On-Line Monitoring of Environment-Assisted Cracking in Nuclear Piping Using Array Probe Direct Current Potential Drop

A direct current potential drop method utilizing array probes with measurement ends maintaining an equalized potential designated as equi-potential switching array probe direct current potential drop (ESAP-DCPD) technique has been developed earlier at Seoul National University. This paper validates ESAP-DCPD technique by showing consistency among experimental measurements, analytical solution and numerical predictions using finite element analysis (FEA) of electric field changes with crack growth in metals. In order to examine its viability as an on-line monitoring of environment assisted crack growth at the inner surface of piping welds, artificial inner surface cracks were introduced in a full-scale weldment mockup pipe and stainless steel metal mockup pipe. The weldment was joined by low alloy steel and stainless steel pipes. The pipes were monitored by using ESAP-DCPD in laboratory environments. Optimization of electrical wiring configuration has produced results with significantly reduced noise for adequately long period of time. Then optimized experimental results were compared with the FEA prediction results for the mockup to show a good agreement. Also a round-robin measurement has been made at three laboratories. It has been found that the developed ESAP-DCPD can detect circumferential cracks with a depth of 40 % of wall thickness in stainless steel with a good detectability for further growth behaviors. For axial cracks, however, the measurements showed poor detectability. Hence the developed ESAP-DCPD system can be used to monitor large circumferential cracks that existing non-destructive examination techniques often fail to detect until leakage takes place.Korea (South). Ministry of Trade, Industry and Energy. Korea Institute of Energy Technology Evaluation and Plannin

SCC crack growth in 316L weld metals in BWR environments

The thermal aging and consequent embrittlement of materials are ongoing issues in cast and duplex stainless steel. Spinodal decomposition is largely responsible for the well known "475??C" embrittlement that results in drastic reductions in ductility and toughness in cast materials. This process is also operative in welds in either cast or wrought stainless steels where delta ferrite is present. While the embrittlement can occur after several hundred hours of aging at 475??C, it can also occur at lower temperatures where ductility reductions have been observed after several tens of thousands of hours at 300??C. The effect of thermal aging on mechanical properties, including tensile, toughness, fatigue and static crack growth has been investigated at room temperature and in 288??C high purity water simulating BWR operating conditions. The measurement of tensile, microhardness and Charpy-impact energy show an increase in strength and a decrease in impact energy after aging for up to 10,000 hours at 430 and 400 ??C. Stress Corrosion Crack (SCC) growth rates have been measured for material in the as-welded, 1000 hour/400??C and 5000 hour/400??C aged weld metal @ 288??C in high purity water containing 300ppb of Oxygen. Fracture toughness (J IC) have been measured in the 5000 hour/400??C aged condition and estimated in the other conditions. Crack growth rates for material in the as welded and aged for 5000 hours @ 400??C have been measured and are generally within the scatter band for wrought material although the aged material data fall at the high end. Unusual in-situ unstable fracture behavior has been experienced at toughness values significantly below (<50%) the room temperature fracture toughness for material that contains an SCC "precrack". In-situ fracture toughness with a fatigue precrack, is still significantly below the air values. This behavior, termed "environmental fracture" requires further investigation

Proton irradiation-decelerated intergranular corrosion of Ni-Cr alloys in molten salt

Better understanding the synergy between radiation and corrosion is necessary to deploy advanced nuclear reactors. Here, the authors contradict the misconception that radiation always results in deleterious effects and show that proton irradiation slows the corrosion of Ni-Cr alloys in 650 °C molten salt

Fuel retention measurements in Alcator C-Mod using accelerator-based in situ materials surveillance

