Fabrication
The company currently focuses its nuclear business on the first part of the fuel cycle, which it markets both domestically and internationally.
At ENUSA we fabricate nuclear fuel at our facilities in Juzbado (Salamanca), whose activities focus on the procurement of uranium and the components required for the process, engineering and the fabrication of fuel assemblies for Spanish and European nuclear power plants, integrating the most innovative technology and the latest advances on the market. There are three types of fuel:
- PWR: Pressurised water reactors, under licence from Westinghouse
- BWR: Boiling Water Reactors, General Electric
- VVER: Pressurised water reactors, in collaboration with Westinghouse
The fabrication of fuel assemblies is divided into two processes:
- A ceramic process in which uranium oxide powder is used to make pellets, these are then placed in zirconium alloy tubes which, once loaded, pressurised and sealed, are called fuel rods.
- A mechanical process in which fuel rods are assembled into fuel assemblies, which are sent to the power plants.
Ceramic processing
The first operation is the reception of drums containing uranium oxide powder. The next step is mixing, which consists of creating a uniform mixture of the virgin uranium oxide powder (UO2) and the recycled clean material (U3O8) and usually a pore former.
We then move on to the pre-pressing and granulation stage, which consists of pressing the powder to form a pellet with a higher density which, once sieved, generates a granulated powder with good flow properties.
The granulated powder is previously mixed with a lubricating powder in a suitable shaker mill, in order to promote the pellet formation during pressing and to guarantee the life of the press.
The pressed pellets undergo a sintering process, i.e. to obtain pellets with the appropriate density and integrity for use in the nuclear reactor. The pellets are then sintered at high temperatures, which increases the strength and hardness of their structure.
The pellets are then ground to the correct dimensions. Nuclear fuel for a reactor is designed with a specific pellet and cladding diameter. The pellet’s diameter allows for a certain clearance between the inner wall of the cladding and the pellet itself according to plan.
Finally, an automatic vision inspection system measures the pellets with lasers and examines them superficially using high-definition cameras. In this way, tablets that do not meet the quality standards set are identified and disposed of.
Recovery of uranium oxide by oxidation. Pellets removed at any stage, especially during the inspection stage, are oxidised and recovered as recycled uranium oxide, which is fed back into the mixer.
Mechanical processing
In this second phase, the first step is the production of end plugs. For this purpose, zircaloy rods are received which, once inspected, are turned into the plugs used to close the fuel rods.
For the fuel rod fabrication process, tubes, to which the end plug has previously been welded, are used for loading the rods, i.e. inserting the pellets into the tubes.
Once loaded, the tubes are fitted with a spring, the second end plug and, after pressurisation with an inert gas, the second end plug is welded on and the fuel rod is complete. Once the rod is finished, it is subjected to a series of quality checks (ultrasonic testing, X-ray, He leakage, eddy current array probes and scanning) to verify that it meets all specification requirements.
The next step is the fabrication of a skeleton, made up of rods, nozzles and grids, which, after inspection, will serve as a frame for inserting the fuel rods.
Final assembly: Due to their different constitution, a difference is made between PWR and BWR fuel assemblies.
Generally speaking, this last operation of the process consists of inserting the fuel rods into the supporting skeleton, finally placing the nozzles and support structures.
The fuel assemblies are subjected to various inspections before being packed in approved containers for transport. Some designs go through a cleaning process before being packed.
The fuel rods are assembled into fuel assemblies that are shipped to the power plants.
From the beginning, our plant has been committed to a continuous process of technological development of its fabrication and inspection equipment in collaboration with leading companies.
From the installation itself, we develop the necessary equipment and processes to undertake the manufacture of the different products with the highest safety, quality and efficiency. The development and optimisation of the inspection and fabrication equipment we use places ENUSA in a privileged position to supply highly advanced equipment for nuclear fuel plants. We have been working in this line of business for several years now, either individually or in collaboration with other partners such as Tecnatom.
Advanced nuclear fuel fabrication and inspection equipment.
- Artificial vision systems for automatic pellet inspection.
- Laser systems for measuring pellet diameters.
- Robots for handling green pellets.
- Ultrasonic inspection systems of welded end plugs
- Passive scanner for inspection of uranium and
gadolinium oxide fuel rods. - Active scanner for the inspection of uranium oxide fuel rods.
- Eddy current testing equipment for fuel tubes.
- Robotic rod transport and positioning systems for final
fuel assembling. - Artificial vision systems for welding stations.
- Automatic X-ray welding analysis systems
- Sistemas robotizados para inspección de fugas de barras combustibles
