Process and control today | Fast reacting Stromag brakes ready for Hinkley Point C nuclear power station
01/17/2022 Altra Industrial Movement
A key part of the UK government’s net zero emissions strategy, two new nuclear reactors at Hinkley Point C are currently under construction by EDF Energy. Stromag has supported the project by supplying specialist brakes for several cranes on site, including those that will lift radioactive uranium fuel rods from the very core of the reactors.
Located in Somerset, South West England, EDF is building two European Pressurized Reactors (EPRs) at Hinkley Point C. When completed, the advanced third-generation pressurized water reactors will provide clean energy to about six million homes.(1)
Building a nuclear power plant is a colossal undertaking that requires a wide range of construction equipment, especially heavy-duty cranes. Several crane OEMs supplying the project have called on Stromag to supply specialist braking systems, each designed to deliver the performance and reliability required for this strictly regulated application environment.
A nuclear crane expert
Stromag is a global manufacturer of high performance braking systems for cranes and hoists. The leading brand of Altra Industrial Motion Corp., the company has a proven track record in providing braking systems for nuclear applications.
Michel Donnay, director of the French factory of Stromag in La Guerche Sur L Aubois, develops: “Our braking technologies have been proven in nuclear facilities in Europe and Asia. We are familiar with the projects that involve the construction of this new generation of EPR. Therefore, the crane OEMs approached us to supply brakes to support the construction of the machinery and pump stations at Hinkley Point C. However, the main challenge was to specify several brake systems for the nuclear fuel transfer systems – the most critical cranes of the whole installation. .”
Raise the reactor core
Nuclear reactors rely on uranium fuel rods, inserted into the core, to generate heat via nuclear fission. However, like any fuel, the bars eventually wear out and need to be replaced. This is achieved by a fuel transfer system inside the reactor building.
The system is made up of heavy-duty cranes that lift spent fuel rods from the reactor when it is offline. These rods are lowered into a separate cooling pond. Then new fuel rods are inserted into the core and fission can restart. Lifting heavy, radioactive uranium fuel rods is an incredibly dangerous process, with crane-mounted power transmission components required to provide incredibly high levels of reliability and redundancy.
At Hinkley Point C, this operation will be carried out by a huge circular crane located inside the reactor building, known as a polar crane. Used once or twice a year, the crane is designed to have a lifting capacity of 300 tonnes. To ensure the crane stops with maximum reliability and redundancy, the crane OEM selected Stromag to supply the service brakes and emergency brakes for the design.
Service and emergency brakes
“The reactor building crane requires two braking systems”, explains Jonathan Balland, Area Sales Manager at Stromag. “The service brakes perform the normal braking operations of the crane when it is in use. These units are usually mounted on the high speed shaft. Emergency brakes are drum mounted and provide very responsive stopping performance if the load drops for any reason.
For service braking, Stromag has specified its C range of electromagnetic disc brakes. Rated for over four million cycles under normal operating conditions, the electromagnetic design eliminates any risk of hydraulic fluid leakage, maximizing reliability. The brake only opens when the power is turned on, otherwise it remains closed. Once energized, only a small current is needed to hold the brake open, ensuring low power consumption in operation.
Hydraulic brakes are preferred for emergency braking applications due to the higher torque this configuration can achieve. While the world’s largest electromagnetic brakes can achieve up to 10 tons of clamping force, there is almost no limit to what hydraulic brakes can achieve, with some in mining applications reaching up to 100 tons of strength. This exceptional performance is essential for the Polar Crane at Hinkley Point C, ensuring that heavy radioactive fuel rods can be stopped short. To meet these application requirements, Stromag specified SH hydraulic disc brakes.
“The key with emergency brakes is to stop the load in the shortest possible distance. Our SH32 brake offers 32 tons of clamping force, but most importantly, with a closing time of less than 0.3 seconds. This ensures that we can offer a reduced minimum travel distance for the load if it starts to fall. For example, braking systems may be needed to stop 300 tonnes of load within 50 centimeters of travel.”
“For such a critical application at Hinkley Point C Pole Bridge, we also had to provide additional clamping force to provide the required redundancy, which we achieved by specifying multiple units. If one brake fails for any reason, another unit can provide the performance needed to stop the load. Jonathan adds.
Besides the brakes, Stromag also supplied couplings, limit switches, hydraulic units (HPU) and monitoring systems.
Stromag guarantees the suitability of its brake systems for all customer applications through rigorous testing and modeling. However, supplying braking systems for the nuclear industry requires achieving the highest possible standards.
Michael says: “As a specialist in nuclear applications, we are accredited to the highest quality specifications. EDF has certified our applicable products as C3, which means that they can be used in all buildings of a nuclear power plant. We undertake customer surveys, independent consultations and assessments to define our critical milestones and certify that all aspects of engineering work is done correctly. Typically, the quality documents we provide for products used on nuclear power plant critical cranes can run up to 1000 pages.”
“We carry out all the engineering work in-house in our factory in France, while offering our crane OEM customers technical support also in their production facilities. We are one of only a handful of companies worldwide that can supply these braking systems for critical nuclear applications.
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