scholarly journals POTENTIAL MITIGATION STRATEGIES FOR PREVENTING STRESS CORROSION CRACKING FAILURES IN HIGH-BURNUP CANDU FUEL

2018 ◽  
Vol 7 (2) ◽  
pp. 127-146 ◽  
Author(s):  
Markus Piro ◽  
Dion Sunderland ◽  
Winston Revie ◽  
Steve Livingstone ◽  
Ike Dimayuga ◽  
...  
Keyword(s):  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Corrosion Cracking ◽  
Lessons Learned ◽  
Mitigation Strategies ◽  
Nuclear Materials ◽  
Characterization Methods ◽  
Candu Reactors ◽  
High Degree ◽  
Fuel Doping

Potential mitigation strategies for preventing stress corrosion cracking (SCC) failures in CANDU fuel cladding that are based on lessons learned on both domestic and international fronts are discussed in this paper. Although SCC failures have not been a major concern in CANDU reactors in recent decades, they may resurface at higher burnup for conventional fuels or with nonconventional fuels that are currently being investigated, such as MOX or thoria-based fuels. The motivation of this work is to provide the foundation for considering possible remedies for SCC failures. Three candidate remedies are discussed, namely improved fabrication methods for fuel appendages, barrier-liner cladding, and fuel doping. In support of this effort, recent advances in experimental characterization methods are described—methods that have been successfully used in non-nuclear materials that can be used to further elucidate SCC behaviour in CANDU fuel. The overall objective is to outline a path forward for characterizing material behaviour as an essential part of investigating remedies to SCC failure. This will allow increased fuel discharge burnup, maximum linear power, and plant manoeuvrability, while maintaining a high degree of reliability.

A Statistical Predictive Model to Prioritize Site Selection for Stress Corrosion Cracking Direct Assessment

2006 ◽  
Author(s):  
Anthony Merle ◽  
P. F. Ehlers
Keyword(s):  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Environmental Parameters ◽  
Predictive Modelling ◽  
Corrosion Cracking ◽  
Direct Assessment ◽  
Degree Of Certainty ◽  
Regression Techniques ◽  
Selection For ◽  
High Degree

Pipeline stress-corrosion cracking (SCC) is an ongoing integrity concern for pipeline operators. A number of different strategies are currently employed to locate and mitigate SCC. Ultrasonic in-line inspection tools have proven capable of locating SCC, but reliability of these tools in gas pipelines remains in question. Rotating hydrotest programs are effectively employed by some companies but may not provide useful information as to the location of SCC along the pipeline. NACE Standard RP0204-2004 (SCC Direct Assessment Methodology) outlines factors to consider and methodologies to employ to predict where SCC is likely to occur, but even this document acknowledges that there are no well-established methods for predicting the presence of SCC with a high degree of certainty. Predictive modelling attempts to date have focused on establishing quantitative relationships between environmental factors and SCC formation and growth; these models have achieved varying degrees of success. A statistical approach to SCC predictive modelling has been developed. In contrast to previous models that attempted to determine direct correlations between environmental parameters and SCC, the new model statistically analyzed data from dig sites where SCC was and was not found. Regression techniques were used to create a multi-variable logistic regression model. The model was applied to the entire pipeline and verification digs were performed. The dig results indicated that the model was able to predict locations of SCC along the pipeline.

Study on Transition of Stress Corrosion Cracking to Sharp Edge Corrosion for a Liquids Pipeline

2018 ◽  
Author(s):  
Jiajun (Jeff) Liang ◽  
Ziqiang (Alex) Dong ◽  
Mengshan Yu ◽  
Mariko Dela Rosa ◽  
Gurwinder Nagra
Keyword(s):  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Synergistic Effects ◽  
Management Strategies ◽  
Crack Tip ◽  
Corrosion Cracking ◽  
Lessons Learned ◽  
Sharp Edge ◽  
Maximum Pressure ◽  
Arrest Growth

Although stress corrosion cracking (SCC) growth is attributed to the synergistic effects of stress and corrosion, these two factors can just as easily become competing mechanisms, with stress cycles driving growth (hydrogen, the by-product of corrosion, may facilitate the growth), and corrosion working to blunt the crack tip and arrest growth. It follows that reducing the maximum pressure and cycling severity can slow down the crack growth or even stop it, and aggressive corrosion can further blunt the sharp crack tip. The Authors have observed, on a particular Polyethylene (PE) tape coated pipeline, instances where SCC has exhibited a propensity to corrode and convert into sharp edge corrosion. This is attributed to the combined effects of limited corrosion protection and low stresses. The focus of the paper is to assist operators in recognizing this phenomenon and integrate lessons learned into pipeline integrity management strategies.

