scholarly journals Integrated Software Environment for Pressurized Thermal Shock Analysis

2011 ◽  
Vol 2011 ◽  
pp. 1-7 ◽  
Author(s):  
Dino Araneo ◽  
Paolo Ferrara ◽  
Fabio Moretti ◽  
Andrea Rossi ◽  
Andrea Latini ◽  
...  
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Boundary Conditions ◽  
Thermal Shock ◽  
Weight Functions ◽  
Software Environment ◽  
System Pressure ◽  
Pressurized Thermal Shock ◽  
Integrated Software

The present paper describes the main features and an application to a real Nuclear Power Plant (NPP) of an Integrated Software Environment (in the following referred to as “platform”) developed at University of Pisa (UNIPI) to perform Pressurized Thermal Shock (PTS) analysis. The platform is written in Java for the portability and it implements all the steps foreseen in the methodology developed at UNIPI for the deterministic analysis of PTS scenarios. The methodology starts with the thermal hydraulic analysis of the NPP with a system code (such as Relap5-3D and Cathare2), during a selected transient scenario. The results so obtained are then processed to provide boundary conditions for the next step, that is, a CFD calculation. Once the system pressure and the RPV wall temperature are known, the stresses inside the RPV wall can be calculated by mean a Finite Element (FE) code. The last step of the methodology is the Fracture Mechanics (FM) analysis, using weight functions, aimed at evaluating the stress intensity factor (KI) at crack tip to be compared with the critical stress intensity factor KIc. The platform automates all these steps foreseen in the methodology once the user specifies a number of boundary conditions at the beginning of the simulation.

RPV Structure Integrity Assessment With Surface Cracks Under PTS

2017 ◽  
Author(s):  
Wei Lu ◽  
Zheng He
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Stress Distribution ◽  
Intensity Factor ◽  
Thermal Shock ◽  
Surface Crack ◽  
Parameter Analysis ◽  
Integrity Assessment ◽  
Pressurized Thermal Shock

As one of the most critical barrier of pressurized-water reactor, Reactor Pressurized Vessel (RPV) is exposed to high temperature, high pressure and irradiation. During the lifetime of RPV, the core belt material will become brittle under the influence of neutron irradiation. The ductile-brittle transition temperature will increase and upper shelf energy will decrease. Thus the structure integrity evaluation of RPV concerning brittle fracture is one of the most important tasks of RPV lifetime management. The non-LOCA accident of Rancho Seco nuclear power plant in 1978 indicates that the emergent cooling transients the sudden cooling down may accompany with the re-pressurize of main loop. The combination of pressure loads and thermal loads may induce a large tensile stress in RPV internal surface, which is the so called pressurized thermal shock (PTS). Due to the existence of welding cladding on the inner surface of RPV, the discontinuity of stress distribution on the cladding-base interface of RPV wall will make calculation of stress-intensity-factor (SIF) difficult. In present research, a two dimensional axial-symmetrical model is built and Finite Element Method (FEM) is adopted to calculate the transient thermal distribution and stress distribution. The influence function method is adopted to calculate crack SIF. Stress distributions in the base and cladding are decomposed respectively and SIFs are calculated respectively to obtain the crack SIF. ASME method is used to calculate the fracture toughness. Present PTS program is validated by the comparative benchmark calculation (the International Comparative Assessment Study of Pressurized Thermal-Shock in Reactor Pressure Vessels). The calculated SIF from present program lies in the reasonable region of the comparing group results. A LOCA transient is investigated with a semi-elliptical surface crack on the RPV beltline region. The temperature and stress distribution along the vessel wall during the transient are given. The stress intensity factors at the deepest and interface point are given respectively. The integrity of RPV under PTS transient is evaluated by comparing stress intensity factor with fracture toughness. Results indicate that the stress intensity factor will not exceed the fracture toughness of the RPV material. The difference between the stress intensity factor and fracture toughness reach a minimum value at the crack tip temperature 20°C. Present research gives a reliable and efficient program to perform RPV structure integrity assessment with surface crack under PTS, which is suitable for further parameter analysis and probabilistic analysis.

