Journal articles: 'LWR models'

1

Oriolo, Francesco, and Sandro Paci. "Heat and mass transfer models in LWR containment systems." Nuclear Engineering and Design 204, no. 1-3 (February 2001): 233–50. http://dx.doi.org/10.1016/s0029-5493(00)00314-9.

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Chopra, O. K., and W. J. Shack. "Overview of Fatigue Crack Initiation in Carbon and Low-Alloy Steels in Light Water Reactor Environments." Journal of Pressure Vessel Technology 121, no. 1 (February 1, 1999): 49–60. http://dx.doi.org/10.1115/1.2883667.

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Recent test data illustrate potentially significant effects of light water reactor (LWR) coolant environments on the fatigue resistance of carbon and low-alloy steels. The crack initiation and crack growth characteristics of carbon and low-alloy steels in LWR environments are presented. Decreases in fatigue lives of these steels in high-dissolved-oxygen water are caused primarily by the effect of environment on growth of short cracks <100 μm in depth. The material and loading parameters that influence fatigue life in LWR environments are defined. Statistical models have been developed to estimate the fatigue lives of these steels in LWR environments, and design fatigue curves have been developed for carbon and low-alloy steel components in LWR environments. The significance of environmental effect on the current Code design curve is evaluated.

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Zhang, H. M., and T. Kim. "Effects of Relaxation and Anticipation on Riemann Solutions of Payne-Whitham Model." Transportation Research Record: Journal of the Transportation Research Board 1710, no. 1 (January 2000): 131–35. http://dx.doi.org/10.3141/1710-15.

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The solutions of Riemann problems of a particular higher-order model—the Payne-Whitham (PW) model—are studied using Roe’s flux splitting scheme as presented by Leo and Pretty. Despite numerous works on higher-order models, little is known about Riemann solutions of these models and how relaxation and anticipation affect these solutions. Riemann solutions of the PW model are computed and compared with those of the Lighthill-Whitham-Richards (LWR) model having the same initial (density) data. It was found that faster relaxation forces the PW model to behave much like the LWR model, that strong anticipation has a stabilizing effect on traffic, and that shock waves travel at different speeds in the PW model than they do in the LWR model. These findings provide a basic checklist for experimental validation of PW-like higher models.

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Raza, Asif, and Ming Zhong. "Lane-based short-term urban traffic parameters forecasting using multivariate artificial neural network and locally weighted regression models: A genetic approach." Canadian Journal of Civil Engineering 46, no. 5 (May 2019): 371–80. http://dx.doi.org/10.1139/cjce-2017-0644.

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Short-term prediction of traffic conditions on urban arterials has recently become increasingly important because of its vital role in the basic traffic management functions and trip decision-making processes. Such information is useful for optimal infrastructure operation, routing, and trip scheduling. However, forecasting models offering a high accuracy at a fine temporal resolution (e.g., 1 or 5 min) and, especially, lane-based are still rare and need special attention. Given the dynamic and stochastic nature of traffic, this study proposes a genetically optimized artificial neural network (GA-ANN) and locally weighted regression (GA-LWR) multivariate models, for short-term traffic prediction using a combination of multiple traffic variables such as volume, occupancy, and speed, during peak and off-peak periods. The proposed 5-min GA-ANN and GA-LWR disaggregate multivariate models show lower average and 95th percentile (P95) errors, when compared to those reported in the literature. In particular, for peak and off-peak time prediction, the GA-ANN disaggregate multivariate models result in most of the average errors being from 2% to 5% and the 95th percentile errors being from 9% to 10%. On the other hand, for peak and off-peak time traffic prediction, the GA-LWR disaggregate multivariate models show that most of the average errors are lower than 5% and the 95th percentile errors are lower than 10%. Meanwhile, for peak and off-peak time prediction, both GA-ANN and GA-LWR disaggregates models show lower MSE of 0.11–1.84. Hence, such techniques are believed useful for developing a robust urban traffic forecasting system.

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Qin, Yanyan, Hao Wang, and Daiheng Ni. "Lighthill-Whitham-Richards Model for Traffic Flow Mixed with Cooperative Adaptive Cruise Control Vehicles." Transportation Science 55, no. 4 (July 2021): 883–907. http://dx.doi.org/10.1287/trsc.2021.1057.

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In the future, road traffic will incorporate a random mix of manual vehicles and cooperative adaptive cruise control (CACC) vehicles, where a CACC vehicle will degrade to an adaptive cruise control (ACC) vehicle when vehicle-to-vehicle communications are not available. This paper proposes a generalized framework of the Lighthill-Whitham-Richards (LWR) model for such mixed vehicular flow under different CACC penetration rates. In this approach, the kinematic wave speed propagating through the mixed platoon was theoretically proven to be the slope of mixed fundamental diagram. In addition, the random degradation from CACC to ACC was captured in mathematical expectation for traffic scenarios where the CACC only monitors one vehicle ahead. Three concrete car-following models, the intelligent driver model (IDM) and CACC/ACC models validated by Partners for Advanced Transit and Highways (PATH) program, were selected as examples to investigate the propagation of small perturbations and shock waves. Numerical simulations were also performed based on the selected car-following models. Moreover, the derived mixed LWR model was applied to solve some traffic flow problems. It indicates that the proposed LWR model is able to describe the propagation properties of both small perturbations and shock waves. The mixed LWR model can also be used to solve some practical problems, such as the queue caused by a traffic accident and the impact of a moving bottleneck. More importantly, the proposed generalized framework admits other CACC/ACC/regular car-following models, including those developed from further experiments.

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Iftikhar, Amir, Zawar H. Khan, T. Aaron Gulliver, Khurram S. Khattak, Mushtaq A. Khan, Murtaza Ali, and Nasru Minallahe. "Macroscopic Traffic Flow Characterization at Bottlenecks." Civil Engineering Journal 6, no. 7 (July 1, 2020): 1227–42. http://dx.doi.org/10.28991/cej-2020-03091543.

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Traffic congestion is a significant issue in urban areas. Realistic traffic flow models are crucial for understanding and mitigating congestion. Congestion occurs at bottlenecks where large changes in density occur. In this paper, a traffic flow model is proposed which characterizes traffic at the egress and ingress to bottlenecks. This model is based on driver response which includes driver reaction and traffic stimuli. Driver reaction is based on time headway and driver behavior which can be classified as sluggish, typical or aggressive. Traffic stimuli are affected by the transition width and changes in the equilibrium velocity distribution. The explicit upwind difference scheme is used to evaluate the Lighthill, Whitham, and Richards (LWR) and proposed models with a continuous injection of traffic into the system. A stability analysis of these models is given and both are evaluated over a road of length 10 km which has a bottleneck. The results obtained show that the behavior with the proposed model is more realistic than with the LWR model. This is because the LWR model cannot adequately characterize driver behavior during changes in traffic flow.

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Imran, Waheed, Zawar H. Khan, T. A. Gulliver, Khurram S. Khattak, Salman Saeed, and M. Sagheer Aslam. "Macroscopic Traffic Flow Characterization for Stimuli Based on Driver Reaction." Civil Engineering Journal 7, no. 1 (January 1, 2021): 1–13. http://dx.doi.org/10.28991/cej-2021-03091632.

