NRG in Petten, Netherlands, has become the first organisation in the world to develop a technique for measuring the deformation of nuclear fuel at the high temperatures and radiation levels during its irradiation in a reactor.

NRG presented the first results from the new technique at the Water Reactor Fuel Performance Meeting (WRFPM) conference in South Korea, which focused specifically on nuclear fuels. “The data from this has advanced our understanding of how nuclear fuels behave in nuclear power stations,” NRG said. “This monitoring technique plays an important part in the research into  – and the development of  –safer and better nuclear fuels.”

Uranium oxide pellets (UO2) in fuel rods can be permanently deformed as a result of the high pressure, temperature and radiation level in the reactor, a phenomenon that is known as nuclear fuel creep.

Using its High Flux Reactor (HFR), NRG has developed a technique in which the deformation of several samples can be monitored simultaneously under operational conditions. The dimensional change samples of metal and ceramics could be determined to an accuracy smaller than one micrometre during irradiation at temperatures between 500 C and 1200C. “This was a tremendous challenge given the extreme conditions in a nuclear reactor,” said NRG, which worked for two years to develop the technique and to prove its feasibility.

The next step will be to measure the deformation of the nuclear fuel, which will be done in 2018 and which will involve collaborating with other partners in the industry. “We now know that the instrument and the measurement principle work and how we can determine the creep of the nuclear fuel at high radiation levels and at high temperatures,” said NRG nuclear fuel expert Steven Knol, 

If operators are better able to predict how nuclear fuel deforms in nuclear power stations, it will be possible to increase electricity production under safe conditions. The new monitoring technique can also be used for research into Accident Tolerant Fuels (ATF), in which NRG is collaborating. This research is intended to make nuclear fuels in nuclear power stations less vulnerable to disasters such as the earthquake and tsunami at Fukushima in 2011. NRG can also carry out creep research on mixed uranium oxide and plutonium oxide (mox) fuel.