Choice of a low operating temperature for the DEMO EUROFER97 divertor cassette

• Published in: Fusion engineering and design Vol. 124; pp. 655 - 658
• Main Authors: Mazzone, Giuseppe, Aktaa, J., Bachmann, C., De Meis, D., Frosi, P., Gaganidze, E., Di Gironimo, G., Mariano, G., Marzullo, D., Porfiri, M.T., Rieth, M., Villari, R., You, J.H.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.11.2017; Elsevier Science Ltd
• Subjects: Activation; Austenitic stainless steel; Creep (materials); DEMO; Divertor cassette; EUROFER97; Fracture toughness; Fusion; Helium; Hydraulics; Neutron fluence; Neutron irradiation; Nuclear reactors; Operating temperature; Structural design; Transition temperature; Divertor cassette; EUROFER97; DEMO; Neutron fluence
• ISSN: 0920-3796; 1873-7196
• DOI: 10.1016/j.fusengdes.2017.02.013

•In this article the lower limit of allowed operation temperature window was defined for reduced activation steel EUROFER97 as structural material of DEMO divertor body.•The underlying rationale and supporting experimental data from a number of irradiation tests were presented.•The motivation of this study was to explore the possibility to use EUROFER97 for water-cooled divertor cassette at temperatures below 350°C.•Literature data showed that the FTTT of EUROFER97 at 6dpa (the expected maximum dose of cassette body after 2fpy) is about 180°C.•This result imposes the guideline on the coolant inlet temperature of the divertor cassette. One of the fundamental input parameters required for the thermo hydraulic and structural design of a divertor cassette is the operation temperature range. In the current design activities to develop European DEMO divertor in the frame of EUROfusion, reduced activation steel EUROFER97 was chosen as structural material for the divertor cassette body considering its low long-term activation and superior creep and swelling resistance under neutron irradiation (You et al., 2016) [1]. For specifying an operation temperature range (i.e. cooling condition) various, often conflicting requirements have to be considered. In this article the lower limit of allowed operation temperature window is defined for EUROFER97 for structural design of DEMO divertor cassette body. The underlying rationale and supporting experimental data from a number of previous irradiation tests are also presented. The motivation of this survey study is to explore the possibility to use EUROFER97 for water-cooled divertor cassette at temperatures below 350°C which has been regarded as limit temperature to preserve ductility under irradiation. Based on the literature data of FTTT (Fracture Toughness Transition Temperature) calibrated by Master Curve method, it is concluded that EUROFER97 at the envisaged maximum dose of 6dpa will have to be operated above 180°C taking the embrittlement due to helium production into account.