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The design and management of infrastructure is a significant challenge for traffic engineers and planners. Accurate traffic characterization is necessary for effective infrastructure utilization. Thus, models are required that can characterize a variety of conditions and can be employed for homogeneous, heterogeneous, equilibrium and non-equilibrium traffic. The Lighthill-Whitham-Richards (LWR) model is widely used because of its simplicity. This model characterizes traffic behavior with small changes over a long idealized road and so is inadequate for typical traffic conditions. The extended LWR model considers driver types based on velocity to characterize traffic behavior in non lane discipline traffic but it ignores the stimuli for changes in velocity. In this paper, an improved model is presented which is based on driver reaction to forward traffic stimuli. This reaction occurs over the forward distance headway during which traffic aligns to the current conditions. The performance of the proposed, LWR and extended LWR models is evaluated using the first order upwind scheme (FOUS). The numerical stability of this scheme is guaranteed by employing the Courant, Friedrich and Lewy (CFL) condition. Results are presented which show that the proposed model can characterize both small and large changes in traffic more realistically. Doi: 10.28991/cej-2021-03091632 Full Text: PDF

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Toptan, Aysenur, Nathan W. Porter, Robert K. Salko, and Maria N. Avramova. "Implementation and assessment of wall friction models for LWR core analysis." Annals of Nuclear Energy 115 (May 2018): 565–72. http://dx.doi.org/10.1016/j.anucene.2018.02.022.

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Hou, Jason, Maria Avramova, and Kostadin Ivanov. "Best-Estimate Plus Uncertainty Framework for Multiscale, Multiphysics Light Water Reactor Core Analysis." Science and Technology of Nuclear Installations 2020 (July 31, 2020): 1–18. http://dx.doi.org/10.1155/2020/7526864.

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Tremendous work has been done in the Light Water Reactor (LWR) Modelling and Simulation (M&S) uncertainty quantification (UQ) within the framework of the Organization for Economic Cooperation and Development (OECD)/Nuclear Energy Agency (NEA) LWR Uncertainty Analysis in Modelling (UAM) benchmark, which aims to investigate the uncertainty propagation in all M&S stages of the LWRs and to guide uncertainty and sensitivity analysis methodology development. The Best-Estimate Plus Uncertainty (BEPU) methodologies have been developed and implemented within the framework of the LWR UAM benchmark to provide a realistic predictive simulation capability without compromising the safety margins. This paper describes the current status of the methodological development, assessment, and integration of the BEPU methodology to facilitate the multiscale, multiphysics LWR core analysis. The comparative analysis of the results in the stand-alone multiscale neutronics phase (Phase I) is first reported for understanding the general trend of the uncertainty of core parameters due to the nuclear data uncertainty. It was found that the predicted uncertainty of the system eigenvalue is highly dependent on the choice of the covariance libraries used in the UQ process and is less sensitive to the solution method, nuclear data library, and UQ method. High-to-Low (Hi2Lo) model information approaches for multiscale M&S are introduced for the core single physics phase (Phase II). In this phase, the other physics (fuel and moderator), providing feedback to neutronics M&S in a LWR core, and time-dependent phenomena are considered. Phase II is focused on uncertainty propagation in single physics models which are components of the LWR core coupled multiphysics calculations. The paper discusses the link and interactions between Phase II to the multiphysics core and system phase (Phase III), that is, the link between uncertainty propagation in single physics on local scale and multiphysics uncertainty propagation on the core scale. Particularly, the consistency in uncertainty assessment between higher-fidelity models implemented in fuel performance codes and the rather simplified models implemented in thermal-hydraulics codes, to be used for coupling with neutronics in Phase III is presented. Similarly, the uncertainty quantification on thermal-hydraulic models is established on a relatively small scale, while these results will be used in Phase III at the core scale, sometimes with different codes or models. Lastly, the up-to-date UQ method for the coupled multiphysics core calculation in Phase III is presented, focusing on the core equilibrium cycle depletion calculation with associated uncertainties.

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Briani, Maya, Emiliano Cristiani, and Paolo Ranut. "Macroscopic and Multi-Scale Models for Multi-Class Vehicular Dynamics with Uneven Space Occupancy: A Case Study." Axioms 10, no. 2 (May 24, 2021): 102. http://dx.doi.org/10.3390/axioms10020102.

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In this paper, we propose two models describing the dynamics of heavy and light vehicles on a road network, taking into account the interactions between the two classes. The models are tailored for two-lane highways where heavy vehicles cannot overtake. This means that heavy vehicles cannot saturate the whole road space, while light vehicles can. In these conditions, the creeping phenomenon can appear, i.e., one class of vehicles can proceed even if the other class has reached the maximal density. The first model we propose couples two first-order macroscopic LWR models, while the second model couples a second-order microscopic follow-the-leader model with a first-order macroscopic LWR model. Numerical results show that both models are able to catch some second-order (inertial) phenomena such as stop and go waves. Models are calibrated by means of real data measured by fixed sensors placed along the A4 Italian highway Trieste–Venice and its branches, provided by Autovie Venete S.p.A.

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Li, Yuanqi, Xiaoliang Qin, Jinhui Luo, Meng Xiao, and Cong Hua. "Uplift Test and Design Method for Bearing Capacity of Isolated Spread Concrete Foundation Slab with Large Width-to-Height Ratio." Advances in Civil Engineering 2018 (November 15, 2018): 1–16. http://dx.doi.org/10.1155/2018/3672868.

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This paper is focused on the experimental study and numerical simulation of isolated spread concrete foundation slab with a large width-to-height ratio (in short ISCFS-LWR) to investigate the failure modes and uplift bearing capacity, as well as the design method of uplift capacity. First, a total of 16 isolated spread concrete foundation slabs with the width-to-height ratio varied from 1.5 to 4 and the hypotenuse slope varied from 10° to 30° were tested under uplift load. Based on the test results, effects of the width-to-height ratio and the hypotenuse slope on uplift bearing capacity of ISCFS-LWR were analyzed and discussed. Then, several numerical models were built using the finite element software ABAQUS and the results of numerical analysis agreed well with the test results. Furthermore, the cross-sectional performance of ISCFS-LWR was studied, and the coefficients of internal force arm were also evaluated further using previous validated numerical models. To obtain the suggested design method of uplift capacity for the foundation slab, effective width correction coefficient k and slope correction coefficient j were introduced to propose a design formula. Finally, the proposed design method was applied to a practical engineering, and the economic indicators obtained from the suggested design method were compared with that from the original design method. The results of this paper showed that the correction coefficient jsks based on numerical analysis agreed well with the recommended correction coefficient jk, and the error was between 1% and 3.4%, by which the reasonability of the proposed design method of uplift capacity for ISCFS-LWR has been proved. It can also be found that the economic benefits of the practical engineering in this paper were obvious due to the suggested design method, and this paper can provide a reference for other engineering practices and the further research work on ISCFS-LWR.

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Maciejewski, M. "Comparison of the one-equation LWR models for density and for speed." IOP Conference Series: Materials Science and Engineering 421 (October 11, 2018): 022020. http://dx.doi.org/10.1088/1757-899x/421/2/022020.

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Bengil, Elizabeth Grace Tunka. "A regional evaluation of lessepsian migrant Upeneus moluccensis (Bleeker, 1855) length and weight relationships from the Mediterranean Sea." Vol:36 Issue:3 36, no. 3 (September 15, 2019): 255–63. http://dx.doi.org/10.12714/egejfas.2019.36.3.06.

