Investigation of Burst Pressures in PWR Primary Pressure Boundary Components

Ihn Namgung,Nguyen Hoang Giang 한국원자력학회 2016 Nuclear Engineering and Technology Vol.48 No.1

In a reactor coolant system of a nuclear power plant (NPP), an overpressure protectionsystem keeps pressure in the loop within 110% of design pressure. However if the systemdoes not work properly, pressure in the loop could elevate hugely in a short time. It wouldbe seriously disastrous if a weak point in the pressure boundary component bursts andreleases radioactive material within the containment; and it may lead to a leak outside thecontainment. In this study, a gross deformation that leads to a burst of pressure boundarycomponents was investigated. Major components in the primary pressure boundary that isstructurally important were selected based on structural mechanics, then, they were usedto study the burst pressure of components by finite element method (FEM) analysis and bynumber of closed forms of theoretical relations. The burst pressure was also used as ametric of design optimization. It revealed which component was the weakest and whichcomponent had the highest margin to bursting failure. This information is valuable insevere accident progression prediction. The burst pressures of APR-1400, AP1000 andVVER-1000 reactor coolant systems were evaluated and compared to give relative marginsof safety.

Investigation of Burst Pressures in PWR Primary Pressure Boundary Components

Namgung, Ihn,Giang, Nguyen Hoang Korean Nuclear Society 2016 Nuclear Engineering and Technology Vol.48 No.1

In a reactor coolant system of a nuclear power plant (NPP), an overpressure protection system keeps pressure in the loop within 110% of design pressure. However if the system does not work properly, pressure in the loop could elevate hugely in a short time. It would be seriously disastrous if a weak point in the pressure boundary component bursts and releases radioactive material within the containment; and it may lead to a leak outside the containment. In this study, a gross deformation that leads to a burst of pressure boundary components was investigated. Major components in the primary pressure boundary that is structurally important were selected based on structural mechanics, then, they were used to study the burst pressure of components by finite element method (FEM) analysis and by number of closed forms of theoretical relations. The burst pressure was also used as a metric of design optimization. It revealed which component was the weakest and which component had the highest margin to bursting failure. This information is valuable in severe accident progression prediction. The burst pressures of APR-1400, AP1000 and VVER-1000 reactor coolant systems were evaluated and compared to give relative margins of safety.

굽힘 모멘트가 증기발생기 마모 전열관 파열 압력에 미치는 영향

이국희(Kuk-Hee Lee),강용석(Yong-Seok Kang) 대한기계학회 2021 大韓機械學會論文集A Vol.45 No.4

본 연구에서 3차원 유한요소해석을 이용하여 증기발생기 전열관에 가해지는 굽힘 모멘트가 마모전열관의 파열 압력에 미치는 영향을 정량화하였다. 다양한 길이와 깊이의 마모 형상이 고려되었다. 굽힘 모멘트를 전열관에 가한 다음에 내압을 가하여 마모 전열관의 파열 압력이 계산되었다. 전열관은 관지지판으로 지지되어 있으므로 압력을 가하는 동안 전열관의 회전 변위는 일정하도록 설정되었다. 마모형상이 길거나 얕은 경우에는 굽힘 모멘트가 파열 압력에 영향이 미미하다. 내압이 가해지는 동안 마모부위와 전열관의 소성 변형에 의해 응력이 재분배되어 굽힘 모멘트가 증가함에 따라 파열 압력이 감소하지 않는다. 마모 길이가 매우 짧고 깊은 경우에는 구조적 불연속에 의한 국부적 응력 증가가 발생하고 응력 재분배가 어려우므로, 굽힘 모멘트가 파열 압력에 미미하게 영향을 미쳐 감소한다. EPRI에서 제시하는 마모 전열관의 파열 압력식은 유한요소해석에서 계산된 파열 압력보다 대체적으로 낮은(보수적인) 값을 예측한다. In this study, the effect of bending moment on the burst pressures of steam generator tubes with wear degradation was quantified using three-dimensional finite element analysis. Various length and depth wear shapes were considered. The bending moment was applied to the tubes, and then, internal pressure was applied to the tubes to determine the burst pressures of worn tubes. Because steam generator tubes were supported by tube support plates, the rotational displacement of tubes under bending moment was set to be constant while applying pressure. When the wear shape was long or thin, the bending moment did not affect the burst pressure. As internal pressure increased, the stress at the wear site was redistributed by plastic deformation. Hence, the burst pressure of worn tubes did not decrease as the bending moment increased. When the wear length was very short and deep, the stress redistribution was difficult owing to structural discontinuity. Hence, the bending moment had a small influence on the burst pressure. The burst pressure equation proposed by the Electric Power Research Institute (EPRI) predicts a value that is generally lower (conservative) than the burst pressures calculated by the finite element analyses.

