Actual Reactor Research Articles

The Detection of Reactor Antineutrinos for Reactor Core Monitoring: an Overview

There have been new developments in the field of applied neutrino physics during the last decade. The International Atomic Energy Agency (IAEA) has expressed interest in the potentialities of antineutrino detection as a new tool for reactor monitoring and has created an ad hoc Working Group in late 2010 to follow the associated research and development. Several research projects are ongoing around the world to build antineutrino detectors dedicated to reactor monitoring, to search for and develop innovative detection techniques, or to simulate and study the characteristics of the antineutrino emission of actual and innovative nuclear reactor designs. We give, in these proceedings, an overview of the relevant properties of antineutrinos, the possibilities of and limitations on their detection, and the status of the development of a variety of compact antineutrino detectors for reactor monitoring.

Numerical and experimental study of hydraulic dashpot used in the shut-off rod drive mechanism of a nuclear reactor

Hydraulic dashpot design for shut-off rod drive mechanism application in a nuclear reactor has been analyzed both numerically and experimentally in this paper. Finite element commercial code COMSOL Multiphysics 4.3 has been used for numerical analysis. Experimental validation has been done at two different cases. Experimental test set-ups and hydraulic dashpot constructions have been described in detail. Various combinations of dashpot oil viscosity and clearance thickness have been analyzed. Important experimental results are also presented and discussed. Pressure distributions in the dashpot chambers obtained from COMSOL are given for both the set-ups. Numerical and experimental results are compared. Dashpot designs have been qualified after detailed analysis and testing on full-scale test stations simulating actual reactor conditions (except radiation).

Modeling of Silver Nanoparticle Formation in a Microreactor: Reaction Kinetics Coupled with Population Balance Model and Fluid Dynamics

Reactive kinetics coupled with population balance model (PBM) and computational fluid dynamics (CFD) was implemented to simulate silver nanoparticles (AgNPs) formation in a microtubular reactor. The quadrature method of moments, multiphase model theory, and kinetic theory of granular flow were employed to solve the model, and the particle size distributions (PSD) were calculated. The simulation results were validated by synthesizing AgNPs experimentally in an actual microtubular reactor for comparison with the PSD. The results confirmed the effectiveness of the model and its applicability in predicting AgNPs formation and its PSD evolution in the microtubular system. Finally, benefiting from its superiority, in that the influence of reactive kinetics and fluid dynamics on particle evolution could be considered separately, the model was employed to verify predictions and inferred conclusions in our previous works, which were difficult to verify through experiment.

Development of a “best representativity” method for experimental data analysis and an application to the critical experiments at the Toshiba NCA facility

For nuclear critical experiments, it is essential to certify similarities of the experiment with the objective of the actual reactor conditions or actual reactor equipment. To judge the applicability of the experimental data, the concept of a “representativity factor” has recently been adopted in the critical experiment field, particularly for fast breeder reactors and future reactor studies. In this study, we extended this concept to the design of a light water reactor system. We developed a new numerical evaluation method and a calculation system. The method is based on a linear combination of the sensitivity coefficient vector of an experiment in which the representativity factor to the target system is maximized to utilize experimental data effectively. Simultaneously, using the measurement data of critical experiments, the method enables us to evaluate calculation errors caused by errors or uncertainties of physical parameters. The derivation of the new calculation method is explained first. We then qualify it with a sample calculation, presenting numerical results for three kinds of critical experiments conducted at the Toshiba Nuclear Critical Assembly facility. Finally, the results are compared with those of an extended bias factor method to clarify the performance of the new method.

