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The need to anticipate high risk of exposure following the generation of a cloud of cold and dense gas beneath a forest canopy introduces a need to examine the processes facilitating exchange with the air above the canopy. It is the concentrations in this above-canopy air that are used to initialize many dispersion models and these concentrations are lower than would be expected if no canopy were present. In the lack of direct experimental studies of trans-canopy dilution in a forested environment, results from a variety of related experiments are used here to illustrate the complexity of the problem and to derive a first-order assessment of the extent of expected dilution. The focus is on the dense gas clouds following accidents involving liquid chlorine, ammonia and carbon dioxide. It is concluded that the dilution would result in above-canopy concentrations between 2% and 50% of average sub-canopy levels, depending on site-specific circumstances. It is also concluded that the relative importance of the various contributing processes is such that detailed incorporation of them in dispersion models would constitute an unjustified complexity unless definitive experimental observations are available. Instead, the consequences of the issues now considered might best be accommodated by reducing predicted downwind concentrations by a factor of about ten with a corresponding extension of the duration of the dispersion event. [Display omitted] • Dispersion model source-term concentrations can be less than sub-canopy by a factor ≈10. • Episodic sweeps, ejections or bursts of turbulence facilitate trans-canopy exchange. • Canopy transparency and PBL influences appear to be major contributing factors. • Studies of trans-canopy exchange of gases are rare; research opportunities abound. [ABSTRACT FROM AUTHOR]

This article concerns the inverse problem of the coupled age-structured population dynamics system with discontinuous diffusion coefficients. The internal observations with two measurements are allowed to obtain the stability result for the inverse problem consisting of simultaneously retrieving two space dependent source terms in the given parabolic system. The proof of the result relies on Carleman estimates and certain energy estimates for parabolic system.

Korea Atomic Energy Research Institute has been developing a pool-type sodium-cooled fast reactor of the Prototype Gen-IV Sodium-cooled Fast Reactor (PGSFR). To assess the effectiveness of the inherent safety features of the PGSFR, the system transients during design basis accidents and design extended conditions are analyzed with MARS-LMR and the subchannel blockage events are analyzed with MATRA-LMR-FB. In addition, the in-vessel source term is calculated based on the super-safe, small, and simple reactor methodology. The results show that the PGSFR meets safety acceptance criteria with a sufficient margin during the events and keeps accidents from deteriorating into more severe accidents.

The Fukushima accident resulted in the melting of the reactor core due to loss of supply of coolant when the reactor stopped from operating conditions. The earthquake and tsunami caused loss of electricity due to the flooding that occurred in the reactor. The absence of the coolant supply after reactor shutdown resulted in heat accumulation, causing the temperature of the fuel to rise beyond its melting point. In the early stages of the accident, operator could not determine the severity of the accident and the percentage of the reactor core damaged. The available data was based on the radiation exposure in the environment that was reported by the authorities. The aim of this paper is to determine the severity of the conditions in the reactor core based on the radiation doses measured in the environment. The method is performed by backward counting based on the measuring radiation exposure and radionuclides releases source term. The calculation was performed by using the PC-COSYMA code. The results showed that the core damage fraction at Dai-ichi Unit 1 was 70%, and the resulting individual effective dose in the exclusion area is 401 mSv, while the core damage fraction at Unit 2 was 30%, and the resulting individual effective dose was 99.1 mSv, while for Unit 3, the core damage fraction was 25% for an individual effective dose of 92.2 mSv. The differences between the results of the calculation for estimation of core damage proposed in this paper with the previously reported results is probably caused by the applied model for assessment, differences in postulations and assumptions, and the incompleteness of the input data. This difference could be reduced by performing calculations and simulations for more varied assumptions and postulations.

We study the existence of solutions of the Riemann problem for a model of two-phase flows. The model has the form of a nonconservative hyperbolic system of balance laws. Based on a phase decomposition approach, we obtain all the wave curves. By developing an analytic method, we can establish a system of nonlinear algebraic equations for each solution of the Riemann problem. The system is under-determined and can be parameterized by the volume fraction in one phase. Therefore, an argument relying on the Implicit-Function Theorem leads us to the existence of solutions of the Riemann problem for the model for sufficiently large initial data. Furthermore, the structure of the Riemann solutions obtained by this method can also be obtained.

