Effects of crack morphology parameters on leak-rate calculations in LBB evaluations

2002 ◽  
Vol 79 (2) ◽  
pp. 99-102 ◽  
Author(s):  
D.L Rudland ◽  
G Wilkowski ◽  
P Scott
Keyword(s):  
Leak Rate ◽  
Crack Morphology ◽  
Morphology Parameters

Impact of PWSCC and Current Leak Detection on Leak-Before-Break Acceptance

2005 ◽  
Author(s):  
Gery Wilkowski ◽  
Rick Wolterman ◽  
Dave Rudland
Keyword(s):  
Fatigue Crack ◽  
Crack Length ◽  
Flow Path ◽  
Critical Crack ◽  
Cracking Behavior ◽  
Critical Crack Length ◽  
Crack Morphology ◽  
Actual Flow ◽  
The Difference ◽  
Morphology Parameters

This paper assesses the effect of using primary water stress corrosion cracking (PWSCC) crack morphology parameters (roughness, number of turns, and actual flow path/pipe thickness) in determining the difference in the leakage crack length, and how the difference in the leaking crack lengths changes typical margins from past LBB submittals and published reports. Several past LBB submittal cases were selected; in addition, cases from generic LBB reports published by EPRI were also selected. The results of the analyses showed that the past submittals by nuclear steam system supply (NSSS) companies frequently used the surface roughness comparable to an air-fatigue crack with no turns and the actual flow path equal to the thickness of the pipe. This condition would give the shortest possible leakage flaw length. The roughness, number of turns, and actual flow path to thickness ratio for PWSCC cracks were determined from photomicrographs of service-removed cracks. When using the PWSCC crack morphology parameters that corresponded to the crack growing parallel to the long direction of the dendritic grains (V.C. Summer and Ringhals cases), then the leakage flaw length increased 69 percent over the air-fatigue crack length at the same leak rate. Using the same critical crack length as was used in the initial LBB submittals and the published documents, the margins on the crack length changed from 1.77 to 6.0 for the initial submittals (which we also reproduced) to 0.88 to 2.74 from our calculations for a PWSCC crack. If the crack grew in the buttered region of the bimetallic weld, then based on metallographic sections from service-removed flaws, there would be a more tortuous flow path. For this crack condition, in all but one case, the margins on the normal operating versus N+SSE crack lengths were below the safety factor of two required for LBB approval. The average margin decreased from 3.39 for the air-fatigue crack to 1.55 for the PWSCC crack growing transverse to the long direction of the dendritic grains. This was about an additional 20 percent decrease in the margin from the case of having the PWSCC grow parallel to the long direction of the dendritic grains. These results show that LBB is difficult to satisfy for PWSCC susceptible pipe using the current SRP 3.6.3 LBB approach. This LBB assessment did not consider the possible development of a long circumferential surface crack, which would be more detrimental to LBB behavior. Such cracking behavior would violate the LBB screening criterion.

Leak Before Break: Studies in Support of New R6 Guidance on Leak Rate Evaluation

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
J. P. Taggart ◽  
P. J. Budden
Keyword(s):  
Gas Flow ◽  
Flow Direction ◽  
Nuclear Industry ◽  
Leak Rate ◽  
Effective Roughness ◽  
Crack Morphology ◽  
Morphology Model ◽  
Flow Through ◽  
Rate Evaluation ◽  
Leak Before Break

The concept of leak-before-break (LBB) is often used in safety cases for pressure systems, particularly, in the nuclear industry. An important factor in making a LBB case is in the prediction of the leak rate of fluid through a crack. This paper presents a summary of a program of work, which had the aim of improving guidance on leak rate evaluation for the LBB procedures in the R6 defect assessment methodology. Methods of calculating leak rates have been reviewed, and this has led to a crack morphology model being proposed, which represents single-phase isothermal compressible flow through a crack. In the crack morphology model, the flow is assumed by default to be fully rough turbulent, and the effective roughness to vary between a local roughness value for narrow cracks and a global value (i.e., the overall crack contours) for wide cracks. The effect of pressure drops due to changes in the flow direction at crack turns has also been included. Calculations using the model show that the friction factor relation due to Spence et al. (1991, “Leakage Flow Through Small Cracks—Report of Second Stage of Experimental Work,” unpublished) gives better agreement with measured flow rates than that due to Button et al. (1978, “Gas Flow Through Cracks,” ASME J. Fluids Eng., 100, pp. 453–458), which tends to overestimate the flow rate for the examples studied. The inclusion of an inertial pressure term arising from changes in overall flow direction appears to be justified.

