Preliminary safety analysis of an in-vessel LOCA for the EU-DEMO WCLL blanket concept

• Published in: Fusion engineering and design 2020-06, Vol.155, p.111560, Article 111560
• Main Authors: D’Onorio, Matteo, Giannetti, Fabio, Porfiri, Maria Teresa, Caruso, Gianfranco
• Format: Article
• Language: English
• Subjects: Breeder reactors; Chemical reactions; DEMO; Electric power generation; Lithium; LOCA; Loss of coolant accidents; Modules; Nuclear power plants; Pressurization; Pressurized water; Safety; Safety margins; Source term; Tokamak devices; Tritium; Tungsten; Vessels; VVPSS; WCLL
• ISSN: 0920-3796; 1873-7196
• DOI: 10.1016/j.fusengdes.2020.111560

•In vessel LOCA simulation and effects of upstream and downstream isolation valves.•Five tanks as suppression system ensure the confinement of radioactive source term.•Uminitigated plasma disruption cause the production of 660 g of hydrogen.•Downstream valves reduce the amount of activated corrosion products in the VV of 33 %.•Tungsten dust, ACP and HTO are moved by steam and discharged into suppression tanks. In-vessel Loss Of Coolant Accident (LOCA) is one of the Design Basis Accident to be considered to support the future DEMOnstration power plant safety assessment. The water-cooled lithium-lead (WCLL) Breeding Blanket (BB) concept relies on Lithium-Lead as breeder, neutron multiplier and tritium carrier. The breeding modules are cooled by two independent pressurized water systems: the fist-wall (FW) and the breeding zone (BZ) coolant systems. The postulated initiating event (PIE) considered for this safety analysis is a double ended pipe rupture of the blanket module first wall channels. This event causes the inlet of coolant into the plasma chamber volume triggering an unmitigated plasma disruption and the pressurization of the Vacuum Vessel (VV) volume. The fusion version of MELCOR code (ver. 1.8.6) is used to evaluate accident consequences for two different scenarios, with the presence and absence of the downstream isolation valves, respectively. The chemical reaction between the coolant and the first wall tungsten layer inside the VV has been considered together with the mobilization of the radioactive source term. Pressure and temperature transient behavior in the tokamak volumes demonstrate that safety margins are respected during the accidental sequence.