Fracture-Mechanics Analysis of the Reactor Pressure Vessel Beznau 1 Based on Thermal-Hydraulics Input Data From KWU-MIX and CFD Analyses

2016 ◽  
Author(s):  
Tomas Nicak ◽  
Richard Trewin ◽  
Elisabeth Keim ◽  
Ingo Cremer ◽  
Sebastien Blasset ◽  
...  
Keyword(s):  
Fracture Mechanics ◽  
Thermal Shock ◽  
Pressure Vessel ◽  
Brittle Failure ◽  
Input Data ◽  
Cold Water ◽  
Reactor Pressure Vessel ◽  
Mechanics Analysis ◽  
Cfd Analyses ◽  
Reactor Pressure

The integrity of a reactor pressure vessel (RPV) has to be ensured throughout its entire life in accordance with the applicable regulations. Typically an assessment of the RPV against brittle failure needs to be conducted by taking into account all possible loading cases. One of the most severe loading cases, which can potentially occur during the operating time, is the loss-of-coolant accident, where cold water is injected into the RPV nearly at operating conditions. High pressure in combination with a thermal shock of the ferritic pressure vessel wall caused by the injection of cold water leads to a considerable load at the belt-line area known as Pressurized Thermal Shock (PTS). Usually the assessment against brittle failure is based on a deterministic fracture-mechanics analysis, in which common parameters like J-integral or stress intensity factor are employed to calculate the load path for an assumed (postulated) flaw during the PTS event. The most important input data for the fracture-mechanics analysis is the transient thermal-hydraulics (TH) load of the RPV during the emergency cooling. Such data can be calculated by analytical fluid-mixing codes verified on experiments, such as KWU-MIX, or by numerical Computational Fluid Dynamics (CFD) tools after suitable validation. In KWU-MIX, which is the standard used for TH calculations within PTS analyses, rather conservative analytical models for the quantification of mixing and, depending on the water level, condensation processes in the downcomer (including simplified stripe and plume formations) are utilized. On the contrary, the numerical CFD tools can provide best-estimate results due to the possibility to consider more realistically the stripe and plume formations as well as the geometry of the RPV in detail. In order to quantify the safety margin inherent to the standard approach, two fracture-mechanics analyses of the RPV Beznau 1 based on thermal-hydraulic input data from KWU-MIX and CFD analyses were performed. Subsequently the resulting loading paths were compared between each other and with material properties obtained from the irradiation surveillance program of the RPV to demonstrate the exclusion of brittle-fracture initiation.

XFEM and Standard Fracture-Mechanics Analyses of the Reactor Pressure Vessel Gösgen Based on Thermal-Hydraulics Input Data From KWU-MIX and CFD Analyses

2019 ◽  
Author(s):  
Alexander Mutz ◽  
Tomas Nicak ◽  
Richard Trewin ◽  
Ingo Cremer
Keyword(s):  
Fracture Mechanics ◽  
Thermal Shock ◽  
Pressure Vessel ◽  
Brittle Failure ◽  
Input Data ◽  
Cold Water ◽  
Reactor Pressure Vessel ◽  
Thermal Hydraulics ◽  
Mechanics Analysis ◽  
Reactor Pressure

