Post Irradiation Examination
Post Irradiation Examination (PIE) is the study of used
Materials in a high radiation environment (such as a reactor) can undergo unique behaviors such as swelling[1] 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:
Fission gas release
As the fuel is degraded or heated the more volatile fission products which are trapped within the uranium dioxide may become free.[2]
Fuel cracking
As the fuel expands on heating, the core of the pellet expands more than the rim which may lead to cracking. Because of the thermal stress thus formed the fuel cracks, the cracks tend to go from the centre to the edge in a star shaped pattern.
In order to better understand and control these changes in materials, these behaviors are studied.[1][2] [3] [4]. Due to the intensely radioactive nature of the used fuel this is done in a hot cell. A combination of nondestructive and destructive methods of PIE are common.
In addition to the effects of radiation and the fission products on materials, scientists also need to consider the temperature of materials in a reactor, and in particular, the fuel. Too high fuel temperatures can compromise the fuel, and therefore it is important to control the temperature in order to control the fission chain reaction.
The temperature of the fuel varies as a function of the distance from the centre to the rim. At distance x from the centre the temperature (Tx) is described by the
- Tx = TRim + ρ (rpellet2 - x2) (4 Kf)−1
To explain this for a series of fuel pellets being used with a rim temperature of 200 °C (typical for a
![]() |
Further reading
Radiochemistry and Nuclear Chemistry, G. Choppin, J-O Liljenzin and J. Rydberg, 3rd Ed, 2002, Butterworth-Heinemann,
References
- ^ Armin F. Lietzke, Simplified analysis of nuclear fuel pin swelling, NASA TN D-5609, 1970
- ^ J.Y. Colle, J.P. Hiernaut, D. Papaioannou, C. Ronchi, A. Sasahara, Journal of Nuclear Materials, 2006, 348, 229.