Fuel Behavior and Post Irradiation Examination
Post Irradiation Examination (PIE) is the study of used nuclear materials such as nuclear fuel. It has several purposes. It is known that by examination of used fuel that the failure modes which occur during normal use (and the manner in which the fuel will behave during an accident) can be studied. In addition information is gained which enables the users of fuel to assure themselves of its quality and it also assists in the development of new fuels. After major accidents the core (or what is left of it) is normally subject to PIE to find out what happened. One site where PIE is done is the ITU which is the EU centre for the study of highly radioactive materials.
Materials in a high radiation environment (such as a reactor) can undergo unique behaviors such as swelling and non-thermal creep. If there are nuclear reactions within the material (such as what happens in the fuel), the stoichiometry will also change slowly over time. These behaviors can lead to new material properties, cracking, and fission gas release.
The thermal conductivity of uranium dioxide is low; it is affected by porosity and burn-up. The burn-up results in fission products being dissolved in the lattice (such as lanthanides), the precipitation of fission products such as palladium, the formation of fission gas bubbles due to fission products such as xenon and krypton and radiation damage of the lattice. The low thermal conductivity can lead to overheating of the center part of the pellets during use. The porosity results in a decrease in both the thermal conductivity of the fuel and the swelling which occurs during use.
According to the International Nuclear Safety Center the thermal conductivity of uranium dioxide can be predicted under different conditions by a series of equations.
The bulk density of the fuel can be related to the thermal conductivity
Where ρ is the bulk density of the fuel and ρtd is the theoretical density of the uranium dioxide.
Then the thermal conductivity of the porous phase (Kf) is related to the conductivity of the perfect phase (Ko, no porosity) by the following equation. Note that s is a term for the shape factor of the holes.
- Kf = Ko(1 − p/1 + (s − 1)p)
Rather than measuring the thermal conductivity using the traditional methods in physics such as Lees' disk, the Forbes' method or Searle's bar it is common to use a laser flash method where a small disc of fuel is placed in a furnace. After being heated to the required temperature one side of the disc is illuminated with a laser pulse, the time required for the heat wave to flow through the disc, the density of the disc, and the thickness of the disk can then be used to calculate and determine the thermal conductivity.
- λ = ρCpα
- λ thermal conductivity
- ρ density
- Cp heat capacity
- α thermal diffusivity
If t1/2 is defined as the time required for the non illuminated surface to experience half its final temperature rise then.
- α = 0.1388 L2/t1/2
- L is the thickness of the disc
For details see
Read more about this topic: Nuclear Fuel
Famous quotes containing the words fuel, behavior, post, irradiation and/or examination:
“Beware the/easy griefs, that fool and fuel nothing./It is too easy to cry “AFRIKA!”/and shock thy street,/and purse thy mouth,/and go home to thy “Gunsmoke,” to/thy “Gilligan’s Island” and the NFL.”
—Gwendolyn Brooks (b. 1917)
“Fatalism, whose solving word in all crises of behavior is “All striving is vain,” will never reign supreme, for the impulse to take life strivingly is indestructible in the race. Moral creeds which speak to that impulse will be widely successful in spite of inconsistency, vagueness, and shadowy determination of expectancy. Man needs a rule for his will, and will invent one if one be not given him.”
—William James (1842–1910)
“A demanding stranger arrived one morning in a small town and asked a boy on the sidewalk of the main street, “Boy, where’s the post office?”
“I don’t know.”
“Well, then, where might the drugstore be?”
“I don’t know.”
“How about a good cheap hotel?”
“I don’t know.”
“Say, boy, you don’t know much, do you?”
“No, sir, I sure don’t. But I ain’t lost.””
—William Harmon (b. 1938)
“You will see Coleridge—he who sits obscure
In the exceeding lustre and the pure
Intense irradiation of a mind,
Which, with its own internal lightning blind,
Flags wearily through darkness and despair—
A cloud-encircled meteor of the air,
A hooded eagle among blinking owls.”
—Percy Bysshe Shelley (1792–1822)
“The Afrocentric exploration of the black past only scratches the surface. A full examination of the ancestry of those who are referred to in the newspapers as blacks and African Americans must include Europe and Native America.”
—Ishmael Reed (b. 1938)