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:
“The particular source of frustration of women observing their own self-study and measuring their worth as women by the distance they kept from men necessitated that a distance be kept, and so what vindicated them also poured fuel on the furnace of their rage. One delight presumed another dissatisfaction, but their hatefulness confessed to their own lack of power to please. They hated men because they needed husbands, and they loathed the men they chased away for going.”
—Alexander Theroux (b. 1940)
“It is an open question whether any behavior based on fear of eternal punishment can be regarded as ethical or should be regarded as merely cowardly.”
—Margaret Mead (1901–1978)
“I can forgive even that wrong of wrongs,
Those undreamt accidents that have made me
Seeing that Fame has perished this long while,
Being but a part of ancient ceremony
Notorious, till all my priceless things
Are but a post the passing dogs defile.”
—William Butler Yeats (1865–1939)
“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)
“If we justify war, it is because all peoples always justify the traits of which they find themselves possessed, not because war will bear an objective examination of its merits.”
—Ruth Benedict (1887–1948)