Sang-Min Lee

Fluid Structure Interaction Analysis on Wall Thinned Pipes

The wall thinning due to erosion, corrosion and flow accelerated corrosion is one of critical issues in nuclear industry. To secure against loss of integrity of pipes with a flaw, ASME Code Section III and Code Case N-597 etc have been used in design and operating stages, respectively. However, despite of their inherent conservatisms, it may reach unanticipated accidents due to degradation at local region. In this paper, a new evaluation scheme is suggested to estimate load-carrying capacities of wall thinned pipes. At first, computational fluid dynamics analyses employing steady-state and incompressible flow are carried out to determine pressure distributions in accordance with conveying fluid. Then, the discriminate pressures are applied as input condition of structural finite element analyses to calculate local stresses at the deepest point. A series of combined analyses were performed for different fluid flow velocities as well as d/t, Rm/t and l/t ratios. The efficiency of proposed scheme was proven from comparison with conventional analyses results and it is recommended to consider the fluid structure interaction effect for exact integrity evaluation.

Development of a Web-Based Integrity Evaluation System for Primary Components in a Nuclear Power Plant

A nuclear power plant is composed of a number of primary components. Maintaining the integrity of these components is one of the most critical issues in nuclear industry. In order to maintain the integrity of these primary components, a complicated procedure is required including periodical in-service inspection, failure assessment, fracture mechanics analysis, etc. Also, experts in different fields have to co-operate to resolve the integrity issues on the basis of inspection results. This integrity evaluation process usually takes long, and thus, is detrimental for the plant productivity. Therefore, an effective safety evaluation system is essential to manage integrity issues on a nuclear power plant. In this paper, a web-based integrity evaluation system for primary components in a nuclear power plant is proposed. The proposed system, which is named as WEBIES (WEB-based Integrity Evaluation System), has been developed in the form of 3-tier system architecture. The system consists of three servers; application program server, user interface program server and data warehouse server. The application program server includes the defect acceptance analysis module and the fracture mechanics analysis module which are programmed on the basis of ASME Sec. XI, Appendix A. The data warehouse server provides data for the integrity evaluation including material properties, geometry information, inspection data and stress data. The user interface program server provides information to all coworkers in the field of integrity evaluation. The developed system provides engineering knowledge-based information and concurrent and collaborative working environment through internet, and thus, is expected to raise the efficiency of integrity evaluation procedures on primary components of a nuclear power plant. Introduction To maintain integrity for primary components operating under high temperature and high pressure in a nuclear power plant, periodical in-service inspection (ISI) and fracture mechanics analysis (FMA) are conducted. Primary components in a nuclear power plant may contain flaws due to manufacturing process or operating conditions. Some of flaws may grow up to a significant size under repetitive fatigue loading. If a flaw is detected during ISI, the fracture mechanics analysis should be conducted to evaluate the integrity of components which accompanies a complicated procedure and special engineering knowledge. In 1990s, a number of pc-based integrity evaluation programs for primary components in a nuclear power plant have been developed [1-3]. However, those pc-based programs provided calculation results only, and thus users experienced difficulties in managing information on integrity evaluation process. Above all, the major document for the integrity assessment such as ASME boiler and pressure vessel code section XI [4] has been subjected to frequent revision, and thus, made those pc-based programs obsolete to use for field application. All correspondences are to be sent to Professor Choi at boong33@skku.edu, Fax: +82-31-290-5276 Key Engineering Materials Online: 2004-08-15 ISSN: 1662-9795, Vols. 270-273, pp 2226-2231 doi:10.4028/www.scientific.net/KEM.270-273.2226

Development of an Integrity Evaluation System for Steam Generator Tubes in a Nuclear Power Plant

Steam generators working in nuclear power plants convert water into steam from heat produced in the reactor core and each of them contains from 3,000 to 16,000 tubes. Since these tubes constitute one of primary barriers under radioactive and high pressure condition, the integrity should be maintained carefully during the operation. The objective of this research is to introduce an integrity evaluation system for steam generator tubes as a substitute of well-trained engineers or experts. For this purpose, a couplet examination has been carried out on the complicated evaluation procedure and an efficient system named as STiES was developed employing three representative integrity evaluation methods: fracture mechanics analysis (crack driving force diagram and J-integral/Tearing modulus method) and limit load method. Exemplary analyses for steam generator tubes with various types of flaws showed good applicability of the proposed integrity evaluation system. So, it is anticipated that the system can be used for the calculation of reference pressure to decide either the continued operation or repair until next outage.

