Chapter 4: Diffusion

Question 1

What is the diffusing species and the matrix solid in corrosion of cladding in water?

Answer 1

Diffusing species: O2 anion

Matrix Solid: ZrO2

Question 2

What are the two main fission gas elemetents released in fuel and what is the matrix where it diffuses?

Answer 2

Xe, Kr disolved in a UO2 matrix

Question 3

What is the diffusion species and matrix solid of void swelling in metals by irradiation?

Answer 3

Diffusion species: V&I

Matrix Solid: Fe-Cr or Fe-Cr-Ni

Question 4

What is the diffusion species and matrix solid of hydriding of cladding?

Answer 4

Diffusion species: H

Matrix Solid: Zr

Question 5

What is the diffusion coefficient influenced by?

Answer 5

Temperature, Crystal Structure, Size of the diffusing atoms, microstructure, concentration and impurities.

Question 6

What are the two types of diffusion? and where does diffusion usually take place?

Answer 6

Interstitial and Substitutional, Surface and Grain Boundary Diffusion

Question 7

What are the 4 types of diffusion coefficients?

Answer 7

Self, Tracer, Intrinsic, and Mutual Diffusion Coefficient

Question 8

What is the self diffusion coefficient?

Answer 8

Descrbies the migration of atoms of a pure element on itself.

Question 9

What is the tracer diffusion coefficient?

Answer 9

Describes the self-diffusion of atoms that are radioactive isotopes of the host (solvent) element.

Question 10

How do we measure self diffusion coefficient?

Answer 10

There is no direct method for measuring self diffusion coeff.

Question 11

How do you measure the tracer diffusion coefficient?

Answer 11

Requires a gradient (and hence a flux) of the tracer but without a gradient (flux) of the solvent.

Question 12

What is intrinsic diffusion coefficient?

Answer 12

describes the mobility of a species in a binary solid, since each species possesses an intrinsic diffusion coefficient which are usually not equal implying concentration gradients of species A and B. (Kirkendall)

Question 13

What is the mutual diffusion coefficient?

Answer 13

Describes the chemical or inter-diffusion coefficient.

Question 14

What is the effect of doping in anion and cation vacancy diffusion coefficients?

Answer 14

No effect, but it does affect the vacancy fraction

Question 15

If we wanted to accelerate cation diffusion should we dope with higher or lower valence cation?

Answer 15

Higher valence cation

Question 16

What does doping with high valence cation impedes?

Answer 16

Anion diffusion

Question 17

What is the effect of doping ZrO2 with CaO or Y2O3?

Answer 17

Accelerates oxygen ion diffusion.

Question 18

What is the main mechanism for oxygen diffusion?

Answer 18

Interstitial

Question 19

What are the two diffusion results of doping Uo2 with Cr2O3?

Answer 19

Cr can go into substitution sites therefore reducing U vacancies and incresing Oxygen vacancies
Cr can also go on interstitial sites therefore increasing U vacancies and decreasing Oxygen vacancies