Fatigue crack initiation and propagation in austenitic stainless steels for light water reactors

The determination of fatigue life of components containing defects usually takes into account crack propagation only. In a real situation, a number of cycles are often required to reach fatigue crack initiation and predictive evaluation of fatigue crack initiation phases of real defects in austenitic stainless steel welded joints are presented. Fatigue crack growth rates in wrought and cast austenitic stainless steels and associated welds are also presented. Effects of various mechanical parameters (R ratio and variable amplitude loading) of a PWR environment and of metallurgical factors (δ ferrite content and ageing in cast austenitic stainless steels) are discussed.     

Environment sensitive cracking in pressure boundary materials of light water reactors

A review of the various forms of environment sensitive cracking in pressure boundary materials of light water reactors is presented. The available methods and the most promising future possibilities of preventive maintenance to counteract the environmental degradation are evaluated. Environment sensitive cracking is considered from the metallurgical, mechanical and environmental points of view. The main emphasis is on intergranular stress corrosion cracking of austenitic stainless steels and high strength Ni-base alloys as well as on corrosion fatigue of low alloy and stainless steels. Additionally, some general ideas on how to predict, reduce, monitor or eliminate environment sensitive cracking in service are presented.     

Feasibility assessment of the alumina-forming duplex stainless steels as accident tolerant fuel cladding materials for light water reactors

Previously, the Fe-based alumina-forming duplex stainless steels (ADSSs) were developed for the application of accident tolerant fuel (ATF) cladding materials for light water reactors (LWRs). The on-going research activities focusing on the feasibility assessment of ADSS alloys for ATF cladding are summarized. A long-term corrosion behavior in simulated LWR environment and short-term corrosion resistance in steam environment at temperature range of 800°C to 1200°C were performed, and the results showed excellent corrosion resistance of ADSS alloys. The tensile properties of ADSS alloys were evaluated at room temperature to 550°C, which showed much higher strength compared with other Fe-based alloys. After accelerated thermal aging at 425°C for 1000 hours, strength of ADSS alloys was increased and the elongation was decreased. However, the elongation of aged ADSS alloys was still greater than 15% because of the presence of ductile austenite phase. Meanwhile, because of the neutron absorption by Ni, Cr, and Fe, the use of ADSS alloys as ATF cladding would have detrimental effects on the fuel cycle length. Nonetheless, it was assessed that the neutronics penalty could be readily overcome by adopting thinner fuel cladding and slightly higher fuel enrichment. Finally, the fabrication of thin-walled tube was introduced. Overall, it has been shown that ADSS alloys could be considered as candidate alloys as ATF cladding materials.     

Residual stresses in austenitic stainless steel primary coolant pipes and welds of pressurized water reactors

Surface and through thickness residual stress measurements were performed on an aged cast austenitic-ferritic stainless steel pipe and on an orbital TIG weld representative of those of primary coolant pipes in pressurized water reactors. An abrasive-jet hole drilling method and a block removal and layering method were used. Surface stresses and through thickness stress profiles are strongly dependent upon heat treatments, machining and welding operations. In the aged cast stainless steel pipe, stresses ranged between −250 and +175 MPa. On and near the orbital TIG weld, the outside surface of the weld was in tension both in the axial and hoop directions, with maximum values reaching 420 MPa in the weld. On the inside surface, the hoop stresses were compressive, reaching −300 MPa. However, the stresses in the axial direction at the root of the weld were tensile within 4 mm depth from the inside surface, locally reaching 280 MPa.     

