Omexom has developed an innovative solution to survey certain parts of a reactor vessel. An ultrasonic robot with an inspection head, controlled from the surface, tracks the ageing effects of assets whose lifespan is set to be extended.
Originally intended to operate for a period of 40 years, French nuclear power plants could see their lifespan extended by 10 to 20 years. As part of its responsibility for looking into the issue and advising the government, the French Nuclear Safety Authority (ASN) has appointed utility EDF to prove the viability of such a scenario, ensuring among other things that the various devices within the reactors remain fully functional and safe over time.
The tools and procedures originally planned for inspecting the reactors address issues that typically arise within a 40-year operational lifetime, not beyond.
One issue requiring a new technological solution not covered by the toolkit for routine reactor maintenance operations, is the need to determine whether the space between the reactor vessel and its components (the so-called “internals”) has remained stable or whether it has increased with age. During the 40-year life of a facility, the internals are extracted from the vessel each time the reactor is shut down, then reinstalled by sliding them along guide rails. These rails can work loose over time, modifying the space between the internals and the vessel. “If the play becomes accentuated,” explains Philippe Bosch, director at Omexom, responsible for NDT Engineering & Services (VINCI Energies) which specialises in non-destructive testing techniques, “the risk is that vibrations occur while the plant is in operation.”
So, what can be done to determine if this is the case? At the request of EDF, Omexom developed an innovative solution that makes it possible to measure the gap between two reactor components at a depth of 20 m, in the reactor pool.
“ERACLES is an innovation that can be put into production very quickly”
Dubbed ERACLES, this innovation, intended to inspect the guide rails for the vessel’s internals, is above all a technological one: while the use of ultrasonics is known for viewing shapes under water, as with an ultrasound scan, the device designed and tested by Omexom is entirely original.
“We had to take into account the specific characteristics of the nuclear environment, reinforce the components coming into contact with water and radioactivity, and control – from the surface – the inspection head operating at a depth of 20 m. And all that with a positioning accuracy of a tenth of a millimetre: the thickness of a sheet of paper,” says Bosch.
The ultrasonics technique is used to alternately measure the female part of the device, integrated into the vessel, and the male part attached to the internals.
This data is then processed by software specially designed to calculate the play between the various sections.
In May 2018, Omexom performed a profilometry inspection of an initial reactor. On the basis of the results, EDF may decide to roll out a programme involving recurring measures for various nuclear power plants. The process developed by Omexom would then move from a stage of ad-hoc exploratory use to industrial launch. Indeed, it was finalised with this in mind, explains Philippe Bosch: “It’s an innovation that can be put into production very quickly. Our client wants to see a process that is controlled in terms of reliability, repeatability, and service time. We work on production reactors that can’t be out of action for too long.”
ERACLES is no longer a prototype. It’s a tool that has been developed over a nearly four-year qualification process, based on digital models, then laboratory measurements, and finally tests under real conditions using a full-scale model reactor. “On completion of a process such as this, you can be sure of your tool,” concludes Philippe Bosch.