Elsevier

Fusion Engineering and Design

Volumes 98–99, October 2015, Pages 1552-1555
Fusion Engineering and Design

Structural damages prevention of the ITER vacuum vessel and ports by elasto-plastic analysis with regards to RCC-MR

https://doi.org/10.1016/j.fusengdes.2015.06.159Get rights and content

Highlights

  • ITER vacuum vessel (VV) is a part of the first barrier to confine the plasma.

  • ITER VV as NPE necessitates a third party organization authorized by the French nuclear regulator to assure design, fabrication, and conformance testing and quality assurance, i.e. ANB.

  • Several types of damages have to be prevented in order to guarantee the structural integrity with regards to RCC-MR.

  • It is usual to employ non-linear analysis when the “classical” elastic analysis reaches its limit of linear application.

  • Several structural analyses were performed with many different global and local models of the whole ITER VV.

Abstract

Several types of damages have to be prevented in order to guarantee the structural integrity of a structure with regards to RCC-MR; 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.

Following RCC-MR, the S-type damages prevention has to be started only when the structural integrity is guaranteed against P-type damages. The verification of the last one on the ITER vacuum vessel and ports has been performed by limit analysis with elasto-(perfectly)plastic material behavior. It is usual to employ non-linear analysis when the “classical” elastic analysis reaches its limit of linear application. Some elasto-plastic analyses have been performed considering several cyclic loadings to evaluate also more realistic structural margins of the against S-type damages.

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:

  • Inertial loads: these are caused by accelerations due to gravity (DW) and seismic events (SL).

  • 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).

  • 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:

  • 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)

There are more references available in the full text version of this article.

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