The operation of the wind turbines downstream is affected by the wake of the wind turbines upstream. Wind turbine wake flow is investigated by applying the actuator disc (AD) method. The modified k-ε turbulence model is proposed by using both the turbulent kinetic energy source term and the dissipation rate source term to improve the standard k-ε turbulence model for coordinating the generation and the dissipation of the turbulent kinetic energy. The dissipation rate parameter C4ε that obeys a parabolic distribution is used, based on theoretical analysis. The force distributed on the AD is also used instead of a constant, as used in the classical AD method. The simulation results were consistent with the measurements that correspond to different kinds of wind turbines and conditions. The nacelle and the inflow turbulence intensity have great influences on accurately simulating the wake, so it is necessary to imitate the rotor along with the nacelle and accurately measure the inflow turbulence intensity. [ABSTRACT FROM AUTHOR]

The potential 14C (carbon-14, radiocarbon) flux from disposal of 14C containing waste into air is compared with the natural 14C emanation rate from soil in order to put the 14C hazard potential from disposal of this waste in perspective with the 14C exposure from cosmogenic origin. Chemical corrosion of neutron irradiated metals, steel and Zircaloy, is bounded by diffusion of water through a thermodynamically stable metal-oxide layer and dissolution of this metal-oxide in a nuclear plant. Many countries process radioactive waste for disposal using cementitious materials, an acknowledged end-point management technique for this waste. The metal-oxides are also stable when these waste forms are embedded in cementitious materials. The 14C release rate from this Zircaloy at these alkaline and reducing conditions is comparable to the natural 14C emanation rate from soil into air. Neutron irradiated graphite and spent ion exchange resins are chemically inert and therefore other release mechanisms need to be assumed. Radiolytic corrosion is used to determine the 14C release rate from this graphite. Moreover, ion exchange—with ingressing anionic species that have a higher affinity than contained anionic 14C—is proposed as a release mechanism for these resins. [ABSTRACT FROM AUTHOR]

Long range transport of radiocaesium derived from local fallout occurred early 1950s, global fallout which occurred mainly late 1950s and early 1960s and the Fukushima accident occurred in 2011 were investigated and presented for ocean surface in the Pacific Ocean. HAM database and its update were used in this study to present whole history of radioccaesium transport in surface layer in the interested region. Since both the main local/global fallout regions and injection of radiocaesium by Fukushima accident occurred in the western North Pacific and constrain of surface current systems which governed surface transport processes were subtropical gyre and subarctic gyre, radiocaesium transport in surface water in the mid latitude was characterized as rapid eastward transport along Kuroshio and Kuroshio extension. Behaviors were similar and repeated for local/global fallout and Fukushima derived radiocaesium. A part of radiocaesium transported/deposited/injected in the mid latitude subducted into ocean interior and the radiocaesium activity concentrations were kept higher rather than those in surface water. [ABSTRACT FROM AUTHOR]

Highlights • Shallow water model with depth variable porosity and dual integral flux closure. • CPU times reduced by 300 to 3000 compared to two-dimensional shallow water models. • Apllications range from floodplain dynamics to flow over microtopography and uran flood modelling • Transient momentum dissipation model shown essential in reproducing refined flow simulations over microtopography and submerged obstacles. Abstract A two-dimensional shallow water model with depth-dependent porosity is presented. The purpose is the coarse grid simulation of shallow flows over complex topographies and geometries. Two flux closures are examined: the Integral Porosity (IP) and Dual Integral Porosity (DIP) closures. Energy losses are described using a subgrid scale model that accounts for bottom and wall friction, transient momentum dissipation and energy losses induced by obstacle submersion. A complete wave propagation property analysis is provided for the IP and DIP closures, yielding more accurate numerical stability constraints than published previously. Five computational examples are presented, including transients in compound and meandering channels, urban dambreak problems with building submersion and runoff over variable microtopography. The ability of the model to deal with subgrid-scale features is confirmed. The DIP flux is shown to be superior to the IP closure. The transient dissipation term is essential in reproducing the effect of obstacles and microtopography. Distinguishing between the building wall- and building roof-induced friction is seen to be essential. The model is validated successfully against a scale model experimental dataset for the submersion of a coastal urban area by a tsunami wave. [ABSTRACT FROM AUTHOR]