Investigation on Levitation and Restitution Mechanisms of FPD Air Handling System

The purpose of this paper is to investigate principles of levitation and restitution of blowing nozzle prior to fabricating a prototype of air handling system. Since air force distributions streaming bottom surface of a flat panel display (FPD) highly dependent on operating as well as design condition and configuration of air handling system, influences of various parameters such as flow rate, supply air pressure, floating height and tilted angle are examined through a series of computational fluid dynamics (CFD) analyses. Moreover, dynamic finite element analyses of the FPD are carried out to assure that an oscillation effect caused by disturbances is not significant. Key findings from the both CFD and structural analysis results are presented and discussed, which can be utilized as technical bases for development of the practical air handling system.

The Pressure-Temperature Limit Curve of System-Integrated Modular Advanced Reactor Against Nonductile Failure

A system-integrated modular advanced reactor is being developed for multi purposes such as electricity production, sea water desalination and so on in Korea. While ASME Codes provide simplified design and operation procedures to determine allowable loadings for pressure retaining materials in components, the procedures are applicable when a temperature change rate associated with startup and shutdown is less than about 56°C/hr. If the procedures are applied to a rapid temperature change, results would be overly conservative. The objective of this research is to assess an applicability of the simplified design procedures to reactor coolant system of the integrated modular reactor with the change rates of 56°C/hr and 100°C/hr. To investigate effects of cooldown rate, heatup rate and surface crack location, systematic three-dimensional finite element analyses are carried out. The resulting pressure-temperature limit curves are compared with those obtained from the ASME Sec. XI operating procedure as well as Sec. III design procedure. Thereby, it was proven that the specific design features significantly affect the safe design region in the pressure-temperature limit curve to prevent a nonductile failure.Copyright

Risk Assessments of Columns Using RBI Program in Petrochemical Plant

Risk-based inspection (RBI) guideline based on API 581 provides a methodology for calculating the risks of equipment in refinery or petrochemical plant. However, there is a major limitation of its application to the petrochemical plant directly since only a representative material is considered in calculating the risk, especially in part of the consequence of failure, even though the equipment is composed of numerous materials. The objectives of this paper are to develop an enhanced RBI program to resolve shortcoming inclusive of the above issue and to evaluate the risks of equipment in petrochemical plant using the program. In this respect, the mole fractions of materials were used to fully incorporate the characteristics of different materials. The proposed RBI program consists of qualitative, semi-quantitative and quantitative risk evaluation modules in which toxic materials as well as representative materials were selected automatically for comparison with those in the current guideline. The RBI program has been applied to evaluate the risks of equipment in Naphtha Cracking Center (NCC) which is a typical facility of petrochemical plant. Thereby, promising evaluation results were obtained and applicability of the proposed RBI program was proven.

Structural Integrity Assessment of Major Nuclear Components Using Probabilistic Fracture Mechanics

The integrity of major components in nuclear power plant should be maintained during operation. In order to maintain the integrity of these components, complicated assessment procedures are required including fracture mechanics analysis, etc. The integrity assessment of components has been performed by using conventional deterministic approaches whilst there are lots of uncertainties to carry out a rational evaluation. In this respect, probabilistic integrity assessment is considered as an alternative method for nuclear component evaluation. The objectives of this paper are to develop an integrity assessment system based on probabilistic fracture mechanics and to estimate the failure probability of major nuclear components containing a defect. The integrity assessment system consists of three evaluation modules which are first order reliability method, second order reliability method and crude Monte Carlo simulation method. The developed system has been applied to evaluate failure probabilities of nuclear structural components such as steam generator tube and piping. The evaluation results showed a promising applicability of the probabilistic integrity assessment system.

Development of Risk-Based Inspection Software for Petrochemical Plant

Risk-based inspection (RBI) guideline based on API 581 provides a methodology for calculating the risks of equipments in refinery or petrochemical plants. However, there are limitations of such application to the petrochemical plant directly since only a representative material is considered in calculating the risk, especially the consequence of failure, even though the equipment is made up of numerous different materials. The objectives of this paper are to develop a proposed RBI software to resolve the above issue and to evaluate the risk of equipments in petrochemical plants using the software. In this respect, the mole fractions of materials were used to incorporate the characteristics of all materials. The proposed RBI software consists of qualitative, semiquantitative and quantitative risk evaluation modules in which toxic materials as well as representative materials were derived automatically for comparison with those in the current guideline. The developed RBI software has been applied to evaluate the risk of equipments in Naphtha Cracking Center (NCC) which is the typical facility of petrochemical plant. Thereby, promising evaluation results were obtained and applicability of the proposed RBI software was proven.Copyright