This paper presents the first in situ time- and space-resolved measurements of deuterium (D) fuel retention in plasma-facing component (PFC) surfaces using Accelerator-based In-situ Materials Surveillance (AIMS) on the Alcator C-Mod tokamak. AIMS is a novel in situ materials diagnostic technique based on the spectroscopic analysis of nuclear reaction products induced in PFC surfaces using an ∼MeV beam of deuterons from a compact linear accelerator in between plasma shots. AIMS measurements of D retention on inner wall PFCs were acquired during diverted and limited plasma operations and during wall conditioning experiments. Intershot measurements demonstrate the local erosion and codeposition of boron films on PFC surfaces with a constant ratio D/B. This is consistent with previous results suggesting that D codeposition with boron is insufficient to account for the net retention observed in Alcator C-Mod. Changes in deuterium concentration during boronization, electron cyclotron and glow cleanings were also measured.United States. Department of Energy (Grant DE-FG02-94ER54235)United States. Department of Energy (DE-FC02-99ER54512

Red Dendrocronológica del Pino de Altura (Pinus hartwegii Lindl.) para estudios dendroclimáticos en México

El bosque de Pinus hartwegii constituye el límite superior arbóreo en las montañas de México. En este estudio se desarrolló una red de cronologías de esta especie, localizadas en volcanes del Eje Neovolcánico Transversal, en el centro del país, y picos elevados de la Sierra Madre Oriental, en el Noreste. El Análisis de Componentes Principales integró las cronologías en dos grupos, uno para el centro y otro para el Noreste, con los que se desarrollaron dos cronologías regionales de 320 años (1690-2009) y 590 años (1420-2009), respectivamente. El fenómeno de El Niño Oscilación del Sur (ENSO) en su fase cálida (El Niño) y fría (La Niña), mostró un impacto significativo en el comportamiento de la variabilidad hidroclimática descrita por ambas series. La Niña produjo condiciones climáticas contrastantes, es decir, secas en el Noreste y húmedas en el centro, mientras que la fase de El Niño originó sequías en ambas regiones, pero sólo durante eventos intensos de ENSO

Red dendrocronológica del pino de altura (Pinus hartwegii Lindl.) para estudios dendroclimáticos en el noreste y centro de México

Resumen. El bosque de Pinus hartwegii constituye el límite superior arbóreo en las montañas de México. En este estudio se desarrolló una red de cronologías de esta especie, localizadas en volcanes del Eje Neovolcánico Transversal, en el centro del país, y picos elevados de la Sierra Madre Oriental, en el noreste. El Análisis de Componentes Principales integró las cronologías en dos grupos, uno para el centro y otro para el noreste, con los que se desarrollaron dos cronologías regionales de 320 años (1690-2009) y 590 años (1420- 2009), respectivamente. El fenómeno de El Niño Oscilación del Sur (ENSO) en su fase cálida (El Niño) y fría (La Niña), mostró un impacto significativo en el comportamiento de la variabilidad hidroclimática descrita por ambas series. La Niña produjo condiciones climáticas contrastantes, es decir, secas en el noreste y húmedas en el centro, mientras que la fase de El Niño originó sequías en ambas regiones, pero solo durante eventos intensos de ENSO

Dendrochronological network of mountain pine (Pinus hartwegii Lindl.) for dendroclimatic studies in northeastern and central Mexico