Plastic Amplification β of the Stress Intensity Factor for Underclad Defect in a Vessel Submitted to a Pressurised Thermal Shock

2011 ◽  
Author(s):  
S. Marie
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Thermal Shock ◽  
Elastic Stress ◽  
Opening Displacement ◽  
Plastic Compression ◽  
Pressurized Thermal Shock ◽  
Calculation Results ◽  
Elastic Unloading

For the assessment of an under-clad defect in a vessel submitted to a pressurized thermal shock, the plasticity is considered through the amplification β of the elastic stress intensity factor KI in the ferritic part of the vessel. The current solution in the French RSE-M Code has been developed from a fitting of F.E. calculation results and specifies to keep constant the amplification (deduced from its value at the maximum loading point) when the stress intensity factor is decreasing. A more physical solution is proposed in this paper to deal with the initial increasing loading phase but also with the unloading phase. It takes into account two phenomena: the amplification of the elastic KI due to the plasticity in the cladding and a plastic zone correction in the ferritic part. The first amplification is determined assuming that the plasticity in the cladding could be represented as an imposed opening displacement on the crack lips. When the loading is decreasing, the model takes into account the initial elastic unloading of the cladding but also the plastic compression which leads to reduce the cladding influence on the loading of the crack tip located in the ferritic part.

Plasticity Correction on the Stress Intensity Factor Evaluation for Underclad Cracks Under Pressurized Thermal Shock Events

2016 ◽  
Author(s):  
Kai Lu ◽  
Jinya Katsuyama ◽  
Yinsheng Li
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Thermal Shock ◽  
Structural Integrity ◽  
Correction Method ◽  
Pressure Vessels ◽  
Ductile Material ◽  
Pressurized Thermal Shock ◽  
Inner Surface

When conducting structural integrity assessments for reactor pressure vessels (RPVs) under pressurized thermal shock (PTS) events, the stress intensity factor (SIF) is evaluated for a surface crack which is postulated near the inner surface of RPVs. It is known that cladding made of the stainless steel is a ductile material which is overlay-welded on the inner surface of RPVs for corrosion protection. Therefore, the plasticity of cladding should be considered in the SIF evaluation for a postulated underclad crack. In our previous study, we performed three-dimensional (3D) elastic and elastic-plastic finite element analyses (FEAs) for underclad cracks during PTS transients and discussed the conservatism of a plasticity correction method prescribed in the French code. In this study, additional FEAs were performed to further investigate the plasticity correction on SIF evaluation for underclad cracks. Based on the 3D FEA results, a new plasticity correction method was proposed for Japanese RPVs subjected to PTS events. In addition, the applicability of the new method was verified by studying the effects of the RPV geometry, cladding thickness and loading conditions. Finally, it is concluded that the newly proposed plasticity correction method can provide a more rational evaluation with a margin to some extent on SIFs of underclad cracks in Japanese three-loop RPVs.

Effect of Stress Intensity Factor Estimation Scheme on the Failure Probability of RPV During Pressurized Thermal Shock

2007 ◽  
Author(s):  
Kunio Onizawa ◽  
Kazuya Osakabe
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Thermal Shock ◽  
Base Metal ◽  
Surface Crack ◽  
Structural Integrity ◽  
Thermal Expansion Coefficients ◽  
Pressurized Thermal Shock ◽  
The Difference

During a pressurized thermal shock (PTS) event, the overlay cladding on the inner surface of reactor pressure vessel (RPV) is subjected to high tensile stress compared to base metal because of the difference in thermal expansion coefficients between cladding and base metal. To calculate a stress intensity factor for a postulated crack considering the stress discontinuity with the plastic yielding of cladding, the scheme developed previously has been incorporated into the PASCAL code for the structural integrity analysis. Using the new scheme, conditional probabilities of crack initiation (PCI) were calculated for a typical RPV with a surface crack or under-clad crack under some PTS transients. The PCI values were quantitatively evaluated as a function of neutron fluence using the PASCAL code. It is concluded that the new scheme reduces significantly the PCI value for a surface crack as compared with the conventional method based on elastic stress analysis.

scholarly journals Analysis of Axial Cracks in Hollow Cylinders Subjected to Thermal Shock by Using the Thermal Weight Function Method

1996 ◽  
Vol 118 (2) ◽  
pp. 146-153 ◽  
Author(s):  
C.-C. Ma ◽  
M.-H. Liao
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Weight Function ◽  
Thermal Shock ◽  
Function Method ◽  
Thermal Loading ◽  
Weight Functions ◽  
Weight Function Method ◽  
Hollow Cylinders

