the integrity of the fuel during the storage period, which is significantly influenced by temperature. Thus, thermal analysis for the canister's components, especially for fuel cladding, is essential to demonstrate its safety. The thermal analysis has been conducted mainly for predicting the peak cladding temperature (PCT) since high temperature of the fuel can promote oxidation and cracking. As the expiration of storage license approaches, fuel transfer to final disposal should be prepared. This also requires a thermal analysis to predict minimum cladding temperature (MCT), which is related with brittleness. So, it is crucial to accurately predict both PCT and MCT during entire storage period. The cladding temperature is primarily influenced by decay heat and ambient conditions. The lifetime PCT may occur during summer at the beginning of storage, while the lifetime MCT occurs during winter at the end of storage. In this study, we calculated the PCT and MCT during the entire storage period using a realistic thermal analysis model and, subsequently, conducted their uncertainty analysis.

Ensuring subcriticality over storage duration, even in accident condition, is one of the important requirements for dry cask designed to store spent fuel from nuclear reactor. To comply this requirement, neutron absorbers are incorporated in the spent fuel basket to decrease the neutron multiplication factor and reactivity. The objectives of this study are to prepare Cd/316L composite for neutron absorber material by powder metallurgy and determine the neutron shielding performance of the obtained composite. Powder mixtures of SS316L with various Cd contents were milled using high energy milling, followed by pressing and sintering at 450 °C and 700 °C. The analyses of the samples were carried out using XRD, SEM-EDS, XRF, and neutron transmittance test. Additionally, the neutron transmittance was also calculated using MCNP5. The results show that transformation of austenite to α-ferrite occurred during powder milling process which remained in the sample after sintering at 450 °C. Transformation of α-ferrite in the milled sample to austenite occurred after sintering at 700 °C. Cd in the samples were predominantly oxidized to form CdO phase during sintering process at both temperature conditions. The loss of Cd content in the Cd/SS316L samples after milling process was approximately 10 %. The Cd content further decreased by approximately 10 and 50 % after sintering at 450 and 700 °C, respectively. Neutron transmittance test shows that the transmittance value for thermal neutron decreased with the increased of Cd in the Cd/316 sample. A good agreement has been obtained between the results from experiment and MCNP calculation.

Vitality is a crucial element in the quality control of live scallops. Nevertheless, the effect of energy fluctuations resulting from the reproductive development of scallops on vitality during storage remains unclear. Changes in the biochemical composition of scallops throughout the year were analyzed, and live scallops with high and low glycogen were selected for dry storage. The results showed that glycogen content fluctuations ranged almost 20-fold between the highest and lowest levels. However, the other proximate composition did not change significantly. Notably, scallops with high glycogen exhibited high levels of ATP and maintained more stable vitality during dry storage. [ABSTRACT FROM AUTHOR]

The presence of hydrogen absorbed by zirconium-based cladding materials during reactor operation can trigger degradation mechanisms and endanger the rod integrity. Ensuring the durability of the rods in extended timeframes like dry storage requires anticipating hydrogen behavior using numerical modeling. In this context, the present paper describes a hydrogen post-processing tool for Falcon – HYPE, a PSI's in-house tool able to calculate hydrogen uptake, transport, thermochemistry, reorientation of hydrides and hydrogen-related failure criteria. The tool extracts all necessary data from a Falcon output file; therefore, it can be considered loosely coupled to Falcon. HYPE has been successfully validated against experimental data and applied to reactor operation and interim storage scenarios to present its capabilities.