Abstract The integrity of a reactor pressure vessel (RPV) has to be ensured throughout its entire life in accordance with the applicable regulations. Typically an assessment of the RPV against brittle failure needs to be conducted by taking into account all possible loading cases. One of the most severe loading cases, which can potentially occur during the operating time, is the loss-of-coolant accident, where cold water is injected into the RPV at operating conditions. High pressure in combination with a thermal shock of the ferritic pressure vessel wall caused by the injection of cold water leads to a considerable load at the belt-line area known as Pressurized Thermal Shock (PTS). Usually the assessment against brittle failure is based on a deterministic fracture-mechanics analysis, in which common parameters like J-integral or stress intensity factor are employed to calculate the load path for an assumed (postulated) flaw during the PTS event. As an alternative to this standard approach a fracture mechanics assessments based on eXtended Finite Element Method (XFEM) approach can be performed. The most important input data for the fracture-mechanics analysis is the transient thermal-hydraulics (TH) load of the RPV during the emergency cooling. Such data can be calculated by analytical fluid-mixing codes verified on experiments, such as KWU-MIX, or by numerical Computational Fluid Dynamics (CFD) tools after suitable validation. In KWU-MIX, which is the standard used for TH calculations within PTS analyses, rather conservative analytical models for the quantification of mixing and, depending on the water level, condensation processes in the downcomer (including simplified stripe and plume formations) are utilized. On the contrary, the numerical CFD tools can provide best-estimate results due to the possibility to consider more realistically the stripe and plume formations as well as the geometry of the RPV in detail. In a previous paper [1] results of standard and XFEM analyses of the RPV Gösgen 1 based on thermal-hydraulics input data from KWU-MIX were presented. This paper presents new results based on thermal-hydraulics input data from CFD. The new results are compared with those from [1] in order to show additional safety margins obtained by using thermal-hydraulics input data from CFD.

Application of XFEM to Model Crack Initiation and Propagation During a PTS Event

2015 ◽  
Author(s):  
Tomas Nicak ◽  
Alexander Mutz ◽  
Elisabeth Keim ◽  
Gottfried Meier
Keyword(s):  
Fracture Mechanics ◽  
Crack Initiation ◽  
Thermal Shock ◽  
Pressure Vessel ◽  
Brittle Failure ◽  
Cold Water ◽  
Operating Time ◽  
Operating Conditions ◽  
Mechanics Analysis ◽  
Severe Loading

The integrity of a reactor pressure vessel (RPV) has to be ensured throughout its entire life in accordance with the applicable regulations. Typically an assessment of the RPV against brittle failure needs to be conducted by taking into account all possible loading cases. One of the most severe loading cases, which can potentially occur during the operating time, is the loss-of-coolant accident (LOCA), where cold water is injected into the RPV at operating conditions. High pressure in combination with a thermal shock of the ferritic pressure vessel wall caused by the injection of cold water leads to severe loading conditions at the beltline area known as Pressurized Thermal Shock (PTS). Usually the assessment against brittle failure is based on a deterministic fracture mechanics analysis, in which common parameters like the J-integral or stress intensity factor are employed to calculate the load path during the PTS event for an assumed (postulated) flaw. Subsequently the results of the fracture mechanics analysis are compared with material properties obtained from the irradiation surveillance program of the RPV to demonstrate the exclusion of brittle fracture initiation. In this paper an alternative novel method for the calculation of the crack initiation and possible crack propagation by means of the eXtended Finite Element Method (XFEM) will be introduced and compared with results of the standard PTS analysis.

scholarly journals Recent verification activities on probabilistic fracture mechanics analysis code PASCAL4 for reactor pressure vessel

2020 ◽  
Vol 7 (3) ◽  
pp. 19-00573-19-00573
Author(s):  
Kai LU ◽  
Jinya KATSUYAMA ◽  
Yinsheng LI ◽  
Yuhei MIYAMOTO ◽  
Takatoshi HIROTA ◽  
...  
Keyword(s):  
Fracture Mechanics ◽  
Pressure Vessel ◽  
Reactor Pressure Vessel ◽  
Probabilistic Fracture Mechanics ◽  
Mechanics Analysis ◽  
Reactor Pressure

CFD-Tools for Assessment of the Reactor Pressure Vessel Integrity in Pressure Thermal Shock Conditions: Thermal-Hydraulic Methods and Main Industrial Results on the French 900 MWe PWR RPV

2009 ◽  
Author(s):  
A. Martin ◽  
F. Lestang ◽  
S. Bellet ◽  
D. Guichard ◽  
C. Vit ◽  
...  
Keyword(s):  
Thermal Shock ◽  
Pressure Vessel ◽  
Cold Water ◽  
Reactor Pressure Vessel ◽  
Fluid Temperature ◽  
Time Duration ◽  
Two Phase ◽  
Safety Margins ◽  
Reactor Pressure ◽  
Fast Fracture