Optimizing the Open-and Closed-Loop Operations of a Batch Reactor

The purpose of this paper is to optimize the function of a batch reactor operating in open and closed loops. A simultaneous optimization method is employed. This optimization method provides optimal solution at a finite number of points in time. However, the actual batch reactor operation may deteriorate if the computed optimal input is improperly applied to the process. In the open-loop operation, an appropriate wave-shaping method is employed to modify the computed optimal discrete input profile to achieve an improved batch operation while simultaneously guaranteeing the enforcements of the path and end-point constraints. In the closed-loop operation, to improve the disturbance rejection capability of the reactor, two optimizer structures based on the nonlinear model predictive control (NMPC) are developed. The first structure is founded on a modified version of a conventional approach which utilizes a variable number of finite elements (VNFE). The second optimizer introduced in this paper is a newly developed scheme which is compared against the first approach. This approach makes use of a variable number of collocation points (VNCP). Simulation studies, considering both of the fixed batch-time problem (FBTP) and minimum batch-time problem (MBTP), are presented in this paper. tch reactor, dynamic optimization, path and end-point constraints, nonlinear model predictive control

Validation studies of computational scheme for high-fidelity fluence estimations of the Swiss BWRs

The paper presents recent activities conducted at the Paul Scherrer Institut (PSI) in relation to the development and validation of an integral calculation methodology based on CASMO-4/SIMULATE-3/MCNPX for accurate estimations of the fast neutron fluence (FNF) accumulated on reactor pressure vessels and internals of the operating Swiss BWRs. With this computational scheme, the default neutron source is set up at the pin-by-pin level with realistic spectrum specifications based on the actual reactor cycle-specific data from validated reference CASMO-4/SIMULATE-3 core analysis models. On this basis, MCNPX models are then applied for optimized calculations of the fast neutron flux at the RPV or at any other location of interest including e.g. at surveillance dosimeters. In that framework, the validation studies conducted so far have included one dosimeter set irradiated in a BWR/6 reactor during two relatively recent operating cycles. Although this first analysis revealed a satisfactory performance when comparing the calculation results to measured data, it was considered necessary to proceed with further sensitivity/optimization studies combined with an enlarged validation basis (i.e. using additional dosimeter sets) in order to strengthen the overall confidence in the scheme both at the qualitative and quantitative level. A summary of the recent progress achieved in these directions is presented in this paper. To start, recalling that BWRs are characterized by very complex and heterogeneous fuel assembly and core designs (e.g. pins with different enrichments and burnable absorber loading, partial length rods, fuel assemblies of different types in the core), the impact of such heterogeneities on FNF estimations is under investigation in order to determine the level of modeling details required for accurate computational schemes to be used for long-term evaluations of modern BWR core designs. Next, additional validation studies based on experimental dosimeter data obtained from the same BWR/6 reactor are presented. These enlarged validation studies involve the analysis of four dosimeter sets, each irradiated during one cycle (including the 3 first reactor operation cycles), and subsequently analyzed at the PSI Hot Lab shortly after the dosimeters extraction. All these additional validation studies are conducted using both the JEFF-3.1.1 and the ENDF/B-VII.0 continuous-energy neutron data libraries in order to assess the sensitivity of the PSI BWR computational scheme also upon the employed nuclear data.

Thermo-hydraulic experimental validation of an integrated modular small reactor operating in full power natural circulation

Small reactors have become a new hotspot of international nuclear energy research. The nuclear heating reactor (NHR) technology developed by Tsinghua University is an important multipurpose small reactor solution with features such as high integration, modular design and full power natural circulation. A new small reactor based on the existing NHR-200 reactor was developed by the Institute of Nuclear and New Energy Technology of Tsinghua University. A full-scale natural circulation test loop with the same operating parameters as the actual reactor was built in order to experimentally validate the natural circulation ability of the reactor primary loop and heat-transfer ability of fuel assemblies and heat exchangers. Corresponding results are given in detail, including parameter validation of the reactor primary loop, flow rules of the natural circulation and heat-transfer coefficients of heaters and heat exchangers, which can be directly used in the actual reactor as a reference for optimization design. Finally, a characteristic parameter k is proposed to represent the natural circulation ability of a system. By using the new data arrangement method in the form of parameter k, comprehensive experimental results of the natural circulation can be represented by a simple integrated expression. The work in this paper is of importance in broadening application fields and pushing forward commercialization of the NHR type reactors.

