3 research outputs found
Nondestructive Characterization of Aged Components
It is known that high energy radiation can have numerous effects on materials. In metals and alloys, the effects include, but may not be limited to, mechanical property changes, physical property changes, compositional changes, phase changes, and dimensional changes. Metals and alloys which undergo high energy self-irradiation are also susceptible to these changes. One of the greatest concerns with irradiation of materials is the phenomenon of void swelling which has been observed in a wide variety of metals and alloys. Irradiation causes the formation of a high concentration point defects and microclusters of vacancies and interstitials. With the assistance of an inert atom such as helium, the vacancy-type defects can coalesce to form a stable bubble. This bubble will continue to grow through the net absorption of more vacancy-type defects and helium atoms, and upon reaching a certain critical size, the bubble will begin to grow at an accelerated rate without the assistance of inert atom absorption. The bubble is then said to be an unstably growing void. Depending on the alloy system and environment, swelling values can reach in excess of 50% !V/Vo where Vo is the initial volume of the material. Along with dimensional changes resulting from the formation of bubbles and voids comes changes in the macroscopically observed speed of sound, moduli, electrical resistivity, yield strength, and other properties. These effects can be detrimental to the designed operation of the aged components. In situations where irradiation has sufficient time to cause degradation to materials used in critical applications such as nuclear reactor core structural materials, it is advisable to regularly survey the material properties. It is common practice to use surveillance specimens, but this is not always possible. When surveillance materials are not available, other means for surveying the material properties must be utilized. Sometimes it is possible to core out a small sample which may be used for material properties measurements. A more appealing solution is to use nondestructive evaluation (NDE) methods
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Nondestructive Characterization of Aged Components
It is known that high energy radiation can have numerous effects on materials. In metals and alloys, the effects include, but may not be limited to, mechanical property changes, physical property changes, compositional changes, phase changes, and dimensional changes. Metals and alloys which undergo high energy self-irradiation are also susceptible to these changes. One of the greatest concerns with irradiation of materials is the phenomenon of void swelling which has been observed in a wide variety of metals and alloys. Irradiation causes the formation of a high concentration point defects and microclusters of vacancies and interstitials. With the assistance of an inert atom such as helium, the vacancy-type defects can coalesce to form a stable bubble. This bubble will continue to grow through the net absorption of more vacancy-type defects and helium atoms, and upon reaching a certain critical size, the bubble will begin to grow at an accelerated rate without the assistance of inert atom absorption. The bubble is then said to be an unstably growing void. Depending on the alloy system and environment, swelling values can reach in excess of 50% !V/Vo where Vo is the initial volume of the material. Along with dimensional changes resulting from the formation of bubbles and voids comes changes in the macroscopically observed speed of sound, moduli, electrical resistivity, yield strength, and other properties. These effects can be detrimental to the designed operation of the aged components. In situations where irradiation has sufficient time to cause degradation to materials used in critical applications such as nuclear reactor core structural materials, it is advisable to regularly survey the material properties. It is common practice to use surveillance specimens, but this is not always possible. When surveillance materials are not available, other means for surveying the material properties must be utilized. Sometimes it is possible to core out a small sample which may be used for material properties measurements. A more appealing solution is to use nondestructive evaluation (NDE) methods
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Fundamental Understanding of Crack Growth in Structural Components of Generation IV Supercritical Light Water Reactors
This work contributes to the design of safe and economical Generation-IV Super-Critical Water Reactors (SCWRs) by providing a basis for selecting structural materials to ensure the functionality of in-vessel components during the entire service life. During the second year of the project, we completed electrochemical characterization of the oxide film properties and investigation of crack initiation and propagation for candidate structural materials steels under supercritical conditions. We ranked candidate alloys against their susceptibility to environmentally assisted degradation based on the in situ data measure with an SRI-designed controlled distance electrochemistry (CDE) arrangement. A correlation between measurable oxide film properties and susceptibility of austenitic steels to environmentally assisted degradation was observed experimentally. One of the major practical results of the present work is the experimentally proven ability of the economical CDE technique to supply in situ data for ranking candidate structural materials for Generation-IV SCRs. A potential use of the CDE arrangement developed ar SRI for building in situ sensors monitoring water chemistry in the heat transport circuit of Generation-IV SCWRs was evaluated and proved to be feasible