The intraspecific variations of phenotypic traits in the early life stages, such as seed germination and seedling establishment, are important components affecting species adaptation and differentiation. As one of the most common ways in which seeds are maintained, dry storage usually affects these traits, by either increasing or decreasing variation among populations. However, little is known about how the interaction between dry storage and population variation of a species affects the performance and adaptability of early life-cycle traits. In this study, we conducted experiments with seeds from ten populations of Elymus nutans along an altitudinal gradient on the eastern Qinghai-Tibet Plateau. Fresh seeds and seeds stored dry for 6 months were used to quantify the temperature thresholds for germination, determine seedling emergence and survival in two common gardens and examine the correlation between these traits and environmental conditions of population provenance. Dry storage increased germination percentage, germination speed and seedling emergence, and decreased intraspecific variation in germination traits of seeds (reduced by 33.36, 52.05 and 20.45% for T b, θT(50) and σ θ T , respectively). Dry storage had little effect on the intraspecific variation of seedling emergence and survival. In addition, the temperature threshold for germination cannot be used to predict seedling emergence and survival in either common garden, regardless of whether seeds were stored or not. These results indicated that it is feasible to use dry-stored seeds to evaluate and select suitable provenances in ecological restoration, and using dry-stored seeds in ecological restoration projects is expected to achieve better vegetation restoration results than fresh seeds. On the other hand, the status of seeds (fresh vs. dry stored) should be considered in an evaluation of the adaptive value of plant functional traits, especially in the early life stages, otherwise, inconsistent conclusions may be drawn. [ABSTRACT FROM AUTHOR]

Decreasing hydride-induced embrittlement of zirconium-based cladding is a significant challenge for the successful dry storage of spent nuclear fuel. Herein, to radically minimize hydride-induced embrittlement, we used nanoparticles as sacrificial agents with a greater affinity than zirconium for hydrogen. Corrosion experiments in the presence of gold (Au) and palladium (Pd) nanoparticles under simulated pressurized water reactor (PWR) conditions revealed that the hydrogen content of the zirconium samples was remarkably reduced, with a maximum decrease efficiency of 53.9% using 65 nm Au and 53.8% using 50 nm Pd nanoparticles. This approach provides an effective strategy for preventing hydride-induced embrittlement of zirconium-based cladding. [ABSTRACT FROM AUTHOR]

The paper analyzes the modern methods of storing spent nuclear fuel and its processing, taking into account the finding of fuel in spent fuel assemblies. Currently, the most common methods involve storage in containers for fuel assemblies filled with a substance that has a high thermal conductivity. Therefore, experimental methods of researching the storage properties of spent fuel assemblies in containers are promising. In the work, research was carried out in the indicated directions with the help of the created experimental stand. A description of the stand itself and the sequence of conducting the experiment are given, as a result of which the necessary experimental data should be obtained. Namely, the heating regimes in the experimental heater were determined, which are close to the real processes of heating spent fuel assemblies loaded into the container. For this purpose, a laboratory autotransformer with a capacity of 4.6 kW was used. The next task was to determine the time required for the heater to go into constant operation. For this purpose, the concept of constant time of the heating process was introduced. FLIR ONE thermal imager was used to determine this parameter, as well as devices that allowed to determine the voltage on the laboratory autotransformer. This made it possible to determine the dependence of the change in the temperature of the heater on time and voltage, as well as the voltage of the heater, which simulates real heating modes. The paper presents the thermographic results of thermal imager measurement of the main areas of the stand. Taking into account that the power of the heater should be about 1.5 kW, the stand was made airtight with pressure control and taking into account the real conditions of storage of spent fuel assemblies, where there may be damage and cracks in the container. As a result of the conducted experimental studies, the optimal heating modes of the heater were determined. [ABSTRACT FROM AUTHOR]

To justify the safety of dry storage, thermal tests of VVER-1000 fuel rods in electrically heated modules in a helium medium were carried out, realizing stationary conditions and a thermal cycling regime with different cycle times and a total test time of 427–468 days. The effect of thermal tests on the elongation of fuel rods that were used in VVER-1000 reactors for one year (fuel burnup of ~20 MW day/kg U) and for six years (burnup of ~70 MW day/kg U) was studied. Fuel rods with high fuel burnup elongated less than those with low burnup. The maximum values of elongation were registered for fuel rods with low burnup: 6.0 mm when tested under stationary conditions and 9.5 mm in the thermal cycling mode. Hoop strain of the fuel rods increased insignificantly. The presence of gas pressure under the cladding provides tensile stresses, creating conditions for the implementation of thermal creep. For fuel rods with lower fuel burnup, the gap between the fuel and the cladding was preserved along the entire height of the core (column). The main mechanism for elongation of fuel rods is the cladding thermal creep under the action of increased effective axial stresses arising from the internal fuel rod gas and the pressure of the fuel column on the spring plunger. Thermal cycling leads to a greater elongation of the fuel rods owing to a higher cladding creep rate at the unsteady-state stage in short cycles. [ABSTRACT FROM AUTHOR]

