New PSI Study For More Detailed Tests Of Nuclear Fuel Cladding

Recent micro-beam measurements at the Swiss Light Source SLS (Paul Scherrer Institut – PSI, ENS Corporate Member) have enabled insights into the crystal structure of hydrides that promote cracks in nuclear fuel cladding.

This fundamental knowledge of the material properties of cladding will help assess safety during storage.

Zirconium alloys are used as cladding for nuclear fuel rods, so providing structural support for the nuclear fuel pellets and an initial barrier to stop fission products from escaping into the reactor water during operation.

During its long history, which includes extensive research and development advances, reactor-type zirconium alloys have proved themselves to be an extremely successful material for this application.

However, when submerged in water during operation in a reactor, at the hot surface of the fuel rod water molecules split into hydrogen and oxygen. Some of this hydrogen then diffuses into the cladding.

It makes its way through the cladding until – when the concentration and conditions are right – it precipitates to form chemical compounds known as zirconium-hydrides, which make the material brittle and prone to cracking.

Using a technique called synchrotron micro-beam X-ray diffraction at the Swiss Light Source SLS, the researchers could study the structure of hydrides during the growth of cracks in fuel cladding at a new level of detail, and the interplay between cracking and hydride formation.

Read the full story on Paul Scherrer Institut Scientific Highlights.

The Swiss Light Source (SLS) at the Paul Scherrer Institut is a third-generation synchrotron light source.

Its main component is the 2.4 GeV electron storage ring of 288 m circumference. It provides photon beams of high brightness for research in materials science, biology and chemistry.

The SLS has, since June 2009, eighteen experimental stations (undulators and bending magnets) and sixteen operational beamlines.