Contrinex’s sensors ensure safe operation at nuclear power station

The high reliability of Contrinex’s uniquely robust inductive sensors is trusted in a Swiss nuclear power plant. The Pressurised-water reactor utilises fuel rods containing radioactive material to produce energy. During operation, bundles of rods are immersed in water using a custom-built grab. Contrinex stainless-steel ‘700 Series’ inductive sensors, available from PLUS Automation, are used to detect the presence of a bundle of fuel rods in the crane’s grab and confirm that the grab is closed before lifting.

Customer application

In the pressurised-water nuclear power station, the reactor core is built from fuel bundles, each containing 200 to 300 fuel rods immersed in water. The water is used to transfer heat energy to the generating turbines as well as acting as a coolant. Core temperatures can exceed 300°C.

Periodically, individual bundles are removed when all their fuel rods are spent. This is done by a customised crane that positions a purpose-built grab directly over the bundle to be moved. The grab is lowered into the water and grips the top of the bundle, which is then lifted out of the core.

Contrinex ‘700 Series’ inductive sensors, which are ideally suited for the hazardous and hostile environment, are used to detect the presence of the bundle in the grab, initiate closure; and sense the position of the grab, allowing lifting only after complete closure. Maintenance occurs only at 18- to 24-month intervals and consequently, exceptional reliability is essential.

Customer solution

Contrinex Extreme ‘700 Series’ inductive sensors excel in extremely demanding environments and are therefore ideal for this application. Constructed from a single piece of V2A/AISI 303 stainless steel, the IP68- and IP69K-rated sensors are pressure-resistant to 80 bar (1160 psi) and are corrosion-resistant.

A 6mm sensing distance is provided by the small M12-diameter, 60mm long, sensors that are embeddable and so are mounted directly in the metal structure of the grab. They are lightweight and exceptionally reliable and so help ensure the correct operation of the grab. Their vacuum-encapsulated electronics ensure excellent resistance to shock and vibration, and therefore no additional electrical or mechanical protection was required in the installation.

The sensors are configured with an industry-standard PNP normally-closed interface, and connection to the customer’s control system is via a flexible PUR-sheathed cable. The M12 connector allows easy disconnection and removal when required. These sensors also offer the IO-Link digital communication protocol.

Because the crane and therefore the sensors can only be accessed at 18- to 24-month intervals during scheduled maintenance, exceptional reliability is required. Therefore, the design of the system also includes double redundancy to allow for damage or premature failure. Four sensors are fitted to each grab, with two identical sensors operating at each sensing point. In the unlikely event that a failure occurs, normal operation is unaffected.