A new method for solving the fission gas diffusion equations with time-varying diffusion coefficient and source term considering recrystallization of fuel grains

A new method is proposed to determine charge diffusion coefficient and transfer velocity to extraction layers. Hole diffusion coefficient in MAPbI3 is constant between 1016 – 1017 cm−3, a hallmark of band transport but overall extraction is interface limited.

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Atomistic Level Molecular Dynamics Analysis and its Integrity in the Interim of Irradiation

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.318.39 ◽

2021 ◽

Vol 318 ◽

pp. 39-47

Author(s):

Ahli K.D. Willie ◽

Hong Tao Zhao ◽

M. Annor-Nyarko

Keyword(s):

Thermal Conductivity ◽

Molecular Dynamics ◽

Mixed Oxide ◽

Md Simulation ◽

Lattice Thermal Conductivity ◽

Gas Diffusion ◽

Mixed Oxide Fuel ◽

Fission Gas ◽

Increasing Temperature ◽

End Members

In this work, molecular dynamics (MD) simulation was utilized in relation to access the thermal conductivity of UO2, PuO2 and (U, Pu)O2 in temperature range of 500–3000 K. Diffusion study on mixed oxide (MOX) was also performed to assess the effect of radiation damage by heavy ions at burnup temperatures. Analysis of the lattice thermal conductivity of irradiated MOX to its microstructure was carried out to enhance the irradiation defects with how high burnup hinders fuel properties and its pellet-cladding interaction. Fission gas diffusion as determined was mainly modelled by main diffusion coefficient. Degradation of diffusivity is predicted in MOX as composition deviate from the pure end members. The concentration of residual anion defects is considerably higher than that of cations in all oxides. Depending on the diffusion behavior of the fuel lattice, there was decrease in the ratio of anion to cation defects with increasing temperature. Besides, the modern mixed oxide fuel releases fission gas compared to that of UO2 fuel at moderate burnups.

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Global fuzzy adaptive asymptotic tracking control for nonlinear reaction-diffusion equations with time-varying coefficients

Journal of the Franklin Institute ◽

10.1016/j.jfranklin.2021.09.026 ◽

2021 ◽

Author(s):

Yanfang Lei ◽

Junmin Li ◽

Ailiang Zhao

Keyword(s):

Tracking Control ◽

Reaction Diffusion ◽

Reaction Diffusion Equations ◽

Diffusion Equations ◽

Time Varying ◽

Varying Coefficients ◽

Nonlinear Reaction ◽

Asymptotic Tracking ◽

Time Varying Coefficients ◽

Fuzzy Adaptive

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Grain Subdivision Fission Gas Swelling Model for UO2

MRS Advances ◽

10.1557/adv.2016.497 ◽

2016 ◽

Vol 1 (35) ◽

pp. 2465-2470

Author(s):

Thomas Winter ◽

Richard Hoffman ◽

Chaitanya S. Deo

Keyword(s):

Grain Size ◽

Grain Boundaries ◽

Gas Diffusion ◽

Fine Grain ◽

Fuel Pellets ◽

Model And Simulation ◽

Nucleation Sites ◽

Fission Gas ◽

High Burnup ◽

Swelling Model

ABSTRACTUnder 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.

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