파열 압력에 따른 튜브 내 고압 수소 누출에 의한 자발점화 현상

이형진(Hyoung Jin Lee),김성돈(Sung Don Kim),김세환(Sei Hwan Kim),정인석(In-Seuck Jeung) 한국연소학회 2012 KOSCOSYMPOSIUM논문집 Vol.- No.45

The spontaneous ignition mechanism of high pressure hydrogen gas released into tube is well-deduced from previous studies. However, those results have a limit because the studies have been conducted at low burst pressure of about 10 MPa. In this study, the process or ignition feature are investigated with higher burst pressure of up to 30 MPa through numerical analysis. The results show that the trend of ignition became to be different with a burst pressure. While two reaction regions is important to initiate the ignition when burst pressure is about 10 MPa, the reaction of the core region does not play a role in ignition inside the tube when a burst pressure is above 20 MPa.

API 5L X65 배관의 신뢰도 평가를 위한 파열압력 분포 추정에 관한 연구

김성준 ( Seong-jun Kim ),김도현 ( Dohyun Kim ),김철만 ( Cheolman Kim ),김우식 ( Woosik Kim ) 한국품질경영학회 2020 품질경영학회지 Vol.48 No.4

Purpose: The purpose of this paper is to present a probability distribution of the burst pressure of API 5L X65 pipes for the reliability assessment of corroded gas pipelines. Methods: Corrosion is a major cause of weakening the residual strength of the pipe. The mean residual strength on the corrosion defect can be obtained using the burst pressure code. However, in order to obtain the pipe reliability, a probability distribution of the burst pressure should be provided. This study is concerned with estimating the burst pressure distribution using Monte Carlo simulation. A response surface method is employed to represent the distribution parameter as a model of the corrosion defect size. Results: The experimental results suggest that the normal or Weibull distribution should be suitable as the probability distribution of the burst pressure. In particular, it was shown that the probability distribution parameters can be well predicted by using the depth and length of the corrosion defect. Conclusion: Given a corrosion defect on the pipe, its corresponding burst pressure distribution can be provided at instant. Subsequently, a reliability assessment of the pipe is conducted as well.

Determination of interaction effect between cracked tube and eggcrate support plate on the burst pressure

Kim, H.S.,Oh, C.K.,Shim, H.J.,Chang, Y.S. Applied Science Publishers ; Elsevier Science Ltd 2014 The International journal of pressure vessels and Vol.117 No.-

Steam generator is one of the major components in the nuclear power plant comprising pressure-retaining boundary. Typically, there are thousands of thin-walled tubes as well as several support plates in a steam generator. According to the operating experience of the steam generators, a lot of cracks have been found in the tubes. Therefore, an accurate integrity assessment of the tubes is crucial for maintaining safety as well as reliability of a nuclear power plant. The steam generator tubes are supported by several support plates, and deformations of the tubes are partially restrained depending on the crack location and the gap between the tube and the support plate. In the authors' previous study, it has been reported that burst pressures for circumferentially cracked tubes are significantly affected by the support plate and existing solutions differ from the actual burst pressure. However, this interaction effect for axially cracked tubes has not been fully investigated while those are frequently occurred during operation. In this paper, therefore, a number of elastic-perfectly plastic finite element analyses were performed considering the contact interaction between the tube and the support plate. The burst pressure is then evaluated in accordance with the lower bounding limit theorem and the support-induced interaction effects on the burst pressure were determined.

Burst Behavior for Mechanically Machined Axial Flaws of Steam Generator Tubings

Hwang, Seong Sik,Kim, Hong Pyo,Kim, Joung Soo 한국부식방식학회 2004 Corrosion Science and Technology Vol.3 No.1

It has been reported that some events of a rupture of seam generator tube have occurred in nuclear power plants around the world. Main causes ofthe leakage are from various types of corrosion in the steam generator(SG) tubings. Primary water stress corrosion cracking(PWSCC) of steam generator tubings have occurred in many tubes in Korean plant, and they were repaired using sleeves or plugs. In order to develop proper repair criteria, it is necessary to ascertain the leak behavior of the tubings. A high pressure leak and burst testing system was manufactured. Various types of Electro Discharged Machined (EDM) notches were developed on the SG tubes. Leak rate and burst pressure were measured on the tubes at room temperature. Burst pressure of the part through wall defected tubes depends on the defect depth. Water flow rates after the burst were independent of the flaw types; tubes having 20 to 60 mm long EDM notches showed similar flow rates regardless of the defect depth. A fast pressurization rate gave the tube a lower burst pressure than the case of a slow pressurization.

