Imploding Bubbles Turn Back Time for Nuclear Reactors

Imagine being able to extend the life of an aging nuclear reactor component by simply using water. Enter cavitation peening. Cavitation peening is a process that uses ultra-high pressurized water to produce vapor bubbles that implode and send shock waves into Alloy 600 materials to produce compressive stresses. This technique removes tensile stresses on the material surface and makes them resistant to stress corrosion cracking. A simple solution to a complex problem!

AREVA completed this innovative new maintenance technique, for the first time in the world, on the reactor vessel closure head (RVCH) at Unit 2 of Exelon’s Byron Generating Station in Illinois during its spring outage. The technique is designed to extend the life of nuclear reactor primary circuit components for more than 20 years and can be used on all reactor designs.

One of the biggest concerns facing the nuclear industry is related to aging systems that stem from stress corrosion cracking (SCC). SCC can lead to increased costs for operation, maintenance, assessment, repair and replacement of boiling water reactor (BWR) and pressurized water reactor (PWR) components. By removing the tensile stresses within the j-groove weld and tube material within each nozzle, AREVA’s cavitation peening process significantly reduces the risk of stress corrosion cracking.

AREVA-cavitation-peening-before-after

AREVA completed the first-of-a-kind surface mitigation project in a sub-30-day outage schedule at Byron last Spring, and is scheduled to perform cavitation peening at Braidwood during its fall outage.

But we aren’t stopping there. AREVA and Exelon are also working with the NRC to obtain approval for inspection relief for cavitation peened components. Currently, reactor vessel heads that have repairs have to be inspected at each refueling outage. But since cavitation peening mitigates the nozzles’ tensile stresses, this will prevent initiation of new stress corrosion cracks. With NRC’s approval, cavitation peening will allow a utility to perform the inspections on a normal basis similar to a non-repaired head, saving money and dose, and effectively turning back the hands of time for the component.

To see how cavitation peening works, watch this MEGA SUMO cavitation peening video and the animated introduction video.