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The length and weight relationships (LWRs) of goldband goatfish found in the coasts of Cyprus was studied, and both prediction capacity of the model as well as a regional prediction capacity by testing developed models from the Mediterranean basin were evaluated. A total of 219 individuals were obtained monthly between November 2017-April 2018. LWR models taken from total length and fork length measurements were developed for female and male samples and combined with a maximum 36% error in estimations. Results indicated that LWR modelling based on sexes does not provide any improvement for uncertainty in the estimations. Evaluations of previously developed models indicate that the majority share a similar performance regarding the distribution of error in estimations. In conclusion, the population of this species shows that there are similar growth properties in both sexes throughout the eastern Mediterranean. Using the same TLWR model for all individuals is therefore applicable for the purpose of further modelling within the Mediterranean basin-scale.

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Bernal, A., M. Pecchia, D. Rochman, A. Vasiliev, and H. Ferroukhi. "METHODOLOGY FOR HIGH-FIDELITY DETERMINISTIC MODELLING OF SWISS LWR FUEL ASSEMBLIES." EPJ Web of Conferences 247 (2021): 06011. http://dx.doi.org/10.1051/epjconf/202124706011.

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The main goal of this work is to perform pin-by-pin calculations of Swiss LWR fuel assemblies with neutron transport deterministic methods. At Paul Scherrer Institut (PSI), LWR calculations are performed with the core management system CMSYS, which is based on the Studsvik suite of codes. CMSYS includes models for all the Swiss reactors validated against a database of experimental information. Moreover, PSI has improved the pin power calculations by developing models of Swiss fuel assemblies for the Monte Carlo code MCNP, with the isotopic compositions obtained from the In-Core Fuel Management data of the Studsvik suite of codes, by using the SNF code. A step forward is to use a neutron code based on fast deterministic neutron transport methods. The method used in this work is based on a planar Method of Characteristics in which the axial coupling is solved by 1D SP3 method. The neutron code used is nTRACER. Thus, the methodology of this work develops nTRACER models of Swiss PWR fuel assemblies, in which the fuel of each pin and axial level is modelled with the isotopic composition obtained from SNF. This methodology was applied to 2D and 3D calculations of a Swiss PWR fuel assembly. However, this method has two main limitations. First, the cross sections libraries of nTRACER lack some of the isotopes obtained by SNF. Fortunately, this work proves that the missing isotopes do not have a strong effect on keff and the power distribution. Second, the 3D models require high computational memory resources, that is, more than 260 Gb. Thus, the nTRACER code was modified, so now it uses only 8 Gb, without any loss of accuracy. Finally, the keff and power results are compared with Monte Carlo calculations obtained by Serpent.

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Towers, John D. "A splitting algorithm for LWR traffic models with flux discontinuous in the unknown." Journal of Computational Physics 421 (November 2020): 109722. http://dx.doi.org/10.1016/j.jcp.2020.109722.

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Morimoto, Susumu, W. F. McClure, Benett Crowell, and Donald L. Stanfield. "Near Infrared Technology for Precision Environmental Measurements: Part 2. Determination of Carbon in Green Grass Tissue." Journal of Near Infrared Spectroscopy 11, no. 4 (August 2003): 257–67. http://dx.doi.org/10.1255/jnirs.372.

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Composting is one of the most desirable techniques for reducing waste volume. To make good compost, the correct proportions of the elements carbon and nitrogen (30: 1 ratio) are important. In this paper, carbon quantification of green grass tissue using near infrared (NIR) technology was studied. Separate studies were conducted for the short-wavelength region (SWR = 700–1100 nm, a range that includes part of the visible spectrum) and long-wavelength region (LWR = 1100–2500 nm). Several spectral pretreatments (such as SNV, derivatives etc.) were implemented to optimise the stepwise multiple linear regression (SMLR) and partial least squares (PLS) calibrations. PLS analysis was conducted for all pretreatments. Results showed that the 2nd derivative of standard normal variate (SNV) pretreatment for the LWR and the SNV pretreatment for the SWR gave the best predictions. To simplify the PLS models, a weight index (WI), was defined as the absolute value of product between the regression vector from PLS analysis and the average spectrum. A simple PLS calibration was developed using selected peak wavelengths of regression vector with a minimum WI. The simple PLS models gave better results than the full PLS calibrations. According to this analysis, the C–H stretching of the first overtone at 1860 nm and the C–H stretching of the third overtone at 874 nm were the key bands for the SWR and LWR, respectively. SMLR analysis was performed on the same spectral data used in the PLS analysis. SMLR calibrations were developed using the key band chosen in PLS analysis. Although the performance of the calibrations were not as good as the PLS calibrations, the SMLR model produced acceptable calibrations for both the SWR and LWR. The simple fact that NIR technology can be used to determine both carbon and nitrogen very quickly makes it an ideal technology for monitoring material going into a composting operation.

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Jia, Wangqiang, Long Yuan, Hongyan Ni, Benling Xu, and Peng Zhao. "Prognostic Value of Platelet-to-Lymphocyte Ratio, Neutrophil-to-Lymphocyte Ratio, and Lymphocyte-to-White Blood Cell Ratio in Colorectal Cancer Patients Who Received Neoadjuvant Chemotherapy." Technology in Cancer Research & Treatment 20 (January 1, 2021): 153303382110342. http://dx.doi.org/10.1177/15330338211034291.

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Background: The objective of this study was to assess the prognostic value of pretreatment platelet-to-lymphocyte ratio (PLR), neutrophil-to-lymphocyte ratio (NLR), and lymphocyte-to-white blood cell ratio (LWR) of CRC patients who received neoadjuvant chemotherapy. Methods: We analyzed the peripheral blood routine parameters and other clinical data of 145 patients with colorectal cancer who had undergone neoadjuvant chemotherapy between January 2011 and February 2014. Pretreatment blood parameters of 145 patients were collected, and PLR, NLR, and LWR were calculated. The utility of PLR, NLR, and LWR in predicting treatment efficacy and patient survival was statistically evaluated using the chi-square test, log-rank test, Kaplan-Meier curves and logistic regression models, and Cox regression models. Results: Receiver operating characteristic curve showed that the best cutoff values of PLR, NLR, and LWR were 154.31, 3.01, and 0.22, respectively. In univariate analysis, tumor location ( P = 0.044), differentiation degree ( P = 0.001), lymph node metastasis ( P = 0.020), and high PLR ( P = 0.042) were significantly correlated with a lower overall response rate (ORR). In addition, clinical stage, lymph node metastasis, and high PLR were correlated with short OS ( P < 0.01) and DFS ( P < 0.01). Moreover, WBC count was correlated with a short OS. Multivariate analysis showed that tumor location ( P = 0.013), differentiation degree ( P = 0.001), and lymph node metastasis ( P = 0.033) were independent predictors of ORR. In addition, lymph node metastasis independently predicted a shorter OS ( P = 0.011). Lymph node metastasis ( P = 0.013) and high PLR ( P = 0.022) were independent prognostic factors for short DFS. Conclusions: For CRC patients who received NAC, clinical pathological stage and lymph node metastasis were correlated with lower ORR and survival, while a high PLR that may be of prognostic relevance in CRC patients receiving NAC.

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Raza, Asif, and Ming Zhong. "Lane-based short-term urban traffic forecasting with GA designed ANN and LWR models." Transportation Research Procedia 25 (2017): 1430–43. http://dx.doi.org/10.1016/j.trpro.2017.05.169.

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Krishnan, Praveena, Tilden P. Meyers, Simon J. Hook, Mark Heuer, David Senn, and Edward J. Dumas. "Intercomparison of In Situ Sensors for Ground-Based Land Surface Temperature Measurements." Sensors 20, no. 18 (September 15, 2020): 5268. http://dx.doi.org/10.3390/s20185268.

