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[en] Highlights: • Neutron noise measurements for void information are simulated by Monte Carlo method. • In the simulations, circular bubbles move upward in a two-dimensional water channel. • The APSD and CCF are obtained using the time series data of the detected neutrons. • The MC simulations reproduce the theoretical structure in the APSDs. • We study APSD and CCF in a water channel where the void velocity varies horizontally. - Abstract: Neutron noise measurements for obtaining void-related information of a void-containing water flow are simulated using the time-dependent Monte Carlo technique. In the simulations, circular bubbles move upward in a two-dimensional water channel. The Auto Power Spectral Density (APSD) and the Cross-Correlation Function (CCF) of the neutrons that penetrate the channel are obtained using the time series data of the detected neutrons. If the void velocity is not exceedingly high and the length of neutron detector is not exceedingly short, the APSD shows a characteristic structure where repeated dips and peaks appear in the low frequency region (f < 100 Hz). The Monte Carlo simulations reproduce the structure in the APSDs. The void velocity can be roughly estimated using the frequencies of the dips and/or the peaks if the detector length is known. A CCF between two axially displaced detectors presents a prominent peak at the time lag that corresponds to the void transit time. Because the maximum point of the CCF can be clearly identified, the CCF is more favorable than the APSD for the purposes of determining the void velocity. The properties of the APSD and the CCF are discussed for a water channel for which the void velocity varies in the horizontal direction.
[en] Highlights: • This paper reviews the evolution of the use of probabilistic risk assessment in the U.S. regulations. - Abstract: This paper provides historical perspectives and insights on the early development of the U.S. nuclear regulatory process and its subsequent evolution towards risk-informed processes. After the landmark Reactor Safety Study (WASH-1400) and the TMI-2 accident, the U.S. Nuclear Regulatory Commission (NRC) began to use probabilistic risk assessment (PRA) methods and insights in regulatory applications as deemed necessary or useful. In 1995, the NRC adopted a policy that promotes increasing the use of probabilistic risk analysis in all regulatory matters to the extent supported by the state of the art to complement the deterministic approach. The NRC then started moving toward a much expanded use of PRAs in what is termed risk-informed regulatory approach. This paper discusses the challenges and the success stories of the use of probabilistic assessment of the risk to support and inform regulatory decisions.
[en] Highlights: • The developed model accurately calculates selected economic and ecological effects of manure transports. • The model is applicable for biogas plant operators with their individual data. • The transport of dry poultry manure can still be financially beneficial for up to 700 km or more. • Manure transports have great potential for reducing emissions. - Abstract: In regions with high livestock density, manure supply often exceeds demand and complete local deployment would lead to severe environmental damage due to over-nutrification. One solution is to use the surplus in other regions, which have lower nutrient-levels. To decrease costs associated with transport the manure can first be used in biogas plants of those regions. To date, however, the economic and ecological consequences of this solution are unclear. Here, we develop a model of the consequences from the perspective of a biogas plant owner and apply it to a case study in Lower-Saxony, Germany. The model determines the maximal profitable manure transport distance from a financial point of view. Furthermore, it examines selected environmental impacts for various scenarios with an assumed transport range of 150 km, a typical distance. For dry poultry manure transport distances up to 700 km and more can be financially advantageous. Emission reductions occurred in all scenarios in the impact categories Greenhouse Gas and Acidification. The model can support decision-makers in the livestock and biogas industries in determining whether to transport manure and, if so, how far.
[en] Highlights: • Microalgal diversity decreased with crust development and succession. • Part of cultivated microalgae still could not be reflected by the pyrosequencing. • Crust unicellular green algae grew faster than the filamentous cyanobacteria. • The lipid productivity of two crust green algae could reach 75 mg L-1 d-1. • Two crust cyanobacteria could be used to construct artificial biocrusts. - Abstract: With the continuing consumption of resources and increasingly prominent environmental issues, microalgal resource utilization has received extensive attention. In this study, based on the microalgal investigation in desert biological soil crusts (BSCs) using pyrosequencing technology, the cultivated crust microalgae were further isolated in order to obtain high quality microalgae for resource utilization. The results showed that with crust development and succession, microalgal diversity gradually decreased, including the number of operational taxonomic units (OTUs) and genus, although Microcoleus always was the dominant genera. Pyrosequencing obtained 630 OTUs of cyanobacteria, 25 OTUs of green algae and 9 OTUs of diatom; however, part of cultivated microalgae still could not yet be detected due to the DNA extraction preferences and errors caused by PCR amplification. After isolation, four strains were purified and cultivated, including two filamentous cyanobacteria Microcoleus vaginatus BSC-06 and Scytonema javanicum BSC-39, and two unicellular green algae Chlorella sp. BSC-24 and Monoraphidium dybowskii BSC-81. The two green algae grew fast (>250 mg L-1 d-1), and achieved high lipid productivity up to 75–85 mg L-1 d-1, with lipid content of 28.7–39.0%, thus was considered as promising feedstock for biodiesel production. In addition, the two crust cyanobacteria could be used to construct artificial cyanobacterial soil crusts in desertification control, although their biomass accumulation was not as high as that in the green algae. Ultimately, combining biodiesel production with desertification control would not only improve desert environments, but also provide ideal places for the local microalgal resource exploitation, further promoting desert socioeconomic development.