Spent fuel behavior of dry storage was simulated in a continuous state from steady-state operation by modifying FRAPCON-4.0 to incorporate spent fuel–specific fuel behavior models. Spent fuel behavior of a typical PWR was compared with that of NuScale Power Module (NPM™). Current PWR discharge burnup (60 MWd/kgU) gives a sufficient margin to the hoop stress limit of 90 MPa. Most hydrogen precipitation occurs in the first 50 years of dry storage, thereby no extra phenomenological safety factor is identified for extended dry storage up to 100 years. Regulation for spent fuel management can be significantly alleviated for LWR-based SMRs. Hydride embrittlement safety criterion is irrelevant to NuScale spent fuels; they have sufficiently lower plenum pressure and hydrogen contents compared to those of PWRs. Cladding creep out during dry storage reduces the subchannel area with burnup. The most deformed cladding outer diameter after 100 years of dry storage is found to be 9.64 mm for discharge burnup of 70 MWd/kgU. It may deteriorate heat transfer of dry storage by increasing flow resistance and decreasing the view factor of radiative heat transfer. Self-regulated by decreasing rod internal pressure with opening gap, cladding creep out closely reaches the saturated point after ∼50 years of dry storage.

Abstract: Elucidating the physiological and ecological mechanisms of seed dormancy and germination is of great significance for species conservation and the application of plant resources. Based on Baskin and Baskin’s classification system for seed dormancy, the cause of dormancy in Tarenaya hassleriana (Cleomaceae) seeds was studied using alternating temperature, cold moist stratification, dry storage, and GA3 soaking treatment. The results indicated that fresh mature T. hassleriana seeds had a combinational dormancy, including a physical dormancy and a type 2 non-deep physiological dormancy, and were photoblastic, with an optimal germination temperature of 35°C. In addition, fresh mature T. hassleriana seeds may be efficiently released from dormancy and promoted to germinate by an alternating temperature of 20 °C/30 °C, cold moist stratification, and cold moist stratification following dry storage. Furthermore, GA3 soaking treatment could also promote dormancy release and subsequent germination at 35 °C, and dry storage treatment could promote dormancy release and subsequent germination at 5-15 °C. These results also suggested that there were complex cross-talks among phytohormone, osmotic potential, and the temperature signaling regulatory pathways during dormancy release and germination of T. hassleriana seeds, which deserve further study.

One of the most important and most easily measurable physical characteristics of plant seeds is their weight, which influences and indicates crucial ecological processes. Seed weight affects spatial and temporal dispersibility, and can also influence seed predation and the germination, growth and survival of seedlings. Providing trait data for species missing from international databases is key to promote studies that advance our understanding of the functioning of plant communities and ecosystems, which is an essential issue in the face of the global climate change and biodiversity loss. Compared to species from Western and Northwestern Europe, those with an Eastern or Central European centre of distribution are underrepresented in most international trait databases. Therefore, the creation of specific trait databases is key to help regional studies. In this respect, it is important not only to collect fresh seeds for weight measurements, but also to measure and process data of seeds preserved in collections and make them available to the broader scientific community. In this data paper we provide seed weight data to fill in missing trait data of plant species of Central and Eastern Europe. Our dataset includes weight measurement for 281 taxa of the Central European flora including also some cultivated and exotic species. The seeds were collected between 1971 and 2021 mostly in Central Europe. One part of the measured seeds was collected in the last decade, the other part is from an older seed collection, but all seeds were measured recently. For each species, we collected a minimum of 3 × 100 intact seeds, if possible. The seeds were air-dried at room temperature (approximately 21 °C and 50% relative humidity) for at least two weeks and measured with an accuracy of 0.001 g using an analytical balance. The thousand-seed weights reported here were calculated based on the measured values. Our goal for the future is to incorporate the seed weight data reported here in a regional database (Pannonian Database of Plant Traits – PADAPT) that gathers plant traits and other plant characteristics for the Pannonian flora. The data presented here will facilitate trait-based analyses of the flora and vegetation of Central Europe.