Simulation of Temperature Distribution in HFCVD Diamond Films Growth on WC-Co Drill Tools in Large Quantities

The substrate temperature distribution in hot filament chemical vapor deposition (HFCVD) diamond films growth on drill tools in large quantities are simulated by the finite volume method (FVM), adopting a detailed 3-D computational model corresponding with the actual reactor. Firstly, the correctness of the simulation model is verified by comparing the temperature data obtained from the simulation with that measured in an actual depositing process, and the results show that the error between them is less than 3%. Thereafter, the influences of several parameters are studied, including the filament separation (D), the length of the filament (L) and the filament-substrate distance (H). The simulation results show the three parameters have different effects on the distribution of temperature field. The influence of D is the greatest, L is followed and then H. The simulation has important theoretical guidance on both the development of HFCVD deposition equipment using for the diamond coating on tools with complex shapes in large quantities and the research of related production process.

Measurement of welding residual stresses of reactor vessels by inherent strain method – Diagnosis of inherent strain distribution function

The fundamental objective of this study is to ensure the safety of nuclear reactors. A few accidents involving leaks from welded zones at the pipe penetration part of reactor vessels or at coolant pipes have been reported at home and abroad. One of the main causes is welding residual stress. Therefore, it is very important to know the welding residual stress in order to maintain the high safety of the plant, estimate the plant life cycle and design an effective maintenance plan. Welded joints of nuclear reactor vessels have complex shapes, and the welding residual stresses also have three-dimensional (3D) complex distributions. In this study, inherent strain-based theory and method are applied to measure the welding residual stresses. The inherent strain method is an analytical method as an inverse problem, using the least squares method, based on the finite element method. So the method gives the most probable value and deviation of residual stress. The reliability of the estimated result is discussed. In this method, inherent strains are unknowns. When residual stresses are distributed complexly in a 3D stress-state, the number of unknowns becomes very large. So, the inherent strain distribution is expressed with an appropriate function to decrease largely the number. A mock-up is idealized for a welded joint at the pipe penetration part of an actual reactor vessel. The inherent strain method is applied to the measure the residual stress of the joint. In this paper, the applicability of the inherent strain distribution function is diagnosed. Ten kinds of functions are applied to estimate the residual stress, and the accuracy and reliability of the analysed results are judged from three points of view, i.e. residuals, unbiased estimate of variance of errors and welding mechanics. The most suitable function is selected, which brings the most reliable result.

CATalytic – Post Processor (CAT-PP): A new methodology for the CFD-based simulation of highly diluted reactive heterogeneous systems

Scaling-up and -down of conventional ideal lab-scale catalytic reactors often introduces strong non-idealities in the flow field which may drastically affect the expected reactor performances and effectiveness. Computational fluid-dynamic (CFD) analysis is required to assess the extent of such non-idealities. In the case of reactive systems, and in particular in the case of heterogeneous catalytic processes, however, computational efforts are huge and, due to the wide range of space and time scales, may become hardly sustainable when detailed chemical kinetics have to be implemented and solved for transient processes. A specific case, encountered in most of the applications of environmental catalysis, is represented by highly diluted process streams, where reactants and products have concentrations of the order of hundreds of part per million and the reaction duty is extremely low. In this case, the reactor fluid dynamic is not affected by the occurrence of chemical reactions, while the activity of the system can be significantly affected by the reactor hydrodynamics. A new simulation approach, named CATalytic – Post-Processor (CAT-PP), is proposed in this paper to treat those systems. Such approach results in a numerical tool which acquires the flow-field data from non-reactive CFD simulations, performed by a commercial code (ANSYS Fluent) and post-processes them by solving the species transport equations with a detailed kinetic scheme. The potential of the proposed approach is demonstrated through its application to the dynamic analysis of a FTIR-operando reactor-cell loaded with a lean-NOx-trap catalyst. It is shown that CAT-PP allows to effectively simulate a transient diluted catalytic process taking care of the actual reactor hydrodynamics even implementing detailed surface (or gas/solid) kinetic schemes.