[en] Highlights: • The reference stress (RS) solutions for plates with embedded elliptical cracks are derived. • The RS solution conservatism due to assuming rectangular cracks are discussed. • The J solutions for the plates are proposed via the reference stress J scheme. • The FE J can be well predicted by the RS solutions under small loads values. • Ignoring side surface stress may result in non-conservative or conservative J evaluation. - Abstract: The reference stress solutions for plates with embedded off-set elliptical cracks under combined biaxial forces and cross-thickness bending are derived based on the Mises yield criterion and net-section collapse principle. The newly developed reference stress solutions are compared with the reference stresses of plates with embedded rectangular cracks evaluated using the available limit load solutions. The developed reference stress solutions have been used to predict J via the reference stress J scheme. Elastic-plastic 3-D finite element (FE) analyses are used to calculate J values along the crack front and the results are compared with the reference stress predictions. The results show that the estimated J values based on the reference stress method with the reference stress solutions developed in this paper are very close to the FE J values, but the predictions may be non-conservative. However, the non-conservatism could be removed by simply applying a constant factor less than 1 to the reference stress solutions when they are used in the reference stress J scheme.
[en] Highlights: • The receptance method can easily deal with the dynamic response of real complex piping systems at various fluid velocities. • The presented method has the advantage of simulating arbitrary supports to pipe systems. • For the same pipe element, the cut-off frequency based on the receptance method is higher than that based on theFEM. - Abstract: In this paper, a new set of six-variable linear partial differential equations of motion of fluid-conveying pipes with general boundary conditions are derived using the Hamilton principle and these equations are solved by the receptance method. The frequencies of the straight pipes conveying fluid with or without elastic supports are determined and the results are compared with experimental ones. Then a fluid-conveying, semi-circular pipe and complex piping system with different kinds of boundary conditions are studied. These pipes are divided into some straight pipe units and are assembled using the receptance method. The numerical results show that the receptance method is efficient for pipes with arbitrary geometrical layouts and support types, and once the dynamic receptance of the elastic support of a piping system is obtained via experiment, its dynamic stability at different fluid velocities can be analysed by the receptance method.
[en] Highlights: • Resolved LESs of turbulent conjugate heat transfer in porous media are carried out. • Three different kinds of porous structures are considered. • Several models for turbulent and dispersion heat fluxes are evaluated by LES data. • Higher order generalized gradient diffusion model of heat flux is most promising. - Abstract: Resolved large eddy simulations (LESs) of turbulent conjugate heat transfer in porous media are performed by the lattice Boltzmann method (LBM) for modelling turbulent and dispersion heat flux terms of the double-averaged energy equation. The considered porous structures are square rod arrays, staggered cube arrays and body centred cubic foam. In the LBM, the double-distribution function method which solves the distribution functions for the velocity and the internal energy is used. For the velocity and thermal fields, the D3Q27 multiple-relaxation-time method and the regularized D3Q19 single-relaxation-time method are applied, respectively. A priori tests using the LES data suggest that the trends of the sum of the dispersion and volume-averaged turbulent heat fluxes can be well captured by the second order gradient diffusion model.
