1- Introduction

2- Stochastic inflation with large N

3- Example model

4- Discussion and conclusions

References

Abstract

We propose a class of single-field, slow-roll inflation models in which a typical number of e-folds can be extremely large. The key point is to introduce a very shallow local minimum near the top of the potential in a hilltop inflation model. In particular, a typical number of e-folds is enhanced if classical behavior dominates around the local minimum such that the inflaton probability distribution is drifted to the local minimum as a whole. After the inflaton escapes from the local minimum due to the stochastic dynamics, the ordinary slow-roll inflation follows and it can generate the primordial density perturbation consistent with observation. Interestingly, our scenario inherits the advantages of the old and new inflation: the typical e-folds can be extremely large as in the old inflation, and slow-roll inflation naturally follows after the stochastic regime as in the new inflation. In our numerical example, the typical number of e-folds can be as large as 101010 , which is large enough for various light scalars such the QCD axion to reach the Bunch-Davies distribution.

Introduction

How long can inflation last? From the observational point of view, the total number of e-folds, N, must be larger than ∼ 50–60, which weakly depends on the inflation scale and thermal history after inflation. On the other hand, an extremely long duration of inflation is often required in certain scenarios. For instance, the relaxation model [1], the stochastic axion scenario [2–5], a quintessence model [6,7] demand the e-folding number of log10 N ∼ O(10), depending on model parameters.1 The purpose of this Letter is to provide a simple single-field, slow-roll inflation model whose typical number of e-folds is extremely large. There is a variety of inflation models which last very long. In the string/axion landscape [10–17], there are many local minima where the old inflation takes place and continues until the inflaton tunnels toward one of the adjacent local minima with a lower energy through bubble formation. In this case, the typical e-folding number can be exponentially large. However, one needs slow-roll inflation after the bubble formation to explain the observed cosmic microwave background (CMB) temperature/polarization anisotropies. For this, one may need another light scalar, in which case the two inflation scales are not related to each other, in general.

1- Introduction

2- Theory and proposed scheme

3- Result and discussion

4- Conclusion

References

Abstract

This paper reveals an analytical perception of electro-optically tunable cascaded Kerr-lens using RbTiOPO4 (RTP) crystal where the advantageous properties of the crystal have been studied to mitigate the limitations of KTiOPO4 (KTP) and BaB2O4 (BBO) in intracavity high power laser generation. An external electric field application to the z-direction of RTP is introducing a phase mismatch condition leading to a nonlinear phase shift within propagating optical waves. Based on simulated endeavors, a maximum effective nonlinear refractive index of ± 1.4053 × 10−13 cm2 /W is calculated by developing a phase shift of ∓4.6 rad. In contrast, KTP and RTP both have almost similar optical properties but due to certain special features like higher damage threshold, less walk-off angle etc., RTP is firmly accepted for high power applications. Additionally, this article is augmented to analyze the self-focusing and defocusing phenomenon owing to the nonuniform distribution of radial intensity of the propagating Gaussian beam. To the best of author’s knowledge, the present analysis manifests the superior performance of RTP that may pave the way to devise a configurable lens analogous to Kerr-lens having an electro-optically tunable focal length.

Introduction

In the past several decades [1–5], cascaded second-order nonlinearity has played a vital role in the generation of cascaded Kerr lens mode-locking [6] that is nothing but a successive combination of two second harmonic generation (SHG) processes (χ(2):χ(2) development) that yields an intensity-dependent large phase mismatch in propagating fundamental waves. Accordingly, the nonlinear phase shift because of the non phasematched condition is also relative to the intensity of the incident beam that is analogous to Kerr medium (χ(3) nonlinearity) [6,7]. Moreover, the performance of this feature may enlarge the third-order nonlinearity of a medium having weak third-order coefficient [8] which is grander than the natural third-order nonlinearity [5] associated with the Kerr electro-optic effect as well. As a consequence of that, cascaded second-order nonlinearity equivalent to third-order nonlinearity [2] plays a significant role in several areas like transistor action [9], electro-optical detection [10], electro-optic switching [11], selffocusing and self-defocusing [9] etc. [12–15]. Although different techniques are emphasized to develop cascaded second-order nonlinearity using various types of crystals where problems like undesirable cavity loss, inaccuracy of incident beam angle, etc [5,16]. have occurred that deters a controllable desired output. In recent years [17,18], an analytical method has been introduced named “electro-optically tunable cascaded nonlinearity” in an exceedingly bulk anisotropic crystals like Potassium Titanyl Phosphate (KTiOPO4, KTP) and Beta Barium Borate (BaB2O4, BBO), etc.