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Land surface temperature (LST) is a key variable in the determination of land surface energy exchange processes from local to global scales. Accurate ground measurements of LST are necessary for a number of applications including validation of satellite LST products or improvement of both climate and numerical weather prediction models. With the objective of assessing the quality of in situ measurements of LST and to evaluate the quantitative uncertainties in the ground-based LST measurements, intensive field experiments were conducted at NOAA’s Air Resources Laboratory (ARL)’s Atmospheric Turbulence and Diffusion Division (ATDD) in Oak Ridge, Tennessee, USA, from October 2015 to January 2016. The results of the comparison of LSTs retrieved by three narrow angle broadband infrared temperature sensors (IRT), hemispherical longwave radiation (LWR) measurements by pyrgeometers, forward looking infrared camera with direct LSTs by multiple thermocouples (TC), and near surface air temperature (AT) are presented here. The brightness temperature (BT) measurements by the IRTs agreed well with a bias of <0.23 °C, and root mean square error (RMSE) of <0.36 °C. The daytime LST(TC) and LST(IRT) showed better agreement (bias = 0.26 °C and RMSE = 0.67 °C) than with LST(LWR) (bias > 1.1 and RMSE > 1.46 °C). In contrast, the difference between nighttime LSTs by IRTs, TCs, and LWR were <0.47 °C, whereas nighttime AT explained >81% of the variance in LST(IRT) with a bias of 2.64 °C and RMSE of 3.6 °C. To evaluate the annual and seasonal differences in LST(IRT), LST(LWR) and AT, the analysis was extended to four grassland sites in the USA. For the annual dataset of LST, the bias between LST (IRT) and LST (LWR) was <0.7 °C, except at the semiarid grassland (1.5 °C), whereas the absolute bias between AT and LST at the four sites were <2 °C. The monthly difference between LST (IRT) and LST (LWR) (or AT) reached up to 2 °C (5 °C), whereas half-hourly differences between LSTs and AT were several degrees in magnitude depending on the site characteristics, time of the day and the season.

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Rompis, Semuel Y. R., and Filmon G. Habtemichael. "Calibration of Traffic Incident Simulation Models Using Field Data." International Journal of Sustainable Transportation Technology 2, no. 1 (April 30, 2019): 19–26. http://dx.doi.org/10.31427/ijstt.2019.2.1.3.

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This study presents a methodology to calibrate a traffic incident simulation model, particularly in a freeway. The queue length was used as the objective of the simulation model calibration in this study. The simulation model was set up using Traffic Simulation Model PTV. VISSIM. Multiple incident durations were simulated, and the generated queue lengths were compared to the observed queue lengths. The observed queue lengths were estimated using the LWR model and shockwave speeds calculated using the field data. The results confirm that calibrated VISSIM incident model can signify the shockwave propagation speeds and queue length in the event of freeway incident. Such a model can be implemented as an instrument for setting up traffic management strategies to alleviate the incident’s impact.

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Jernkvist, Lars O. "Modelling of fine fragmentation and fission gas release of UO2 fuel in accident conditions." EPJ Nuclear Sciences & Technologies 5 (2019): 11. http://dx.doi.org/10.1051/epjn/2019030.

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In reactor accidents that involve rapid overheating of oxide fuel, overpressurization of gas-filled bubbles and pores may lead to rupture of these cavities, fine fragmentation of the fuel material, and burst-type release of the cavity gas. Analytical rupture criteria for various types of cavities exist, but application of these criteria requires that microstructural characteristics of the fuel, such as cavity size, shape and number density, are known together with the gas content of the cavities. In this paper, we integrate rupture criteria for two kinds of cavities with models that calculate the aforementioned parameters in UO2 LWR fuel for a given operating history. The models are intended for implementation in engineering type computer programs for thermal-mechanical analyses of LWR fuel rods. Here, they have been implemented in the FRAPCON and FRAPTRAN programs and validated against experiments that simulate LOCA and RIA conditions. The capabilities and shortcomings of the proposed models are discussed in light of selected results from this validation. Calculated results suggest that the extent of fuel fragmentation and transient fission gas release depends strongly on the pre-accident fuel microstructure and fission gas distribution, but also on rapid changes in the external pressure exerted on the fuel pellets during the accident.

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Tiftikçi, A., and C. Kocar. "Investigation of turbulence models for a fully-periodic LWR unit-cell in lattice-Boltzmann framework." Progress in Nuclear Energy 104 (April 2018): 160–71. http://dx.doi.org/10.1016/j.pnucene.2017.09.011.

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Vikram, Durgesh, Partha Chakroborty, and Sanjay Mittal. "Exploring the Behavior of LWR Continuum Models of Traffic Flow in Presence of Shock Waves." Procedia - Social and Behavioral Sciences 104 (December 2013): 412–21. http://dx.doi.org/10.1016/j.sbspro.2013.11.134.

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Aragón-Noriega, E. Alberto, Edgar Alcántara-Razo, Jesús G. Padilla-Serrato, Guillermo Rodríguez-Domínguez, and Sergio G. Castillo-Vargasmachuca. "Morphological notes on Pinnaxodes gigas Green, 1992 (Brachyura, Pinnotheridae) emphasizing on length-weight relationship under multi-model approach." Crustaceana 92, no. 9 (October 4, 2019): 1081–97. http://dx.doi.org/10.1163/15685403-00003932.

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Abstract This study describes biometric characteristics of the pea crab Pinnaxodes gigas, a symbiont of the geoduck clam Panopea globosa in the eastern-central Gulf of California. Differences were observed in the coefficient of allometry when length-weight relationships (LWR) were analysed under a multi-model approach. The winner model for LWR in females was that exhibiting two phases (”two-segments” and “broken-stick”), while in males the models cubic and quadratic, presenting a continuous change in coefficient of allometry along all sizes, were chosen as the best. The relationships of carapace width, length and height were also tested for females with the two-segment model and the breakpoint was found at 20 mm carapace width for these three relationships. It is concluded that the breakpoint must be related to the size-at-maturity reached by females, and that these changes in dimensions correspond to an adaptation in the female’s shape for carrying the egg clutch.

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Friedrich, Jan, Oliver Kolb, and Simone Göttlich. "A Godunov type scheme for a class of LWR traffic flow models with non-local flux." Networks & Heterogeneous Media 13, no. 4 (2018): 531–47. http://dx.doi.org/10.3934/nhm.2018024.

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Grandi, Gerardo, Rodolfo Ferrer, and Tamer Bahadir. "APPLICATION OF STUDSVIK’S CMS5 CODE SYSTEM TO ACCIDENT TOLERANT FUEL CORE DESIGN AND ANALYSIS." EPJ Web of Conferences 247 (2021): 02020. http://dx.doi.org/10.1051/epjconf/202124702020.

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The possible deployment of Accident Tolerant Fuels (ATF) for currently-operating Light Water Reactors (LWR) has prompted interest in the use of Studsvik’s CMS5 code system to support the analysis of such advanced ATF core designs. Various ATF concepts have been proposed; for example, uranium silicide (U3Si2) fuel, together with iron-based (FeCrAl) cladding. The purpose of this work is to showcase the application of the CMS5 code system, which includes the CASMO5 advanced lattice physics code and the SIMULATE5 three-dimensional nodal simulator, to the analysis of a U3Si2/FeCrAl ATF concept. Given that the CMS5 code system was designed from inception to enable the analysis of advanced core designs, only minor changes to the CASMO5 lattice physics code and SIMULATE5 core simulator are necessary. The current CASMO5 586 energy-group nuclear data library provides all the necessary data to support the generation of homogenized data for downstream use by SIMULATE5 for ATF. The SIMULATE5 nodal code, which features a simplified fuel pin model, requires updating various thermophysical properties corresponding to the U3Si2/SiC ATF fuel and the gaseous conductance models. An equilibrium core for the Integral Inherently Safe (I2S) LWR design developed by the Georgia Institute of Technology was selected. The results of the CMS5 simulation were compared with those in the literature and were found to be in good agreement, giving us confidence that the CMS5 package can be used in the modeling of LWR systems with ATF technology.