Microstructure and Microchemistry of Inconel 600 STEAM Generator Tubing

2000 ◽  
Vol 6 (S2) ◽  
pp. 356-357
Author(s):  
V. Perovic ◽  
A. Perovic ◽  
G.C. Weatherly ◽  
A.M. Brennenstuhl
Keyword(s):  
Grain Boundary ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Analytical Electron Microscopy ◽  
Corrosion Cracking ◽  
Steam Generators ◽  
Intergranular Stress Corrosion ◽  
Candu Reactors ◽  
Inconel 600 ◽  
Water Reactors

Inconel 600 is an austenitic Ni-Cr-Fe alloy which is extensively used for tubing in steam generators of pressurized light water reactors (PWR) and CANDU heavy water reactors, because of its excellent mechanical properties and corrosion resistance. However, there have been instances of intergranular stress corrosion cracking of tubes in operating steam generators. The chemistry and the structure of grain boundaries and grain boundary precipitation have emerged as factors of prime importance in understanding stress corrosion cracking and intergranular attack of nickel-base alloys (see e.g. ref. l).In this study analytical electron microscopy was used to determine the microstructure of grain boundary and matrix precipitates, grain boundary chromium content and dislocation substructure of selected steam generating tubes of CANDU reactors. The results of the in-service materials are compared with as-received material. Two JEOL 2010 STEM instruments were used in this study.

Stress Corrosion Cracking of Structural Nuclear Materials: Influencing Factors and Materials Selection

2020 ◽  
Vol 10 (1) ◽  
pp. 5-24
Author(s):  
Renato Altobelli Antunes ◽  
Mara Cristina Lopes de Oliveira
Keyword(s):  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Alloy Composition ◽  
Scientific Literature ◽  
Corrosion Cracking ◽  
Nuclear Materials ◽  
Metallic Materials ◽  
Materials Selection ◽  
Complex Interactions ◽  
Successful Design

Stress Corrosion Cracking (SCC) plays a central role in the development of improved structural nuclear materials. Complex interactions between microstructure, alloy composition, manufacturing and environmental factors make the understanding of this phenomenon difficult. This work aimed at reviewing the scientific literature on the SCC behavior of structural nuclear materials in order to identify the main factors that govern this phenomenon. Additionally, the interaction between these factors and materials selection is discussed in order to provide a comprehensive basis for the successful design of metallic materials with improved resistance to SCC.

Mitigating the Stress Corrosion Cracking of Zircaloy-4 Fuel Sheathing: Siloxane Coatings Revisited

2016 ◽  
Vol 2 (2) ◽  
Author(s):  
Graham A. Ferrier ◽  
Mohsen Farahani ◽  
Joseph Metzler ◽  
Paul K. Chan ◽  
Emily C. Corcoran
Keyword(s):  
Wear Resistance ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Nuclear Reactor ◽  
Corrosion Cracking ◽  
Candu Reactors ◽  
Graphite Coating ◽  
Water Reactors ◽  
And Performance ◽  
Graphite Coatings

For more than 50 years, a thin (3–20 μm) graphite coating has played an important role in limiting the stress corrosion cracking (SCC) of Zircaloy-4 fuel sheathing in CANDU® nuclear reactors. Siloxane coatings, which were examined alongside graphite coatings in the early 1970s, demonstrated even better tolerance against power-ramp-induced SCC and exhibited better wear resistance than graphite coatings. Although siloxane technology developed significantly in the 1980s/1990s, siloxane coatings remain unused in CANDU reactors, because graphite is relatively inexpensive and performs well in-service. However, advanced CANDU designs will accommodate average burnups, exceeding the threshold tolerable by the graphite coating (450  MWh/kgHE). In addition, siloxane coatings may find applicability in pressurized and boiling water reactors, wherein the burnups are inherently larger than those in CANDU reactors. Consequently, a commercially available siloxane coating is evaluated by its present-day chemistry, wear resistance, and performance in hot, stressful, and corrosive environments. After subjecting slotted Zircaloy-4 rings to iodine concentrations exceeding the estimated in-reactor concentration (1  mg/cm3), mechanical deflection tests and scanning electron microscopy (SEM) show that the siloxane coating outperforms the graphite coating in preserving the mechanical integrity of the rings. Furthermore, the baked siloxane coating survived a 50-day exposure to thermal neutron flux ((2.5±0.1)×1011  n/cm2 s) in the SLOWPOKE-2 nuclear reactor at the Royal Military College of Canada.

