1 Degradations of Incoloy 800 Steam Generator Tubing (original) (raw)
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Nuclear Engineering and Design, 1998
The outside diameter stress corrosion cracking at tube support plates became the dominating ageing mechanism in steam generator tubes made of Inconel 600. A variety of maintenance approaches were developed and implemented worldwide to enable safe and reliable plant operation with affected tubes. Despite different philosophical and physical backgrounds involved, all applied approaches satisfy relevant regulatory requirements. The main goal followed in this paper is to quantify the degree of safety which is achieved through the implementation of selected maintenance approaches. A method is proposed which measures the operational safety and availability through three efficiency parameters: probability of steam generator tube rupture; predicted accidental leak rates through the defects in the tube bundle; and number of plugged tubes. An original probabilistic model quantifies the probability of tube rupture, while procedures available in literature were used to evaluate the accidental leak rates. A numerical example is based on data from the Krs' ko NPP (PWR 623 MWe). The maintenance strategies analyzed are: (a) traditional defect depth (40%) plugging criterion; (b) alternate plugging criterion (bobbin coil voltage as defined by EPRI and US NRC); (c) combination of traditional and alternate plugging criteria; and (d) no plugging at all. Advantages of the defect specific approaches (b) and (c) over the traditional one (a) are clearly shown. The efficiency of the traditional approach (a) is shown to be comparable to the no plugging at all approach (d). Finally, a sensitivity analysis aimed at ranking of the input parameters is presented. Uncertain failure models are shown to be the major contributor to the scatter of obtained results.
ICONE15-10707 Operational Performance Indicators of PWR Steam Generators
In the early days of design of generation I, II or III nuclear power plants, it was assumed that the operational life cycle of steam generators would be the same or similar to that of the other key components in the reactor primary heat transport system (reactor vessel, core, piping, primary coolant pumps, etc.). However, the widespread degradation of the steam generator tubing that has occurred at a number of plants has shown this original assumption was incorrect or at least too optimistic. Traditionally, the tube plugging rate is the most commonly used indicator of the extent of tube degradation and overall steam generator fitness-for-service. However, the tube plugging rate does not provide a complete picture about the extent of degradation and its impact on steam generator and power plant performance. This paper seeks to identify the more appropriate steam generator performance indicators, namely the steam generator failure rate and the steam generator repair rate. In this pape...
Predicting tube repair at French nuclear steam generators using statistical modeling
Nuclear Engineering and Design, 2014
Electricité de France (EDF) currently operates a total of 58 Nuclear Pressurized Water Reactors (PWR) which are composed of 34 units of 900 MWe, 20 units of 1300 MWe and 4 units of 1450 MWe. This report provides an overall status of SG tube bundles on the 1300 MWe units. These units are 4 loop reactors using the AREVA 68/19 type SG model which are equipped either with Alloy 600 thermally treated (TT) tubes or Alloy 690 TT tubes. As of 2011, the effective full power years of operation (EFPY) ranges from 13 to 20 and during this time, the main degradation mechanisms observed on SG tubes are primary water stress corrosion cracking (PWSCC) and wear at anti-vibration bars (AVB) level. Statistical models have been developed for each type of degradation in order to predict the growth rate and number of affected tubes. Additional plugging is also performed to prevent other degradations such as tube wear due to foreign objects or high-cycle flow-induced fatigue. The contribution of these degradation mechanisms on the rate of tube plugging is described. The results from the statistical models are then used in predicting the long-term life of the steam generators and therefore providing a useful tool toward their effective life management and possible replacement.
Reactor Loose Part Damage Assessments on Steam Generator Tube Sheets
Nuclear Technology, 2012
To my advisor, Dr. Mike Doster I give my appreciation. Truly, it is men like him that have made a difference in the course of many lives. Five classes and a thesis later I owe him a great deal of my fascination with Nuclear Engineering and my love of thermal-hydraulics, Monte Carlo techniques and a better appreciation on deterministic transport methods. Without his cultivating efforts my evolution from pond scum to amoeba to small gelatinous multi-cellular creature would not have been possible. It is to him that I owe a fighting chance at becoming worthy of the title of Nuclear Engineer. To Dr. Bourham and Dr. Chu; who both have graciously taken time out of their schedules to read, review and solidify this work. Your thoughts and inputs are appreciated. To my friends and colleagues, I give collective thanks. Without sounding boards for thoughts and ideas or without those times to distract me, this work would not be what it is. I appreciate times come and gone and hope for more times to be as memorable as these. To my parents; thank you. It is because of both you that I am here today. You give me strength and wisdom in ways you cannot know. These pieces of paper are but a beginning. v TABLE OF CONTENTS LIST OF TABLES .
2004
Steam generators (SGs) are crucial components of pressurized water reactors. The failure of the steam generator as a result of tube degradation by corrosion has been a major cause of Pressurized Water Reactor (PWR) plant unavailability. Steam generator problems have caused major economic losses in terms of lost electricity production through forced unit outages and, in cases of extreme damage, as additional direct cost for large-scale repair or replacement of steam generators. Steam generator tubes are susceptible to failure by a variety of mechanisms, the vast majority of which are related a corrosion. The feedwater that enters into the steam generators under normal operating conditions is extremely pure, but nevertheless contains low levels (generally in the μg/l concentration range) of impurities such as iron, chloride, sulphate, silicate, etc. When water is converted to steam and exits the steam generator, the non-volatile impurities are left behind. As a result, their concentra...