All the answers to your questions on the improvement plan at AREVA NP's Le Creusot facility

  • 1. What are the activities of the Le Creusot facility?

    Creusot Forge is one of the only forges in the world capable of manufacturing forged parts for the heavy components required for nuclear islands. In addition to a forge, it has a foundry, two machining workshops, a workshop for cutting samples and a laboratory for conducting mechanical tests and chemical analyses.
    The Le Creusot facility performs forging, heat treatment and machining of large-dimension forged or cast steel parts weighing up to nearly 260 tonnes: reactor vessel head, steam generator dome, pressurizer bottom head, etc.

    Landmark dates

    1782: start of foundry activities
    1876: first steam power hammer (500 tonnes)
    2006: acquisition by the AREVA group
    2009: revamp of the 11,300-tonne press
    2014: new 9,000-tonne press coupled with a 200-tonne manipulator
    2017: investment plan representing over 8 million euros

    Key figures for 2017

    220 employees
    2 presses (9,000 and 11,300 tonnes)
    14 furnaces
    27 machining units

  • 2. What actions have been undertaken by the AREVA group since the purchase of the forge for the upkeep of the industrial facility and to meet the demands of the nuclear industry?

    As of the buyout in 2006, AREVA implemented actions to bring the plant up to the standards of the AREVA group and the nuclear industry. AREVA has invested 200 million euros at the Le Creusot site since the acquisition, in particular on the revamp of the 11,300-tonne press and the purchase of a new 9,000-tonne press coupled with a 200-tonne manipulator.

    The workforce on this site has doubled since 2006 and staff training is a key pillar for the maintenance and the development of skills.

    AREVA NP confirms the forge as one of its priorities with over 8 million euros of investments in 2017 with the aim of ensuring the quality of the parts produced.

  • 3. What is forging?

    Forging is a process of forming parts from a steel ingot by alternating heating (temperature rise in the furnace) and pressing to give the desired shape to the part. Forging makes it possible to give the parts high-performance mechanical characteristics.

    Once the parts have been shaped, their final mechanical characteristics remain to be imparted to them and this is obtained in the most homogeneous way possible using a process of quality heat treatment.

    The forge receives two different types of ingots from the steelworks: solid ingots and hollow ingots. These ingots can weigh between 75 and 262 tonnes. The ingots have a slightly conical shape to facilitate release from the mold and have grooves to avoid surface defects. They are transported from the steelworks by rail.

    Note, the head and the foot of the ingot are discarded. Discarding the top section enables zones of significant carbon segregation in the ingot to be eliminated. The foot is essentially used for manipulation - its presence is not systematic.

  • 4. How are the components manufactured and assembled?

    The components’ forged parts, cast parts and future internals (tubes, internal casings, stainless steel disks, etc.) are machined and progressively assembled by welding, sub-assembly by sub-assembly. AREVA NP carries out these operations in its Le Creusot and Saint-Marcel facilities.

  • 5. What is meant by quality heat treatment?

    "Quality heat treatment" consists in heating the part for several days at temperatures up to 1000°C to give the steel the desired characteristics.

    Creusot Forge has a range of nine heat treatment furnaces in which the parts are heated according to pre-established treatment cycles.

    These cycles will alternate controlled heating phases with phases of homogenization and cooling at different speeds (water or air quenching).

  • 6. What is quenching?

    Quenching is carried out after the heat treatment phases: it consists of fast water cooling to fix the characteristics of the steel.

  • 7. What is machining?

    Machining consists in setting to the dimensions of use specified by the customer, with millimeter precision.

    The machining is carried out when the part has passed the mechanical tests. In addition to the mechanical tests, non-destructive examinations are performed on the part.

    After machining, the forged part is assembled with other parts by welding, sub-assembly by sub-assembly, to form the component itself. AREVA NP carries out these operations at its Le Creusot and Saint-Marcel facilities.

  • 8. What is a manufacturing file? What distinguishes it from the end-of-manufacturing report?

    The manufacturing file tracks the chronology of the various steps in the manufacture of a part and it covers all the technical requirements to be met. This file gathers together all the tracking sheets that guarantee traceability of manufacturing operations and operation reports, chemistry, heat treatment, mechanical properties, welds, etc. that attest to the conformity of the part.

    The manufacturing file for a forged or cast part (a shell for example) counts on average 400 pages.