증기발생기 마모 전열관 파열압력 평가법

이국희,강용석,김홍덕 대한기계학회 2019 大韓機械學會論文集A Vol.43 No.1

The burst pressure for steam generator tubes with wear degradation is the most important information used to assess the structural integrity of the tubes. This paper provides two methods for determining the burst pressure for wear degraded tubes. First, a method is given to determine the burst pressure using a finite element analysis based on the idealized stress-strain model and a geometrically non-linear analysis. Second, based on the provided finite element analysis, this paper provides a closed-form burst-pressure solution for tubes with wear degradation. Wide ranges of wear degradation geometries (the depth, length, and shape) are considered. For validation, the proposed methods are compared with existing burst test data, and the results show good agreements overall. 마모 열화가 발생된 증기발생기 전열관의 파열 압력은 전열관 구조건전성 평가를 위한 가장 기초적인 자료이다. 본 논문은 마모 전열관의 파열 압력을 계산하기 위한 2가지 기법을 제시한다. 먼저, 이상화된 응력-변형률 모델과 기하학적 비선형 해석에 기반한 유한요소해석 기법이 제시된다. 두 번째로, 유한요소해석 결과를 이용하여 도출된 마모 전열관의 파열 압력식이 제시된다. 이 파열압력식에는 다양한 마모 형상(깊이, 길이, 모양)이 고려되었다. 검증을 위하여 제시된 방법들은 기존에 수행된 파열 시험 결과와 비교되었고, 제시된 방법으로 계산된 파열 압력은 적절성을 보였다.

돔 형상 변화에 따른 복합재 압력용기의 구조 거동 예측

황태경(Taekyung Hwang),박재범(Jaebyum Park),김형근(HyungKun Kim),도영대(Youngdae Doh) 한국추진공학회 2008 한국추진공학회 학술대회논문집 Vol.2008 No.11

동일 보스 오프닝에 대해 여러 형상의 돔을 설계할 수 있는 복합재 압력용기용 형상 식이 제시되었고, 이러한 돔 형상 변화에 따른 복합재 압력용기의 성능(파열압력*내부용적/복합재무게) 변화를 유한요소 응력해석과 시험을 통해 규명하였다. 해석을 통해 예측한 돔 형상 변화에 따른 압력용기의 파열압력이 시험 결과와 좋은 일치를 나타내었다. 전반적으로 돔 형상이 낮아짐에 따라 압력용기 내부 용적이 증가하였으나, 파열 압력은 저하되는 현상을 나타내었다. 보스 오프닝 비(ρo)가 0.54 이상인 경우, 돔 형상이 낮아짐에 따라 파열 압력이 저하되어 성능 저하가 나타났다. 그러나 보스 오프닝 비(ρo)가 0.34이하 경우 돔 형상 변화에 따른 파열 압력 저하가 크지 않음으로 성능의 큰 변화가 없었다. Dome shape design method of filament wound (FW) composite pressure vessel, which can create various dome shape with fixed boss opening, was suggested. And, the performance indices (PV/W) for composite pressure vessel with same boss opening but different dome shape were investigated by finite element analysis (FEA) and hydro-test. The FEA showed good agreement with test results for burst pressure. Generally, as the dome shape of pressure vessel was changed to flat dome, the inner volume is increased and the burst pressure is decreased. In the case of above ρo=0.54, the performance index showed decreased value due to the low burst pressure. However, at ρo=0.35, the dome shape change brings not significant reduction of burst pressure and performance index.

스크래치가 존재하는 파열판의 소성변형률 기반 파열압력 평가

김만원(Maan-Won Kim),신인환(In-Hwan Shin),부명환(Myung-Hwan Boo) 대한기계학회 2018 대한기계학회 춘추학술대회 Vol.2018 No.12

The rupture disc is an important part for safely protecting the pressure vessel by bursting when the pressure vessel reaches a preset pressure. The failure pressure of the rupture disc can be predicted through engineering evaluation equation or numerical analysis such as finite element analysis at the design stage. The designed ruture pressure is verified by the test. However, a careful approach must be taken to apply existing evaluation methods to the disc which has scratches on its surface made during installation process because scratch makes a local stress concentration and disc material has usually a large deformation capability. In this study, the burst pressure was calculated by elastic plastic finite element analysis according to the position, shape, and depth of the scratch. The difference between the strength-based evaluation method and the plastic strain-based evaluation method was examined. It is appeared that the plastic strain-based evaluation method predicts more accurately the burst pressure of the rupture disc with scratches than the strength-based approach. The plastic strain-based finite element analysis results were compared with the burst test results and confirmed to be in good agreement.