Control Rod Drive Mechanisms (CRDM) are located at the heart of the nuclear island. Mounted on the reactor pressure vessel head, they control the fission rate and the chain reaction that occurs inside reactors operated with thermal neutrons
CRDM lower, raise and keep in position assemblies of control rods inside a nuclear reactor. The rods are made of materials that are capable of absorbing free neutrons and hence they control the amount of free neutrons available to cause fission of the nuclear fuel and hence stop or slow down the nuclear reaction. Each reactor requires between 50 and 90 CRDMs.
Given their location close to the nuclear reactor, CRDM tubes are manufactured to extremely tight tolerances. They are mainly made of alloy 690.
Valinox Nucléaire, a subsidiary of Vallourec, is one of two companies in the world that can supply alloy 690 tubes for CRDMs. Drawing from its vast experience in the manufacture of steam generator tubes, Valinox Nucléaire brings the highest level of quality to nuclear power plants, including a signal-to-noise ratio of 20:1 and above to meet the most stringent safety requirements.