Abstract In this paper, we consider the wave equation of variable coefficients with Balakrishnan–Taylor damping, time-varying delay and source term. By establishing some Lyapunov functionals which are equivalent to the energy of the system and using the potential well method to deal with the source term, we prove a general stability result. [ABSTRACT FROM AUTHOR]

In this paper, we present high order discontinuous Galerkin methods for the Ripa model. This model maintains the steady state. To achieve the well-balanced property, we first reformulate the governing equations and propose to construct a novel source term approximation. In addition, we apply a flux modification technique to construct the numerical fluxes. Rigorous numerical analysis as well as extensive one- and two-dimensional numerical results all verify that the proposed methods are well-balanced for the steady state, keep genuinely high order accuracy in smooth regions for smooth solutions, and enjoy good resolutions for discontinuous solutions. [ABSTRACT FROM AUTHOR]

This paper is devoted to possibilities of a semi-analytical approximation of nonlinear wave equations with nonlinearities depending on the absolute value of the unknown function, which arise in different areas of physics and mechanics. The main difficulty of analysis of such equations is that the derivation of their rigorous solution is highly sophisticated, while their numerical solution requires burdensome computational costs. Using the traveling wave ansatz, we first reduce the wave equation to a nonlinear ordinary differential equation. Then, applying Frasca's method, we construct its general solution in terms of the nonlinear Green's function. For particular nonlinearities, it is shown that the first-order approximation of the Green's function solution is numerically comparable with the solution obtained by the well-known numerical method of lines. The contribution of the higher order terms is studied for a particular nonlinearity. [ABSTRACT FROM AUTHOR]

Knowledge of the mechanism of crud deposition in light water reactors is key to modeling its growth and effects. Empirical and mechanistic models of crud exist throughout the literature, yet the argument persists whether the crud source term originates more from soluble or particulate species. Here it is shown that the crud source term must be principally particulate in nature, as soluble deposition mechanisms cannot account for crud thicknesses observed in reactors. [ABSTRACT FROM AUTHOR]

In this paper, we introduce high order well-balanced discontinuous Galerkin methods for shallow water equations over non-flat bottom topography, which preserve the lake at rest steady state. To achieve the well-balanced property, we propose to construct the numerical fluxes based on the hydrostatic reconstruction idea and to be in combination with a novel source term approximation as well as a decomposition algorithm. Rigorous theoretical analysis and extensive numerical results all verify that the current methods maintain the well-balanced property. In addition, numerical results also indicate that the resulting methods enjoy the ability to accurately capture small perturbations of the lake at rest steady state and keep the genuine high order accuracy for smooth solutions. [ABSTRACT FROM AUTHOR]

Abstract: To assess and optimize vortex generators (VGs) for flow separation control, the effect of these devices should be modelled in a cost and time efficient way. Therefore, it is of interest to extend integral boundary layer models to analyse the effect of VGs on airfoil performance. In this work, the turbulent boundary layer formulation is modified using a source term approach. An additional term is added to the shear‐lag equation, to account for the increased dissipation due to streamwise vortex action in the boundary layer, forcing transition at the VG leading edge where applicable. The source term is calibrated and a semi‐empirical relation is set up and implemented in XFOIL. The modified code is capable of addressing the effect of the VG height, length, inflow angle, and chordwise position on the airfoil's aerodynamic properties. The predicted polars for airfoils with VGs show a good agreement with reference data, and the code robustness is demonstrated by assessing different airfoil families at a wide range of Reynolds numbers. [ABSTRACT FROM AUTHOR]