For the Reactor Pressure Vessel (RPV) assessment and lifetime evaluation of the nuclear plants, French Utilities apply a series of calculations including thermal-hydraulic, thermo mechanical and fracture mechanics studies in order to study the Pressurized Thermal Shock (PTS) in the downcomer caused by the safety injection. Within the frame of the plant lifetime project, integrity assessments of the French 900 MWe (3-loops) series RPV have been performed. A gain for safety margins to fast fracture of the RPV can be found with a 3D modeling of thermal-hydraulics loads. From a physical phenomena point of view, the results of the system code analysis (CATHARE computation) of the PTS transient induce two kinds of scenarios: single phase and two-phase flows in the cold leg. In the case where the cold legs are partially filled with steam, it becomes a two-phase problem and new important effects occur. Thus, an advanced prediction of RPV thermal loading during these transients requires sophisticated two-phase, local scale, 3D codes. For that purpose, a program has been set up to extend the capabilities of the NEPTUNE_CFD two-phase solver which is the tool able to solve two-phase flow configuration. At the same time, a simplified approach has shown that for this kind of scenario where the cold leg is weakly uncovered, a free surface calculation (without phase change) was sufficient to respect the necessary criteria of safety. Considering the time duration of 3D computation and the large number of cases, EDF and AREVA-NP decided to share the effort. The two teams use the NEPTUNE_CFD code (coupled with the thermal solid SYRTHES code) for thermal-hydraulic computations. The thermo mechanical code used is CALORI. According to this approach and to reduce the CPU time, two computations have been performed for 2″ and 3″ Small Break Loss Of Coolant Accident (SBLOCA) on a one-third RPV model. Computations on a complete RPV model have been performed to demonstrate the relevance of the one-third RPV model. The studies have been performed by two independent teams from EDF and AREVA-NP. The investigated configuration corresponds to the injection of cold water in the RPV during a penalizing representation of a primary break transient and its impact on the solid part formed by cladding and base metal. Numerical results are given in terms of fluid temperature in the cold legs and in the downcomer. The obtained numerical description of the transient is used as boundary conditions for a full mechanical computation of the stresses. The results show that such a complete thermal-hydraulic and mechanical 3-dimensional analysis improves the evaluation of the consequences of the loading on the stress fields and eventually the margins to fast fracture of the RPV. The good agreement observed between a one-third RPV model and a complete RPV model results confirms the validity of the approach.

Influence Factors of Fracture Mechanics Analysis of Reactor Pressure Vessel under Pressurized Thermal Shock

2019 ◽  
Vol 795 ◽  
pp. 333-339
Author(s):  
Juan Luo ◽  
Jia Cheng Luo
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Thermal Shock ◽  
Neutron Irradiation ◽  
Pressure Vessel ◽  
Influence Factors ◽  
Pressurized Thermal Shock ◽  
Inner Surface ◽  
Mechanics Analysis ◽  
Reactor Pressure

When the reactor pressure vessel (RPV) is subjected to pressurized thermal shock (PTS), the cooling water injected by the emergency core cooling system (ECCS) will generate a large temperature difference in the wall thickness of the pressure vessel. On the other hand, the fracture toughness of the RPV material decreases a lot under long-term neutron irradiation. Under this condition, the PTS transient may cause a rapid growth of defects in the inner surface of the vessel, resulting in failure of the pressure vessel. In this paper, the fracture mechanics analysis method of RPV under pressurized thermal shock is studied. The thermal analysis and structural analysis of the pressure vessel are performed by finite element method. The stress intensity factor and fracture toughness are obtained through calculation. At the same time, the influence factors of fracture mechanics analysis of RPV under PTS condition are analyzed. The effects of different crack size, crack type, load transient, and neutron irradiation flux on the PTS fracture mechanics analysis results are evaluated. Results show that the larger the ratio of length to depth for axial inner surface cracks, the easier RPV crack grows. Under small break condition, the circumferential cracks are safer than axial cracks. The longer the operating time, the more severe the embrittlement of RPV materials, which will lead to the failure of RPV more easily. For the two typical PTS transients studied in this paper, the re-pressurization condition is safer than the small break condition. The results can provide basis for structural integrity assessment of RPV under PTS condition.

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