7-1- Non-Power Applications

7-2- Scientific Applications

7-3- Medical and Biological Applications

7-4- Industrial Applications

7-5- Food Processing and Agriculture

References

Abstract

Non-power applications of nuclear energy are briefly reviewed. Scientific applications are noted such as dating geological formations, minerals and historical artefacts, and radionuclide labelling to study biological, chemical and physical processes. Medical applications are considered with unsealed and sealed sources of radiation used both in therapy and diagnosis. Utilisation of nuclear energy is described in various industrial applications and food processing.

NON-POWER APPLICATIONS

Nuclear energy is an important source of CO2-free baseload electricity providing an excellent alliance with renewables which need underpinning baseload for when the wind does not blow or the sun shine. However, nuclear applications are not just limited to power generation. The nonpower uses of nuclear energy include many useful applications in science, medicine, industry, food preservation and agriculture. Applications use either radiations such as in accelerators and gamma irradiators or a combination of chemical properties and radiations emitted by radionuclides such as in radioactive tracers and radiopharmaceuticals (Tsoulfanidis, 2018). During the use of nuclear energy radioactive waste can be generated, which must be managed with particular care owing to its inherent radiological, biological, chemical and physical hazards. Producers and users of radioactive materials must be sure that a waste management strategy exists prior to the start of waste generation (IAEA, 2017a).

Introduction

Experimental

Results and discussion

Conclusion

References

Abstract

There are proliferation issues with the Plutonium Uranium Redox Extraction process due to the possibility of recovering plutonium. The objective of this research was to evaluate diferent organic extraction ligands that can remove uranium from the nuclear waste and to determine the most efective organic solvent for extracting uranium only, from alkaline media. The results indicate that Alamine 336 in xylene has zero (0%) extraction capability for surrogate fssion products at an optimum extraction time of 15 min. Aliquat 336 in xylene has an extraction percentage of 72% for uranium in 60 min. However, Aliquat 336 in toluene extracted 82% of the uranium from the feed solution after 30 min, decreasing to 76% after 60 min.

Introduction

A large amount of uranium in the environment is caused by human activities such as mining and milling of other minerals and also from operations of reactors, reprocessing of spent nuclear fuel (SNF) and its disposal [1, 2]. It is also of great commercial interest due to its application in the nuclear industry especially in the use and development of new radiopharmaceuticals and radioisotopes [3]. The uranium waste contains insoluble precipitates formed when the target plates uranium–aluminum alloy are dissolved during the production of Mo-99 [4]. The remaining insoluble residue contains about 90% of enriched uranium that is present in the mixture of various oxidation states. A process of ammonium carbonate-based dissolution has been developed for uranium recovery from the waste generated by an alkaline dissolution process used for the production of the medical isotope Mo-99 [5]. Uranium recovery from residue was achieved with three successive ammonium carbonate–peroxide leaches with fnal decontamination factors from low values of 1–10 Cs-137, Ru-106, and Sb-125 to infnity.