In this work, a study has been conducted to carry out a qualitative analysis for the evaluation of radiation exposure from SMART reactor. Since SMART reactor is large LOCA proof therefore, a small break has been considered as a Design Basis Accident (DBA) with continuous leakage of coolant. The onsite and offsite source term of different isotopes have been evaluated and compared with CHASNUPP-1 and KORI-1 NPPs. For this purpose, a kinetic model has been developed and implemented in MATLAB to carry out the simulation of onsite and offsite source term. The developed model uses ORIGEN 2.2 core inventory as a subroutine. The coolant inventory has been evaluated with 0.25% failed fuel fraction and compared with CHASNUPP-1 and KORI-1 NPPs. A contradiction from Kim and Kang (1999) work has been observed with a significant difference in core and coolant inventory calculations. Noble gases source term of SMART reactor has been found 18.90 g whereas 0.0043 g of iodine source term has been evaluated within a day with a major contribution of 131 I with 0. 0032 g. However, 5.3 g of cesium source term has been found to release from SMART reactor with a major contribution of 135 Cs, which contributes 4.40 g within a day. 140 Ba has a dominant contribution in offsite source term with 0.00409 g during SBLOCA with 1% core damage fraction. The evaluated source term of SMART reactor is four times less than KORI-1 and 1.5 times less from CHASNUPP-1 NPP under same conditions. [ABSTRACT FROM AUTHOR]

In CANDU type reactors there are two situations for irradiated fuel bundles to remain accidentally in the air. One is represented by End Fitting Failure accident when one or more fuel bundles are ejected from the channels during the fuel handling process. The second one is determined by the uncovering of fuel bundles in the Spent Fuel Pool (SFP) due to a partial or total loss of cooling followed by a progressive evaporation of the water. In both cases there is a potential for the release of radio-nuclides that is dependent on the irradiation history and the duration between unloading of the bundle from the core and the entering into the atmosphere. The paper is devoted to investigate the release in these cases. The inventory at the moment of the accidentally entering into the atmosphere is calculated by ORIGEN code. The source term into the containment, and respectively in the SFP building, is obtained by treating the fuel degradation and the release from the fuel elements by ICARE module of ASTEC code. The most important influence factors on the source term formation (such as the velocity of the ventilation, the residence time) are identified and discussed. In a realistic CANDU SFP loss of cooling accident the potential of release is reduced due to relative fuel low burnup, long residence time, and specific configuration of the storage. The uncovering of the first plane of fuel bundles needs around 15 days for the heat-up and evaporation of water. In such case, a small convection ( v  ≥ 1.E−05 m/s) is enough to keep the temperature of the claddings under the failure thresholds. The paper identifies and investigates some other cases (with violation of the operational procedures) with a relevant release of fission products. The results are presented for the Caesium element. [ABSTRACT FROM AUTHOR]

Based on kinetic model equation, a unified gas-kinetic scheme for axisymmetric flow (UGKS-AS) is proposed in the whole flow regimes. The flux transport of UGKS-AS is based on a reduced gas distribution function of a time integral solution of the full 3D BGK model. In the cylindrical coordinate system, the local time evolution of convection and source terms for the macroscopic and microscopic flow variables is fully coupled with particle free transport and collisions. As a result, a multiple scale UGKS-AS is developed and used for the flow simulation from the free molecular transport to the Navier–Stokes solutions. In comparison with the full 3D UGKS method for axisymmetric flow, the present scheme is much more efficient and gives accurate solution in all flow regimes. Different from operator splitting methods with decoupled treatment of particle transport and collision, for the Navier–Stokes solution in the continuum regime the UGKS-AS doesn't have the constraint on the time step being less than the particle collision time. To further improve the efficiency of the scheme for steady state solution, an implicit UGKS-AS method is also developed. A large number of numerical tests for axisymmetric flow are conducted by the proposed explicit and implicit UGKS-AS, which include inner and outer, steady and unsteady, low and high speed flows. Some tests are very challenging due to the delicate capturing of very small flow variations. The good agreement among the solutions from the present scheme and other analytical, numerical, and experimental studies, validates the high accuracy and efficiency of the UGKS-AS for non-equilibrium flow simulation in all regimes. [ABSTRACT FROM AUTHOR]

