Acoustic gas caracterisation in a uranium rod in a nuclear storage pool

Taking measurements on uranium fuel assemblies, directly in the deactivation pools of nuclear power plants, is a complex goal, but a useful one for multiplying measurements and applications effectively.

Today, in order to measure the pressure or internal composition of a rod's fission gases, it is necessary to carry out heavy operations that generate radiological exposure for those involved (extraction of the rod to be analyzed, transport of the rod in specialized packaging subject to approval by the French Nuclear Safety Authority, receipt of the rod in a specialized laboratory to analyze the gas contained inside, then disposal of the rod as waste).

Implementation directly in the deactivation pool would therefore make it possible to avoid heavy, costly and sensitive operations from a nuclear safety/radiological protection point of view, and reduce the production of nuclear waste.

In recent years, EDF, IES and probe manufacturer SONAXIS have therefore been working together to make progress towards this goal, which has involved substantial work to optimize signal processing and produce operational sensors that are sufficiently miniaturized for use in a fuel assembly bundle. Work was also carried out to demonstrate that it was possible to use the sensors without direct manual assistance in a configuration close to that of an assembly in a fuel deactivation pool. In particular, it was necessary to come up with a design for a prototype carrier that would enable the positioning and bearing force of the sensor on a rod to be controlled. Finally, different rod configurations, representative of the EDF fleet (tube thickness, springs, oxidation level), were tested and their impact on the measurement was quantified.