The effects of hydride amount (20–850 wppm), orientation (circumferential and radial), and temperature (room temperature, 100 °C, 200 °C) on the axial mechanical properties of Zircaloy-4 cladding were comprehensively examined. The fraction of radial hydride fraction in the cladding was quantified using PROPHET, an in-house radial hydride fraction analysis code. Uniaxial tensile tests (UTTs) were conducted at various temperatures to obtain the axial mechanical properties. Hydride orientation has a limited effect on the axial mechanical behavior of hydrided Zircaloy-4 cladding. Ultimate tensile stress (UTS) and associated uniform elongation demonstrated limited sensitivity to hydride content under UTT. Statistical uncertainty of UTS was found small, supporting the deterministic approach for the load-failure analysis of hydrided Zircaloy-4 cladding. These properties notably decrease with increasing temperature in the tested range. The dependence of yield strength on hydrogen content differed from temperature to temperature. The ductility-related parameters, such as total elongation, strain energy density (SED), and offset strain decrease with increasing hydride contents. The abrupt loss of ductility in UTT was found at ∼700 wppm. Demonstrating a strong correlation between total elongation and offset strain, SED can be used as a comprehensive measure of ductility of hydrided zirconium alloy.

Two units of the Chinshan nuclear plant are in the decommissioning process. However, the fuel assemblies residing in the core cannot be discharged, and it becomes an obstacle for the future decommissioning works. Even though the utility plans to construct a building containing all the dry casks, the utility still wants to remove the fuel in the core as soon as possible. Thus, the plant staffs have planned to use the New Fuel Storage Building (NFSB) which is an existing building as a temporary storage space for 14 dry casks. Because the original purpose of the NFSB is not for the spent fuel storage, related safety analyses should be conducted. This study has used the Computational Fluid Dynamics (CFD) methodology to analyze the temperature distribution of the NFSB space filled with the dry casks. The gateway of the NFSB is the main passage for air exchange with the atmosphere. Influence of different opening types on the gateway is also investigated in this study. Based on the results, the thermal safety for the NFSB containing 14 dry casks can be ensured by passive air cooling. [ABSTRACT FROM AUTHOR]

• An integrated dry storage analysis code was developed, enabling comprehensive simulations from reactor operation to extended dry storage. • Analysis of various discharge burnup levels and wet storage periods demonstrate cladding hoop strain below 3 % and hoop stress below 90 MPa. • Decreasing heat load by extending wet storage effectively prevents cladding creep and reduces spent fuel temperature, improving safety conditions. • Discharge burnup has a significant effect on spent fuel integrity, but under current PCT limits, no identified threat to spent fuel integrity during dry storage up to 70 MWd/kgU burnup. This study introduces an integrated analysis code (GIFT/COBRA-SFS) for spent fuel analysis during dry storage. The integrated code performs dry storage simulations including dry storage cask thermal analysis and fuel analysis based on steady-state operation history. Assuming a reference assembly, dry storage cask, and identical assembly loading, integrated analyses were performed by varying discharge burnups ranging from 50 to 70 MWd/kgU and wet storage periods to ensure PCT remain below 400 °C. Within the range of discharge burnup and PCT, hoop stress remained below 90 MPa, mitigating the degradation due to hydride reorientation. Cladding hoop strain results also remained below 3 %, suggesting no failure due to creep rupture. Considering results, impact of discharge burnup and wet storage duration on spent fuel integrity was analyzed. An increase in discharge burnup results in elevated pressure and decay heat due to fission products, increasing cladding deformation and hoop stress during the dry storage of spent nuclear fuel. Reducing heat load by increasing wet storage time effectively decreases temperature and hinders creep deformation. However, fuel pellet swelling during wet storage decreases internal void volume, thereby increasing rod internal pressure. As a result, despite the temperature difference, change of hoop stress is limited with increasing wet storage time. The simulated conditions of this study confirm that there is no apparent threat to dry storage from a regulatory perspective up to discharge burnup of 70 MWd/kgU. Moreover, under the simulated discharge burnups, enhancing dry storage safety is feasible with additional months or years of wet storage, which can alleviate cladding hoop strain. [ABSTRACT FROM AUTHOR]

The effect of a humid nitrogen atmosphere with an oxygen content of 0.08, 0.48, 1.30 vol % and a temperature of 300°С on the change in the structure of the RBMK-1000 fuel composition vs. the size of the defect in the fuel cladding was investigated. It was demonstrated that in the case of fuel cladding damage with an area of more than 0.8 mm2, SNF storage in a nitrogen atmosphere with an oxygen content of more than 0.5 vol % at a temperature of 300°C brings about a rather rapid oxidation of the fuel composition to U3O8. Thus, dry storage of SNF should be carried out without access to oxygen. [ABSTRACT FROM AUTHOR]