Considerable efforts have been taken to estimate the radioactive source term by using integrated computer models, but uncertainties exist in using these models, partly due to the fact that the results cannot be validated using real-world large-scale experiments. The purpose of this research is to identify the MAAP4 phenomenological model parameters with large influences in predicting environmental releases. The identified parameters were compared for different accident scenarios and plant configurations. Two-step screening of the influential model parameters through the Latin hypercube-rank correlation and the one-at-time method was used for the comparative analysis. From the integral analyses, it was found that the source term error propagation was much larger in the containment and in the secondary system. However, error propagation was not necessarily larger inside the containment than in the secondary system. There are common phenomenological parameters with significant influences on the source term simulations: primary depressurization, molten core-concrete interaction, and cladding oxidation models. More focused research regarding the effect of aforementioned identified phenomenological models on the source term calculations would be necessary to better predict the amount of environmental radionuclides release for the severe accidents. However, the detailed uncertainty and sensitivity analysis involving phenomenological model parameters may have to be done in a plant-specific way. Some phenomenological model parameters that showed significant impact on the global source term uncertainty in one plant type did not necessarily have the same impact on another plant. A sensitivity study involving a typical PWR may not have same implications in other designs, even if a same accident scenario with similar accident phenomena is analyzed. Such sensitivity study would be much more beneficial for standardized plant designs. [ABSTRACT FROM AUTHOR]

Complex rainfall situations can generate overland flow with complex hydrodynamic characteristics, affecting the surface configuration (i.e. sheet erosion) and environment to varying degrees. Reliable numerical simulations can provide a scientific method for the optimization of environmental management. A mesoscopic numerical method, the lattice Boltzmann method, was employed to simulate overland flows. To deal with complex rainfall, two schemes were introduced to improve the lattice Boltzmann equation and the local equilibrium function, respectively. Four typical cases with differences in rainfall, bed roughness, and slopes were selected to test the accuracy and applicability of the proposed schemes. It was found that the simulated results were in good agreement with the experimental data, analytical values, and the results produced by other models. [ABSTRACT FROM AUTHOR]

In this paper, we consider the following viscoelastic coupled wave equation with a delay term utt - L1u - ∫t0 g1 (t - s)L1u(s)ds + µ1 ut(x, t) + µ2 ut(x, t - τ2 (t)) + f1 (u, υ) = 0, υtt - L2 υ - ∫t0 g2 (t - s)L2 υ(s)ds + α1 υt(x, t) + α2 υt(x, t - τ2 (t)) + f2 (u, υ) = 0, in a bounded domain. Under appropriate conditions on µ1, µ2, α1 and α2, we prove global existence of the solutions by combining the energy method with the Faedo-Galerkin's procedure. Furthermore, we study the asymptotic stability in using an appropriate Lyapunov functional. Finally, we show that the decay rates are the same as those obtained in [23]. [ABSTRACT FROM AUTHOR]

Three years ago, the Waste Isolation Pilot Plant (WIPP) experienced its first minor accident involving a radiological release. Late in the evening on February 14, 2014, a waste container in the repository underwent a chemical reaction that caused the container to overheat and breach, releasing its contents into the underground. Following a lengthy recovery process, the facility recently resumed waste disposal operations. The accident released significant levels of radioactivity into the disposal room and adjacent exhaust drifts, and although no one was present in the underground at the time of the release, a total of 22 workers tested positive for very low level of radiation, presumably from some of the radioactive material that was released above ground through a small leak in the HEPA filtration system. The dominant radionuclides released were 241Am and 239 + 240Pu in a ratio that matched the content of the drum from Los Alamos National Laboratory (LANL) that was eventually identified as the breached container. From the air particulate monitoring and plume modeling, it was concluded that the dose, at the nearest location accessible to the general public, from this radiation release event would have been less than 0.01 mSv (< 1 mrem/year). This level is well below the 0.1 mSv/year (10 mrem/year) regulatory limit for DOE facilities established by the US Environmental Protection Agency (EPA).While no long-term impacts to public health or the environment are expected as a result of the WIPP radiation release, the limited ventilation and residual contamination levels in the underground are still a concern and pose a major challenge for the full recovery of WIPP. This article provides an up-to-date overview of environmental monitoring results through the WIPP recovery and an estimate of the long-term impacts of the accident on the natural and human environment. [ABSTRACT FROM AUTHOR]