Pinus hartwegii is a high elevation species forming the upper treeline in Mexico-from volcanoes of the Transmexican Volcanic Belt in central Mexico and from high elevation peaks of the Sierra Madre Oriental in northeastern Mexico. Pure stands of hartwegii pine have been severely logged in the past affecting the proper functioning of the ecosystem, impacting water yield, biodiversity, and other ecosystem services in detriment of the wellbeing of dense human settlements in the Valley of Mexico. In addition to land-use changes, climate warming may threat this ecosystem by altering their health, favoring the recruitment over the treeline where is not adapted, and affecting its dynamics, growth rates, and ecological relationships with associated species. Given the dendrochronological potential of hartwegii pine to produce centuries-long time series useful to analyze high and low frequency climate variability, and influence of atmospheric circulatory patterns, the objective of this study was to develop a network of treering chronologies for central and northeastern Mexico, analyze its potential for dendroclimatic reconstructions and to determine the potential impact and teleconnections of atmospheric circulatory patterns. Nine ring-width series of hartwegii pine were developed for the upper conifer forest of some of the main volcanic peaks in the Valley of Mexico and two more series were produced from trees located at the highest peaks in the Sierra Madre Oriental. A Principal Component Analysis of the chronologies defined two eigenvectors with the highest climate variability, the first component integrated several chronologies from central Mexico, e.g., Nevado de Colima, Pico de Orizaba, Iztaccihuatl, and la Malinche, and the second component from northeastern Mexico included Cerro Potosí, N.L. and Cerro La Viga, Coahuila. The chronologies with a common climate response were integrated into representative regional ring-width series, one of them was the chronology for the Transmexican Volcanic Belt with 320 years length (1690-2009), whereas the one for the northeastern region covered the last 590 years (1420-2009). The regional chronology for central Mexico indicated below normal growth (\u3c1.0) as related to droughts for the periods 1698-1702, 1716-1720, 1746-1760, 1806-1813, 1841-1859, 1890-1894, 1935-1940, 1970-1979, and 2000-2004. Similarly, below normal growth for the northeastern ring-width series took place in periods 1450-1460, 1508-1538, 1565-1576, 1661-1673, 1696-1705, 1757-1765, 1784-1790, 1804-1808, 1844-1849, 1866-1894, 1915-1933, and 1998-2003. Wet episodes (\u3e1.0) were common in both representative series for the periods 1726 to 1728, 1753 to 1755, 1791 to 1797, 1831 to 1837, 1895 to 1914, 1923 to 1926, 1940 to 1941, 1957 to 1958, 1965 to 1969, 1985 to 1987, and 2001 to 2005. Verification of some of the detected droughts was done by comparisons with historical records of grain yields, colonial rogation ceremony records, dendroclimatic reconstructions, instrumental climate data, and climatic indices (Palmer Drought Severity Index, Southern Oscillation Index, Tropical Rainfall Index). Contrasting the regional ring-width indices for the common period (1690-2009) did not show a significant association (r= 0.087, p\u3c0.05), however, both regional dendrochronological series responded to dry and wet episodes for particular years and showed opposite conditions (dipole) for some other years (i.e., wet in the center, dry in the north, and vice versa). This finding indicates that the chronologies responded mostly to local or regional climatic conditions but in certain periods may have been impacted by circulatory patterns affecting larger areas in northern and central Mexico. ENSO is the most important phenomena determining climatic differences between regions. In this study, the Niña conditions (cold phase) was characterized by producing dry conditions in the north and wet conditions in central Mexico (periods 1869 to 1874, 1886 to 1887, 1915 to 1917, 1955 to 1956, 1970 to 1975, and 1988 to 1999); however, other Niña events produced droughts in both regions as in years 1892, 1893, 1922, 1942, and 1998; but others did not have any significant impact such, i.e., 1903, 1908-1910, 1924, 1949, 1954, 1964, and 2007. On the other hand, the El Niño (warm phase) produced dry conditions in both regions, but only during intense ENSO events, that is 1880, 1888, 1899, 1905, 1913, 1918, 1929-1930, 1940, 1963, 1970, 1972, 1976, 1983, 1991, and 1997. A comparison between the ring-with indices of the regional chronology representative of the Transmexican Volcanic Belt and a seasonal (January-September) mean precipitation for the region indicated a significant association (r= 0.8, p\u3c0.000) between both variables. It was not found a significant association with temperature. Even though temperature at high elevations may limit physiological processes for the species, precipitation seems to be the most limiting factor for growth. The wide distribution range of hartwegii pine from Mexico to Guatemala provides an excellent opportunity to expand the current network of treeline chronologies to better understand climate variability and impacts of climate change