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Higuchi, Makoto, and Katsumi Sakaguchi. "Review and Consideration of Unsettled Problems on Evaluation of Fatigue Damage in LWR Water." Journal of Pressure Vessel Technology 129, no. 1 (June 1, 2006): 186–94. http://dx.doi.org/10.1115/1.2409316.

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Reduction in the fatigue life of structural materials of nuclear components in Light Water Reactor (LWR) water was initially detected and examined by the authors in the 1980s, who subsequently directed considerable effort to the development of a method for evaluating this reduction quantitatively. Since the first proposal of equations to calculate environmental fatigue life reduction for carbon and low-alloy steels was published in 1985 by Higuchi and Sakamoto (J. Iron Steel Inst. Jpn. 71, pp. 101–107), many revisions were made based on a lot of additional fatigue data in various environmental and mechanical test conditions. The latest models for evaluation using Fen of the environmental fatigue life correction factor were proposed for carbon and low alloy steels in the year 2000 and for austenitic stainless steel, in 2002. Fen depends on some essential variables such as material, strain rate, temperature, dissolved oxygen and sulfur concentration in steel. The equation for determining Fen is given by each parameter for each material. These models, having been developed three to five years ago, should be properly revised based on new test results. This paper reviews and discusses five major topics pertinent to such revision.

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Rochman, Dimitri A., Alexander Vasiliev, Abdelhamid Dokhane, and Hakim Ferroukhi. "Uncertainties for Swiss LWR spent nuclear fuels due to nuclear data." EPJ Nuclear Sciences & Technologies 4 (2018): 6. http://dx.doi.org/10.1051/epjn/2018005.

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This paper presents a study of the impact of the nuclear data (cross sections, neutron emission and spectra) on different quantities for spent nuclear fuels (SNF) from Swiss power plants: activities, decay heat, neutron and gamma sources and isotopic vectors. Realistic irradiation histories are considered using validated core follow-up models based on CASMO and SIMULATE. Two Pressurized and one Boiling Water Reactors (PWR and BWR) are considered over a large number of operated cycles. All the assemblies at the end of the cycles are studied, being reloaded or finally discharged, allowing spanning over a large range of exposure (from 4 to 60 MWd/kgU for ≃9200 assembly-cycles). Both UO2 and MOX fuels were used during the reactor cycles, with enrichments from 1.9 to 4.7% for the UO2 and 2.2 to 5.8% Pu for the MOX. The SNF characteristics presented in this paper are calculated with the SNF code. The calculated uncertainties, based on the ENDF/B-VII.1 library are obtained using a simple Monte Carlo sampling method. It is demonstrated that the impact of nuclear data is relatively important (e.g. up to 17% for the decay heat), showing the necessity to consider them for safety analysis of the SNF handling and disposal.

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Simoni, Michele D., and Christian G. Claudel. "A Fast Lax–Hopf Algorithm to Solve the Lighthill–Whitham–Richards Traffic Flow Model on Networks." Transportation Science 54, no. 6 (November 2020): 1516–34. http://dx.doi.org/10.1287/trsc.2019.0951.

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Efficient and exact algorithms are important for performing fast and accurate traffic network simulations with macroscopic traffic models. In this paper, we extend the semianalytical Lax–Hopf algorithm in order to compute link inflows and outflows with the Lighthill–Whitham–Richards (LWR) model. Our proposed fast Lax–Hopf algorithm has a very low computational complexity. We demonstrate that some of the original algorithm’s operations (associated with the initial conditions) can be discarded, leading to a faster computation of boundary demands/supplies in network simulation problems for general concave fundamental diagrams (FDs). Moreover, the computational cost can be further reduced for triangular FDs and specific space–time discretizations. The resulting formulation has a performance comparable to the link transmission model and because it solves the original LWR model for a wide range of FD shapes, with any initial configuration, it is suitable to solve a broad range of traffic operations problems. As part of the analysis, we compare the performance of the proposed scheme with that of other well-known computational methods.

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Higuchi, Makoto. "Revised Proposal of Fatigue Life Correction Factor Fen for Carbon and Low Alloy Steels in LWR Water Environments." Journal of Pressure Vessel Technology 126, no. 4 (November 1, 2004): 438–44. http://dx.doi.org/10.1115/1.1767860.

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The fatigue life of carbon and low alloy steels decreases with reduction in strain rate in high temperature water such as in the case of a light water reactor coolant. The fatigue life reduction also depends on temperature and dissolved oxygen. The fatigue life correction factor Fen has been proposed as a method to assess the fatigue life reduction in such environments. Three different models for calculating Fen for carbon and low alloy steels have been proposed by Higuchi et al., Chopra et al., and Mehta. These models were compared using considerable environmental fatigue data that were tested and published in Japan and USA and piled up in the database “JNUFAD” by the author. These models give somewhat different results in the specific conditions and a revised model for calculating Fen is thus proposed by remedying the particular drawbacks of each. In this model, the same formula is used for carbon and low alloy steels and S*,T*,O*, and ε˙* are adopted in the formula after reevaluating every parameter. The revised proposal shows better correlation with the test data than the previous models.

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Vasiliev, Alexander, Marco Pecchia, Dimitri Rochman, Hakim Ferroukhi, and Erwin Alhassan. "On the impact of nuclear data uncertainties on LWR neutron dosimetry assessments." EPJ Web of Conferences 239 (2020): 22003. http://dx.doi.org/10.1051/epjconf/202023922003.

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In this work, an overview on the relevance of the nuclear data (ND) uncertainties with respect to the Light Water Reactors (LWR) neutron dosimetry is presented. The paper summarizes results of several studies realized at the LRT laboratory of the Paul Scherrer Institute over the past decade. The studies were done using the base LRT calculation methodology for dosimetry assessments, which involves the neutron source distribution representation, obtained based on validated CASMO/SIMULATE core follow calculation models, and the subsequent neutron transport simulations with the MCNP® software. The methodology was validated using as reference data results of numerous measurement programs fulfilled at Swiss NPPs. Namely, the following experimental programs are considered in the given overview: PWR “gradient probes” and BWR fast neutron fluence (FNF) monitors post irradiation examination (PIE). For the both cases, assessments of the nuclear data related uncertainties were performed. When appropriate, a cross-verification of the deterministic and stochastic based uncertainty propagation techniques is provided. Furthermore, the observations on which particular neutron induced reactions contribute dominantly to the overall ND-related uncertainties are demonstrated. The presented results should help with assessing the overall impact of the various nuclear data uncertainties with respect to dosimetry applications and provide relevant feedback to the nuclear data evaluators.

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Khan, Zawar Hussain, Thomas Aaron Gulliver, and Waheed Imran. "A Macroscopic Traffic Model Based on the Safe Velocity at Transitions." Civil Engineering Journal 7, no. 6 (June 1, 2021): 1060–69. http://dx.doi.org/10.28991/cej-2021-03091710.

