Probability of Fracture and Life Extension Estimate of the High-Flux Isotope Reactor Vessel

1998 ◽  
Vol 120 (3) ◽  
pp. 290-296 ◽  
Author(s):  
S.-J. Chang
Keyword(s):  
Transition Temperature ◽  
Hydrostatic Pressure ◽  
Fracture Probability ◽  
Reactor Vessel ◽  
Numerical Results ◽  
Life Extension ◽  
Time Interval ◽  
High Flux ◽  
Vessel Steel ◽  
Pressure Test

The state of the vessel steel embrittlement as a result of neutron irradiation can be measured by its increase in ductile-brittle transition temperature (DBTT) for fracture, often denoted by RTNDT for carbon steel. This transition temperature can be calibrated by the drop-weight test and, sometimes, by the Charpy impact test. The life extension for the high-flux isotope reactor (HFIR) vessel is calculated by using the method of fracture mechanics that is incorporated with the effect of the DBTT change. The failure probability of the HFIR vessel is limited as the life of the vessel by the reactor core melt probability of 10−4. The operating safety of the reactor is ensured by periodic hydrostatic pressure test (hydrotest). The hydrotest is performed in order to determine a safe vessel static pressure. The fracture probability as a result of the hydrostatic pressure test is calculated and is used to determine the life of the vessel. Failure to perform hydrotest imposes the limit on the life of the vessel. The conventional method of fracture probability calculations such as that used by the NRC-sponsored PRAISE CODE and the FAVOR CODE developed in this Laboratory are based on the Monte Carlo simulation. Heavy computations are required. An alternative method of fracture probability calculation by direct probability integration is developed in this paper. The present approach offers simple and expedient ways to obtain numerical results without losing any generality. This approach provides a clear analytical expression on the physical random variables to be integrated, yet requires much less computation time. In this paper, numerical results on 1) the probability of vessel fracture, 2) the hydrotest time interval, and 3) the hydrotest pressure as a result of the DBTT increase are obtained. Limiting the probabilities of the vessel fracture as a result of hydrotest to 10−4 implies that the reactor vessel life can be extended up to 50 EFPY (100 MW) with the minimum vessel operating temperature equal to 85°F.

A Fracture Probability Integral for HFIR Accident Analysis

2004 ◽  
Author(s):  
Shih-Jung Chang
Keyword(s):  
Fracture Toughness ◽  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
Fracture Probability ◽  
Reactor Vessel ◽  
Operating Life ◽  
Vessel Steel ◽  
Ductile Brittle Transition Temperature ◽  
Probability Calculation ◽  
Probability Of Fracture

The state of the reactor vessel steel embrittlement as a result of neutron irradiation is reflected by its increase in ductile-brittle transition temperature (DBTT) in fracture toughness versus temperature curve. Higher DBTT implies a decrease in fracture toughness and an increase in the chance of vessel fracture in brittle fracture mode. The extent of degradation that the High Flux Isotope Reactor (HFIR) vessel has experienced is characterized by its probability of fracture that is defined as a probability count of the number of critical cracks in the reactor vessel based on a distribution of possible cracks. In this paper, the fracture probabilities under the accident pressure conditions against possible HFIR operating life are calculated for the safety analysis of the reactor vessel. Conventional methods of fracture probability calculation such as that adopted by the NRC-sponsored PRAISE CODE and the FAVOR CODE developed in this Laboratory are based on Monte Carlo simulation. Heavy computations are required. The present calculations are based on a new method of fracture probability calculation that was developed by applying direct probability integration [1]. This method offers simple and expedient procedure to obtain numerical values of fracture probability yet retains all possible features that a Monte Carlo simulation can possibly accomplish.