This article presents the experimental results of mechanical properties of fuel rod claddings from E110 zirconium alloy in the longitudinal direction that operated in fuel assemblies of VVER-1000 nuclear reactors to the fuel burnup of ~20 and ~70 MW d/kg U before and after post-radiation annealing at 380°C for 468 days. The changes in strength and plastic properties of the cladding in longitudinal direction were analyzed in comparison with its properties before and after irradiation and with their changes in the transverse direction. The changes in mechanical properties of the cladding are explained as a function of radiation damage of its structure. [ABSTRACT FROM AUTHOR]

Hydride reorientation, which occurs under hoop stress during cooling, stands out as a primary mechanism for material degradation in spent fuel management. The radial hydride fraction (RHF) is strongly involved in the mechanical integrity of cladding, highlighting the necessity for a robust modeling framework for quantitative analysis. However, the predictability of previous thermodynamic models for hydride reorientation in reactor-grade Cold Worked Stress Relieved (CWSR) Zircaloy has been hindered due to the intricate nature of hydride reorientation and the difficulties in characterizing microstructures. Recent successful EBSD characterization of reactor-grade CWSR Zircaloy has revealed valuable insights into microstructural characteristics of hydrides, enabling advancements in the modeling framework of hydride reorientation. This study aims to develop a thermodynamic model specifically focused on predicting the RHF. The developed thermodynamic model, based on classical nucleation theory, integrates aforementioned microstructural findings, combined with the Hydride-Nucleation-Growth-Dissolution (HNGD) model to capture transient precipitation behavior during cooling. Extensive experimental validations demonstrate enhanced predictability of the model. Additionally, the study examines the sensitivities of hydride reorientation to hydrogen concentration, applied stress, and cooling rate. It also provides predictions on reorientation behavior for engineering implications such as extension of wet storage, matrix hardening, recrystallization, and thermal cycling, supported by plausible explanations rooted in the underlying physical mechanisms elucidated through the model. [ABSTRACT FROM AUTHOR]

Spent nuclear fuel (SNF) assemblies (FAs), composed of bundled radioactive fuel rods, are stored in stainless-steel canisters as an interim dry storage option until permanent storage solutions are available. Accidental damage to these canisters may occur during handling or transportation events. If such events occur, it is necessary to assess the integrity of FAs before long-term storage. Since the canisters are sealed shut and can only be opened in special handling facilities, non-destructive evaluation (NDE) is critical for detecting the FAs from the canister's exterior surface. In this study, two multi-task machine learning (ML) classifiers, a k -nearest neighbors (k -NN) and a convolutional neural network (CNN), are developed to simultaneously detect and localize internal FA damage. The classifiers were trained and tested on a dataset collected via experimental modal analysis on a 2/3-scale mock-up canister. The canister was excited from the bottom plate while accelerometers were also attached on the bottom plate at arbitrary locations to record the structural response. The differences in frequency response functions (FRFs) between an intact fully loaded canister basket (FLCB) system and the canister with simulated internal damage were calculated and used as input to the ML models. Results showed that both classifiers achieved high accuracy on the testing set. The k -NN classifier produced macro-F1 scores of 1.00 for the damage detection task and 0.996 for the localization task. The macro-F1 scores of the CNN were 0.991 for damage detection and 0.964 for damage localization. Additionally, dropout layers were added to the fully connected layers of the CNN to introduce model uncertainty. By testing the model 1,000 times, probability density functions (PDFs) were generated, and it was confirmed that the CNN produced confident predictions in both the damage detection and localization tasks. This multi-task ML method contributes to advancing NDE of SNF canisters and holds potential for field applications in inspecting actual SNF canisters. [ABSTRACT FROM AUTHOR]