1- Introduction

2- Quantum mechanics on (anti)-de Sitter spaces

3- Free particle

4- Harmonic oscillator

5- Pseudoharmonic oscillator

6- Conclusion

References

Abstract

All commutation relations are modified in (anti)-de Sitter background and the Heisenberg uncertainty principle is changed to the so-called extended uncertainty principle (EUP). In this scenario, the commutators between position and momentum operators are functions of the position space variables, instead of a constant and the coordinate representation of the momentum operators for this model becomes coordinate dependent. In the AdS space, a lower bound on momentum uncertainty arises, which is not present in the dS space. In this paper, we present an exact solution of the D-dimensional free particle, the harmonic oscillator and pseudoharmonic oscillator in AdS and dS spaces. The eigenfunctions are determined for both cases and the energy eigenvalues are obtained.

Introduction

The idea of noncommutative spacetime is quite old. It has been incorporated in quantum fields by Snyder [1, 2] in order to regularize the divergences in quantum field theories. Snyder model admits a fundamental length scale and it is invariant under the Lorentz group action. However, this idea was largely forgotten due to the remarkable success of the renormalization theory in quantum electrodynamics. After the work of Kontsevich [3], Snyder model has attracted great attention. Modern candidates for a theory of quantum gravity and string theory suggests that the structure of spacetime may be noncommutative at scales close to the Planck length.

1- Introduction

2- Data acquisition and control system

3- Capabilities

4- Conclusion

References

Abstract

The application possibilities of the nuclear microprobe are constantly evolving which places new requirements on the data acquisition and microbeam control systems. MeV SIMS experiments for example, require the ability to pulse a continuous beam and steer it in the X-Y plane. For channeling RBS and STIM experiments, the sample needs to be rotated over two axes. Once it is positioned in the channeling direction, patterned irradiation may be needed. Additionally, with the evolution of digital electronics, it is now possible and sometimes preferred to perform signal processing in the digital domain as oppose to analogue signal chains in NIM modules.
In this work we present the most recent upgrades to the data acquisition and control system developed at Rudjer Boskovic Institute. A data acquisition/control system based on a Xilinx Virtex 6 FPGA was developed which can evolve with the microprobe and be reconfigured for various applications. The real time reprogrammable nature of the FPGA coupled with a modular design approach, allow for the ADCs, processing algorithms and communication protocols to be interchanged and upgraded while keeping a constant user interface through the SPECTOR software package.

Introduction

The modern nuclear microprobe is a very flexible platform on which a wide variety of experiments can be performed. To maintain this degree of flexibility, the data acquisition and control system has to be able to interconnect and synchronize the many different subsystems that make up a nuclear microprobe. Not every experiment performed on the microprobe is the same and therefore beam modification requirements, sample positioning and even the type of data acquisition varies. The standard solution is to use nuclear instrumentation modules (NIM) and manually connect only the modules that are required for the experiment. NIMs are the foundation of the nuclear data acquisition and control industry because they provide a flexible, reconfigurable, easy to use platform which can be adapted and used for a wide variety of experiments. However experiments today have become very complex and require precise control of many parameters. This in turn requires many interconnected modules, which limits the performance, increases complexity and introduces noise. Digital Field Programmable Gate Array (FPGA) technology has evolved significantly and can be used in conjunction with NIM for modern experiments. FPGA technology has been readily used for DAQ systems and many commercial solutions exist as described by Bettiol et al. [1]. However no ideal solution exists and there is always a balance between the complexity of the DAQ system and its usability. This paper builds upon the work of M. Bogovac et al. [2] by adapting more of a modular design philosophy and removing limitation of a closed system. The reprogrammable nature of FPGAs make it a versatile tool for a wide variety of applications and to fully take advantage of this, the hardware and software surrounding the FPGA has to be designed with this in mind. The implementation of this design philosophy to the upgrade of the data acquisition and control system for the nuclear microprobe and developments to the SPECTOR software package [3] are presented.