Fracture Probability Integral Applied to Reactor Vessel Life Estimate1

2001 ◽  
Vol 123 (3) ◽  
pp. 346-354
Author(s):  
Shih-Jung Chang
Keyword(s):  
Fracture Toughness ◽  
Monte Carlo Simulation ◽  
Random Variables ◽  
Temperature Shift ◽  
Fracture Probability ◽  
Reactor Vessel ◽  
Vessel Steel ◽  
Radiation Induced ◽  
Probability Integral ◽  
Probability Of Fracture

The conventional method of fracture probability calculations such as that adopted by the NRC-sponsored PRAISE CODE and the FAVOR CODE developed in this laboratory are both based on Monte Carlo simulation. Heavy computations are required. A new method of fracture probability calculation is developed by direct probability integration. The preliminary version of the development was published in an earlier paper. More detailed development of the method is presented here. The present approach offers simple and expedient method to obtain numerical values of fracture probability. This method can be applied to problems as general as the method of Monte Carlo simulation. This approach also provides a clear physical picture on the meaning of the probability of fracture. Parametric studies are made in this paper to show the variation of the numerical values of the probabilities of fracture as a result of the change of the standard deviation of either fracture toughness or the radiation-induced temperature shift. Also, it is shown numerically that a limiting probability can be obtained if the standard deviation of the fracture toughness approaches zero that implies a deterministic fracture toughness. It confirms the theoretical proof shown in Eq. (11). The limiting probability is the simplistic probability of crack count used by this author where both toughness and temperature shift are assumed to be deterministic values. The general probability of fracture developed here is simply a generalization of the crack count, except the crack count is selected with the appropriate fracture toughness in the toughness distribution. The toughness for the problem considered here is then multiplied by the appropriate temperature shift in the distribution function of the temperature shift. Although the present development is based on linear fracture mechanics assumption and applied to the radiated reactor vessel steel, there is no difficulty in viewing the present development as a general formulation that is capable of handling as many random variables as required by the fracture model. The multiplicity of the integration corresponds to the number of random variables. The probability integral is applied in this paper to calculate the probability of fracture for the high flux isotope reactor (HFIR) vessel that has been weakened due to the radiation embrittlement. The random variables used here are the crack length, the fracture toughness, and the radiation-induced temperature shift that is needed in the parametric representation of the radiated vessel steel.

Fabrication and study the effect of the laser on the properties of the compound Tl2-xHgxBa2-ySryCa2Cu3O10+δ superconductor

2018 ◽  
pp. 168
Author(s):  
A. Kareem Dahash Ali ◽  
Nihad Ali Shafeek
Keyword(s):  
Transition Temperature ◽  
Solid State ◽  
Hydrostatic Pressure ◽  
Electrical Properties ◽  
Co2 Laser ◽  
Temperature Shift ◽  
Unit Cell ◽  
X Ray Diffraction ◽  
X Ray ◽  
Structural And Electrical Properties

This study included the fabrication of    compound (Tl2-xHgxBa2-ySryCa2Cu3O10+δ) in a manner solid state and under hydrostatic pressure ( 8 ton/cm2) and temperature annealing(850°C), and determine the effect of the laser on the structural and electrical properties elements in the compound, and various concentrations of x where (x= 0.1,0.2,0.3 ). Observed by testing the XRD The best ratio of compensation for x is 0.2 as the value of a = b = 5.3899 (A °), c = 36.21 (A °) show that the installation of four-wheel-based type and that the best temperature shift is TC= 142 K  .When you shine a CO2 laser on the models in order to recognize the effect of the laser on these models showed the study of X-ray diffraction of these samples when preparing models with different concentrations of the values ​​of x, the best ratio of compensation is 0.2 which showed an increase in the values ​​of the dimensions of the unit cell a=b = 5.3929 (A °), c = 36.238 (A°). And the best transition temperature after shedding laser is TC=144 K. 