Dry storage systems are one of the storage methods for spent nuclear fuel used in many countries that operate nuclear power plants. To ensure the safe storage of spent nuclear fuel, dry storage systems are designed to maintain radiation shielding, thermal management, and subcritical and mechanical integrity. In addition, these systems must be able to withstand earthquakes, tornadoes, floods, extreme temperatures, and other operating and design-based accident conditions. In order to develop a model with safety and economic feasibility by analyzing various dry storage systems, a vertically dry storage module was proposed, and evaluations were performed on safety evaluation along with design requirements. As a result of the evaluation, all of the safety design requirements were met. This evaluation's results can be used as basic data for the detailed design of the dry storage module to proceed with further research, including the preparation of a safety analysis report and experimental verification for licensing applications. [ABSTRACT FROM AUTHOR]

One of the factors capable of resulting in deconfinement of fuel element cladding upon long term storage of spent nuclear fuel (SNF) is reorientation of hydrides. This work estimates the extent of reorientation of hydrates in unirradiated gas filled specimens of fuel element claddings of VVER-1000 reactor (Zr‒1% Nb) under the conditions simulating conditions of dry storage. The specimens with the hydrogen content of 100 and 200 ppm were exposed to thermomechanical tests according to various scenarios at hoop stresses in cladding up to 100 MPa. It has been established that the extent of reorientation of hydrides and related decrease in plasticity of cladding material are insignificant. The most significant factor influencing the extent of reorientation is the level of hoop stresses. [ABSTRACT FROM AUTHOR]

Reorientation of hydrides in the course of dry storage of spent nuclear fuel is a possible mechanism for the degradation of the properties of fuel claddings made of alloy E110 (Zr–1% Nb) based on spongy zirconium in VVER reactors. To determine the degree of reorientation of hydride precipitates in fuel claddings under conditions that simulate the conditions of dry storage, a series of tests have been performed for unirradiated samples with a hydrogen content of 100 and 200 wppm at various levels of circumferential stresses up to 100 MPa for 40 days. The orientation of hydride precipitates is determined using metallographic measurements. To assess the mechanical characteristics, the ring specimens have been tested for static uniaxial tension. The hydrides are analyzed using transmission electron microscopy and X-ray diffraction analysis. It is shown that test conditions lead to partial reorientation of hydride precipitates, which contributes, in turn, to a decrease in the plasticity. [ABSTRACT FROM AUTHOR]

The present SF management concept in Lithuania envisages that spent RBMK-1500 fuel will be stored in dry storage containers for 50 years, before being disposed of in a deep geological repository. However, the risk that a deep geological repository will not be constructed at the planned time should be taken into account, and the extension of SF storage over 50 years should be considered. This paper presents a comparison of gamma and neutron dose rate distributions and variations with planned and extended storage times for cast iron and metal–concrete containers loaded with RBMK-1500 SF. All calculations were performed using the SCALE computer codes system. The modeling results show that the overall shielding properties of the CONSTOR® RBMK-1500 container containing the same neutron and gamma sources are better than those of the CASTOR® RBMK-1500 container. During an extended storage period (from 50 to 300 years), the total dose rate would decrease considerably and the dose rate due to neutrons would become dominant for both containers. [ABSTRACT FROM AUTHOR]

The timing of germination has long been recognized as a key seedling survival strategy for plants in highly variable alpine environments. Seed dormancy and germination mechanisms are important factors that determining the timing of germination. To gain an understanding of how these mechanisms help to synchronize the germination event to the beginning of the growing season in two of the most popular Primula species (P. secundiflora and P. sikkimensis) in the Hengduan Mountains, Southwest China, we explored their seed dormancy and germination characteristics in the laboratory and their soil seed bank type in the field. Germination was first tested using fresh seeds at two alternating temperatures (15/5 and 25/15°C) and five constant temperatures (5, 10, 15, 20, and 25°C) in light and dark, and again after dry after-ripening at room temperature for 6 months. Germination tests were also conducted at a range of temperatures (5–30, 25/15, and 15/5°C) in light and dark for seeds dry cold stored at 4°C for 4 years, after which they were incubated under the above-mentioned incubation conditions after different periods (4 and 8 weeks) of cold stratification. Base temperatures (Tb) and thermal times for 50% germination (θ50) were calculated. Seeds were buried at the collection site to test persistence in the soil for 5 years. Dry storage improved germination significantly, as compared with fresh seeds, suggesting after-ripening released physiological dormancy (PD); however, it was not sufficient to break dormancy. Cold stratification released PD completely after dry storage, increasing final germination, and widening the temperature range from medium to both high and low; moreover, the Tb and θ50 for germination decreased. Fresh seeds had a light requirement for germination, facilitating formation of a persistent soil seed bank. Although the requirement reduced during treatments for dormancy release or at lower alternating temperatures (15/5°C), a high proportion of viable seeds did not germinate even after 5 years of burial, showing that the seeds of these two species could cycle back to dormancy if the conditions were unfavorable during spring. In this study, fresh seeds of the two Primula species exhibited type 3 non-deep physiological dormancy and required light for germination. After dormancy release, they had a low thermal requirement for germination control, as well as rapid seed germination in spring and at/near the soil surface from the soil seed bank. Such dormancy and germination mechanisms reflect a germination strategy of these two Primula species, adapted to the same alpine environments.