Probability of Rupture for WWER-1000 Main Piping

2020 ◽  
Author(s):  
Yaroslav Dubyk ◽  
Maksym Zarazovskii ◽  
Sergii Ageiev ◽  
Vladislav Filonov
Keyword(s):  
Fracture Toughness ◽  
Nuclear Power ◽  
Power Plants ◽  
Crack Opening ◽  
Aging Effect ◽  
Random Variable ◽  
Operating Conditions ◽  
Emergency Situations ◽  
Crack Morphology ◽  
Morphology Parameters

Abstract A probability of rupture for WWER-1000 main piping was calculated based on the Failure Assessment Diagram (FAD), treating material properties of welds (the most likely zone for crack growing and its nucleation) and crack morphology parameters as stochastic values. In order to perform probabilistic calculations, Critical Temperature of Brittleness (CTB, WWER’s analogue of PWRs transition temperature which used to index the Fracture Toughness curve) and Yield (Ultimate) Strength as well were fitted by normal distribution, based on experimental data taken from the manufacture documentation of Ukrainian Nuclear Power Plants (NPPs). A set of calculations were conducted for Normal Operating conditions (NOC), Safe Shutdown Earthquake (SSE) and several emergency situations like: shaft jamming of a reactor cooling pump and break of the piping’s, connected to the considered ones (a set of LOCA events). Based on static and dynamic calculations, the most loaded zones were selected, where the cracks were postulated. Crack opening area was calculated according to original developed procedure, which accounts for membrane and linear stress components through the wall thickness. The Henry-Fauske flow model is used with modified parameters accounting for crack morphology as a normally distributed random variable. It is an important part of analysis, since different crack types have great differences in friction, bend protrusion and flow length parameters. The rupture probabilities for Main Circulating Piping were calculated with accounting for thermal aging effect. It was proven, that crack morphology parameters highly affect the leak rate and its distribution becomes more scattered. Among the mechanical characteristic, a Fracture toughness has more influence rather than Ultimate of Yield strength.

Leak Before Break: Studies in Support of New R6 Guidance on Leak Rate Evaluation

2005 ◽  
Author(s):  
J. P. Taggart ◽  
P. J. Budden
Keyword(s):  
Flow Direction ◽  
Nuclear Industry ◽  
Leak Rate ◽  
Pressure Drops ◽  
Effective Roughness ◽  
Crack Morphology ◽  
Morphology Model ◽  
Safety Cases ◽  
Rate Evaluation ◽  
Leak Before Break

The concept of leak-before-break (LBB) is often used in safety cases for pressure systems, particularly in the nuclear industry. An important factor in making a LBB case is in the prediction of the leak rate of fluid through a crack. This paper presents a summary of a programme of work, which had the aim of improving guidance on leak rate evaluation for the LBB procedures in the R6 defect assessment methodology. Methods of calculating leak rates have been reviewed, and this has led to a crack morphology model being proposed, which represents single-phase isothermal compressible flow through a crack. In the crack morphology model, the flow is assumed by default to be fully rough turbulent, and the effective roughness to vary between a local roughness value for narrow cracks, to a global value (i.e. the overall crack contours) for wide cracks. The effect of pressure drops due to changes in the flow direction at crack turns has also been included. Calculations using the model show that the friction factor relation due to Spence et al. gives better agreement with measured flow rates than that due to Button et al., which tends to overestimate the flow rate for the examples studied. The inclusion of an inertial pressure term arising from changes in overall flow direction appears to be justified.

Comparison of Leak Rates From Alloy 82/182 Butt Weld Cracks for Leak-Before-Break Applications

2006 ◽  
Author(s):  
A. D. Nana ◽  
K. K. Yoon
Keyword(s):  
Fatigue Crack ◽  
Leak Rate ◽  
Alloy 600 ◽  
Base Metals ◽  
Butt Weld ◽  
System Pressure ◽  
Crack Morphology ◽  
Piping Systems ◽  
The Impact ◽  
Leak Before Break

The discovery of leaking cracks in Alloy 82/182 bimetal welds at the V.C. Summer Nuclear Station has lead the industry to reassess the Leak-Before-Break (LBB) analysis of the reactor coolant system pressure boundary piping components involving Alloy 600 base metals and Alloy 82/182 welds. The leaking cracks were attributed to primary-water-stress-corrosion-cracking (PWSCC). To-date, LBB analysis submittals to the NRC have not considered PWSCC cracks in bimetal welds or Alloy 600 base metals and the leak rate calculations have only considered the conventional fatigue crack morphology. There are limited observed in-service leakage cracks of Alloy 82/182 pipe butt welds with plant measured leak rate data. Effects of PWSCC induced crack morphology involving these welds is investigated through various modeling techniques. The differences in leakage prediction when evaluating as a fatigue crack versus assessing as a PWSCC crack is addressed for various PWR LBB piping systems. The impact of this finding to the overall LBB assessment is discussed. Additionally, the LBB results are compared against the results from another paper.