The Bending, Buckling, and Flexural Vibration of Simply Supported Polygonal Plates by Point-Matching

1961 ◽  
Vol 28 (2) ◽  
pp. 288-291 ◽  
Author(s):  
H. D. Conway
Keyword(s):  
Hydrostatic Pressure ◽  
Boundary Conditions ◽  
Flexural Vibration ◽  
Frequency Equation ◽  
Numerical Results ◽  
Special Technique ◽  
Point Matching ◽  
Buckling Loads ◽  
Simply Supported ◽  
Flexural Vibrations

The bending by uniform lateral loading, buckling by two-dimensional hydrostatic pressure, and the flexural vibrations of simply supported polygonal plates are investigated. The method of meeting the boundary conditions at discrete points, together with the Marcus membrane analog [1], is found to be very advantageous. Numerical examples include the calculation of the deflections and moments, and buckling loads of triangular square, and hexagonal plates. A special technique is then given, whereby the boundary conditions are exactly satisfied along one edge, and an example of the buckling of an isosceles, right-angled triangle plate is analyzed. Finally, the frequency equation for the flexural vibrations of simply supported polygonal plates is shown to be the same as that for buckling under hydrostatic pressure, and numerical results can be written by analogy. All numerical results agree well with the exact solutions, where the latter are known.

Local Hydrostatic Pressure Test for Cylindrical Vessels

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
H. Al-Gahtani ◽  
A. Khathlan ◽  
M. Sunar ◽  
M. Naffa'a
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Hydrostatic Pressure ◽  
Cylindrical Vessel ◽  
Geometrical Parameters ◽  
The Finite Element Method ◽  
Wide Range ◽  
Pressure Test ◽  
Local Test ◽  
Alternative Test

The juncture of a small cylindrical nozzle to a large cylindrical vessel is very common in the pressure vessel industry. Upon fabrication, it is required that the whole structure is subjected to pressure testing. The test can be expensive as it necessitates pressurizing the whole structure typically having a large volume. Hence, it is proposed to make a “local test,” which is considerably simpler as it involves capping the small nozzle and testing only a relatively small portion of the structure. This paper investigates the accuracy and reliability of such an alternative test, using the finite-element method. Two different finite-element types are used in the study, specifically a shell-based element and a solid-based element. The verification of the finite-element results for two different cases shows that the models used in the study are valid. It also proves that the two element types yield very similar stress results. In addition, the study includes a numerical investigation of more than 40 different nozzle-to-vessel junctures with a wide range of parameters for the nozzle and vessel. The results indicate that the use of cylindrical caps that are slightly larger than the nozzle is not recommended as it produces stresses that are significantly different from those for the original required pressure test. As such, the study provides an estimate of the smallest size of the cap that may be used in the local test to generate stresses that agree with the full test. For most practical geometries, it is shown that the size of the cap needs to be at least 2–30 times larger than that of the nozzle, depending on the geometrical parameters of the juncture.

PED Certified Recuperator for Micro Gas Turbines

2017 ◽  
Author(s):  
Yves De Vos ◽  
Jean-Paul Janssens ◽  
Leo van Kooten ◽  
Jörg Alexnat
Keyword(s):  
Hydrostatic Pressure ◽  
Gas Turbines ◽  
High Performance ◽  
Modular Design ◽  
Quality Management System ◽  
Operating Time ◽  
Operating Point ◽  
Maximum Deviation ◽  
Operating Pressure ◽  
Pressure Test

