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Mechanical design : validation of mechanical components in the nuclear field

Cryopumps analysis within ITER project frame : using simulation to make testing more efficient

ITER’s request was to ensure their cryopumps’ compliance to norm EN13445 regarding resistance under stress of "Unfired pressurized containers".
We ran calculations under different types of thermo-mechanical loadings, thus enabling thorough validation of the structure’s robustness.

ITER is one of the most ambitious energy projects in the world today. It will be the first fusion device to produce net energy.

In France, near Aix-en-Provence, 35 nations are collaborating to build the world’s largest Tokamak, a magnetic fusion device that has been designed to prove the feasibility of nuclear fusion as a large-scale and carbon-free source of energy.

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Within this international environment, ITER Organization has called for PHIMECA’s expertise (on behalf of the NOVAE consortium, led by ARIAL INDUSTRIES) in structural analysis to validate mechanical components of the ITER Vacuum System(see vacuum system), such as the cryopumps.

The complex pumps have been tailored for the very specific applications and requirements of the ITER project. All are based on cryopanels, cooled with supercritical helium.

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PHIMECA’s mission has been to support ITER at different steps of the pumps’ pre-production process :

• First, prior to manufacturing, check pumps’ mechanical behaviour under all relevant load cases. This allowed the identification of some problematic areas on the pump preliminary design. Some changes have therefore been advised.

• Second, after some design modifications due to the first analysis, but also due to manufacturing constraints encountered by the industrial, check the mechanical behaviour of the as-built pump.

These are two similar steps (except that the analysed geometry is slightly different) which have led to the delivery of a complete analysis report and an ANSYS model archive.

During these two iterations, PHIMECA has performed thermo-mechanical calculations by finite element modelling of the cryopump using ANSYS Workbench software :

• FE model build-up from the CAD geometry provided by the client. ANSYS Design Modeler has been used to simplify the geometry, for instance with the use of shell elements.

• Definition of material properties and especially thermo-mechanical ones (thermal expansion and thermal conductivity coefficients)

• Mechanical loads’ definition from the Load Specification of the pump :
o Deadweight
o Operational Pressures
o Seismic events (definition of the Floor Response Spectra)
o Hydrostatic Pressure (accidental load case, pump full of water)
o Ice accumulation on cryogenic circuit surfaces (accidental load case).

• Thermal loads’ definition. Conduction, convection and radiation phenomena are modelled in ANSYS. An example of temperature profile in operation is given below.

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• Modal analysis is then performed in order to know the dynamic behaviour of the component and be able to implement the Response Spectrum method in ANSYS. (See modal deformed shape in Figure 4).

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• Combination of the single loads to model all the load cases required to validate the component.

• Post-processing of the stresses following the criteria of EN13445 (Unfired Pressure Vessel, Part 3 : Design) :
o Primary stresses criteria (membrane and membrane plus bending) ;
o Principal stresses criteria in case of tri-axial state of stress ;
o Fatigue criteria on primary and secondary stresses.

• Conclusion and writing of the analysis report.

Thanks to the calculations PHIMECA performed, the cryopump design has been validated in accordance with EN13445 standards. The component has now entered test phase (see testing phase) freed of the fear of failure occurring while testing.


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PHIMECA Engineering est une société d’ingénierie spécialisée dans l’évaluation et l’optimisation des performances des produits et des systèmes. Sa vocation est de proposer des solutions en ingénierie robuste et en fiabilité en s’appuyant sur un socle scientifique solide, un esprit d’entreprise et des valeurs morales partagés par tous ses collaborateurs.