SIMULATION OPTIMIZATION OF THE HEAT TRANSFER CONDITIONS IN HFCVD DIAMOND FILM GROWTH INSIDE HOLES

Finite volume method (FVM) is adopted in the present investigation to simulate the temperature and reactant gas velocity distributions in hot filament chemical vapor deposition (HFCVD) diamond film growth inside holes, using a detailed 3D computational model well in accordance with the actual reactor. The influences of the heat transfer characteristic of the substrate and the auxiliary heat transfer conditions are firstly studied by control variable method (CVM), including the thermal conductivity of the substrate k, the size of the red bronze support block V(x × y × z), the cooling water flux Qw, the reactant gas flux Qg, the arrangement of the gas outlets A out and the emissivities of the different solid surfaces ϵ. Thereafter, the substrate temperature data measured in the actual HFCVD reactor with three chosen groups of parameters are compared with those obtained from the simulations, presenting similar trends and small deviations less than 5%. Moreover, the auxiliary heat transfer conditions are optimized for both the WC- Co and SiC substrates based on the simulation and measurement results, and corresponding deposition parameters are also determined. Furthermore, HFCVD diamond films are deposited on the inner surfaces of both the substrates under the optimized conditions. The characterization results show that high-quality diamond films with uniform thickness and fine-faceted crystals are obtained, indicating that this optimization method focusing on the heat transfer conditions is feasible and correct.

Verification and Validation of One-Dimensional Flow-Accelerated Corrosion Evaluation Code

A six-step procedure based on three-dimensional (3-D) computational fluid dynamics codes and a coupled model of electrochemistry and oxide layer growth models was proposed to estimate local wall thinning due to flow-accelerated corrosion (FAC), and they were applied to evaluate wall-thinning rates, residual lifetimes of the pipes, and applicability of countermeasures against FAC. A verification and validation (V&V) evaluation based on a comparison of calculated and measured wall thinning confirmed that the wall-thinning rate could be predicted with an accuracy within a factor of 2 and that residual wall thicknesses after 1 year of operation could be estimated with an error of <20%.To mitigate one of the disadvantages of the 3-D FAC code, which is the large amount of computational time needed, and to evaluate FAC occurrence probability for entire plant systems, a one-dimensional (1-D) FAC code was developed by applying 1-D mass transfer coefficients and geometrical factors. High-FAC occurrence zones along entire cooling systems and the effects of countermeasures on mitigating the risks could be evaluated within a small amount of computer time. Prior to application of the easy-to-handle FAC code for plant analysis, its accuracy and applicability should be confirmed based on V&V processes. From comparison of maximum wall-thinning rates calculated with the 1-D FAC code, those calculated with the 3-D FAC code, and measured results for experimental loops and secondary piping of an actual pressurized water reactor plant, it was confirmed that the calculated wall-thinning rates agreed with the measured ones within a factor of 2.

Kinetic Monte Carlo simulation of escaping core plasma particles to the scrape-off layer for accurate response of plasma-facing components

During normal and disruptive operations in tokamak devices the escaped core plasma particles are a potential threat to the divertor and nearby component lifetime as well as plasma contamination. Comprehensive enhanced physical and numerical models are developed and implemented in the upgraded High Energy Interaction with General Heterogeneous Target Systems (HEIGHTS) package to accurately predict the impact of the escaped particles on plasma-facing and nearby components. An ab initio Monte Carlo-based kinetic model of the escaping core particles is developed for integration with the magnetohydrodynamic (MHD) models of the initiated edge plasma where the escaping particles are used as an input volume source. The paper describes details of the 3D Monte Carlo kinetic model, validation and benchmarking and simulation results for both National Spherical Torus Experiment and ITER devices using actual reactor design and magnetic configurations. The simulation results are being implemented self-consistently with various HEIGHTS models that include surface erosion, divertor plasma generation, plasma MHD evolution, heat conduction and detailed photon transport of line and continuum radiation.