The timing of germination has long been recognized as a key seedling survival strategy for plants in highly variable alpine environments. Seed dormancy and germination mechanisms are important factors that determining the timing of germination. To gain an understanding of how these mechanisms help to synchronize the germination event to the beginning of the growing season in two of the most popular Primula species (P. secundiflora and P. sikkimensis) in the Hengduan Mountains, Southwest China, we explored their seed dormancy and germination characteristics in the laboratory and their soil seed bank type in the field. Germination was first tested using fresh seeds at two alternating temperatures (15/5 and 25/15°C) and five constant temperatures (5, 10, 15, 20, and 25°C) in light and dark, and again after dry after-ripening at room temperature for 6 months. Germination tests were also conducted at a range of temperatures (5–30, 25/15, and 15/5°C) in light and dark for seeds dry cold stored at 4°C for 4 years, after which they were incubated under the above-mentioned incubation conditions after different periods (4 and 8 weeks) of cold stratification. Base temperatures (T b) and thermal times for 50% germination (θ 50) were calculated. Seeds were buried at the collection site to test persistence in the soil for 5 years. Dry storage improved germination significantly, as compared with fresh seeds, suggesting after-ripening released physiological dormancy (PD); however, it was not sufficient to break dormancy. Cold stratification released PD completely after dry storage, increasing final germination, and widening the temperature range from medium to both high and low; moreover, the T b and θ 50 for germination decreased. Fresh seeds had a light requirement for germination, facilitating formation of a persistent soil seed bank. Although the requirement reduced during treatments for dormancy release or at lower alternating temperatures (15/5°C), a high proportion of viable seeds did not germinate even after 5 years of burial, showing that the seeds of these two species could cycle back to dormancy if the conditions were unfavorable during spring. In this study, fresh seeds of the two Primula species exhibited type 3 non-deep physiological dormancy and required light for germination. After dormancy release, they had a low thermal requirement for germination control, as well as rapid seed germination in spring and at/near the soil surface from the soil seed bank. Such dormancy and germination mechanisms reflect a germination strategy of these two Primula species, adapted to the same alpine environments. [ABSTRACT FROM AUTHOR]

Cultivation of desert cyanobacteria in wastewater can lead to the optimal redistribution of regional resources and is likely to solve two global problems, i.e., wastewater pollution and desertification. However, the potential of using wastewater instead of traditional artificial culture media to cultivate sand-consolidating cyanobacteria for desert management is not well understood. This study compares undistilled and distilled wastewater with an artificial culture medium (BG110) to explore the potential of wastewater as a replacement culture medium for Scytonema javanicum. The results show that the photosynthetic activity (Fv/Fm) of S. javanicum was inhibited in the undistilled wastewater and was lower than that in distilled water and the culture medium. The lowest Chl-a concentration and the highest concentration in BG110 were found in distilled wastewater. However, there was no difference in the biomass (dry weight) between the undistilled wastewater and BG110 at the end of the experiment. After long-term dry storage of the biomass collected after cultivation, there was no difference in the photosynthetic recovery between S. javanicum cultivated in undistilled wastewater and that cultivated in BG110. Accordingly, although wastewater depressed the Chl-a content, it did not affect the biomass accumulation and subsequent photosynthetic recovery after long-term storage. The results reveal the significant potential of cultivating sand-consolidating cyanobacterium in wastewater and using this technology as a new nutrient redistribution method in human settlements and desert areas. [ABSTRACT FROM AUTHOR]