News & Seminars
March 2017 - The Challenge Of Straightening Zirconium Fuel Clad Tube
Nuclear electrical power generation reactors are powered by uranium fuel.
To separate the uranium and prevent contamination of the reactor coolant, the uranium fuel must be contained in a robust environment that can withstand the high temperatures and the intense neutron radiation as nuclear fission takes place.
The material used to contain the uranium must have important characteristics such as high thermal conductivity, high strength, high resistance against corrosion and high dimensional stability.
The containment of the nuclear fuel is normally a tube made from various Zirconium Alloys.
These tubes are referred to as “Fuel Clad Tubing” or “Fuel Cladding”
Each Zirconium Fuel Clad Tube is filled with natural or enriched uranium pellets and sealed.
A complete nuclear fuel cell assembly consists of a number of tubes contained in a rigid assembly.
Extreme care has to be taken during the manufacture of Zirconium Fuel Clad Tubing to prevent any excessive cold working of the tube. Cold working causes the material to be susceptible to Hydride Orientation within the high temperature water environment in which they operate.
During manufacture the tubes have to be formed, finished and at the same time not be subjected to excessive cold working. The desired accuracy of tube straightness is of particular importance and therefore straightening the tube without excessive working of the material is challenging.
It is in this difficult nuclear arena that Turner has succeeded in becoming the foremost supplier of Fuel Clad Tube straightening machinery.
Our history in serving the Nuclear tubing industry spreads over 4 decades, during which our understanding of the problems and their solution has been slowly learned.
For this challenging straightening application, the most modern 10 Roll computer driven machinery are now normal, replacing older 6 Roll machines.
Turner has long been at the forefront in precision straightening machine innovation and specialized straightening applications and has developed important features applicable to straightening this particular product.
These features prevent the possibility of resulting Hydride Orientation in the tube by ensuring that the amount of pressure applied to the tube during straightening is kept to a very low level.
Some of these features are:-
- Special Rolls which feature specific profiled regions which reduce the amount of friction applied to the tube as it is straightened.
- Load Cells positioned strategically within each roll pair which measure the amount of roll pressure being applied to the tube.
- Analytical Software which receives the data from the load cells and ensures that the amount of cold working applied to the tube does not exceed set points maintaining roll pressure at a very low, safe level.
The very special Roll Profiles ensure that the amount of friction generated between the Roll and the Tube is kept to the absolute minimum.
The Load Cells monitor the direct pressure applied by the rolls to the tube during straightening.
Analytical Software within the CASAM system monitors the load applied by each roll on the tube and provides control of the machine.
The Load Cell signal conditioning and amplification is carried out by highly accurate, custom designed and built electronic circuits.
The Turner CASAM system [now in its 3rd decade of operation] has additional operational Modes and Calculating Algorithms for use on this specific straightening application.
A typical Turner 10 Roll CASAM machine for straightening Zirconium Nuclear Fuel Clad Tubing guarantees performance on all the important characteristics required in the final product.
Because of the need to prevent even the slightest marking or contamination of the tube during straightening, the majority of Turner machines for the nuclear industry are supplied as complete straightening lines including fully integrated entry and exit tube handling equipment.
Turner Zirconium Fuel Clad Tubing straightening machines are in use throughout the world, in China, Korea, Sweden, Canada and the United States America.