Structural Response of a Large Pressure Vessel to Dynamic Loading

This report presents a feasibility study on structural analysis of pressure-containing structures subject to external blast loads using finite element and volume simulation software. A basic understanding of the main factors influencing the results of such analyses was established in an earlier study. An extensive series of computations have now been performed and the results are presented and discussed in detail in this report. These involve a 3-D simulation of a large steel vessel of hypothetical design containing pressurised water and subject to an explosive blast from a charge located directly underneath the lower torispherical end. The top is closed by a flat lid arrangement. The properties of the explosive material, the air and water environments and the vessel steel were taken from the literature. For the latter, elastic-plastic material properties at 20°C have been considered. The vessel is located in a bunker and by using FSR boundary conditions the reflections of the pressure waves on the bunker walls are also considered. To provide a cross-check on the computational results, some simplified analyses were performed using engineering and empirical formulae to estimate the pressure loads need to produce yielding and failure of the vessel, as well as of the corresponding quantities of explosives that would be needed to produce sufficient shock wave pressures.JRC.F.4-Safety of future nuclear reactor

New Analytical Stress Formulae for Arbitrary Time Dependent Thermal Loads in Pipes

Analytical solutions with several new features have been developed for temperature and elastic thermal stress distributions for a hollow circular cylinder under sinusoidal thermal transient loading at the inner surface. The approach uses a finite Hankel transform in a general form for any transient thermal loading for a hollow cylinder. Using the properties of Bessel functions, an analytical solution for temperature distribution through wall thickness was derived for a special case of sinusoidal transient thermal loading on inner pipe surface. The solutions for associated thermal stress components were developed by means of the displacement technique. To the authors’ knowledge, this is first time a complete set of such analytical expressions has been openly published.JRC.F.4-Nuclear design safet

A Prospective Study for Probabilistic Approach of Thermal Fatigue in Mixing Tees

The work performs a prospective study on probabilistic approach of thermal fatigue in mixing tees (Civaux 1 damage case) by means of the limit state function and Monte Carlo simulation. It is based on previous work where a deterministic assessment for thermal fatigue crack growth in high-cycle loadings, under the large nonlinear gradient stress profiles through wall-thickness due to sinusoidal thermal loading, has been done.The probabilistic approach considers variability in initial crack depth and Paris law C scaling parameter by means of specific probability density distributions. The crude Monte Carlo Simulations are performed using specific routines implemented in MATLAB software with Statistics Toolbox, and probabilities of failure are derived using the failure function which is defined based on a limit state given by the critical crack depth. The results were checked against predictions from empirical cumulative distribution and a good agreement was found. An important task was to estimate distribution function for fatigue lives after finding probabilities failure associated with corresponding fatigue lives by means of the failure function approach. Using specific MATLAB functions from Statistic Toolbox, for both axial and circumferential crack growth the pdf, associated mean value of the fatigue life and CoV have been estimated. The log-normal distribution has been found to best fit the results from failure function approach with MCS, for both cases.JRC.F.4-Safety of future nuclear reactor

Assessment of Thermal Fatigue Crack Growth in the High Cycle Domain under Sinusoidal Thermal Loading - An Application - Civaux 1 Case

The assessment of fatigue crack growth due to cyclic thermal loads arising from turbulent mixing presents significant challenges, principally due to the difficulty of establishing the actual loading spectrum. So-called sinusoidal methods represents a simplified approach in which the entire spectrum is replaced by a sine-wave variation of the temperature at the inner pipe surface. The amplitude can be conservatively estimated from the nominal temperature difference between the two flows which are mixing; however a critical frequency value must be determined numerically so as to achieve a minimum predicted life. The need for multiple calculations in this process has lead to the development of analytical solutions for thermal stresses in a pipe subject to sinusoidal thermal loading, described in a companion report. Based on these stress distributions solutions, the present report presents a methodology for assessment of thermal fatigue crack growth life. The critical sine wave frequency is calculated for both axial and hoop stress components as the value that produces the maximum tensile stress component at the inner surface. Using these through-wall stress distributions, the corresponding stress intensity factors for a long axial crack and a fully circumferential crack are calculated for a range of crack depths using handbook K solutions. By substituting these in a Paris law and integrating, a conservative estimate of thermal fatigue crack growth life is obtained. The application of the method is described for the pipe geometry and loadings conditions reported for the Civaux 1 case. Additionally, finite element analyses were used to check the thermal stress profiles and the stress intensity factors derived from the analytical model. The resulting predictions of crack growth life are comparable with those reported in the literature from more detailed analyses and are lower bound, as would be expected given the conservative assumptions made in the model.JRC.F.4-Nuclear design safet

Benchmark Analyses for Fracture Mechanics Methods for Assessing Sub-Clad Flaws - NESC-VI Final Report

