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PASCAL (PFM analysis of Structural Components in Aging LWR) is a PFM (Probabilistic Fracture Mechanics) code for evaluating the failure probability of aged pressure components. PASCAL has been developed as a part of the JAERI's research program on aging and structural integrity of LWR components, in order to respond to the increasing need of the probabilistic methodology in the regulation and inspection of nuclear components with the objective to provide a rational tool for the evaluation of the reliability and integrity of structural components.
In order to improve the accuracy and reliability of the analysis code, some new fracture mechanics models or computational techniques are introduced considering the recent progress in the state of the art and performance of PC. Thus some new analysis models and original methodologies were introduced in PASCAL such as the elastic-plastic fracture criterion based on R6 method, a new crack extension model of semi-elliptical crack evaluation and so on. Moreover a function to evaluate the effect of embrittlement recovery by annealing of irradiated RPV is also introduced in the code based on the USNRC R.G. 1.162(1996). The code has been verified through various failure analysis results and international PTS round robin analysis ICAS which had been organized by the Principal Working Group 3 of OECD/NEA/CSNI. In order to attain a high usability, PASCAL Ver.1 with GUI provides an exclusive FEM pre-processor Pre-PASCAL for generating the input load transient data, a GUI system for generating the input data for PASCAL main processor of main solver and post-processor for output data.
Pre-PASCAL is an exclusive 3-D FEM preprocessor for generating the input transient data provided with 3 RPV mesh models and two simple specimen mesh models, i.e. CT and CCP. Almost the same input data format with that of PASCAL main processor is used. Output data of temperature and stress distribution during the given transient has also the same format as PASCAL main processor. Thus the output data can be directly used as the input data of main processor.
PASCAL main solver
PASCAL main solver is a PFM (Probabilistic Fracture Mechanics) code for analyzing the conditional probability of crack initiation, crack arrest and vessel failure of the vessel under a pressure and thermal transient load. An ordinal PC with MS-Windows can be used. Many original functions are introduced.
PASCAL Ver.1_8B(2005) with GUI
PASCAL Ver.1_8B with GUI is the Load Module of the main processor with three functions:
User support GUI system for generating the input data,
Execution of main solver,
Post-processing GUI system of out put data for generating graphic illustration by using MS-EXCEL.
new version differs from previous version in the following features:
The source program of main solver of PASCAL_1_8_B is included.
Some minor corrections in GUI display were performed.
An English instruction of PrePASCAL (an exclusive FEM preprocessor for input data generation) is included. This instruction is installed in the Directory 'PrePASCAL'.
Main features of PASCAL:
Elasto-plastic fracture analysis based on R6 method is introduced. A fracture transition from brittle to ductile tearing can be analyzed based on the treatment of crack extension analysis of R6 method. An accuracy of failure probability around upper shelf temperature can significantly be improved. Thus, this code can be applicable to other components which exhibit the ductile fracture mode.
Initial flaw of an infinite edge crack and a semi-elliptical crack can be analyzed. For semi-elliptical crack extension analysis, three simulation models, i.e., Model 1, 2 and 3 are introduced as described later. Based on Model 3, an accurate crack extension analysis including the crack aspect ratio during extension can be performed compared with existing codes which employ a simplified analysis procedure.
Semi-elliptical initial flaw of a given aspect ratio, given length and given geometry and aspect ratio distribution can be analyzed.
An approximate method is introduced to evaluate the influence of overlay cladding by dividing the stress distribution into three distributions and superposing the stress intensity factors obtained from each distribution. In this method the overlay cladding is assumed to be sufficiently thin compared to base metal.
The effect of WPS is evaluated based on the assumption that the crack initiation and extension does not occur when the stress intensity factor is decreasing.
The effect of embrittlement recovery by thermal annealing of a vessel can be evaluated based on the method prescribed by USNRC R.G. 1.162-1996.
Effect of the crack detection capability by inspection can be evaluated.
Importance sampling and stratified sampling are used in Monte Carlo simulation. Functions to optimize the sampling number and cell dividing procedure in the stratified Monte Carlo simulation are introduced.
Various requirements of analyses can be supported by theuser input options and various material characteristics and many stress intensity factor solutions.
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Keywords: annealing, cladding, elasto-plastic fracture criterion, failure probability, light-water reactors, probabilistic fracture mechanics, reactor pressure vessel, structure.