Characterization of fission gas bubbles in irradiated U-10Mo fuel

The swelling of irradiated UO2 has been attributed to the migration and agglomeration of fission gas bubbles in a thermal gradient. High temperatures and thermal gradients obtained by electron beam heating simulate reactor behavior and lead to the postulation of swelling mechanisms. Although electron microscopy studies have been reported on UO2, two experimental procedures have limited application of the results: irradiation was achieved either with a stream of inert gas ions without fission or at depletions less than 2 x 1020 fissions/cm3 (∼3/4 at % burnup). This study was not limited either of these conditions and reports on the bubble characteristics observed by transmission and fractographic electron microscopy in high density (96% theoretical) UO2 irradiated between 3.5 and 31.3 x 1020 fissions/cm3 at temperatures below l600°F. Preliminary results from replicas of the as-polished and etched surfaces of these samples were published.

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Dynamic Characterization of a Valveless Micropump Considering Entrapped Gas Bubbles

Journal of Heat Transfer ◽

10.1115/1.4024461 ◽

2013 ◽

Vol 135 (9) ◽

Cited By ~ 3

Author(s):

Songjing Li ◽

Jixiao Liu ◽

Dan Jiang

Keyword(s):

Numerical Simulation ◽

Theoretical Model ◽

Experimental Studies ◽

Gas Bubbles ◽

Chamber Pressure ◽

Dynamic Characterization ◽

Valveless Micropump ◽

Performance Deterioration ◽

Trapped Gas

Unexpected gas bubbles in microfluidic devices always bring the problems of clogging, performance deterioration, and even device functional failure. For this reason, the aim of this paper is to study the characterization variation of a valveless micropump under different existence conditions of gas bubbles based on a theoretical modeling, numerical simulation, and experiment. In the theoretical model, we couple the vibration of piezoelectric diaphragm, the pressure drop of the nozzle/diffuser and the compressibility of working liquid when gas bubbles are entrapped. To validate the theoretical model, numerical simulation and experimental studies are carried out to investigate the variation of the pump chamber pressure influenced by the gas bubbles. Based on the numerical simulation and the experimental data, the outlet flow rates of the micropump with different size of trapped gas bubbles are calculated and compared, which suggests the influence of the gas bubbles on the dynamic characterization of the valveless micropump.

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Properties of the high burnup structure in nuclear light water reactor fuel

Radiochimica Acta ◽

10.1515/ract-2017-2831 ◽

2017 ◽

Vol 105 (11) ◽

Cited By ~ 7

Author(s):

Thierry Wiss ◽

Vincenzo V. Rondinella ◽

Rudy J. M. Konings ◽

Dragos Staicu ◽

Dimitrios Papaioannou ◽

...

Keyword(s):

Mechanical Properties ◽

Nuclear Fuel ◽

Experimental Studies ◽

Fuel Pellet ◽

Extended Defects ◽

Safety Margins ◽

Fission Gas ◽

High Burnup ◽

Formed Structure

AbstractThe formation of the high burnup structure (HBS) is possibly the most significant example of the restructuring processes affecting commercial nuclear fuel in-pile. The HBS forms at the relatively cold outer rim of the fuel pellet, where the local burnup is 2–3 times higher than the average pellet burnup, under the combined effects of irradiation and thermo-mechanical conditions determined by the power regime and the fuel rod configuration. The main features of the transformation are the subdivision of the original fuel grains into new sub-micron grains, the relocation of the fission gas into newly formed intergranular pores, and the absence of large concentrations of extended defects in the fuel matrix inside the subdivided grains. The characterization of the newly formed structure and its impact on thermo-physical or mechanical properties is a key requirement to ensure that high burnup fuel operates within the safety margins. This paper presents a synthesis of the main findings from extensive studies performed at JRC-Karlsruhe during the last 25 years to determine properties and behaviour of the HBS. In particular, microstructural features, thermal transport, fission gas behaviour, and thermo-mechanical properties of the HBS will be discussed. The main conclusion of the experimental studies is that the HBS does not compromise the safety of nuclear fuel during normal operations.

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