In this paper, a three-dimensional body force model for predicting compressor performance and stability is implemented in the Ansys CFX. The influence of the blade rows on the flow field is represented by the source terms of CFX-solver equation. At first, a high-speed and high-pressure-ratio transonic compressor with the clean inlet is investigated. The overall performance and the flow fields are in agreement well with those of the experimental date, so the model is reliable and correct. Then, the effects of the circumferential distortions in the inlet total pressure and the total temperature on the compressor performance and flow field are also illustrated, respectively. In summary, the proposed body force model is suitable to investigate the flow field of the compressor with the inlet distortions. [ABSTRACT FROM AUTHOR]

Sediment transport model in shallow water admits steady-state solutions in which the non-zero flux gradient is exactly balanced by the source term. In this paper, we develop high-order well-balanced central weighted essentially non-oscillatory schemes for the sediment transport model. In order to maintain the well-balanced property, we first reformulate the governing equations by an equivalent form and propose a novel reconstruction procedure for the Runge-Kutta flux. Rigorous theoretical analysis as well as extensive numerical examples all suggest that the present schemes preserve the well-balanced property. Moreover, the resulting schemes keep genuine high-order accuracy for general solutions. [ABSTRACT FROM AUTHOR]

Parameterizing the dissipative effects of small, unresolved coastal features, is fundamental to improve the skills of wave models. The established technique to deal with this problem consists in reducing the amount of energy advected within the propagation scheme, and is currently available only for regular grids. To find a more general approach, Mentaschi et al., 2015b formulated a technique based on source terms, and validated it on synthetic case studies. This technique separates the parameterization of the unresolved features from the energy advection, and can therefore be applied to any numerical scheme and to any type of mesh. Here we developed an open-source library for the estimation of the transparency coefficients needed by this approach, from bathymetric data and for any type of mesh. The spectral wave model WAVEWATCH III was used to show that in a real-world domain, such as the Caribbean Sea, the proposed approach has skills comparable and sometimes better than the established propagation-based technique. [ABSTRACT FROM AUTHOR]

We consider the Riemann problem for the system of shallow water equations with horizontal temperature gradients (the Ripa system). The model under investigation has the form of a nonconservative system, and it is hyperbolic, but is not strictly hyperbolic. We construct all solutions of the Riemann problem. It turns out that there may be up to three distinct solutions. A resonant phenomenon which causes the colliding shock waves is observed, where multiple waves associated with different characteristic fields propagate with the same shock speed. [ABSTRACT FROM AUTHOR]

The main objective of this study is to investigate the mass transfer phenomena affecting the emission of acetone from a porous solid. In order to simulate this type of emission in a laboratory-scale and in a repeatable way it was decided to set up a system consisting of a dry solid layer with an underlying wet layer. This type of investigation aims to give a scientific basis for the understanding of the factors affecting emission rates when sampling solid area sources with a wind tunnel system. This in turn is important in order to make results obtained with different devices somehow comparable. The study was carried out by following a modellistic and an experimental approach, and then comparing the results. The comparison of experimental and modelled results shows a good agreement, proving that the developed model is able to describe the phenomenon, thereby taking into account the phenomenon intra-solid gas diffusion, as well as capillary rise of the liquid. As a final result, the proposed model is capable to describe properly how the emission rate from a porous solid is affected by the sweeping airflow velocity, which was the final purpose of this study. Although the developed model is valid for the simplified experimental set-up studied (consisting of a dry solid layer with an underlying wet layer and involving the use of pure acetone), the understanding of the phenomena affecting mass transfer in this simplified situation can be transferred to the investigation of diffusion of other compound through more complex solids. [ABSTRACT FROM AUTHOR]

Ghana is in the process of converting its fuel from Highly Enriched Uranium (HEU) to Lowly Enriched Uranium (LEU). Radioactive fission and activation products generated in the irradiated nuclear fuel are hazardous to personnel, environment and the public. Investigation into the levels of radiation dose will help in a safe and efficient core conversion process. Two computer codes used were ORIGEN-S; for computing changes in the isotopic concentrations during neutron irradiation and radioactive decay as well as to determine the source term and MCNP6; which used the source term estimated by ORIGEN-S code to calculate the dose rate. The criticality of the core at different heights above the bottom of the core was also obtained. Most of the radionuclides present after the core depletion contributed to the source term of 1.767 × 10 13 ± 0.0008 photons/sec which was observed after thirty days of the cooling period. The dose rates ranged between 3.51 × 10 −25 ± 0.0003 mGy/h and 4.27 × 10 4 ± 0.0006 mGy/h at different positions above the reactor core, the control room (wall, door and window) and the rabbit room. The criticality (k eff ) also decreased from 0.99442 ± 0.00006 to 0.01238 ± 0.00002 as the core moved from the bottom of the reactor vessel to the top. [ABSTRACT FROM AUTHOR]