1- Introduction

2- Experimental

3- Model development

4- Results and discussion

5- Conclusion

References

Abstract

The effect of viscosity on heat transfer behaviour is analyzed for binary mixtures (ionic liquid + water and nanofluid + water) over the base fluid (water). Viscosities of 1-butyl-3-methylimidazolium bromide with water under ambient pressure are studied at different concentrations (0.1–0.6% w/w) and temperatures (296–336 K). Viscosities of nanofluid (γ-Al2O3/water) are estimated at the same concentration and temperature range and then compared with the ionic liquid solution. Viscosity of aqueous 1-butyl-3-methylimidazolium bromide solution increases with concentration and decreases with temperature. A similar trend is observed for γ-Al2O3/water. In addition, a model is developed with response surface methodology and artificial neural network to predict the viscosity of 1-butyl-3-methylimidazolium bromide with water.

Introduction

Viscosity is a property which describes the internal friction of a moving fluid. It is an important thermophysical property in fluid flow and heat transfer. In many fluid flow problems, viscosity is assumed to be a constant parameter. However, viscosity varies with temperature when the flow is associated with transfer of heat. To accurately model the flow behaviour and estimate heat transfer rates, it is essential to consider the variation of viscosity with temperature [1,2]. When compared with other thermophysical properties viscosity demonstrates a considerable variation. Hence it becomes necessary to incorporate the correction in the fluid flow model based on the behaviour of fluid with respect to temperature-dependent viscosity [3]. The variation in temperature-dependent viscosity plays a major role in laminar heat transfer and friction factor for non-circular conduits or ducts of different geometries [3–5]. It has been shown that the variation in temperaturedependent viscosity in a curved circular tube with water as a working fluid, plays a relatively major role on velocity and thermal profiles, compared to other thermophysical properties like specific heat, thermal conductivity and density [6]. In regards to viscosity variation, it results in a larger local Nusselt number when compared with that obtained from using constant viscosity [3,7]. The use of constant viscosity ignores the effect of decreased flow resistance leading to the generation of the secondary flow of fluid and its impact on convective heat transfer enhancement. Frictional losses in the fluid – the result of the microscopic interaction of molecules between layers – are governed by the viscosity of the fluid.

I- Introduction

II- Operation Principle and Sensor Design

III- Experimental Setup

IV- Results

V- Conclusions

References

Abstract

Liquid level sensing is nowadays a relevant issue in a broad range of applications, forcing the sensors performance and cost to be evaluated in parallel. This work proposes a fiber opticbased liquid level sensor system using a Fabry-Pérot interferometer (FPI) embedded into a polyurethane resin diaphragm. The FPI is based on microcavities generated upon catastrophic fuse effect, enabling the fiber recycling and sensors fabrication in a cost-effective way, compared to traditional methods. To enable the simultaneous temperature control, a Fiber Bragg Grating was used as thermal reference sensor to compensate the temperature cross-sensitivity. The sensor prototype was tested in a field application, using two different configurations, an open chamber configuration, where the diaphragm is in contact with the atmosphere, and a closed chamber configuration, revealing sensitivities of 4.4±0.1 pm/mm and 1.57 ± 0.04, respectively. These sensitivity values are within the figures of merit for diaphragm-based sensors recently reported.

INTRODUCTION

NOWADAYS, the monitoring of the liquid-air interface is required to infer level in a wide variety of applications such as, for instance, fuel supply systems, oil reservoirs, wastewater treatment plants [1]. Other relevant applications can be found in medical treatments, chemical processing and pharmaceutical development, demanding high resolution on liquid level detection [2]. Traditionally, liquid level sensing is mainly based on mechanic and electrical techniques, such as capacitance and radio frequency admittance [3], float type devices as magnetic floating gauge [4], ultrasonic and radar based sensing [3]. Despite that electrical-based sensors are widely employed, their applicability is limited when the sensing medium is conductive, potentially explosive and erosive [5], [6]. Optical fiber-based sensors have been considered an attractive prospect for liquid level monitoring, due to its unique advantages, such as electromagnetic immunity, electrical insulation, compatibility with remote sensing and sensor multiplexing. Moreover, these advantages render optical fiber appropriate for long term, reliable level measurements in special conditions [7]–[9]. Distinct operation principles are behind optical-based sensing, namely refractive index variation. These sensors measure the liquid level based on the immersed sensor length which lead to a specific effective surrounding refractive index and several implementation examples can be found: etched Fiber Bragg Grating (FBG) [6], etched chirped FBG [2] or long period grating (LPG) [10]. An additional technology is based on excessively tilted FBG that generates a fast and slow-axis due to its birefringence [11]. However, due to its length (102 m), these sensors are restricted to a reduced range liquid measurement.

