Innovation sometimes hinges on tiny details. Details which, however, become extremely important when it comes to replacing the conventional graphite braids with equivalent Teflon (PTFE) ones to improve the reliability of operation of valves used in radiation exposure hazard areas by. Before such a deployment could be authorised, an EDF team conducted a validation test campaign which earn it the nuclear engineering innovation award.
A new requirement
Until today, PTFE braids have been used outside nuclear reactor containment vessels. When conditions allow, could all valves, irrespective of their place of installation, take advantage of PTFE, a material which divides the friction level by 5 and thus allow easier valve operation? To answer this question, EDF needed to test the behaviour and sealing properties of Teflon braids (provided by two different suppliers) before and after irradiation. The energy company entrusted this difficult mission to Cetim, which designed a suitable cycling and sealing test bench that met unprecedented requirements. “After cycling tests under normal conditions of use, we wanted the seals to be kept under pressure during the gamma ionisation phase” , says Laetitia Biringer, design engineer at EDF. Therefore, Cetim developed a modular test bench which makes it possible to remove the mechanical device representative of the valve head while keeping the seal in loaded condition. Then it became possible to transfer the device, without any loss of tightening force, to the Belgian laboratory tasked with its irradiation. The performance and sealing properties of the braids (which did not exhibit any radioactive contamination) were then tested again at Cetim.
Validation of the Teflon solution
The operation was conducted several times with a gradual increase in the radiation dose. “The tests allowed us to confirm that the Teflon braids do not lose their performance or sealing properties after irradiation. From now on, they can be deployed everywhere in our nuclear plants when the conditions allow this” , concludes Franck Milliard, design engineer at EDF.
