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Grain Subdivision Fission Gas Swelling Model for UO2

Published online by Cambridge University Press:  04 July 2016

Thomas Winter ,
Richard Hoffman  and
Chaitanya S. Deo
Thomas Winter*
Affiliation:
Nuclear & Radiological Engineering Program, George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, United States
Richard Hoffman
Affiliation:
Nuclear & Radiological Engineering Program, George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, United States
Chaitanya S. Deo
Affiliation:
Nuclear & Radiological Engineering Program, George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA, United States
*
*(Email: wintertc@gatech.edu)
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Abstract

Under high burnup UO2 fuel pellets can experience high burnup structure (HBS) at the rim also known as rim effect. The HBS is exceptionally porous with fine grain sizes. HBS increases the swelling further than it would have achieved at a larger grain size. A theoretical swelling model is used in conjunction with a grain subdivision simulation to calculate the swelling of UO2. In UO2 the nucleation sites are at vacancies and the bubbles are concentrated at grain boundaries. Vacancies are created due to irradiation and gas diffusion is dependent on vacancy migration. In addition to intragranular bubbles, there are intergranular bubbles at the grain boundaries. Over time as intragranular bubbles and gas atoms accumulate on the grain boundaries, the intergranular bubbles grow and cover the grain faces. Eventually they grow into voids and interconnect along the grain boundaries, which can lead to fission gas release when the interconnection reaches the surface. This is known as the saturation point. While the swelling model used does not originally incorporate a changing grain size, the simulation allows for more accurate swelling calculations by introducing a fractional HBS based on the temperature and burnup of the pellet. The fractional HBS is introduced with a varying grain size. Our simulations determine the level of swelling and saturation as a function of burnup by combining an independent model and simulation to obtain a more comprehensive model.

Keywords

nuclear materialsnucleation & growthU
Type
Articles
Information
MRS Advances , Volume 1 , Issue 35: Materials Design , 2016 , pp. 2465 - 2470
Copyright
Copyright © Materials Research Society 2016 

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References

REFERENCES

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