1- Introduction

2- Vibration and sound calculation

3- Results and discussion for plates

4- Results and discussion for plate strips

5- Conclusions

References

Abstract

Rectangular plates are important components in structures such as vehicles and bridges. The noise radiated by vibrating plates is mainly determined by three factors: the mean-square vibration, the radiation efficiency of the plates and the directivity of the sound. Although the first two factors have been widely investigated, much less attention has been paid to the directivity. The aim of this study is to investigate the directivity indices for rectangular plates subjected to either a single point force or multiple incoherent forces. Particular attention is given to plates with a large aspect ratio, referred to as plate strips. New definitions of directivity index are introduced that are more appropriate to such plate strips. The vibration of the plates is calculated from a modal superposition method based on approximate modal solutions of the plates with various boundary conditions. The Rayleigh integral method is used to obtain the sound pressure radiated from the vibrating plates, assuming that they are set in an ideal infinite baffle. Directivity indices of sound are firstly determined for plates with a small aspect ratio, and then for plate strips with a larger aspect ratio. Examples are given to illustrate the effects of the structural boundary conditions, and the effect of the baffle. For distributed incoherent excitation, as often found in practice, it is shown that the sound directivity pattern in the far field corresponding to the width direction varies insignificantly along the length of the strips; this is different from a single point force excitation. It is also found that the noise radiation from different concrete plates is approximately omnidirectional in the plane perpendicular to the longitudinal direction. Plates and plate strips are much less directional at high frequencies than the corresponding rigid piston. Nevertheless, the maximum value of directivity increases at high frequency as the number of modes in a one-third octave band increases. The dominant directions of sound radiation from plates are mainly controlled by the acoustical wavelength and vibrational wavelength, while the structural boundary conditions and the presence of the baffle have only a minor influence on them. Finally it is shown that, for the prediction of sound directivity of plate strips under distributed incoherent excitation, a two-dimensional vibro-acoustic model can be used in place of the three-dimensional one.

Introduction

Plates with different sizes and aspect ratios are widely used as important structural components in vehicles, airplanes, industrial machinery, buildings and bridges. They are also important components in the radiation of noise when the structures are subjected to dynamic loading. For the purpose of predicting and mitigating noise from complex structures, it is helpful to understand the sound radiation from vibrating plates; particularly common are those with rectangular shape. Two important factors that influence the radiated sound power of a vibrating plate are the spatiallyaveraged vibration velocity and the radiation efficiency of the plate. In addition, the sound directivity also plays an important role in determining the distribution of sound pressure for external radiation problems. The radiation efficiency of a rectangular plate has been extensively studied, both for individual modes of vibration and for broadband excitation. Wallace [1] derived the modal radiation efficiency of simply-supported rectangular plates set in an infinite rigid baffle, based on the far-field acoustic intensity on a hemisphere of large radius. Gomperts [2,3] studied the modal radiation efficiency of rectangular plates with different boundary conditions.

18-1- Atomic Magnetic Dipole Moment

18-2- Magnetization 18.3. Magnetic Induction

18-4- Potential Energy of Magnetic Dipole Moment

18-5- Larmor Precession

18-6- Quantum Theory of Diamagnetism

18-7- Paramagnetism

18-8- Hund’s Rule

18-9- Crystal Field Splitting

Suggested Reading

Abstract

The next four chapters are devoted exclusively to magnetism, a very important property of solids from the technological point of view. This chapter begins with an estimation of the atomic magnetic dipole moments responsible for the existence of magnetism in solids. The matrix representation of magnetization, magnetic susceptibility, and magnetic induction in magnetic solids has been presented. Classical and quantum theories of diamagnetism and paramagnetism have been described in reasonable detail. The magnetic susceptibility of paramagnetic solids obeys the Curie law at high temperatures. The chapter concludes with a statement of Hund’s rule, which is applied to evaluate the effective atomic magnetic moments in transition and rare-earth elements. It was noted that quenching of the orbital magnetic moment takes place due to the presence of an inhomogeneous crystal field.

