Lingen : un site dédié à l'assemblage de combustible

Le site de Lingen fabrique des assemblages de combustible pour les réacteurs à eau pressurisée (REP) et les réacteurs à eau bouillante (REB). Outre la production de combustible, Lingen fournit de la poudre de dioxyde d’uranium appauvri (UO2) et des crayons de gadolinium (Gd) pour toutes les activités de Framatome.

Cette usine est la seule  de Framatome en Europe à disposer des équipements et des homologations permettant de recevoir et d’expédier l’ensemble des assemblages intermédiaires de combustible nucléaire (poudre d’UO2, pastilles d’uranium naturel enrichi et d’uranium ré-enrichi, crayons de combustible).

Le site de Lingen est spécialisé dans les technologies, les équipements et les processus-clés de la fabrication de combustible nucléaire, notamment le procédé de soudage USW (Upset Shape Welding, procédé par lequel l’échauffement provient de la résistance des pièces à souder à un courant électrique) pour les crayons de combustible, le système automatisé d’inspection des pastilles APIS (Automatic Pellet Inspection System, un système automatique d'inspection des pastilles de combustibles nucléaires) et la technologie de fours de frittage BTU.

Le site fournit les processus USW et APIS aux autres usines de fabrication de combustible Framatome ainsi qu’aux exploitants. Il possède également la capacité de répondre aux commandes spécifiques telles que le désassemblage des éléments de combustible neuf pour la récupération d’uranium ou pour leur réassemblage et leur utilisation dans une autre centrale nucléaire.

Le site de Lingen, qui bénéficie d’une homologation illimitée, est spécialisé dans la fabrication de composants et d’assemblages de combustible (conversion, production de pastilles et de crayons de combustible, assemblage de combustible).

Main stages of the fabrication process

1. Conversion

The raw material, enriched uranium hexafluoride (UF6), is shipped from an enrichment facility and delivered in a solid state inside steel cylinders. As a prerequisite for further steps, UF6 is converted into uranium dioxide (UO2) powder, using a dry conversion process designed and patented by AREVA that does not produce any uranium-containing process waste or emissions—making it significantly more environmentally-friendly. The cylinder is heated to sublimate the UF6 before being made to react with water vapor and hydrogen to form UO2 powder. A by-product of this transformation, gaseous hydrogen fluoride, is discharged and cooled down together with excess water vapor. The hydrogen and water vapor condense to form hydrofluoric acid 40%, which is sold as reusable material with industrial applications.

º2. Pellet production 

The pellet production stage involves processing UO2 powder into uranium pellets—a process known as pelletizing. The powder is ground, compacted and grained to give it fluid characteristics, while lubricants and pore-former agents ensure the pellets can be pressed. This pre-treated UO2 powder is pelletized in rotary presses, into “greenlings,” which are then sintered in an oven for two to three hours at a temperature of 1,780°C to increase their density and strength. Afterwards, the pellets undergo a high precision grinding process to reach their target diameter. A fully automated laser-optical measurement system finally checks all pellets for dimensional accuracy.

3. Fuel rod production 

In the following stage, pellets are stacked in fuel columns and inserted into zirconium alloy cladding tubes, which are welded on one side using vibration technology or a force-monitored slide-in unit. The cladding tube is then furnished with a compression spring, evacuated to a welding chamber, flooded with helium and welded under pressure. Welded on both sides, the fuel rod ensures that no radioactive material leaks during reactor irradiation at a later stage. The completed fuel rod is subjected to several tests, including enrichment analysis of the contained pellets, helium-leakage tests as well as visual inspection.

4. Assembly 

The fabrication of a fuel assembly for pressurized water reactors (PWR) begins by welding spacers and a control rod guide tube to a mechanically stable supporting structure. Fuel rods are then fully inserted inside–following a predetermined loading plan—and sealed off with the head and foot pieces. Finally, the fuel assembly is cleaned, subjected to comprehensive final tests and stored in a suspended state in subsurface fuel assembly storage until dispatch. Ready-to-mount support structures are used in the fabrication of fuel assemblies for boiling water reactors.

Products manufactured at Lingen site

  • BWR fuel: ATRIUM 11, ATRIUM 10
  • PWR fuel: Focus, HTP, GAIA
  • Gadolinium pellets
  • Cr-doped pellets
  • MELOX powder
  • Disassembly of fuel elements
  • Technology transfers (equipment & services)