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The increasing volume of vehicles on the road has had a significant impact on traffic flow. Congestion in urban areas is now a major concern. To mitigate congestion, an accurate model is required which is based on realistic traffic dynamics. A new traffic model is proposed based on the conservation law of vehicles which considers traffic dynamics at transitions. Traffic alignment to forward conditions is affected by the time and distance between vehicles. Thus, the well-known Lighthill, Whitham, and Richards (LWR) model is modified to account for traffic behavior during alignment. A model for inhomogeneous traffic flow during transitions is proposed which can be used to characterize traffic evolution. The performance of the proposed model is compared with the LWR model using the Greenshields and Underwood target velocity distributions. These models are evaluated using the Godunov technique and numerical stability is guaranteed by considering the Courant, Friedrich, and Lewy (CFL) condition. The results obtained show that the proposed model characterizes the flow more realistically, and thus can provide better insight into traffic behavior for use in controlling congestion and pollution levels, and improving public safety. Doi: 10.28991/cej-2021-03091710 Full Text: PDF

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Higuchi, Makoto, Kazuya Tsutsumi, Akihiko Hirano, and Katsumi Sakaguchi. "A Proposal of Fatigue Life Correction Factor Fen for Austenitic Stainless Steels in LWR Water Environments." Journal of Pressure Vessel Technology 125, no. 4 (November 1, 2003): 403–10. http://dx.doi.org/10.1115/1.1613945.

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The fatigue life of austenitic stainless steel has recently been shown to undergo remarkable reduction with decrease in strain rate and increase in temperature in water. Either of these parameters as a factor of this reduction has been examined quantitatively and methods for predicting the fatigue life reduction factor Fen in any given set of conditions have been proposed. All these methods are based primarily on fatigue data in simulated PWR water owing to the few data available in simulated BWR water. Recent Japanese fatigue data in simulated BWR water clearly indicated the effects of the environment on fatigue degradation to be milder than under actual PWR conditions. A new method for determining Fen in BWR water was developed in the present study and a revised Fen in PWR water is also proposed based on new data. These new models differ from those previously used primarily with regard to the manner in which strain amplitude is considered to affect Fen in the environment.

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Agelet, Lidia Esteve, Charles R. Hurburgh, Feng Mao, James J. Gaunt, and Say Kee Ong. "Permeation Studies of PVC Pipes with near Infrared Spectroscopy." Journal of Near Infrared Spectroscopy 15, no. 5 (October 2007): 283–89. http://dx.doi.org/10.1255/jnirs.737.

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Polyvinyl chloride (PVC) pipes are commonly used to transport drinking water. Although PVC is resistant to natural environmental conditions, organic solvents may attack the pipe wall causing swelling, softening, water lines failure and drinking water pollution. Leaks from underground storage tanks and random accidental spills of organic solvents or fuels place the pipes in contact with organic solvents. Near infrared (NIR) spectroscopy was used to track the permeation of PVC pipes by three major organic solvents (toluene, benzene and gasoline) at different concentrations. Partial least squares (PLS) calibrations with NIR spectra and reference data gave accurate models with R2 > 0.9, relative performance determinant ( RPD) > 3 and low standard errors of prediction ( SEP). These models could predict the permeation status measured by mm of solvent moving front, weight gain, or days under permeation. A second study correlated pipe permeation susceptibility to pure toluene in mm h−1/2 to the pipe spectra. Spectra differences from several pipe brands and sizes were modelled with locally weighted regression (LWR), resulting in models with accuracy ( RPD) of around 5. NIR was a suitable tool to evaluate the permeation of PVC pipes and to predict the susceptibility of PVC pipes to permeation.

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Canuti, E., A. Petruzzi, F. D'Auria, and T. Kozlowski. "Sensitivity Studies for the Exercise I-1 of the OECD/UAM Benchmark." Science and Technology of Nuclear Installations 2012 (2012): 1–10. http://dx.doi.org/10.1155/2012/817185.

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OECD/NEA has initiated an international Uncertainty Analysis in Modeling (UAM) benchmark focused on uncertainties in modeling of Light Water Reactor (LWR). The first step of uncertainty propagation is to perform sensitivity to the input data affected by the numerical errors and physical models. The objective of the present paper is to study the effect of the numerical discretization error and the manufacturing tolerances on fuel pin lattice integral parameters (multiplication factor and macroscopic cross-sections) through sensitivity calculations. The two-dimensional deterministic codes NEWT and HELIOS were selected for this work. The NEWT code was used for analysis of the TMI-1, PB-2, and Kozloduy-6 test cases; the TMI-1 test case was investigated using the HELIOS code. The work has been performed within the framework of UAM Exercise I-1 “Cell Physics.”

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Sánchez, V. H., M. Thieme, and W. Tietsch. "Validation and Application of the Thermal Hydraulic System Code TRACE for Analysis of BWR Transients." Science and Technology of Nuclear Installations 2012 (2012): 1–9. http://dx.doi.org/10.1155/2012/247482.

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The Karlsruhe Institute of Technology (KIT) is participating on (Code Applications and Maintenance Program) CAMP of the US Nuclear Regulatory Commission (NRC) to validate TRACE code for LWR transient analysis. The application of TRACE for the safety assessment of BWR requires a throughout verification and validation using experimental data from separate effect and integral tests but also using plant data. The validation process is normally focused on safety-relevant phenomena for example, pressure drop, void fraction, heat transfer, and critical power models. The purpose of this paper is to validate selected BWR-relevant TRACE-models using both data of bundle tests such as the (Boiling Water Reactor Full-Size Fine-Mesh Bundle Test) BFBT and plant data recorded during a turbine trip event (TUSA) occurred in a Type-72 German BWR plant. For the validation, TRACE models of the BFBT bundle and of the BWR plant were developed. The performed investigations have shown that the TRACE code is appropriate to describe main BWR-safety-relevant phenomena (pressure drop, void fraction, and critical power) with acceptable accuracy. The comparison of the predicted global BWR plant parameters for the TUSA event with the measured plant data indicates that the code predictions are following the main trends of the measured parameters such as dome pressure and reactor power.

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Shaffer, Ronald E., and Roger J. Combs. "Comparison of Spectral and Interferogram Processing Methods Using Simulated Passive Fourier Transform Infrared Remote Sensing Data." Applied Spectroscopy 55, no. 10 (October 2001): 1404–13. http://dx.doi.org/10.1366/0003702011953540.

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Computer-generated synthetic single-beam spectra and interferograms provide a means of comparing signal processing strategies that are employed with passive Fourier transform infrared (FT-IR) sensors. With the use of appropriate radiance models and spectrometer characteristics, synthetic data are generated for one-, two-, and four-component mixtures of organic vapors (ethanol, methanol, acetone, and methyl ethyl ketone) in two passive FT-IR remote sensing scenarios. The single-beam spectra are processed by using Savitsky–Golay smoothing and first-derivative and second-derivative filters. Interferogram data are processed by Fourier filtering using Gaussian-shaped bandpass digital filters. Pattern recognition is performed with soft independent modeling of class analogy (SIMCA). Quantitative models for the target gas integrated concentration-path-length product are built by using either partial least-squares (PLS) regression or locally weighted regression (LWR). Pattern recognition and calibration models of the filtered spectra or interferograms produced comparable results. Discrimination of target analytes in complex mixtures requires a sufficiently large temperature differential between the infrared background source and analyte cloud. Quantitative analysis is found to be possible only when the temperature of the analyte cloud is stable or known and differs significantly from the background temperature. Net analyte signal (NAS) methods demonstrate that interferogram and spectral processing methods supply identical information for multivariate pattern recognition and calibration.

