Please cite this article in press as: R. Lo Frano, et al., Fluid dynamics analysis of loss of vacuum accident of ITER cryostat, Fusion Eng. Des. (2015), http://dx.doi.org/10.1016/j.fusengdes.2015.12.038 ARTICLE IN PRESS G Model FUSION-8408; No. of Pages 6 Fusion Engineering and Design xxx (2015) xxx–xxx Contents lists available at ScienceDirect Fusion Engineering and Design jo ur nal home p age: www.elsevier.com/locate/fusengdes Fluid dynamics analysis of loss of vacuum accident of ITER cryostat Rosa Lo Frano ∗ , Donato Aquaro, Nicola Olivi University of Pisa – DICI, Pisa, Italy h i g h l i g h t s • Analysis of the Cryostat LOVA (CrLOVA) by Ansys © CFX. • Investigation of the consequences of different breach sizes of the Cryostat boundary. • Magnet Quench (MQ) and No Magnet Quench (NMQ) cases are discussed. • Evaluation of mass flow, temperature and pressure evolution in the Cryostat environment. • The pressure values in LOVA conditions are below the design limit pressure. a r t i c l e i n f o Article history: Received 11 September 2015 Received in revised form 11 December 2015 Accepted 14 December 2015 Available online xxx Keywords: Cryostat LOVA Magnet Quenching CFX a b s t r a c t The cryostat is one of the most important components of the ITER reactor because it provides a vacuum environment limiting the convective heat exchange between the components, especially the magnets. That’s why it is designed to withstand negative pressure loads. In this paper a postulated breach of the cryostat boundary leading accident conditions involving the ingress of air into the ITER cryostat has been analyzed with ANSYS © CFX. In the performed fluid-dynamic simulations suitable geometry, materials properties and initial and boundary conditions, thoroughly discussed, have been used. The main results indicated that the cryostat, even in the worst condition, seemed to withstand well LOVA without any relevant mechanical failure. The maximum pressure value resulted below the design limit pressure for the cryostat of 0.2 MPa for this accident. Finally it is worthy to remark that these results will be used for a further in depth evaluation of the structural performances of the cryostat itself. © 2015 Elsevier B.V. All rights reserved. 1. Introduction ITER will be an experimental reactor based on the Tokamak concept of magnetic confinement; inside which the plasma is con- tained in a doughnut-shaped vacuum vessel. In particular ITER will be the first occasion to demonstrate licensable fusion safety and environmental potential of fusion. The interaction between the plasma edge and the surrounding surfaces is a key engineering issue. ITER uses superconducting magnets to maximize the efficiency and limit the energy consumption. Since superconducting coils must be maintained at very low temperature, the vacuum vessel (VV) is positioned inside the cryo- stat (Fig. 1); in this way the convective heat transfer between magnets and cryostat is negligible during the normal operation. ∗ Corresponding author. In addition thermal shields (TS), which are cooled at 80 K, enve- lope the high temperature components facing magnets in order to avoid the radiant heat transfer. The cryostat (Cr) is the most important containment barrier against the release of radioactive products in ex-vessel accident conditions [1]. In consideration of that its structural integrity should be evaluated under possible accident sequences, such as loss of coolant accidents (LOCA), loss of coolant flow accidents (LOFA) and loss of vacuum accidents (LOVA) [2–4]. It is expected that the ingress of air would quench the super- conducting coils (with an immediate plasma shutdown because of abrupt changes in the magnetic fields) and result in a temperature increase of about 55 K. In [3] CrLOVA with helium leakage is treated, while Honda et al. [2] studied with MELCOR code the air ingress accident from an adjoining room. In this study, instead, the Cryostat LOVA (CrLOVA), as a conse- quence of breach of the cryostat boundary, has been investigated [5,6] by carrying out fluid-dynamic simulations with ANSYS © CFX http://dx.doi.org/10.1016/j.fusengdes.2015.12.038 0920-3796/© 2015 Elsevier B.V. All rights reserved.