Cracking in feedwater pipework of light water reactors: Causes and remedies

The present paper deals with cracking in ferritic pipework of light water reactor (BWR) feedwater systems whose causes are unsuitable design and manufacture and, at least occasionally, unsuitable water quality. Thus in two BWR plants in the German Federal Republic large circumferential cracks have been found in the circumferential welds in the main feedwater pipelines immediately adjacent to the reactor pressure vessel, and in a further BWR large longitudinal cracks have been found in pipe bends of the reactor water purification pipework connected to the main feedwater pipelines.The piping regions near the reactor pressure vessel feedwater nozzles represent a boundary region of varying thermodynamic states of the pressurised water. The reactor pressure vessel is heated to saturation temperature by the radioactive decay heat, and then cooler water, and sometimes (during start-up) cold water is injected into the reactor pressure vessel in order to maintain a constant water level about 2 m above the upper edge of the feedwater nozzles. In order to improve the state of knowledge regarding the stressing conditions under prevailing operating conditions, extensive strain and temperature measurements have been carried out. The results of these measurements carried out in several BWRs confirm the occurrence of rapid temperature changes in the feedwater pipework in the regions where it connects to the reactor pressure vessel, leading to varying stresses which at times reach the plastic region. These processes are triggered by special operating states such as start-up and shut-down or hot standby operation with feedwater flows smaller than 6% relative to normal operation under full load.     

An implicit numerical scheme for the simulation of three-dimensional two-phase flows in light water nuclear reactors

ABSTRACT

An implicit numerical scheme is presented for solving the two-fluid model widely used in the analysis of a gas–liquid two-phase flow in light water nuclear reactors (LWRs). The pressure equation is established by combining the momentum and mass conservation equations. The implicit calculation of each governing equation is separated into phase- and space-link steps. In the phase-link step, the interfacial momentum and heat transfers are implicitly calculated. Then the solution accounting for the convection and diffusion terms is calculated simultaneously in space. The phase- and space-link steps are repeated for convergence. The numerical scheme is implemented in CUPID, which is a multidimensional two-phase flow analysis code for LWRs, and verified against a set of conceptual two-phase flow problems which include typical thermal hydraulic phenomena in LWRs. Calculations are performed using four numerical schemes, semi-implicit ICE and SMAC schemes, an implicit scheme, and an implicit scheme with increased time step size, and the results are discussed.     

Photocatalytic membrane reactors for hydrogen production from water

Hydrogen is considered today a promising environmental friendly energy carrier for the next future, since it produces no air pollutants or greenhouse gases when it burns in air, and it possesses high energy capacity. In the last decades great attention has been devoted to hydrogen production from water splitting by photocatalysis. This technology appears very attractive thanks to the possibility to work under mild conditions producing no harmful by-products with the possibility to use renewable solar energy. Besides, it can be combined with the technology of membrane separations making the so-called photocatalytic membrane reactors (PMRs) where the chemical reaction, the recovery of the photocatalyst and the separation of products and/or intermediates simultaneously occur. In this work the basic principles of photocatalytic hydrogen generation from water splitting are reported, giving particular attention on the use of modified photocatalysts able to work under visible light irradiation. Several devices to achieve the photocatalytic hydrogen generation are presented focusing on the possibility to obtain pure hydrogen employing membrane systems and visible light irradiation. Although many efforts are still necessary to improve the performance of the process, membrane photoreactors seem to be promising for hydrogen production by overall water splitting in a cost-effective and environmentally sustainable way.     

Concentrating versus non-concentrating reactors for solar water detoxification

Solar detoxification of a pure model compound (dichloroacetic acid) as well as of real waste waters was studied. Different types of reactors, light concentrating and non-concentrating were used and their advantages and disadvantages were compared and discussed. For this purpose a dimensionless number, the photoreactor number was introduced. Also the influence of different electron accepters (hydrogen peroxide and oxygen) on the degradation process was studied, both in the model system and the real waste water system.     

Performance evaluation of Zircaloy reflector for pressurized water reactors

This paper presents detailed analyses of a pressurized water reactor with a new reflector design using zirconium metal. The optimization of the reflector design has been performed using a two‐dimensional fuel assembly reflector model. The three‐dimensional core calculation results with the optimized reflector were compared against those with the existing water reflector and iron reflector. The high scattering cross section of zirconium enhances neutron reflections from the reflector to the core, increasing the peripheral assembly powers. From the analysis based on the equilibrium core, it was noted that the cycle length can be extended, and the pin peaks can be decreased when using zirconium reflector. The analysis has been performed for the optimized power reactor 1000 core with combustion engineering type fuel assemblies using the CASMO‐4E/SIMULATE‐3 (Studsvik Scandpower, Inc., Waltham, MA, USA) code system and SERPENT (VTT Technical Research Centre of Finland, Vuorimiehentie 3, 02150 Espoo, Finland) code, with ENDF/B‐VI data. Copyright © 2015 John Wiley & Sons, Ltd.     