In this paper, a gas-kinetic Bhatnagar–Gross–Krook (BGK) scheme is developed for simulating natural convection in a rotating annulus, which arises in many scientific and engineering fields. Different from most existing methods for the solution of the incompressible Navier–Stokes (N–S) equations with the Boussinesq approximation, compressible full N–S equations with allowable density variation are concerned. An appropriate BGK model is constructed for the macroscopic equations defined in a rotating frame of reference. In particular, in order to account for the source (non-inertial) effects in the BGK model, a microscopic source term is introduced into the modified Boltzmann equation. By using the finite volume method and assuming the flow is smooth, the time-dependent distribution function is simply obtained, from which the fluxes at the cell interface can be evaluated. For validation, a closed rotating annulus with differentially heated cylindrical walls is studied. A conventional N–S solver with the preconditioner is used for comparison. The numerical results show that the present method can accurately predict the variation of the Nusselt number with the Rayleigh number, but no preconditioning is required due to its delicate dissipation property. The computed instantaneous streamlines and temperature contours are also investigated, and it is verified that the Rayleigh–Bénard convection in a rotating annulus is very similar to that in a classical stationary horizontal enclosure. [ABSTRACT FROM AUTHOR]

The Fukushima Daiichi Nuclear Power Plant accident of March 11 2011 led to a significant release of radionuclides in the environment. More than 99% of the release activity in the atmosphere was due to highly volatile radionuclides such as I, Te, Cs, Xe, Kr. Fairly quickly after the accident, the main release events had been identified and their consequences roughly assessed. Most releases were dispersed over the Pacific Ocean whereas about 20% was dispersed over the Japan main highland causing areas of significant deposit. Since then, the understanding of the different episodes has been greatly enhanced. It is appropriate to review what happened in terms of releases into the atmosphere, transport, and deposition of radionuclides on the Japanese territory. We describe here, the current state of understanding of the release phase of the accident and the means used to achieve it. Numerous radiological measurements taken in the Japanese environment enabled the scientists to substantially reconstruct the four main sequences of contamination, to identify the probable trajectories of the radioactive plumes, and to link them with precipitation data to explain the areas of deposition. The measurements were supplemented by modelling techniques. The most significant progress come from the quantification of the atmospheric releases, the improvement of meteorological data to better take into account the influence of the complex orography on the plumes trajectories and the modelling of deposition processes. Notwithstanding more realistic simulations, progress is still to be made to accurately estimate people exposure due to the release phase of the FDNPP accident. An important result is that the bulk of the deposition was mostly generated at the beginning of the precipitation, by light rain in less than one hour. The scavenging of plume transported in altitude generates high deposition zones. Therefore, they do not necessarily match the zones within which inhalation exposure to the radioactive plumes was the largest. [ABSTRACT FROM AUTHOR]

In the frame of severe accident topic for pressurized water reactor, the physical-chemistry of Ru fission products were experimentally studied to better understand their behavior inside the reactor coolant system in air or air/steam atmospheres. The tests consisted in vaporizing RuO2 at 1200 °C and the ruthenium oxides are transported through a controlled thermal gradient tube made of quartz or pre-oxidized stainless steel. Results show that the major part up to 95% is deposited along the tube, the remaining part being transported almost under gaseous form attributed to RuO4. Impact of carrier gas, temperature profile and nature of the tube are discussed. [ABSTRACT FROM AUTHOR]

Transport and deposition of fission products within the primary coolant circuit during severe accident condition have significant effect on the amount of released radionuclides in the containment. In this study, a new code, STRCS, compatible with RELAP5/SCDAP code, has been developed that calculates the fission products’ transport through the piping system. The homogeneous and heterogeneous nucleation, aerosol agglomeration, aerosol and vapor deposition and aerosol resuspension are considered in this code. The developed code was validated through international standard problems STROM SR11 and PHEBUS FPT-1 experiments. The STRCS predictions are in good agreement with the ISPs published results, although the obtained results deviate from the PHEBUS FPT-1 experimental data. [ABSTRACT FROM AUTHOR]