Recent Experience With Weld Overlay Repair of Indications in Alloy 182 Butt Welds in Two Operating PWRs

2006 ◽  
Author(s):  
Warren Bamford ◽  
Bruce Newton ◽  
Don Seeger
Keyword(s):  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Corrosion Cracking ◽  
Lessons Learned ◽  
Recent Experience ◽  
Weld Overlay ◽  
Butt Welds ◽  
The Future ◽  
Plant Personnel ◽  
Key Steps

Recent service experience with Alloy 182/82 butt welds in PWR primary piping and its joints with major components has revealed stress corrosion cracking. This mechanism of environmental cracking is known to have long incubation times, so these incidences of cracking have not been numerous to date, but it is becoming increasingly evident that this may not be the case in the future. This paper provides a summary of two recent repairs which were performed as a result of the finding of indications during in-service inspections. The weld overlay repairs followed the guidelines of code case N504, but a number of supplementary requirements were added. In each case, the repair had to be initiated with no warning other than the knowledge that the inspection was underway. The design of the weld overlay repair was done while the repair equipment was being mobilized, and the repair went as planned, with the final inspections showing that the weld overlay was flawless. In each case excellent cooperation between the plant personnel, the engineering designers, the inspectors, and the welders made for an excellent end product. In addition to a review of the processes used for each of the key steps in the repair, a review of lessons learned will be provided, so that operating plants which may face similar issues in the future can benefit from this experience.

Nano-Scale Characterization of Stress Corrosion Cracking in a Failed Alloy C-276 Component

CORROSION ◽  
10.5006/3742 ◽  
2021 ◽  
Author(s):  
Des Williams ◽  
Jared Smith ◽  
Kevin Daub ◽  
Matthew Topping ◽  
Fei Long ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Ion Beam ◽  
Microstructural Analysis ◽  
Chemical Characterization ◽  
Corrosion Cracking ◽  
Corrosion Mechanism ◽  
Characterization Methods ◽  
Cracking Mode

A failure analysis was performed on an alloy C-276 pull rod which underwent unexpected brittle, intergranular fracture after exposure to 280°C-300°C aqueous solutions designed to replicate secondary side environments in nuclear energy systems: Pb-containing alkaline (pH300°C 8.5-9.5), and sulfate-containing acidic solutions (pH280°C 3-5). The component was characterized using advanced electron microscopy methods to demonstrate the benefits of these techniques for determining the nanoscale chemical, mechanical, and material factors contributing to failure, and to provide insight into the mechanisms of stress corrosion cracking (SCC) responsible for failure. Site-specific transmission electron microscopy specimens containing crack tips were prepared using focused ion beam. Nanoscale chemical characterization methods revealed that Pb was present in some oxidized regions of cracks, suggesting that the element may be inhibiting or impairing the passivity of the Cr-rich oxide. Complementary nanoscale microstructural analysis was performed. At an intergranular to transgranular cracking mode transition, it was observed that the transgranular crack (and corrosion process) propagated along the (110) crystallographic plane. Also, the cracking mode was highly dependent on the tensile stress direction relative to grain boundary orientation, the crystallographic orientation of grains and geometrically necessary dislocation structures. A comparison of results with proposed mechanisms for SCC of Ni alloys in similar environments are discussed; the highly directional nature of cracking is consistent with a slot-tunnel corrosion mechanism.

Initiation Stress Threshold Irradiation Assisted Stress Corrosion Cracking Criterion Assessment for Core Internals in PWR Environment

2011 ◽  
Author(s):  
Benoit Tanguy ◽  
Ce´dric Pokor ◽  
Anthony Stern ◽  
Philippe Bossis
Keyword(s):  
Stainless Steel ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Constant Load ◽  
Corrosion Cracking ◽  
Mitigation Strategies ◽  
Localized Deformation ◽  
Pressurized Water ◽  
Radiation Induced ◽  
Recirculation Loop

Irradiation assisted stress corrosion cracking (IASCC) is a problem of growing importance in pressurized water reactors (PWR). An understanding of the mechanism(s) of IASCC is required in order to provide guidance for the development of mitigation strategies. One of the principal reasons why the IASCC mechanism(s) has been so difficult to understand is the inseparability of the different IASCC potential contributors evolutions due to neutron irradiation. The potential contributors to IASCC in PWR primary water are: (i) radiation induced segregation (RIS) at grain boundaries, (ii) radiation induced microstructure (formation and growth of dislocations loops, voids, bubbles, phases), (iii) localized deformation under loading, (iv) irradiation creep and transmutations. While the development of some of the contributors (RIS, microstructure) with increasing doses are at least qualitatively well understood, the role of these changes on IASCC remains unclear. Parallel to fundamental understanding developments relative to IASCC, well controlled laboratory tests on neutron irradiated stainless steels are needed to assess the main mechanisms and also to establish an engineering criterion relative to the initiation of fracture due to IASCC. First part of this study describes the methodology carried out at CEA in order to provide more experimental data from constant load tests dedicated to the study of initiation of SCC on neutron irradiated stainless steel. A description of the autoclave recirculation loop dedicated to SCC tests on neutron irradiated materials is then given. This autoclave recirculation loop has been started on July 2010 with the first SCC test on an irradiated stainless steel (grade 316) performed at CEA. The main steps of the interrupted SCC tests are then described. Second part of this paper reports the partial results of the first test performed on a highly neutron irradiated material.

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