• Title, Summary, Keyword: Plugging Criteria

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Tube Plugging Criteria for the Non-Regenerative Heat Exchanger in the Steam Generator Blowdown System of Nuclear Power Plant (증기발생기 취출수계통 비재생열교환기 전열관 관막음 기준 설정)

  • Kim, Hyeong-Nam;Choe, Seong-Nam;Yu, Hyeon-Ju;Choe, Jin-Hyeok
    • Proceedings of the KWS Conference
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    • pp.38-40
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    • 2006
  • Nuclear power plants are urged to reduce operating and maintaining costs to remain competitive as well as to increase the safety preventing the radioactive material to the atmosphere. To reduce the cost and to increase the safety, the inspection of balance-of-plant heat exchanger becomes important. However, there are some problems for plugging the heat exchanger tubes since the criterion and its basis are not clearly described. The codes and standards related to show the tube plugging criteria may not exist currently. In this paper, a method to establish the tube plugging criteria of BOP heat exchangers is introduced and the tube plugging criteria for the non-regenerative heat exchanger in the steam generator blow-down system of nuclear power plant. This method relies on the similar method used to establish the plugging criteria for the steam generator tubes.

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Evaluation of Plugging Criteria on Steam Generator Tubes and Coalescence Model of Collinear Axial Through-Wall Cracks

  • Lee, Jin-Ho;Park, Youn-Won;Song, Myung-Ho;Kim, Young-Jin;Moon, Seong-In
    • Nuclear Engineering and Technology
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    • v.32 no.5
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    • pp.465-476
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    • 2000
  • In a nuclear power plant, steam generator tubes cover a major portion of the primary pressure-retaining boundary. Thus very conservative approaches have been taken in the light of steam generator tube integrity According to the present criteria, tubes wall-thinned in excess of 40% should be plugged whatever causes are. However, many analytical and experimental results have shown that no safety problems exist even with thickness reductions greater than 40%. The present criterion was developed about twenty years ago when wear and pitting were dominant causes for steam generator tube degradation. And it is based on tubes with single cracks regardless of the fact that the appearance of multiple cracks is more common in general. The objective of this study is to review the conservatism of the present plugging criteria of steam generator tubes and to propose a new coalescence model for two adjacent through-wall cracks existing in steam generator tubes. Using the existing failure models and experimental results, we reviewed the conservatism of the present plugging criteria. In order to verify the usefulness of the proposed new coalescence model, we performed finite element analysis and some parametric studies. Then, we developed a coalescence evaluation diagram.

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A Study on Development of a Plugging Margin Evaluation Method Taking Into Account the Fouling of Shell-and-Tube Heat Exchangers

  • Hwang, Kyeong-Mo;Jin, Tae-Eun;Kim, Kyung-Hoon
    • Journal of Mechanical Science and Technology
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    • v.20 no.11
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    • pp.1934-1941
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    • 2006
  • As the operating time of heat exchangers progresses, fouling caused by water-borne deposits and the number of plugged tubes increase and thermal performance decreases. Both fouling and tube plugging are known to interfere with normal flow characteristics and to reduce thermal efficiencies of heat exchangers. The heat exchangers of Korean nuclear power plants have been analyzed in terms of heat transfer rate and overall heat transfer coefficient as a means of heat exchanger management. Except for fouling resulting from the operation of heat exchangers, all the tubes of heat exchangers have been replaced when the number of plugged tubes exceeded the plugging criteria based on design performance sheet. This paper describes a plugging margin evaluation method taking into account the fouling of shell-and-tube heat exchangers. The method can evaluate thermal performance, estimate future fouling variation, and consider current fouling level in the calculation of plugging margin. To identify the effectiveness of the developed method, fouling and plugging margin evaluations were performed at a component cooling heat exchanger in a Korean nuclear power plant.

A Study on the Development of Plugging Margin Evaluation Method Reflected the Fouling of a Shell-and-Tube Heat Exchanger (다관원통형 열교환기의 파울링 현상을 고려한 관막음 여유 평가법 개발 연구)

  • Hwang, Kyeong-Mo;Jin,Tae-Eun
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.28 no.11
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    • pp.1384-1389
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    • 2004
  • As operating time of heat exchangers progresses, fouling generated by water-borne deposits and the number of plugged tubes increase and thermal performance decreases. Both fouling and tube plugging are known to interfere with normal flow characteristics and to reduce thermal efficiencies of heat exchangers. The heat exchangers of domestic nuclear power plants have been analyzed in terms of the heat flux and heat transfer coefficient at test conditions as a means of heat exchanger management. Except for the fouling level generated in operation of heat exchangers, also, all of the tubes of heat exchangers have been replaced when the number of plugged tubes exceeds the plugging criteria based on design performance sheet. This paper describes the plugging margin evaluation mettled reflected the fouling of shell-and-tube heat exchangers, which can evaluate the thermal performance for heat exchangers, estimate the future fouling variations, and reflect the current fouling level. To identify the effectiveness of the developed method, the fouling and plugging margin evaluations were performed for a component cooling heat exchanger in a nuclear power plant.