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Rożeń, Antoni. "Modelling of a passive autocatalytic hydrogen recombiner – a parametric study." Nukleonika 60, no. 1 (March 1, 2015): 161–69. http://dx.doi.org/10.1515/nuka-2015-0002.

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Abstract Operation of a passive autocatalytic hydrogen recombiner (PAR) has been investigated by means of computational fluid dynamics methods (CFD). The recombiner is a self-active and self-adaptive device used to remove hydrogen from safety containments of light water nuclear reactors (LWR) by means of a highly exothermic reaction with oxygen at the surface of a platinum or palladium catalyst. Different turbulence models (k-ω, k-ɛ, intermittency, RSM) were applied in numerical simulations of: gas flow, heat and mass transport and chemical surface reactions occurring in PAR. Turbulence was found to improve mixing and mass transfer and increase hydrogen recombination rate for high gas flow rates. At low gas flow rates, simulation results converged to those obtained for the limiting case of laminar flow. The large eddy simulation technique (LES) was used to select the best RANS (Reynolds average stress) model. Comparison of simulation results obtained for two- and three-dimensional computational grids showed that heat and mass transfer occurring in PAR were virtually two-dimensional processes. The effect of hydrogen thermal diffusion was also discussed in the context of possible hydrogen ignition inside the recombiner.

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Arenas, C., R. Bratton, F. Reventos, and K. Ivanov. "Uncertainty Analysis of Light Water Reactor Fuel Lattices." Science and Technology of Nuclear Installations 2013 (2013): 1–10. http://dx.doi.org/10.1155/2013/437409.

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The study explored the calculation of uncertainty based on available cross-section covariance data and computational tool on fuel lattice levels, which included pin cell and the fuel assembly models. Uncertainty variations due to temperatures changes and different fuel compositions are the main focus of this analysis. Selected assemblies and unit pin cells were analyzed according to the OECD LWR UAM benchmark specifications. Criticality and uncertainty analysis were performed using TSUNAMI-2D sequence in SCALE 6.1. It was found that uncertainties increase with increasing temperature, whilekinfdecreases. This increase in the uncertainty is due to the increase in sensitivity of the largest contributing reaction of uncertainty, namely, the neutron capture reaction238U(n,γ) due to the Doppler broadening. In addition, three types (UOX, MOX, and UOX-Gd2O3) of fuel material compositions were analyzed. A remarkable increase in uncertainty inkinfwas observed for the case of MOX fuel. The increase in uncertainty ofkinfin MOX fuel was nearly twice the corresponding value in UOX fuel. The neutron-nuclide reaction of238U, mainly inelastic scattering (n,n′), contributed the most to the uncertainties in the MOX fuel, shifting the neutron spectrum to higher energy compared to the UOX fuel.

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Yousif, Eltayeb, Zhijian Zhang, Zhaofei Tian, and Hao-ran Ju. "Simulation and Analysis of Small Break LOCA for AP1000 Using RELAP5-MV and Its Comparison with NOTRUMP Code." Science and Technology of Nuclear Installations 2017 (2017): 1–13. http://dx.doi.org/10.1155/2017/4762709.

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Many reactor safety simulation codes for nuclear power plants (NPPs) have been developed. However, it is very important to evaluate these codes by testing different accident scenarios in actual plant conditions. In reactor analysis, small break loss of coolant accident (SBLOCA) is an important safety issue. RELAP5-MV Visualized Modularization software is recognized as one of the best estimate transient simulation programs of light water reactors (LWR). RELAP5-MV has new options for improved modeling methods and interactive graphics display. Though the same models incorporated in RELAP5/MOD 4.0 are in RELAP5-MV, the significant difference of the latter is the interface for preparing the input deck. In this paper, RELAP5-MV is applied for the transient analysis of the primary system variation of thermal hydraulics parameters in primary loop under SBLOCA in AP1000 NPP. The upper limit of SBLOCA (10 inches) is simulated in the cold leg of the reactor and the calculations performed up to a transient time of 450,000.0 s. The results obtained from RELAP5-MV are in good agreement with those of NOTRUMP code obtained by Westinghouse when compared under the same conditions. It can be easily inferred that RELAP5-MV, in a similar manner to RELAP5/MOD4.0, is suitable for simulating a SBLOCA scenario.

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Lo Frano, R., and G. Forasassi. "Buckling of Imperfect Thin Cylindrical Shell under Lateral Pressure." Science and Technology of Nuclear Installations 2008 (2008): 1–8. http://dx.doi.org/10.1155/2008/685805.

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The strength of thin shells, under external pressure, is highly dependent by the nature of imperfection. This paper investigates buckling behaviour of imperfect thin cylindrical shells with analytical, numerical, and experimental methods in conditions for which, at present, a complete theoretical analysis was not found in literature. In general, collapse is initiated by yielding, but interaction with geometrical instabilities is meaningful, in that imperfections reduce the load bearing capacity by an amount of engineering significance also when thickness is considerable. The aim of this study was to conduct experiments that are representative of buckling, in the context of NPP applications as, for instance, the IRIS (international reactor innovative and secure) and LWR steam generator (SG) tubes. At Pisa University, a research activity is being carried out on the buckling of thin walled metal specimen, with a test equipment (and the necessary data acquisition facility) as well as numerical models were set up by means FEM code. The experiments were conducted on A-316 test specimens, tubes with and without longitudinal welding. The numerical and experimental results comparison highlighted the influence of different types of imperfections on the buckling loads with a good agreement between the finite-element predictions and the experimental data.

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Barrachin, Marc. "Corium Experimental Thermodynamics: A Review and Some Perspectives." Thermo 1, no. 2 (August 11, 2021): 179–204. http://dx.doi.org/10.3390/thermo1020013.

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More than 30 years ago a specialist meeting was held at Joint Research Center Ispra (Italy) from 15 to 17 January 1990 to review the current understanding of chemistry during severe accidents in light water reactors (LWR). Let us consider that, at the end of the 1980s, thermodynamics introduced in the severe accident codes was really poor. Only some equilibrium constants for a few simple reactions between stoichiometric compounds were used as well as some simple correlations giving estimates of solidus and liquidus temperatures. In the same time, the CALPHAD method was developed and was full of promise to approximate the thermodynamic properties of a complex thermochemical system by the way of a critical assessment of experimental data, a definition of a simple physical model and an optimisation procedure to define the values of the model parameters. It was evident that a nuclear thermodynamic database had to be developed with that new technique to obtain quite rapidly prominent progress in the knowledge of thermochemistry in the severe accident research area. Discussions focused on the important chemical phenomena that could occur across the wide range of conditions of a damaged nuclear plant. The most pressing need for improved chemical models is identified with condensed phase mixtures to model the corium progression. This paper reviews more than 30 years of experimental data production in the field of corium thermodynamics. This work has been conducted through multiple international programs (EURATOM, ISTC, OECD) as well as through more specific studies conducted at the national scale. This research has been capitalised in specific databases such as NUCLEA and TAF-ID, databases developed at IRSN and at CEA, respectively, and are now used in degradation models of the severe accident simulation codes. This research is presented in this paper. In the conclusion, we outline the research perspectives that need to be considered in order to address today’s and tomorrow’s issues.