119: Effect of Epididymitis on Semen Biochemical and Sperm Morphology Parameters

2005 ◽  
Vol 173 (4S) ◽  
pp. 32-32
Author(s):  
Petra Huwe ◽  
Roelof Menkveld ◽  
Martin Ludwig ◽  
Wolfgang Weidner
Keyword(s):  
Sperm Morphology ◽  
Morphology Parameters

Complete remission and increased leak rate. Where is the balance in the complex treatment of rectal cancer?

2004 ◽  
Vol 42 (05) ◽  
Author(s):  
M Kassai ◽  
L Illényi ◽  
Ö Horváth ◽  
G Horváth ◽  
Y Al-Farhat
Keyword(s):  
Rectal Cancer ◽  
Complete Remission ◽  
Leak Rate ◽  
Complex Treatment

Microcracks in Silicon Wafers I: Inline Detection and Implications of Crack Morphology on Wafer Strength

2016 ◽  
Vol 6 (1) ◽  
pp. 126-135 ◽  
Author(s):  
Matthias Demant ◽  
Tim Welschehold ◽  
Marcus Oswald ◽  
Sebastian Bartsch ◽  
Thomas Brox ◽  
...  
Keyword(s):  
Silicon Wafers ◽  
Crack Morphology

scholarly journals Human Oral Mucosal Stem Cells Reduce Anastomotic Leak in an Animal Model of Colonic Surgery

2021 ◽  
pp. 1-8
Author(s):  
Ilan Kent ◽  
Cyrus Jahansouz ◽  
Amandeep Ghuman ◽  
Baruch Shpitz ◽  
Debora Kidron ◽  
...  
Keyword(s):  
Stem Cells ◽  
Anastomotic Leak ◽  
Murine Model ◽  
Colonic Anastomosis ◽  
Colon Surgery ◽  
Leak Rate ◽  
Colonic Surgery ◽  
Colon Wall ◽  
Anastomotic Leak Rate ◽  
Suture Anastomosis

<b><i>Background:</i></b> Anastomotic leak is regarded as one of the most feared complications of bowel surgery; avoiding leaks is a major priority. Attempts to reduce or eliminate leaks have included alternate anastomotic techniques. Human oral mucosa stem cells (hOMSC) are self-renewing and expandable cells derived from buccal mucosa. Studies have shown that hOMSC can accelerate tissue regeneration and wound healing. The objective of this study was to evaluate whether hOMSC can decrease anastomotic leak rates in a murine model of colon surgery. <b><i>Methods:</i></b> Two experiments were performed. In the first study, mice underwent colonic anastomosis using five interrupted sutures. hOMSC (<i>n</i> = 7) or normal saline (NS; <i>n</i> = 17) was injected into the colon wall at the site of the anastomosis. To evaluate whether hOMSC can impact anastomotic healing, the model was stressed by repeating the first experiment, reducing the number of sutures used for the construction of the anastomosis from five to four. Either hOMSC (<i>n</i> = 8) or NS (<i>n</i> = 20) was injected at the anastomosis. All mice that survived were sacrificed on postoperative day 7. Anastomotic leak rate, mortality, daily weight, and daily wellness scores were compared. <b><i>Results:</i></b> In the five-suture anastomosis, there were no differences in anastomotic leak rate, mortality, or daily weight. Mice that received hOMSC had significantly higher wellness scores on postoperative day 2 (<i>p</i> &#x3c; 0.05). In the four-suture anastomosis, there was a significant decrease in leak rate (70% [NS] vs. 25% [hOMSC], <i>p</i> = 0.029) and higher wellness scores in mice that received hOMSC (<i>p</i> &#x3c; 0.05). <b><i>Conclusion:</i></b> Our study suggests that injecting hOMSC at the colonic anastomosis can potentially reduce anastomotic leak and improve postoperative wellness in a murine model of colon surgery.

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