The sixth project of the Network for Evaluating Structural Integrity (NESC-VI) deals with the fracture mechanics analysis of a set of 3 tests on beam specimens with simulated sub-surface flaws, which were performed by NRI Re¿ plc for the PHARE project ¿WWER Cladded Reactor Pressure Vessel Integrity Evaluation (with Respect to PTS Events)¿. The objectives were as follows: ¿ to assess the capability to predict whether the cracks propagating into the cladding arrest or cause full fracture, and ¿ to assess the capability to predict the location of first initiation: near-surface or deep crack tip. The project was launched in December 2006 and completed in March 2009. It brought together a group of 10 organisations from NESC to perform comparative analyses of selected tests, based on a comprehensive datapack prepared by NRI. The investigations focussed almost exclusively on assessing the capability to predict the location of first initiation. The main results are as follows: ¿ Comparison of analyses performed by individual partners showed that the FE simulations produced consistent predictions of the observed force vs. load-line displacement (or crack mouth opening displacement) behaviour. However the differences in predicted crack tip stress intensity, KJ, as a function of applied loading were greater than those found in similar intercomparisons made as part of previous NESC projects. This underlines the importance of periodically performing such exercises. ¿ The influence of two modelling factors on KJ was clearly established: firstly for this type of specimen, for which the clad makes up almost 12% of the cross-section, the associated residual stresses have a significant effect in reducing KJ values and therefore need to be considered in "best-estimate" analysis. The second concerns the use of 2-D or 3-D models: in this case the 2D FE models underestimated KJ values and are considered non-conservative. ¿ For this combination of test specimen geometry and flaw, constraint loss is expected at the near-surface tip. A range of constraint parameters were evaluated (elastic T-stress, elastic-plastic T-stress and Q) to confirm this. However only in two cases these were used in quantitative analyses: constraint-modified FAD and KIeff, both using elastic T-stress. These indicate that fracture is likely to initiate at lower (deep) tip, which is consistent with the limited high-speed video camera evidence. In general more systematic application of 2- parameter approaches is needed. ¿ Both local approach models predicted initiation of cleavage fracture first from the lower crack front for medium and higher loads. Concerning the capability to predict whether the cracks propagating into the cladding arrest or cause full fracture, the two analyses performed indicate that when the load at first pop-in is low, crack arrest in the clad can be correctly predicted on the basis of the J-R curve, but that further work is needed to ensure the reliability of such approaches over the full load range.JRC.F.4-Safety of future nuclear reactor

Fracture Tests to Study the Behaviour of Simulated Sub-Surface Flaws in a Reactor Pressure Vessel Steel - a Continuation of the NESC-IV project

The NESC-IV project (2000 - 2005) addressed the transferability of fracture toughness data from laboratory specimens to applications that assess the integrity of reactor pressure vessels. This project included a series of uniaxial bend tests on large beams with a simulated shallow, sub-surface flaw. The results of these experiments pointed towards a significant constraint-loss effect in the ductile-to-brittle transition temperature range of the used steel, but in view of the inherent scatter in fracture toughness of low alloy steels in the given regime, further testing was recommended. Therefore the scope of present project was to perform a set of six additional tests with nominally identical test piece geometry, material and loading arrangements, so as to obtain a statistically more relevant data set. The Institute for Energy contracted the Nuclear Research Institute in Rez to perform these experiments. Following the successful execution of the tests, a preliminary fracture mechanics analysis was made to compare estimates of the stress intensity values at failure with the material's Master Curve. The results confirmed the constraint-loss effect, which had been observed in the previous NESC-IV test series. Moreover it was found that some aspects needed further attention, such as detailed finite element modelling of the experimental arrangements and accurate characterization of the test material's fracture toughness. The latter should also consider material inhomogeneity issues.JRC.F.4-Safety of future nuclear reactor

PVP2008-61853 THERMAL FATIGUE CYCLIC-DOWN SHOCKS ON 316L MODEL PIPE COMPONENTS

ABSTRACT There is a continuing need for reliable thermal fatigue analysis tools to ensure that high safety levels are maintained in the main coolant lines of light water reactors. To advance the accuracy and reliability of thermal fatigue load determination, a combined experimental and numerical investigation has been conducted on cylindrical components of 316L stainless steel subjected to cyclic thermal shocks of varying intensity. Slightly different experimental conditions were applied in each test to explore the effect of ∆T max values of increasing severity, the effect of a superimposed static axial load and a reduced test piece wall thickness. Particular attention is given in this work to the influence of a constant tensile axial load on the quenching down shock damage. A comparison between thermal down-shock tests with and without additional constant tensile load is analysed in details here below

The future of road transport

A perfect storm of new technologies and new business models is transforming not only our vehicles, but everything about how we get around, and how we live our lives. The JRC report “The future of road transport - Implications of automated, connected, low-carbon and shared mobility” looks at some main enablers of the transformation of road transport, such as data governance, infrastructures, communication technologies and cybersecurity, and legislation. It discusses the potential impacts on the economy, employment and skills, energy use and emissions, the sustainability of raw materials, democracy, privacy and social fairness, as well as on the urban context. It shows how the massive changes on the horizon represent an opportunity to move towards a transport system that is more efficient, safer, less polluting and more accessible to larger parts of society than the current one centred on car ownership. However, new transport technologies, on their own, won't spontaneously make our lives better without upgrading our transport systems and policies to the 21st century. The improvement of governance and the development of innovative mobility solutions will be crucial to ensure that the future of transport is cleaner and more equitable than its car-centred present.JRC.C.4-Sustainable Transpor

Simulation and modelling of thermal fatigue damage in austenitic piping components

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Simulation and Modelling of Thermal Fatigue Damage in Austenitic Piping Components (thesis)

Abstract not availableJRC.F-Institute for Energy (Petten