A study on the evaluation of performance of the PSC inner containment dome with large openings during prestress transfer

A linear three dimensional finite element (FE) analysis has been carried out for the loading condition at pre-stress transfer of a representative test specimen for a typical pre-stressed concrete (PSC) inner containment (IC) dome with due emphasis on the local behaviour of the steel plate concrete interfaces at the steam generator (SG) openings. The FE model includes the pre-stressing ducts and passive reinforcements. The FE analysis results have been compared with the past experimental results for the same representative test specimen. Due thrust has been put on the objective of predicting the possibility of separation at the steel plate concrete interfaces.An attempt has been made in corroborating the findings of the past two FE analytical studies on the linear behaviour of the PSC IC dome (with large SG openings) of the same actual double containment reactor building of the typical 220MWe capacity Indian nuclear power plant. Finally important conclusions in line with the desired objectives have been made based on the summary observations of all the studies conducted on this typical PSC IC dome.

Comparative efficiency of shear, elongation and turbulent droplet breakup mechanisms: Review and application

The study of phase dispersion of two immiscible fluids in different flows requires identifying the relevant breakup mechanisms. We propose here a detailed investigation of droplet breakup in a multifunctional exchanger-reactor of the vortex generator type in which transfer intensification is due to longitudinal vortical structures. We compare the efficiency of the mean gradients and turbulent mechanisms in droplet breakup in this industrial reactor. This efficiency is essentially characterized by the resulting distribution of droplet diameters. Then, the roles of the mean flow and the turbulent field, intensity, energy spectrum, and turbulence scales are examined in relation to the liquid/liquid dispersion in order to explore the governing mechanisms of drop breakup. In the complex flow considered here – nonhomogeneous and anisotropic turbulence at moderate Reynolds numbers (<15,000) – with weak turbulence intensity (about 10%), it can be demonstrated that turbulent breakup mechanisms largely dominate mean flow effects; elongation and shear effects are shown to have minor effects on the breakup mechanisms. Moreover, the global characteristic scales of the flow are not the relevant parameters in predicting the final size of the emulsion, but instead the Kolmogorov microscale, implying that the residence time in the reactor is not a limiting factor. Hence, the local dissipation rate governs the performance of the actual multifunctional reactor. This study provides some insight in the design and scaling-up of multiphase reactors.

An experimental investigation on self-leveling behavior of debris beds using gas-injection

Studies on the self-leveling behavior of debris beds are crucial in the assessment of core-disruptive accidents (CDAs) that could occur in sodium-cooled fast reactors (SFRs). To further clarify this behavior, a series of experiments has been performed in which nitrogen gas has been percolated uniformly through particle beds. Although in the past, several experiments have been conducted to investigate this behavior, most of these were under comparatively lower gas velocities, the findings of which might be not directly applicable to actual reactor accident conditions. Current experiments were conducted in a cylindrical tank with the dimensions of 310mm in inner diameter and 1000mm in height, in which nitrogen gas, water and different kinds of solid particles, simulate the fission gas, coolant and fuel debris, respectively. During experiments, to accomplish the bubble-based leveling as expected in actual reactor conditions, two experimental approaches, termed respectively as the gas pre-charge method and the pressure-adjustment method, have been attempted. Through elaborate comparisons and evaluations, it is found that compared to the gas pre-charge way the pressure-adjustment method can alleviate the liquid disturbance from the bottom inlet pipelines more effectively throughout the whole experimental process. Further, based on the experimental observations and quantitative data obtained, influence of various experimental parameters on the self-leveling, including gas flow rate, water depth, particle size, particle density as well as boiling mode is checked and compared. From the analyses, it is also observed that, the convection in the water pool, though is not so evident for previous studies at lower gas velocities, is newly identified to play a significant role in this work, especially for the experimental runs using larger-size lower-density particles at comparatively higher gas flow rates and water depths. Current work provides critical evidence and a large palette of favorable data for a better understanding of CDAs and improved verifications of computer models developed in advanced fast reactor safety analysis codes.