In this study, stress intensity factors for axial cracks in hollow cylinders subjected to thermal shock are determined by using the thermal weight function method. The thermal weight function is a universal function for a given cracked body and can be obtained from any arbitrary mechanical loading system. The thermal weight function may be thought of as Green’s function for the stress intensity factor of cracked bodies subject to thermal loadings. Once the thermal weight function for a cracked body is determined, the stress intensity factor for any arbitrary distributed thermal loading can be simply and efficiently evaluated through the integration of the product of the temperature and the correspondent thermal weight function. A numerical boundary element method for the determination of thermal weight functions for axial cracks in hollow cylinders is used in this study to evaluate the transient stress intensity factor. As a demonstration, some examples of axial cracks in hollow cylinders subjected to thermal shock are solved by using the thermal weight function method, and the results are compared with available results in the published literature.

Effects of Plasticity on the Stress Intensity Factor Evaluation for Underclad Crack Under Pressurized Thermal Shock Events

2015 ◽  
Author(s):  
Jinya Katsuyama ◽  
Ling Huang ◽  
Yinsheng Li ◽  
Kunio Onizawa
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Thermal Shock ◽  
Evaluation Method ◽  
Correction Method ◽  
Ductile Material ◽  
Pressurized Thermal Shock ◽  
Inner Surface ◽  
Plastic Correction

When the structural integrity of reactor pressure vessel (RPV) under pressurized thermal shock (PTS) events is assessed, an underclad crack is postulated at the inner surface of RPV and the stress intensity factor (SIF) corresponding to the driving force of non-ductile crack propagation, is evaluated for this crack. On the inner surface of RPV, cladding of the stainless steel is overlay-welded as a means for corrosion protection. Because the cladding is a ductile material, it is important to evaluate the SIF for postulated underclad crack considering the plasticity of cladding. A SIF evaluation method, which takes the effect of plasticity into account using a plastic correction method, has been established in France. In this study, we examined the SIF evaluation method established in France for underclad cracks during PTS transients. The elastic and elastic-plastic analyses based on the finite element method considering PTS events and inner pressure were performed using three-dimensional models including an underclad semi-elliptical crack with different geometry. We discussed the conservativeness of plastic correction method based on the analysis results.

Fracture Mechanics Analysis of a PWR Under PTS Using XFEM and Input From TRACE

2019 ◽  
Author(s):  
Diego F. Mora ◽  
Roman Mukin ◽  
Oriol Costa Garrido ◽  
Markus Niffenegger
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Fracture Mechanics ◽  
Intensity Factor ◽  
Boundary Conditions ◽  
Three Dimensional ◽  
Element Model ◽  
Integrity Assessment ◽  
Mechanics Analysis ◽  
Dynamic Cooling

Abstract In this paper, an integrity assessment of a reference Reactor Pressure Vessel (RPV) under Pressurized Thermal Shock (PTS) is performed. The assessment is based on a multi-step simulation scheme, which includes the thermo-hydraulic, thermo-mechanical and fracture mechanics analyses. The proposed strategy uses a three dimensional (3D) finite element model (FEM) of the RPV with the Abaqus code to solve the thermo-mechanical problem for the scenario of a Large-Break Loss-of-Coolant Accident (LBLOCA). In order to obtain the boundary conditions for the thermal analysis, the thermo-hydraulic results from a 3D RPV model developed in the system code TRACE are used. The fracture mechanics analysis is carried out on submodels defined on the areas of interest. Submodels containing cracks or flaws are also located in regions of the RPV where there might be a concentration of stresses during the PTS. The calculation of stress intensity factor (SIF) makes use of the eXtended FEM (XFEM) approach. The computed SIF of the postulated cracks at the inner surface of the RPV wall are compared with the ASME fracture toughness curve of the embrittled RPV material. For different transient scenarios, the boundary conditions were previously calculated with a computational fluid dynamics (CFD) model. However, cross-verification of the results has shown consistency of both CFD and TRACE models. Moreover, the use of the later is very convenient for the integrity analyses as it is clearly less computationally expensive than CFD. Therefore, it can be used to calculate different PTS scenarios including different break sizes and break locations. The main findings from fracture mechanics analyses of the RPV subjected to LBLOCA are summarized and compared. The presented results also allow us to study the influence of the dynamic cooling plume on the stress intensity factor in more detail than with the conventional one-dimensional method. However, the plumes calculated with both approaches are different. How much this difference affects the integrity assessment of the RPV is discussed in the paper.

Sign in / Sign up

Export Citation Format

Share Document