Summary: The blood flow model in arteries admits the steady state solutions, for which the flux gradient is nonzero, and is exactly balanced by the source term. In this paper, by means of hydrostatic reconstruction, we construct a high order discontinuous Galerkin method, which exactly preserves the dead‐man steady state, which is characterized by a discharge equal to zero (analogue to hydrostatic equilibrium). Moreover, the method maintains genuine high order of accuracy. Subsequently, we apply the key idea to finite volume weighted essentially non‐oscillatory schemes and obtain a well‐balanced finite volume weighted essentially non‐oscillatory scheme. Extensive numerical experiments are performed to verify the well‐balanced property, high order accuracy, as well as good resolution for smooth and discontinuous solutions. [ABSTRACT FROM AUTHOR]

The JRODOS ( J ava-based R eal-time O nline D ecisi O n S upport) is a decision support system for off-site emergency management for releases of radioactive material into the environment. This paper documents the application of JRODOS by the Hong Kong Observatory in accident consequence assessment and emergency preparedness studies. For operational considerations, the most computational efficient dispersion model in JRODOS, ATSTEP, is adopted. Verification studies for JRODOS's ATSTEP model have been conducted. Comparison with tracer experiment results showed that under neutral atmospheric conditions and distances up to 50 km, the JRODOS simulation outputs were in general of the same order of magnitude with the tracer data. To further evaluate the capability of JRODOS in short-range simulation, a case study on the Fukushima nuclear power plant accident was also carried out. JRODOS was able to produce realistic simulation results which were comparable to the actual airborne monitoring data of the Cs-137 ground deposition from the Fukushima accident. Furthermore, the results of a comprehensive study to assess the potential consequences of accidents at a nearby nuclear power station are presented. Simulation using the French S3 source term for the Guangdong Nuclear Power Station at Daya Bay showed that the projected effective doses within Hong Kong remain far below the IAEA generic criteria of projected dose for urgent protective actions in sheltering/evacuation, while the projected equivalent dose in thyroid may meet the IAEA generic criteria for use of thyroid blocking agent at some areas in the northeastern part of Hong Kong, at distances of up to about 40 km from Daya Bay depending on the prevailing weather conditions in different seasons. [ABSTRACT FROM AUTHOR]

This paper focuses on the source term estimation in AP1000 Nuclear Power Plant (NPP) under severe accident condition. Methods that utilize MELCOR code can evaluate the source term, but the evaluation process is time-consuming. Also, the reference values in NUREG-1465 can be directly used as the severe accident source term; however, it was initially proposed for second–generation reactors and it has difficulty in simulating changes in release fraction along with accident process. In this paper, the Improved Simplified Source Term (ISST) code was developed based on the IAEA’s Simplified Source Term model (SST) presented in IAEA-TECDOC-1127. In addition, the models for core uncovery stage and adiabatic heating-up stage were optimized in this work; taking into account the Accumulator (ACC) and the Core Makeup Tank (CMT) of the emergency core cooling system. Moreover, four fission products release evaluation models were integrated into ISST, making it applicable for the source term evaluation of AP1000 reactor under severe accident initiated by LBLOCA condition. To verify the developed ISST code, the IAEA’s SST, MELCOR and the reference source term in NUREG-1465 were differently used to evaluate the source term released into the containment in a LBLOCA of the AP1000 nuclear power plant. The results obtained from the models in the ISST code were analyzed and compared with each other, and with those obtained from NUREG-1465, IAEA’s SST and MELCOR. Compared with results calculated with the IAEA’s SST, the results calculated with ISST are closer to those calculated using MELCOR. ISST is computationally faster than MELCOR, hence it gives the source term calculation results quicker. Compared with results calculated with MELCOR, the results calculated with ISST are more conservative for Cs and I while the result derived from NUREG-1465 for noble gases is more conservative. [ABSTRACT FROM AUTHOR]