The design and certification of a high performance recuperator for micro gas turbines is presented. The component has been developed and built for a 100kWel micro gas turbine. The recuperator heated up compressed air at 3.5 bar with exhaust gas near atmospheric pressure and recuperates 300 kWth at an effectiveness of 90%. This concept can readily be adapted for other micro gas turbines due to its modular design. The certification has been realized under Pressure Equipment Directive 97/23/EC, equivalent to ASME Boiler and Pressure Vessel Code, covering closed pressurized devices. However, minor leakage in the recuperator is allowed, thus requiring an inventive design and validation approach for meeting the certification requirements. This leak is caused by weld porosity: the heat exchanging core plates are laser welded, having over 1200 meters of sealing weld length in a single recuperator. The maximum allowable leak amounts to 3 10−6 mm2 per meter weld length. The maximum leak was 0.2% of the massflow on the pressurized side at the nominal operating point, and therefore did not adversely affect the effectiveness of the recuperator. The finite element calculations and the resulting design loops on components and weld connections are presented. Validation of the entire component is done under the Experimental Design Method. A hydrostatic pressure test at 8.4 bar and ambient temperature is executed in the presence of a certified notified body to demonstrate that the welds are sufficiently robust. This pressure is higher than the operating pressure to simulate the effect of temperature on the steel properties. A laser scanner is used to map the deformation of the unit under pressure and subsequently referenced to its original state. The maximum deviation measured is equal to 0.26 mm for the pressurized part, which is acceptable considering the size of the unit is 1000mm × 600mm × 1000mm. The strain levels went back to the values before putting the unit under pressure, indicating there are no residual deformations. The test is further accompanied with leakage rate measurements before and after the hydrostatic pressure test. If the difference between these leakages rates is within limits, the recuperator will pass the test. The measured total leakage area is 0.4 mm2, well below the maximum allowable value, and equivalent to 0.01% of the massflow at the nominal operating point. This means the recuperator passed the test successfully. Furthermore, a burst test was executed to determine the safety factor and to identify the weakest element of the design. The burst pressure is observed at 18.3 bar, resulting in a safety margin of 218% and 523% in reference to the PED and operational design pressures, respectively. The component responsible for failure has been further optimized for the next generation of recuperators. Field data confirm that the lifetime of the high performance recuperator meets the requirements of 40.000 h operating time. Additionally, the traceability of the serial produced components is handled by the audited quality management system. It covers the used materials, including lot traceability, the measured process characteristics and welder certifications. The approach can also be used for ASME certification.

scholarly journals Performance Sensitivity to the High-Order Statistics of Time Interval Variables in Cellular Networks

2020 ◽  
Vol 2020 ◽  
pp. 1-16
Author(s):  
Felipe A. Cruz-Pérez ◽  
Genaro Hernandez-Valdez ◽  
Andrés Rico-Páez ◽  
Sandra L. Castellanos-López ◽  
José R. Miranda-Tello ◽  
...  
Keyword(s):  
Cellular Networks ◽  
System Performance ◽  
Performance Metrics ◽  
Numerical Results ◽  
Time Interval ◽  
Forced Termination ◽  
Mobile Cellular ◽  
Interval Variables ◽  
Mobile Cellular Networks ◽  
Forced Termination Probability

Cell dwell time (DT) and unencumbered interruption time (IT) are fundamental time interval variables in the teletraffic analysis for the performance evaluation of mobile cellular networks. Although a diverse set of general distributions has been proposed to model these time interval variables, the effect of their moments higher than the expected value on system performance has not been reported in the literature. In this paper, sensitivity of teletraffic performance metrics of mobile cellular networks to the first three standardized moments of both DT and IT is investigated in a comprehensive manner. Mathematical analysis is developed considering that both DT and IT are phase-type distributed random variables. This work includes substantial numerical results for quantifying the dependence of system level performance metrics to the values of the first three standardized moments of both DT and IT. For instance, for a high mobility scenario where DT is modeled by a hyper-Erlang distribution, we found that call forced termination probability decreases around 60% as the coefficient of variation (CoV) and skewness of DT simultaneously change from 1 to 20 and from 60 to 2, respectively. Also, numerical results confirm that as link unreliability increases the forced termination probability increases while both new call blocking and handoff failure probabilities decrease. Numerical results also indicate that for low values of skewness, performance metrics are highly sensitive to changes in the CoV of either the IT or DT. In general, it is observed that system performance is more sensitive to the statistics of the IT than to those of the DT. Such understanding of teletraffic engineering issues is vital for planning, designing, dimensioning, and optimizing mobile cellular networks.

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