    The end-of-manufacturing report (EMR) on the other hand contains all the documents attesting that the contractual requirements have been met according to the provisions agreed with the customer. As such, it does not include the entire manufacturing file. The EMR is transmitted to the customer.

  • 9. What types of checks are performed on the parts to demonstrate their quality?

    Two types of checks are carried out on forged or cast parts and on welds during their manufacture:

    • Non-destructive examination (NDE):  visual inspection and checking of the integrity of parts at the surface (liquid penetrant examination and magnetic particle examination) and in depth (ultrasonic and radiographic inspection), eddy current tests and laser telemetry.
    • Destructive tests (on samples taken from the parts) aim to verify the mechanical properties and the structure of the parts. These are mainly mechanical tests (tensile tests, impact tests, hardness tests and Pellini tests), chemical analyses and grain size measurements.

    For a 900 MW reactor steam generator, more than 450 tests are carried out.

  • 10. What do non-destructive tests consist in?

    Non-destructive examinations are processes used for controlling the quality of forged parts. The surface is checked by liquid penetrant examination (see question 11) and by magnetic particle examination (see question 12) in addition to visual inspection. The internal structure is checked by ultrasound or radiographic examination.

  • 11. What is liquid penetrant examination?

    Liquid penetrant examination is a non-destructive means of inspecting surfaces: it detects surface defects. A colored penetrating liquid is applied manually to the surface of the part which is then rinsed. The application of a developer reveals penetrant which had been trapped by any defects present.

  • 12. What is Magnetic Particle Examination?

    Magnetic particle examination is a type of non-destructive surface and sub-surface control used for materials containing iron: it can detect surface or underlying cracks (up to a few millimeters in depth).
    Magnetic particle examination involves magnetizing the workpiece using a magnetic field. An indicator product is applied to the surface. This product is attracted to any discontinuities.

  • 13. What is ultrasonic examination?

    Ultrasonic examination is a non-destructive method that will detect all defects such as cracks, inclusions, porosities, etc. in metal materials and welds.
    Similar to medical ultrasound systems, it consists of emitting and propagating an ultrasonic wave in the part to be inspected and then collecting and analyzing the wave. The diagnosis is made on the basis of the analysis of the signals received, the presence of a defect being signaled by the reception of echoes arising from the reflection or diffraction of the beam. The analysis of the echo informs about the location of the defect.

  • 14. What do the mechanical tests consist of?

    Mechanical (or destructive) tests consist in checking whether the mechanical properties of the steel of a forged part meet the requirements of the customer before continuing manufacture.

    To carry out these tests, up to 100 test samples (test pieces) are taken directly from the material of the forged part. The test piece is machined to correspond to a given mechanical test. The sampling is carried out in directions and thicknesses corresponding to the customer's specifications (at half thickness, quarter thickness, skin, lengthwise direction, crosswide direction, etc.).

    Four families of test samples are taken for a given type of mechanical test: tensile test, impact test, Pellini test, hardness test (left to right on the infographics).

    A metallographic examination is also carried out to verify the structure of the forged part. These tests and examinations are supplemented by chemical analyses of the steel.

    Since the implementation of the improvement plan, the test pieces are kept throughout the life cycle of the forged part.

  • 15. What is a tensile test?

    The tensile test is a mechanical test to measure the elasticity and the breaking strength of the steel. The test consists in gradually stretching the test piece at both ends until it fractures. The test is carried out at different temperatures according to the applicable standards and the customer's specific requirements: ambient and hot (from 150°C to 350°C).

    Four values are recorded:

    • Yield point: maximum tensile force beyond which the sample or test piece cannot regain its initial shape.
    • Tensile strength: maximum stress sustained by the sample or test piece before fracture.
    • Elongation: measurement of the stretch of the test piece at breaking point.
    • Reduction in area: measures the reduction in cross section of the test piece after fracture, relative to the initial section.
  • 16. What is an impact test?

    Impact resistance is the ability of a material to absorb energy under the effect of an impact. The objective of this test is to measure the toughness of the steel, i.e. the impact strength of the forged part. The test consists in dropping a pendulum on a test piece in which a V-notch has been machined. The pendulum fractures the test specimen. Measuring the pendulum's rise height makes it possible to measure the energy absorbed by the steel on fracture. The test is carried out at different temperatures between -100°C and +100°C.

  • 17. What is a Pellini test?

