• Nuclear Engineering and Technology
• /
• v.47 no.3
• /
• pp.332-339
• /
• 2015

The leak before break (LBB) concept is widely used in designing pipe lines in nuclear power plants. According to the concept, the amount of leaking liquid from a pipe should be more than the minimum detectable leak rate of a leak detection system before catastrophic failure occurs. Therefore, accurate estimation of the leak rate is important to evaluate the validity of the LBB concept in pipe line design. In this paper, a program was developed to estimate the leak rate through circumferential cracks in pipes in nuclear power plants using the Henry-Fauske flow model and modified Henry-Fauske flow model. By using the developed program, the leak rate was calculated for a circumferential crack in a sample pipe, and the effect of the flow model on the leak rate was examined. Treating the crack morphology parameters as random variables, the statistical behavior of the leak rate was also examined. As a result, it was found that the crack morphology parameters have a strong effect on the leak rate and the statistical behavior of the leak rate can be simulated using normally distributed crack morphology parameters.

• Journal of the Korean Society of Safety
• /
• v.32 no.6
• /
• pp.1-8
• /
• 2017

P-PIE is a program developed to estimate failure probability of pipes and pressure vessels considering fatigue and stress corrosion crack growth. Using the program, crack growth simulation was performed with an initially existing crack in order to examine the effects of initial crack depth distribution on the leak probability of pipes. In the simulation stress corrosion crack growth was considered and several crack depth distribution models were used. From the results it was found that the initial crack depth distribution gives great effect on the leak probability of pipes. The log-normal distribution proposed by Khaleel and Simonen gives lower leak probability compared other exponential distribution models. The effects of the number and the quality of pre-service and in-service inspections on the leak probability were also examined and it was recognized that the number and the quality of pre-service and in-service inspections are also give great effect on the leak probability. In order to reduce the leak probability of pipes in plants it is very important to improve the quality of inspections. When in-service inspection is performed every 10 years and the quality of inspection is above the very good level, the leak probability shows nearly constant value after the first inspection for an initially existing crack.

• Nuclear Engineering and Technology
• /
• v.56 no.1
• /
• pp.132-140
• /
• 2024

In the event of a severe accident in Sodium Cooled Fast Reactors (SFR), the sodium combustion aerosols along with fission product aerosols would migrate to the environment through leak paths of the Reactor Containment Building (RCB) concrete wall under positive pressure. Understanding the characteristics of sodium aerosol transport through concrete leak paths is important as it governs the environmental source term. In this context, experiments are conducted to study the influence of various parameters like pressure, initial mass concentration, leak path diameter, humidity etc., on the transport and deposition of sodium aerosols in straight leak paths of concrete. The leak paths in concrete specimens are prepared by casting and the diameter of the leak path is measured using thermography technique. Aerosol transport experiments are conducted to measure the transported and plugged aerosol mass in the leak paths and corresponding plugging times. The values of differential pressure, aerosol concentration and relative humidity taken for the study are in the ranges 10-15 kPa, 0.65-3.04 g/m³ and 30-90% respectively. These observations are numerically simulated using 1-Dimensional transport equation. The simulated values are compared with the experimental results and reasonable agreement among them is observed. From the safety assessment view of reactor, the approach presented here is conservative as it is with straight leak paths.

• Nuclear Engineering and Technology
• /
• v.48 no.5
• /
• pp.1264-1272
• /
• 2016

The accurate estimation of leak rate through cracks is crucial in applying the leak before break (LBB) concept to pipeline design in nuclear power plants. Because of its importance, several programs were developed based on the several proposed flow models, and used in nuclear power industries. As the flow models were developed for a homogeneous pipe material, however, some difficulties were encountered in estimating leak rates for bimaterial pipes. In this paper, a flow model is proposed to estimate leak rate in bimaterial pipes based on the modified Henry-Fauske flow model. In the new flow model, different crack morphology parameters can be considered in two parts of a flow path. In addition, based on the proposed flow model, a program was developed to estimate leak rate for a crack with linearly varying cross-sectional area. Using the program, leak rates were calculated for through-thickness cracks with constant or linearly varying cross-sectional areas in a bimaterial pipe. The leak rate results were then compared and discussed in comparison with the results for a homogeneous pipe. The effects of the crack morphology parameters and the variation in cross-sectional area on the leak rate were examined and discussed.

• Journal of the Korean Society of Safety
• /
• v.32 no.5
• /
• pp.168-178
• /
• 2017