Modeling of fixed bed methanation reactor for syngas production: Operating window and performance characteristics

The present work focuses on the development of phenomenological model for the bio-syngas to methane conversion process. One dimensional heterogeneous and pseudo-homogeneous model were simulated for a typical pilot plant scale fixed bed methanator processing 55mol/h of CO (total molar flow rate of 310mol/h) with inlet composition of H2/CO=3, CO2/CO=1, CH4/CO=0.5 at 550K and 1atm. Performance of the fixed bed reactor at different operating conditions like CO2/CO ratio, H2/CO ratio, effect of H2O in the feed was studied. It was found that for feeds that were not pre-enriched with hydrogen, presence of water and water gas shift activity was found to decrease the catalyst inventory substantially. CO2 in the inlet feed stream would help to decrease the temperature due to dilution effect and more importantly, can be chosen to maximize methane yield per mole of CO converted. Further, the model was simulated to predict the performance characteristics of reactor with a mixture containing two types of catalyst, one of them being specifically added to increase H2/CO ratio in feed through water gas shift reaction. The work also laid the importance of incorporating pore diffusion and external mass transfer locally in the computation of actual catalyst inventory and reactor volume. The work was useful in selection of operating window and assessing the various viable options for an industrial reactor. The model developed will serve in selection of operability window for commercialization of substitute natural gas synthesis (SNG) process.

Thin uranium dioxide films with embedded xenon

The ion beam assisted deposition (IBAD) method was applied as a means to incorporate Xe atoms into UO2 films to fabricate reference samples that are representative of an irradiated nuclear fuel without an actual reactor irradiation. The characterization of Xe content and the films microstructure was performed using Rutherford backscattering spectroscopy (RBS), atomic force microscopy (AFM), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDXS). A set of UO2 films with excellent control of Xe content ranging from ∼1.0 to 4.0at.% was fabricated. The thin UO2〈Xe〉 films deposited on single crystalline 4H–SiC substrates were found to be composed primarily of randomly oriented nanocrystalline grains and a small fraction of amorphous material. TEM analysis detected no Xe-filled bubbles at a scale of 2.5nm or larger.

Simulation and experimental research on the substrate temperature distribution in HFCVD diamond film growth on the inner hole surface

The substrate temperature distribution in HFCVD diamond film growth on the inner hole surface is simulated by the finite volume method in the present study, adopting a detailed 3-D computational model agreeing with the actual reactor. Firstly, the influences of several key deposition parameters are studied by the control variable method, including the cooling condition C, the filament temperature Tf, the filament diameter d and the substrate aperture D. Afterwards, the substrate temperatures in the actual reactor are measured. Deviations between the simulated and measured temperature values are all less than 5%, and the substrate temperature distribution trends in the measurement results are well coincident with those in the simulation results. Furthermore, corresponding deposition experiments are also conducted, the results of which can further validate the correctness of the simulations. Finally, the optimized deposition parameters are used to deposit diamond films on the inner hole surfaces of the WC–Co substrates with apertures of either 6mm or 8mm. The characterizations show that homogeneous diamond films with fine-faceted diamond crystals are obtained, indicating that this deposition parameter optimization method is feasible for fabricating high-quality diamond films on the inner hole surfaces.

0213 電気抵抗トモグラフィ法による粒子充填層内液二相脈動流の可視化計測(OS2-3 混相流の多次元可視化計測,OS2 混相流の多次元可視化計測)

A fixed bed reactor that operates in gas-liquid co-current down flow is called Trickle Bed Reactor (TBR). In this study, authors employed the lab-scale TBR, made of 68, 100mm inner diameter acrylic column, packed with particles of two sizes (3, 5 mm) that are used in the actual reactor. Liquid and gas were injected from the top of the column and cross-sectional liquid distribution was captured at the bottom of the column by electrical resistance tomography (ERT). ERT is a tomographic technique that provides the cross-sectional conductivity distribution at the rate of about 50 frames per second by injecting current and measuring voltages between the 16 electrodes that are attached around the column. By analyzing the spatial and temporal characteristics of the liquid distribution obtained by ERT, the relationship between operation condition and flow regime transition and property of pulsing flow was revealed.