    The objective of the Pellini test is to determine the capability of the base material not to diffuse a defect in a weld when the part is subjected to an impact, with temperature as a variable. The characteristic of this sample is to present a weld bead which contains a notch. The test consists in dropping a weight on the sample.

    Under the effect of the impact, the notch causes the steel to bend. Depending on the temperature (up to -130°C), this notch remains localized at the weld bead or extends. The propagation level of the crack is then evaluated as a function of the temperature.

    Eight samples are generally necessary to determine the so-called nil-ductility temperature of the steel, i.e. the negative temperature from which the specimen cracks.

  • 18. What is a hardness test?

    This mechanical test aims to measure the hardness of the steel. The hardness is the resistance offered by the metal to the penetration of another harder material. The test consists in measuring the indent left by a penetrator or punch applied with a given force. The smaller the indent, the harder the steel. The punch is made of diamond or tungsten carbide and has a ball, cone or pyramid shape according to the test.

    This sample family is also used to carry out chemical analyses and the micrography of the steel.

  • 19. What is a shell?

    A shell is a hollow cylindrical or conical metal part. Primary cooling system components such as the reactor vessel, the pressurizers and the steam generators are fabricated by assembling various parts, including several large diameter shells.

  • 20. What is a conventional ingot?

    Cast in a steel mill and then solidified, a conventional ingot or solid ingot is a block of metal cast in a cast iron mold, used to forge upset parts such as bottom or closure heads as well as the legs of the primary cooling system. Creusot Forge uses conventional ingots weighing between 70 and 262 tonnes.

  • 21. What is a hollow ingot?

    Cast in the steel mill and then solidified, the hollow ingot is intended for hollow cylindrical parts of large diameter such as shells. The development of the hollow ingot has made it possible to eliminate drilling or coring operations and thus to limit the rate of carbon segregation on the surface of hollow parts.

  • 22. What is a directional solidification ingot?

    The directional solidification ingot (or LSD ingot from the French "Lingot à Solidification Dirigée) uses a specific pouring process. The creation of an ingot of large cross-section compared to its height coupled with the use of a cast iron plate at its bottom makes it possible to direct the solidification and to orient the carbon towards the upper part of the ingot. This part can then be removed by sawing.

    In partnership with the Industeel steel maker, AREVA NP is developing a new model of directional solidification ingot to improve control of the carbon segregation phenomenon.

  • 23. What is a steam generator channel head?

    The channel head is the bottom part of the steam generator. It is an upset-forged part from a conventional (solid) ingot. It features two pipes to which a stainless steel nozzle is welded in order to connect the steam generator to the primary legs. One of the two pipes is welded to the hot leg (water at 320°C coming from the reactor vessel into the steam generator) and the second pipe is welded to the crossover leg (water returning to the reactor vessel). The channel head also features two manholes so that service technicians can access the steam generator to carry out maintenance operations during outages.

  • 24. How is carbon content measured?

    Carbon content is measured in steel by spectrometry and chemical analysis.

  • 25. Which components are potentially affected by the phenomenon of carbon segregation?

    The components concerned by the carbon segregation phenomenon are the upset-forged parts produced from conventional or solid ingots. Parts such as tube plates, pressurizer bottom heads and RPV domes have been analyzed. Steam generator channel heads were identified as the parts most likely to have high carbon concentration zones. In France a measurement campaign was carried out on the nuclear fleet in service to demonstrate that the carbon levels measured in the channel heads concerned did not affect the nuclear safety and quality of the parts.

  • 26. What processes does Creusot Forge use to limit the presence of carbon in the final part?

    It is the forging process that helps migrate carbon segregation to areas that will be discarded and then machined by material removal.
    In the case of upset-forged parts such as domes, plates or primary legs, Creusot Forge first proceeds by cropping the discard section of the ingot. This process eliminates an area of high carbon segregation.

  • 27. What are Le Creusot's new manufacturing processes to control carbon segregation?

    AREVA NP, alongside EDF, committed in 2017 to conducting a long-term expert assessment program which consists in producing specimen parts in order to improve knowledge of the carbon segregation phenomenon, to provide the additional characterizing data and increase the margins in the studies produced. In addition, AREVA NP has launched the development of new manufacturing processes and is investing more than 8 million euros in 2017 in new production capacity for its Le Creusot facility to control carbon segregation in future components.