In order to prevent major and chemical accidents, some of the plants which would like to install and operate hazard chemicals handling facilities must submit Off-site Consequence Analysis due to recent arisen leak accidents since 2015. A lot of chemical industrials choose gas detectors as mitigation equipment to early detect gas vapor. The way of placement of gas detectors has two methods; Code-based Design(CBD) and Performance-based Design. The CBD has principles for gas detectors to be installed with consideration for the place that is expected to accumulate gas, and the leak locations according to legal standards and technical guidelines, and has a possibility to be unable to detect by these rules to locate gas detectors by vapor density information. The PBD has two methods; a Geographic Method and Scenario based Method. The Scenario-based Method has been suggested to make up for the Geographic Coverage Method. This Scenario-based Method draw the best optimum placement of gas detectors by considering leak locations, leak speed information, leak directions and etc. However, the domestic placement guidelines just refers to the CBD. Therefore, this study is to compare existing placement location of gas detectors by the domestic CBD with placement locations, coverages and the number of gas detectors in accordance with the Scenario-based Method. Also this study has measures for early detecting interest of Vapor Cloud and suitable placement of gas detectors to prevent chemical accidents. The Phast software was selected to simulate vapor cloud dispersion to predict the consequence. There are two cases; an accident hole size of leak(8 mm) from API which is the highst accident hole size less than 24.5 mm, and a normal leak hole size from KOSHA Guide (1.8 mm). Detect3D was also selected to locate gas detectors efficiently and compare CBD results and PBD results. Currently, domestic methods of gas detectors do not consider any risk, but just depend on domestic code methods which lead to placement of gas detectors not to make personnels recognize tolerable or intolerable risks. The results of the Scenario-based Method, however, analyze the leak estimated range by simulating leak dispersion, and then it is able to tell tolerable risks. Thus it is considered that individuals will be able to place gas detectors reasonably by making objectives and roles flexibly according to situations in a specific plant.

• Journal of the Korean Society of Safety
• /
• v.24 no.5
• /
• pp.6-12
• /
• 2009

This study performed an experiment for the danger of an electric shock in the human body, which is directly touched or approached to the exposure of buried metals in a leak caused by certain ground faults at a buried cable in street lamp. In the results of the experiment, the dangerous of electric shocks due to the earth specific resistance and wet and submersion of the earth surface represents a high level as the human body is directly touched to the buried metal at a leak point. In addition, it can be seen that the safety of the human body is influenced by the earth specific resistance, separated distance from buried metals, and shape of buried metals at around the leak point.

• Journal of the Korean Society of Safety
• /
• v.35 no.5
• /
• pp.15-21
• /
• 2020

Quantitative risk assessment (QRA) is used as a legal or voluntary safety management tool for the hazardous material industry and the utilization of the method is gradually increasing. Therefore, a leak frequency analysis based on reliable generic data is a critical element in the evolution of QRA and safety technologies. The aim of this paper is to derive the leak frequency function that can be applied more flexibly in QRA based on OGP report with high reliability and global utilization. For the purpose, we first reviewed the data on the 16 equipments included in the OGP report and selected the predictors. And then we found good equations to fit the OGP data using non-linear regression analysis. The various expectation functions were applied to search for suitable parameter to serve as a meaningful reference in the future. The results of this analysis show that the best fitting parameter is found in the form of DNV function and connection function in natural logarithm. In conclusion, the average percentage error between the fitted and the original value is very small as 3 %, so the derived prediction function can be applicable in the quantitative frequency analysis. This study is to contribute to expand the applicability of QRA and advance safety engineering as providing the generic equations for practical leak frequency analysis.

• Journal of the Korean Institute of Gas
• /
• v.3 no.2 s.7
• /
• pp.43-52
• /
• 1999

An experimental chamber was fabricated to observe the gas diffusion behavior of leak gas from underground city-gas pipeline. It was made of acryl so that feeding of gas and the measuring points of the gas could be varied in each experiment. The MOS sensors were used to measure the concentrations of leak gas. The soil media such as the Jumunjin standard sand and the granite weathered soil were used to measure the gas diffusion and the change of leak gas concentrations was measured with time for various gas flow rate. As the distance between the leak point of gas and the measuring point of MOS sensor decreases, or the leak rate increases, the detection time of gas at a measuring points decreases and the gas concentration increases quickly and the concentration of the gas at steady state also increases. As the density of granite weathered soil is higher than that of Jumunjin standard sand for compaction, the detection time of leak gas in the granite weathered soil was longer than that in the Jumunjin standard soil. The leak gas concentrations in the granite weathered soil were lower than those in the Jumunjin standard sand at the beginning of gas leaking from a pipe, but inverse phenomenon was occured at steady state.

• Journal of the Korean Institute of Gas
• /
• v.23 no.6
• /
• pp.74-80
• /
• 2019

Hydrogen refueling stations that use compressed hydrogen at high pressure provide safety distances between facilities in order to ensure safety. Most accidents occurring in hydrogen stations are accidental leaks. When a leak occurs, various types of ignition sources generate a jet flame. Therefore, the analysis of leaked gas diffusion and jet flame due to high pressure hydrogen leakage is one of the most important factor for setting the safety distance. In this study, the leakage accidents that occur in the hydrogen refueling station operated in high pressure environment are simulated for various leakage source sizes. The results of this study will be used as a reference for the future safety standards.

• Journal of the Korean Society of Safety
• /
• v.16 no.3
• /
• pp.31-34
• /
• 2001

Cause of Bucheon LPG refueling station accident could not be clearly verified because of opposite talking of men reponsible for the accident the accident, damaged by BLEVE and fire, and no systematic fire investigation. After two and half years, recently first judgement has been carried out. But competitive arguement is going on and first leak point of massive LPG will not be clearly identified with evidences acquired by now. This accident gave us many instructions and advices. Specially, massive LPG leak can result in pool fire and safety of underground-installed storage tank is proved by no damage in the strong BLEVE.