Solar water splitting for hydrogen production with monolithic reactors

The present work proposes the exploitation of solar energy for the dissociation of water and production of hydrogen via an integrated thermo-chemical reactor/receiver system. The basic idea is the use of multi-channelled honeycomb ceramic supports coated with active redox reagent powders, in a configuration similar to that encountered in automobile exhaust catalytic aftertreatment.Iron-oxide-based redox materials were synthesized, capable to operate under a complete redox cycle: they could take oxygen from water producing pure hydrogen at reasonably low temperatures (800 °C) and could be regenerated at temperatures below 1300 °C. Ceramic honeycombs capable of achieving temperatures in that range when heated by concentrated solar radiation were manufactured and incorporated in a dedicated solar receiver/reactor. The operating conditions of the solar reactor were optimised to achieve adjustable, uniform temperatures up to 1300 °C throughout the honeycomb, making thus feasible the operation of the complete cycle by a single solar energy converter.     

Photocatalytic reactors for treating water pollution with solar illumination. III: a simplified analysis for recirculating reactors

A solar photoreactor operated in the batch, recirculating mode is analyzed in terms of very simple observable variables such as the impinging photon flux, the incident area, the initial concentration, the flow rate, the reactor volume and a property defined as the Observed Photonic Efficiency. The proposed equipment is made of a tubular reactor, a tank, a pump and the connecting pipes. The analysis is formulated in terms of the photon input corresponding to an equivalent batch system that is derived as a new reaction coordinate for photoreactions. Employing several plausible approximations, the pollutant concentration evolution in the tank is cast in terms of very simple analytical solutions.Process photonic efficiencies are defined for the system operation and calculated with respect to the maximum achievable yield corresponding to the differential operation of the solar recirculating reactor.     

A dynamic two-dimensional heterogeneous model for water gas shift reactors

A dynamic, heterogeneous, two-dimensional model for packed-bed water gas shift reactors is presented. It can be applied to both high and low temperature shifts, and at scales ranging from industrial (for power plant applications) to small (such as automotive fuel cell applications). The model is suitable for any catalyst for which kinetic data are available, and shows excellent agreement with available experimental data for non-equilibrium conditions. The model is applied to an IGCC-TIGAS polygeneration plant to examine the dynamic behavior of the WGS units. The development of catalyst hot-spots is predicted during start-up or transition between steady states under certain conditions.     

A review on hydrogen generation,explosion, and mitigation during severe accidents in light water nuclear reactors

Progress of severe accident (SA) can be divided into core degradation and post core meltdown. An important phenomena during severe accidents is the hydrogen generation from exothermal reaction between oxidation of core components, and molten core concrete interaction (MCCI). During the severe accidents, a large amounts of hydrogen is produced, deflagrated and consequently the containment integrity is violated. Therefore, the main objectives of this study is to highlight the source of hydrogen production during SA. First, a thorough literature review and main sources of hydrogen production, hydrogen reduction systems are introduced and discussed. Based on the available results, the amount of produced hydrogen in a typical pressurized water reactor (PWR) and a boiling water reactor (BWR) are estimated to be 1000 and 4000 kg, respectively during in-vessel phase. The average rate of hydrogen production is about 1 kg/s during reflooding of a degraded core. Also, about 2000 kg hydrogen is produced during MCCI for a PWR. The lower and upper range of hydrogen required to initiate combustion is 4.1 and 74 vol percent, respectively. In this paper a review is provided of what has been done in the literature with regard to hydrogen generation in severe accidents of nuclear power plants. In addition, the review identifies the literature gaps and underlines the need of developing a systematic hydrogen management strategy. A hydrogen management strategy is proposed in order to maintain the containment integrity against the probable combustion or hydrogen explosion loads.     