ATOMIC MAGNETIC DIPOLE MOMENT

In an atom, electrons revolve around the nucleus and the nucleus contains protons and neutrons. An atom as a whole is electrically neutral, but it consists of moving charged particles that may behave as magnetic dipoles. An electron in an atom has two motions: orbital and spin. Similarly, protons and neutrons also possess orbital and spin motions inside the nucleus. Therefore, the magnetic moment of an electron has two principal contributions, which are the orbital and spin magnetic moments. There is also a third contribution to the magnetic moment arising from the spin-orbit interaction. If the spin and orbital motions are assumed to be independent of each other, then the spin-orbit contribution vanishes and the total magnetic moment of the ith electron m ! ei is the vector sum of its orbital and spin contributions, i.e.,

1- Introduction

2- The trans-log cost function model

3- Data

4- Results and discussion

5- Conclusion and policy implications

References

Abstract

This study suggests a simple economic model to analyze electricity grid that consists of different power sources. The substitutability of renewable energy for nuclear power in Korean electricity transmission network is investigated by suggested model. The monthly data from January 2006 to December 2013 reported by Electricity Power Statistics Information System (EPSIS) of Korea Power EXchange (KPX) are used. To estimate the elasticities of substitution among four power sources (i.e. coal, natural gas, nuclear power, and renewable energy), this paper uses the trans-log cost function model on which local concavity restrictions are imposed. The estimated Hicks-Allen and Morishima elasticity of substitution shows that renewable electricity and nuclear power are complementary. The results also evidenced that renewable electricity and fossil fueled thermal power generation are substitutes.

Background

Nuclear power has been a controversial issue worldwide. Specifically, there are many questions whether nuclear power plants can be continuously used in the future and, if not, whether renewable energy can substitute nuclear power. In Korea, the Moon Jae-in administration, established in 2017, is in favor of renewable energy and proposed the Korean government’s new long-term plan of electricity supply, which recommends the suspension of two nuclear power plants under construction [1]. After serious debate, the Committee for Public Debate of Sin-Gori Units No. 5$6 finally allowed continuing construction of those plants. The debate reflects Korea’s increasing fear of the risk of nuclear power since the Fukushima Daiichi accident in Japan, followed by the great earthquake in 2011 [2]. Fear of nuclear power is a global phenomenon. Global electricity generation from nuclear power plants in 2013 was less than its average between 2001 and 2010. The main driver of this decline was the shutdown of nuclear power plants in Japan, Germany, and the US [3]. The IAEA [4] reports that the rapid shutdown of nuclear power plants, beginning in the 2010s, has affected the current capacity of global nuclear power. Yet, the same report states that nuclear power still accounts for one-third of the total low carbon power generation and renewable energy cannot easily substitute nuclear power because of its intermittent characteristic. The IAEA projects that increasing global demand for electricity, especially in emerging economies, may lead to the expansion of nuclear power use, which presents a paradox concerning nuclear power [4]. Although nuclear power is inexpensive and a massive electricity supplier with low carbon emissions, simultaneously, it could bring about a fatal accident. CO2 emission from fossil fuel use is a common problem and seen as a significant cause of global climate change. In the electricity industry, however, the reduction of fossil fuel-based thermal power generation creates instability in the power supply. Nuclear power generation is a strong alternative as a substitute for thermal power generation [4]. As mentioned, however, nuclear power generation faces strong opposition as it has latent risks. Facing these two problems, CO2 emission and nuclear power’s risk, renewable energy is being discussed as an effective solution. However, as the IAEA report [4] points out, the technological and economic problems associated with renewable energy are still the basis of argument whether renewable energy is unsuitable for the base-load of the electricity system. Moreover, Madrigal and Stoft pointed out that intermittency of renewable energy such as wind power and photovoltaic affects grid stability [5].

