Structural damages prevention of the ITER vacuum vessel and ports by elasto-plastic analysis with regards to RCC-MR
Introduction
The ITER Tokamak Vacuum Vessel (VV) is a torus-shaped (with 13 m height and 20 m diameter), double-wall structure that surrounds the plasma with Stainless Steel of 316L(N) IG, low Nitrogen ITER Grade as a main structural material. It features a band of upper ports, equatorial ports, and lower (divertor) ports to allow access for plasma heating, fuelling, diagnostics, and in-vessel component services, see Fig. 1. It is supported by the lower port gravity supports. The interspace between the VV walls is filled with cooling water to remove heat deposited during plasma operation; to bake the vessel to promote ultra-high vacuum conditions in the plasma chamber; to maintain the VV temperature; and to remove decay heat loads in in-vessel components in the event of a loss of cooling or loss of flow to those components.
The VV is a part of the first barrier to confine plasma. It protects superconducting magnets (enveloping the VV) by shielding and also the environments against nuclear active materials. Following the Preliminary Safety Report [1], the RCC-MR code [2] has been chosen for the Tokamak Vacuum Vessel. RCC-MR classifies the structural damages in two types: the P-type damages which can result from the application to a structure of a steadily and regularly increasing loading or a constant loading and the S-type damages during operational loading conditions which can only result from repeated application of loadings associated to the progressive deformations and fatigue. Some other phenomena exist such as the buckling or the fast fracture which are not strictly speaking a type of damage. For this reason these last one are not a part of paper's scope.
Section snippets
Load condition [3]
As discussed in [4], the mechanical loads acting on the VV can be divided into five independent categories:
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Inertial loads: these are caused by accelerations due to gravity (DW) and seismic events (SL).
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Electromagnetic (EM) loads: these are normally a strong design driver and act upon nearly all conductive structures during transient events (e.g. Major Plasma Disruption MD, Vertical Displacement Events VDE, and Magnet Current Fast Discharge MFD).
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Pressure loads: these include coolant (CP coolant
Non-linear structural analysis
Some previous assessments [5], [6] proposed the verification of structural integrity of the ITER VV Conceptual Baseline Design (2010) before to launch the manufacturing phase mainly based on elastic analysis. However the design modifications proposed by Domestic Agencies (and the manufacturers) associated to some revised interface loads require to verify one more time the structural integrity.
The structural analyses were performed with many different global models [6]: 360-degree whole vessel
Conclusion
The ITER Tokamak Vacuum Vessel structural integrity have been guaranteed for critical zones with regards to RCC-MR [2] considering the load specification [3] by using non-linear structural analysis. In this case two types of damages have been prevented:
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The P-type damages which can result from the application to a structure of a steadily and regularly increasing loading or a constant loading. In this case, some limit analyses have been performed using elasto-(perfectly) plastic material behavior
ITER disclaimer
The views and opinions expressed herein do not necessarily reflect those of the ITER Organization.
Acknowledgments
The authors acknowledge the support of members of ITER IO Vacuum Vessel Section, Tokamak Integration Section and Systems Engineering, Analysis and Standards Section for the various activities reported in this paper. The authors underline also the strong effort made by the domestic agencies and manufacturers in these topics.
References (8)
Structural analysis of the ITER vacuum vessel regarding 2012 ITER project-level loads
Fusion Eng. Des.
(2014)- et al.
Preliminary Safety Report – RPrS: Rapport Préliminaire de Sûreté, v3.0
(2012) - Design and Construction Rules for Mechanical Components of Nuclear Installation, RCC-MR, French Association for the...
ITER Vacuum Vessel Load Specification, v3.3
(2011)
Cited by (4)
Development of a thermo-mechanical behaviour model adapted to the ITER vacuum vessel material
2021, Fusion Engineering and DesignCitation Excerpt :Fatigue (by progressive cracking); time independent fatigue and time dependent fatigue. As for the finite element analysis, the justification of the structural integrity is made through the elastic route, and when the design criteria cannot be satisfied, several non-linear approaches to the mechanical material behaviour can be considered [5]. The assessment of the cyclic loading conditions (S-type) cannot be done until the P-type damage criteria are satisfied.
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ITER vacuum vessel structural analysis completion during manufacturing phase
2016, Fusion Engineering and DesignCitation Excerpt :It is usual to employ non-linear analysis when “classical” elastic analysis reaches its limit of linear application. By the same way, some elasto-plastic analyses have been performed considering cyclic loadings to evaluate also more realistic structural margins against S-type damage, see Ref. [6]. Structural analyses of conceptual design were performed with many different global models [5,6] which are mostly covered by shell finite elements models (see Fig. 3) and also local analyses using solid elements (see Fig. 4).
Preliminary dynamic analysis of the forces on the COMPASS-U tokamak foundations
2019, Proceedings of SPIE - The International Society for Optical Engineering