[en] Highlights: • Significant improvement of turbine rim sealing flow prediction by LES. • Mechanisms of inherent unsteady flow structures in rim sealing flows. • Clockwise vortex of mean flow within the rim gap, which is in contrast with the flow field observed in the classic rotor-stator cavity model. • Establish and validate analysis strategy to investigate unsteady flow structure characteristics. • Possible evidence of Taylor–Couette instabilities in rim seal flows. - Abstract: Unsteady flow phenomena unrelated to the main gas-path blading have been identified in a number of turbine rim seal investigations. This unsteadiness has significant influence on the sealing effectiveness predicted by the conventional steady RANS (Reynolds-averaged Navier–Stokes) method, thus it is important for turbine stage design and optimisation. This paper presents CFD (computational fluid dynamics) modelling of a chute type rim seal that has been previously experimentally investigated. The study focuses on inherent large-scale unsteadiness rather than that imposed by vanes and blades or external flow. A large-eddy simulation (LES) solver is validated for a pipe flow test case and then applied to the chute rim seal rotor/stator cavity. LES, RANS and unsteady RANS (URANS) models all showed reasonable agreement with steady measurements within the disc cavity, but only the LES shows unsteadiness at a similar distinct peak frequency to that found in the experiment, at 23 times the rotational frequency. The boundary layer profile within the chute rim seal clearance has been scrutinised, which may explain the improvement of LES over RANS predictions for the pressure drop across the seal. LES results show a clockwise mean flow vortex. A more detailed sketch of the rim sealing flow unsteady flow structures is established with the help of the LES results. However, there are some significant differences between unsteadiness predicted and the measurements, and possible causes of these are discussed.
[en] Highlights: • The shear layer reattachment length xR, shear layer transition length xTr, and bubble width W all shrink significantly with ReD for ReD 4. • The xR and W both are large for the blunt cylinder and small for the hemispherical cylinder. • Following xR, W and xTr, both time-mean pressure coefficient (Cp) and fluctuating (rms) pressure coefficient Cp′ in the bubble are highly sensitive to ReD for ReD 4, but less so for ReD > 104. • Magnitudes of Cp and Cp′ are large near the separation and around the reattachment, respectively. - Abstract: Experiments were conducted to study the characteristics of the leading edge separation bubble on an axial cylinder with different nose shapes at different angles of attack and Reynolds numbers. The blunt, conical and hemispherical cylinder noses were examined. The angle of attack α and Reynolds number ReD, based on cylinder diameter D, were varied from 0° (axial) to 3.5° and from 1.5 × 103 to 4.2 × 104, respectively. The time-mean pressure coefficient (Cp) and fluctuating (rms) pressure coefficient Cp′ were measured on the cylinder surface at x/D = 0.15, 1.0 and 2.5. The shear layer reattachment length xR, shear layer transition length xTr, and bubble height W were determined by particle image velocimetry (PIV) and flow visualization techniques. The xR, xTr, and W all shrink substantially with increasing ReD upto ReD = 104. For ReD > 104, variations in xR and W are insignificant but xTr keeps shrinking. At a given ReD, xR and W retreat progressively from the blunt nose to the conical and then to the hemispherical; meanwhile, xTr is prolonged. Following xR, W and xTr, both time-mean pressure coefficient (Cp) and fluctuating (rms) pressure coefficient Cp′ in the bubble are highly sensitive to ReD for ReD 4, but less so for ReD > 104. The magnitude of Cp is large near the separation and much smaller around and behind the reattachment. On the other hand, Cp′ is small near the separation but large around the reattachment. In the case of the hemispherical nose, the Cp magnitude is smallest of all. The Cp′ is highest for the blunt nose but lowest for the hemispherical. An increase in α leads to an elongation of xR and W and a reduction of xTr for all three noses.
[en] The effective Radiation Protection Programme (RPP) for Nuclear Power Plant (NPP) is a crucial factor for protecting workers, public, and the environment against the radiological hazards a raised during the lifetime of the nuclear power plant. In this research an Operational Radiation Protection Programme (ORPP) has been designed based on the regulations and the requirements of the Sudanese Nuclear and Radiological Regulatory Authority (SNRRA) as well as on the requirements and the radiation safety guides of the International Atomic Energy Agency (IAEA), The designed ORPP covered the areas of; Assignment of responsibilities, Classification of working areas, Local rules and supervision of work, Protective clothing and personal protective equipment, Facilities, shielding and equipment, Removal or reduction in intensity of sources of radiation, Work planning and work permit, Monitoring and dose assessment, Health surveillance, Release Consequence Assessment, Emergency planning and response, Information and Training, Quality assurance, Audits and review . The designed ORPP was compared with the requirements of a number of international and regional regulatory bodies as well as with those of the operational radiation protection programme for the research reactor at the reactor center of National Nuclear Research Institute (NNRI) of the Ghana Atomic Energy Commission, to ensure the effectiveness of the designed ORPP. The Pressurized Water Reactor (PWR) manufactured by Wasting House is considered to be the type of the reference NPP upon which the ORPP is designed. (Author)