Hydrogen uptake into Zr-based fuel claddings

Fig.1: For the first time intrinsic resistivity of oxides directly measured at metal-oxide interface of irradiated Zr alloy claddings
Fig.2: Resistivity at oxide-metal interface

A new method for direct electrical conductivity measurements at nanoscale


In this study the conductivity/resistivity of oxide formed on Zircaloy-2 nuclear fuel cladding is measured.

The same cladding grade (LK3/L) is used to compare the oxide formed after short and long residence times, respectively 3 and 9 cycles, in a Boiling Water Reactor (BWR). The oxide in the vicinity of the metal-oxide interface is studied. The measurements were carried out using a novel technique developed at PSI, using micromanipulators (micromanipulator) inside a FIB/SEM to probe different thicknesses of oxide and hence directly measure the resistance and calculate the resistivity of that thickness of oxide.

The results from the 3 and 9 cycle oxides are compared. It is demonstrated that the resistivity of the oxide in the vicinity of the interface of the 9-cycle cladding increases with distance from the interface, much faster than that of 3-cycle cladding to a maximum level. The study is correlated to previous work, performed at PSI, characterizing these 2 materials by EPMA and other techniques.


Oxide conductivity measurement on spent fuel

  • Hydrogen deteriorates the mechanical properties of fuel rod cladding
    (possible problem for handling and transport of spent fuel after long dry storage)
  • Low resistivity of the protective oxide reduces the H-uptake
  • Direct measurement of the conductivity would deliver critical info for the validation of models

Experimental new findings:

The resistivity of the oxide at the metal interface increases with distance from the interface
- the structure of the oxide layer near the interface is critical for H-pickup

Nb-containing alloys show lower resistivity in the oxide close to the metal interface
- better performance with respect to hydrogen pick-up (I.e. lower HPUF)

The resistivity in the oxide close to the metal interface increases with reactor  time
higher hydrogen uptake late in life

Relevance: the model is better understood, new influences on cladding development.