Study on Plugging Criteria for Thru-wall Axial Crack in Roll Transition Zone of Steam Generator Tube (증기발생기 전열관 확관천이부위 축방향 관통균열의 관막음 기준에 관한 연구)

  • Park, Myeong-Gyu;Kim, Yeong-Jong;Jeon, Jang-Hwan;Kim, Jong-Min;Park, Jun-Su
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.20 no.9
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    • pp.2894-2900
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    • 1996
  • The stream generator tubes represent an integral part of a major barrier against the fission product release to the environment. So, the rupture of these tubes could permit flow of reactor coolant into the secondary system and injure the safety of reactor coolant system. Therefore, if the crack was detected during In-Service Inspection of tubes the cracked tube should be evaluated by the pulgging criteria and plugged or not. In this study, the fracture mechanics evaluation is carried out on the thru-wall axial crack due to Primary Water Stress Corrosion Cracking in the roll transition aone of steam generator tube to help the assurence the integrity of tubes and estabilish the plugging criteria. Due to the Inconel which is used as tube material is more ductile than others, the plastic instability repture theory was used to calculate the critical and allowable crack length. Based on Leak Before Break concept the leak rate for the critical crack length and the allowable leak rate are compared and the safety of tubes was given.

Assessment of Steam Generator Tubes with Multiple Axial Through-Wall Cracks (축방향 다중관통균열이 존재하는 증기발생기 세관 평가법)

  • Moon, Seong-In;Chang, Yoon-Suk;Kim, Young-Jin;Lee, Jin-Ho;Song, Myung-Ho;Choi, Young-Hwan
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.28 no.11
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    • pp.1741-1751
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    • 2004
  • It is commonly requested that the steam generator tubes wall-thinned in excess of 40% should be plugged. However, the plugging criterion is known to be too conservative for some locations and types of defects and its application is limited to a single crack in spite of the fact that the occurrence of multiple through-wall cracks is more common in general. The objective of this research is to propose the optimum failure prediction models for two adjacent through-wall cracks in steam generator tubes. The conservatism of the present plugging criteria was reviewed using the existing failure prediction models for a single crack, and six new failure prediction models for multiple through-wall cracks have been introduced. Then, in order to determine the optimum ones among these new local or global failure prediction models, a series of plastic collapse tests and corresponding finite element analyses for two adjacent through-wall cracks in thin plate were carried out. Thereby, the reaction force model, plastic zone contact model and COD (Crack-Opening Displacement) base model were selected as the optimum ones for assessment of steam generator tubes with multiple through-wall cracks. The selected optimum failure prediction models, finally, were used to estimate the coalescence pressure of two adjacent through-wall cracks in steam generator tubes.

Structural Integrity Evaluation of Steam Generator Tube with Two Parallel Axial Through-Wall Cracks

  • Moon Seong In;Kim Young Jin;Lee Jin Ho;Song Myung Ho;Park Youn Won
    • Nuclear Engineering and Technology
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    • v.36 no.4
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    • pp.327-337
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    • 2004
  • It is commonly required that tubes with defects exceeding $40\%$ of wall thickness in depth should be plugged; however, this criterion is too conservative for some locations and for some types of defects. Many studies have been done with the aim of developing an alternative plugging criteria, and these studies have shown that steam generator tubes with a certain range of axial through-wall cracks could remain in service without any safety or reliability problems. However, these studies have been limited, thus far, to consideration of single cracked tubes, necessitating a study on multiple cracks, which are commonly found. A crack coalescence model applicable to steam generator tubes with two collinear axial through-wall cracks was proposed in the previous study. In this paper, the investigation is extended to the parallel axial cracks spaced in a circumferential direction, because parallel axial cracks are more frequently detected during in-service inspections than collinear axial cracks. Interaction effects between two parallel cracks are evaluated by performing elastic and elastic-plastic finite element analyses.

Optimum Failure Prediction Model of Steam Generator Tube with Two Parallel Axial Through-Wall Cracks (두개의 평행한 축방향 관통균열이 존재하는 증기발생기 세관의 최적 파손예측모델)

  • Lee, Jin-Ho;Song, Myung-Ho;Choi, Young-Hwan;Kim, Nak-Cheol;Moon, Seong-In;Kim, Young-Jin
    • Proceedings of the KSME Conference
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    • pp.1186-1191
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    • 2003
  • The 40% of wall criterion, which is generally used for the plugging of steam generator tubes, may be applied only to a single crack. In the previous study, a total of 9 failure models were introduced to estimate the local failure of the ligament between cracks and the optimum coalescence model of multiple collinear cracks was determined among these models. It is, however, known that parallel axial cracks are more frequently detected during an in-service inspection than collinear axial cracks. The objective of this study is to determine the plastic collapse model which can be applied to the steam generator tube containing two parallel axial through-wall cracks. Nine previously proposed local failure models were selected as the candidates. Subsequently interaction effects between two adjacent cracks were evaluated to screen them. Plastic collapse tests for the plate with two parallel through-wall cracks and finite element analyses were performed for the determination of the optimum plastic collapse model. By comparing the test results with the prediction results obtained from the candidate models, a plastic zone contact model was selected as an optimum model.

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