Hydrogen-based membrane biofilm reactors for nitrate removal from water and wastewater

H₂-based membrane biofilm reactor (MBfR), a kind of autotrophic denitrification system, is a novel and special membrane bioreactor using hydrogen as inorganic electron donor to reduce nitrate and nitrite in water and wastewater. In this paper, the state of the art of recent research on denitrification through H₂-based MBfRs is reviewed, including theoretical fundamentals, key influencing factors, possible problems and applications. Hydrogen/nitrate counter-diffusion has been described as Dual substrates limitations. The denitrifying bacteria in H₂-based MBfR were summarized. The key factors affecting the performance of H₂-based MBfR were listed in terms of substrate concentrations, membrane materials, reactor types, biofilm management and operation conditions. The pH value, salinity, dissolved oxygen, HRT (hydraulic retention time) and carbon source have been identified as main operational conditions affecting H₂-MBfR performance. Furthermore, membrane fouling in H₂-based MBfRs was emphasized. H₂-MBfR was proved excellent in denitrification based on its high performance for groundwater, IX brine and aquaculture wastewater treatment. Several aspects may be considered in future works were proposed.     

Photocatalytic reactors for treating water pollution with solar illumination: A simplified analysis for n-steps flow reactors with recirculation

The concentration of dissolved oxygen in water, in equilibrium with atmospheric air (ca. 8 ppm at 20 °C), defines the limits of all practical oxidizing processes for removing pollutants in photocatalytic reactors. To solve this limitation, an alternative approach to that of a continuously aerated reactor is the use of a recirculating system with aeration performed after every cycle at the reactor entering stream. As defined by the nature of a single recirculating step (the need of a reactor operation at a rather low concentration range), this procedure results in a very low photonic efficiency (thus requiring a large photon collecting area and consequently increasing the capital cost). The design engineer will have to resort to a series of several reactors with recirculation. This solution may then lead to a very high Photonic Efficiency for the entire process (i.e., a reduced light harvesting area) at the price of an increase in the required capital cost (due to the larger number of reactors). This paper provides a very simple analysis and analytical expressions that can be used to estimate, for a desired degree of degradation, a trade-off solution between a high number of reactors and a very large surface area to collect the solar photons.     

蓄光型自发光材料简介及应用

蓄光型自发光材料又称为光致光超长余辉蓄光材料、非放射性蓄光材料、无电源自发光材料等。该材料主动吸蓄太阳光、灯光、紫外光、杂散光等可见光5～10分钟后,就可在黑暗中持续发光12小时以上,并可根据实际需要,使其发出红、绿、蓝、黄、紫等多种彩色光。目前,蓄光型自发光材料制品有发光涂料、油漆、发光油墨、发光釉料、发光塑料、发光橡胶、发光皮革、发光玻璃、发光陶瓷、发光装饰石、发光铝塑复合板、发光工艺品等。由于其     

Engineering high-entropy materials for electrocatalytic water splitting

The multicomponent combinations of metals in nanoscale noble metal-free high-entropy materials possess distinctive physiochemical properties, which endow them with rich accessible active sites, strong synergistic effect, and entropy-stabilization effect, enabling them to be promising for driving electrocatalytic water splitting. Herein, an interview of the progress achieved for the synthesis of noble metal-free high-entropy materials and catalytic mechanisms toward water splitting is provided. Some typical synthesis strategies have been systematically reviewed to highlight the advances in synthesizing highly efficient and noble-metal-free high-entropy catalysts. Next, the distinctive advantages of high-entropy materials for the electrochemical water splitting are also manifested to show their great promise for serving as advanced electrocatalysts. Moreover, some representative examples regarding the electrocatalytic oxygen evolution reaction, hydrogen evolution reaction, and overall water splitting based on noble-metal-free high-entropy catalysts are also discussed. In the end, future directions and new energy conversion technologies that can be enabled by the application of noble-metal-free high-entropy materials are outlined.     

Thermal-hydraulic modeling and transient analysis of pressurized water reactors

This paper examines a new dynamic moving boundary thermal-hydraulic fuel pin model (FUELPIN) for the transient analysis of a pressurized water reactor (PWR). FUELPIN is developed to accommodate the reactor core thermal-hydraulic model of the fuel pin and adjacent coolant flow channel, with detailed thermal conduction in fuel elements. Transient analyses using a known thermal-hydraulic analysis code, COBRA, and FUELPIN linked with a PWR system analysis code show that the thermal margin gains more by a transient MDNBR approach than the traditional quasi-steady methodology for a PWR. The studies of the nuclear reactor system show that moving boundary formulation is highly suitable for the transient thermal-hydraulic analysis of PWRs.