I. Introduction

II. Statement of the Problem and its Solution

Conclusions

References

Abstract

In this article the interaction of transverse-electric (TE) and transverse-magnetic (TM) waves with space-time nonmagnetic multiperiodically modulated filling of the waveguide is considered under the assumption of small modulation indexes. TE and TM fields in the waveguide are described by the longitudinal components of magnetic and electric vectors, respectively. The wave equations for the specified components are received from Maxwell equations, which are reduced to the Mathieu-Hill equations by changing variables. The solutions of these equations in the frequency domain of “weak” interaction of signal wave with modulation wave (the Wulff-Bragg condition is not satisfied) was found with an accuracy of terms proportional to in the first degree of modulation indexes. It is shown, that TE and TM fields in the waveguide in the approximation, indicated above, consist of the sum of three space-time harmonics with different amplitudes. An analytical expression is also found for the frequency around which a “strong” interaction between the signal wave and the waveguide modulation wave can occur.

INTRODUCTION

The propagation of electromagnetic waves in periodically modulated media has been considered in many articles [1-5]. In the articles [6] and [7] were discussed the features of the propagation of electromagnetic waves in a waveguide with two-periodic modulated dielectric filling. In this article the propagation of the signal TE and TM waves in the waveguide of arbitrary cross section filled with a multiperiodically modulated in space and time filling is considered. As noted in the articles [8] and [9] multiperiodically modulated media can represent the certain interest at carrying out of researches in various fields of science and in designing various radio engineering devices.

1- Introduction

2- Methodology

3- Results and discussion

4- Conclusion

References

Abstract

This paper aims at radiation monitoring and activity inversion when radionuclides are transported in duct or a pipe. The Lagrangian trajectory model was established, and a quick numerical method was used to simulate radioactive aerosols transport and radioactive decay in a wall-bounded flow. Total 12 cases were studied in the simulation according to the particle diameter and density. The dimensionless deposition velocity has been validated by comparing with Wood’s predictions and the experienced gravitational settling velocity. The results show that turbophoresis has a significant effect on particle transport in the wall-bounded flow, leading to particles migration and concentrating near the wall or channel center. It will cause particles to move with different velocities in the streamwise direction, so that their residence times in channel will be complexly distributed. In addition, the gravity settling will enhance the disequilibrium of particle distribution. The activity losses are obtained in detail including particle deposition ratio and radioactive decay. One radionuclide with half-life 7 s was employed in simulation, and the activity error between the estimated and initial values is up to about 40%. The activity error decreases if the half-life becomes large. When the half-life is 7.5 and 0.5 times larger than the mean time spent by airflow through the channel if the gravity is considered or not respectively, the final activity error will be less than ±5% in the present simulation setup.

Introduction

The regulatory guide 1.45 published by U.S. Nuclear Regulatory Commission mentions that it is very important to continuously monitor and quantify the reactor coolant leakage for ensuring the safe operation of the facility (Regulatory guide 1.45, 2008). One of the efficient methods to consider for incorporation in the technical specifications is to monitor airborne particulate radioactivity. Some short half-lived nuclides are considered such as 19O, 16N, 13N, 18F and 3 H. During the monitoring, airborne particles are sampled and pumped in pipe lines. According to the requirements by the International Organization for Standardization (ISO), a representative sample is necessary in monitoring the activity concentrations of radioactive substances (ISO, 2889). The losses of aerosol particles in the transport lines due to particle deposition therefore needs to be determined. The depositions during particle transport in a turbulent flow include gravitational settling and sedimentations on the walls caused by Brownian diffusion, turbophoresis, thermophoresis and other factors.