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COSTA, Edson Vinícius, Henrique Torres VENTURA, Elsio Antônio Pereira FIGUEIREDO, Fabyano Fonseca e. SILVA, Leonardo Siqueira GlÓRIA, Rodrigo Mezêncio GODINHO, Marcos Deon Vilela de RESENDE, and Paulo Sávio LOPES. "Multi-trait and repeatability models for genetic evaluation of litter traits in pigs considering different farrowings." Revista Brasileira de Saúde e Produção Animal 17, no. 4 (December 2016): 666–76. http://dx.doi.org/10.1590/s1519-99402016000400010.

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SUMMARY We aimed to compare multi-trait and repeatability models to estimate genetic parameters for the traits number of piglets born alive (NBA) and alive at 3 week of age (NP3), litter weight at birth (LW0) and at 3 week of age (LW3), and mean piglet weight at birth (MW0) and at 3 week of age (MW3), considering the first three farrowings of Landrace sows. Heritability (h2) estimates showed an increasing pattern up to the third farrowing for LW0 and MW3. For NBA, NP3, LW3, and MW0 h2 increased from the first to the second and decreased from the second to the third farrowing. In general, heritability estimated in the repeatability model was lower than the mean of the estimates in the multi-trait model. The traits LWO, MW0, and MW3 presented high genetic correlation among different farrowings (0.961–0.997), while NBA, NP3, and LW3 (0.092–0.986) presented irregular values among farrowings. The corrected Akaike information criterion shows that the repeatability model is not indicated for almost all of the studied traits. These results indicate that the multi-trait model is recommended for genetic evaluation of the traits number of piglets born alive and alive at 3 week of age, litter weight and mean piglet weight at birth and 3 week of age, in different farrowings, as different traits.

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Peña Giraldo, Mauricio Vladimir, Edilberto Carlos Vivas Gonzales, and Carol Ivonn Rodríguez Feliciano. "Modelamiento Dinámico y control LQR de un Quadrotor." Avances Investigación en Ingeniería 13, no. 1 (December 1, 2010): 71. http://dx.doi.org/10.18041/1794-4953/avances.1.359.

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Este trabajo deduce el modelo dinámico de un Quadrotor, que consiste en una estructura central donde se encuentran las baterías y la aviónica del dispositivo unida a cuatro largueros con un conjunto propulsor (motor-hélice) en el extremo de cada larguero, formando una cruz perfecta brindando la posibilidad de sustentarse en el aire controlando su orientación y traslación. Múltiples artículos hablan de este modelo dinámico en los cuales se hacen suposiciones para vehículos bajo techo, simplificando considerablemente la complejidad del modelo. Por esta razón se modela físicamente la dinámica del vehículo como un sistema no lineal tomando en cuenta fenómenos aerodinámicos de las hélices. Luego se realiza una linealización del modelo y una comparación entre los modelos “real” y “linealizado” usando un control LQR estabilizante.

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Chabanne, Delphine, Hugh Finn, Chandra Salgado-Kent, and Lars Bedjer. "Identification of a resident community of bottlenose dolphins (Tursiops aduncus) in the Swan Canning Riverpark, Western Australia, using behavioural information." Pacific Conservation Biology 18, no. 4 (2012): 247. http://dx.doi.org/10.1071/pc120247.

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Identifying appropriate management units is vital for wildlife management. Here we investigate one potential management unit — resident communities of bottlenose dolphins — using information from ranging, occupancy, and association patterns. We identify a resident community of Indo-Pacific bottlenose dolphins (Tursiops aduncus) in the Swan Canning Riverpark, Western Australia based on: ranging patterns, sighting rates, Lagged Identification Rates (LIR), and three measures of social affinity and structure (Simple Ratio Index, preferred dyadic association analyses, and Lagged Association Rates (LAR)). The analyses yielded an estimated ‘community size’ of 17–18 individuals (excluding calves). High seasonal sighting rates (> 0.75 sightings per season) and a long mean residence time (ca. nine years) indicated year-round residency. The model best-fitting the LIR (emigration and mortality) also supported this. The social structure of dolphins was species-typical, characterized by significant dyadic associations within agesex classes (permutation test; P < 0.001), stronger associations among adult males than among adult females (LAR males > LAR females), and temporally stable associations (LAR > null LAR). Constant companions or long-lasting association models best explained adult male and female LARs. While behavioural information identified a resident community in the Riverpark, genetic and demographic information is needed to assess its appropriateness as a management unit.

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Perrin, C., V. Andréassian, and C. Michel. "Simple benchmark models as a basis for model efficiency criteria." River Systems 17, no. 1-2 (July 28, 2006): 221–44. http://dx.doi.org/10.1127/lr/17/2006/221.

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Naumov, Vadim, Sergey Gusak, and Andrey Naumov. "Small nuclear power plants for power supply in arctic regions: assessment of spent nuclear fuel radioactivity." Nuclear Energy and Technology 4, no. 2 (November 26, 2018): 119–25. http://dx.doi.org/10.3897/nucet.4.30677.

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The purpose of the present study is the investigation of mass composition of long-lived radionuclides accumulated in the fuel cycle of small nuclear power plants (SNPP) as well as long-lived radioactivity of spent fuel of such reactors. Analysis was performed of the published data on the projects of SNPP with pressurized water-cooled reactors (LWR) and reactors cooled with Pb-Bi eutectics (SVBR). Information was obtained on the parameters of fuel cycle, design and materials of reactor cores, thermodynamic characteristics of coolants of the primary cooling circuit for reactor facilities of different types. Mathematical models of fuel cycles of the cores of reactors of ABV, KLT-40S, RITM-200M, UNITERM, SVBR-10 and SVBR-100 types were developed. The KRATER software was applied for mathematical modeling of the fuel cycles where spatial-energy distribution of neutron flux density is determined within multi-group diffusion approximation and heterogeneity of reactor cores is taken into account using albedo method within the reactor cell model. Calculation studies of kinetics of burnup of isotopes in the initial fuel load (235U, 238U) and accumulation of long-lived fission products (85Kr, 90Sr, 137Cs, 151Sm) and actinoids (238,239,240,241,242Pu, 236U, 237Np, 241Am, 244Cm) in the cores of the examined SNPP reactor facilities were performed. The obtained information allowed estimating radiation characteristics of irradiated nuclear fuel and implementing comparison of long-lived radioactivity of spent reactor fuel of the SNPPs under study and of their prototypes (nuclear propulsion reactors). The comparison performed allowed formulating the conclusion on the possibility in principle (from the viewpoint of radiation safety) of application of SNF handling technology used in prototype reactors in the transportation and technological process layouts of handling SNF of SNPP reactors.

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Kamau, Kiruma Melchizedecs, Prof Johana K. Sigey, Dr Jeconia A. Okelo, and Dr James Okwoyo. "Inhomogeneous LWR Traffic Flow Model and its Application to Kisii – Kisumu Highway in Kenya." SIJ Transactions on Computer Science Engineering & its Applications (CSEA) 02, no. 06 (December 11, 2014): 12–17. http://dx.doi.org/10.9756/sijcsea/v2i6/0207720102.

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Cuzzola, Francesco A., and Sergio Bittanti. "ROBUST FAULT DETECTION BY LFR MODELS." IFAC Proceedings Volumes 35, no. 1 (2002): 173–78. http://dx.doi.org/10.3182/20020721-6-es-1901.00760.

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Kudinov, Y. I., F. F. Pashchenko, A. Y. Kelina, D. I. Vasutin, E. S. Duvanov, and A. F. Pashchenko. "Analysis of Control System Models with Conventional LQR and Fuzzy LQR Controller." Procedia Computer Science 150 (2019): 737–42. http://dx.doi.org/10.1016/j.procs.2019.02.007.

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Journal articles on the topic 'LWR models'

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