The Vacuum Vessel (VV) of the International Thermonuclear Experimental Reactor (ITER) is designed to maintain its structural integrity up to a pressure value of 0.15 MPa. Postulated accidental scenarios LOCA, occurring in the in-vessel components cooling water systems, required a dedicated safety Pressure Suppression System (PSS) aimed to condense the steam released from the VV. It is called VVPSS and is composed of four tanks of 100 m3 each, partially filled with water: 60 m3 in the three Large LOCA Tanks (LLTs) and 40 m3 in the single Small LOCA Tank (SLT). Along with the steam, hydrogen is carried into the VVPSS tanks, produced by radiolysis and thermolysis in the VV. The possible hydrogen deflagration or combustion (with dedicated ignitors) in the larger cover gas of the SLT must be numerically investigated, for evaluating the water inventory lost due to reverse flow and possible hazardous water hammer. In this scenario, 48 reverse flow tests in the SLT were numerically simulated with RELAP5 mod 3.3, performing a sensitivity analysis on the hydrogen oxidation process, pressurization slope, check valve closure time and thermodynamic conditions. No hazardous water hammer was observed (1 bar of overpressure near the valve) and the maximum water mass lost (closure valve in 10 s) resulted of about 7200 kg, not enough for compromising the SLT condensation capabilities, even if reverse flow occurs during the first phases of the small LOCA transient.
Thermo-Hydraulic And Fluid-Dynamic Analyses of The Reverse Flow In The Iter Vacuum Vessel Pressure Suppression System Due To Hydrogen Deflagration Accident
Alessio Pesetti
Primo
Membro del Collaboration Group
;Fontanelli Stefano;Raucci Michele;Donato AquaroUltimo
Membro del Collaboration Group
2021-01-01
Abstract
The Vacuum Vessel (VV) of the International Thermonuclear Experimental Reactor (ITER) is designed to maintain its structural integrity up to a pressure value of 0.15 MPa. Postulated accidental scenarios LOCA, occurring in the in-vessel components cooling water systems, required a dedicated safety Pressure Suppression System (PSS) aimed to condense the steam released from the VV. It is called VVPSS and is composed of four tanks of 100 m3 each, partially filled with water: 60 m3 in the three Large LOCA Tanks (LLTs) and 40 m3 in the single Small LOCA Tank (SLT). Along with the steam, hydrogen is carried into the VVPSS tanks, produced by radiolysis and thermolysis in the VV. The possible hydrogen deflagration or combustion (with dedicated ignitors) in the larger cover gas of the SLT must be numerically investigated, for evaluating the water inventory lost due to reverse flow and possible hazardous water hammer. In this scenario, 48 reverse flow tests in the SLT were numerically simulated with RELAP5 mod 3.3, performing a sensitivity analysis on the hydrogen oxidation process, pressurization slope, check valve closure time and thermodynamic conditions. No hazardous water hammer was observed (1 bar of overpressure near the valve) and the maximum water mass lost (closure valve in 10 s) resulted of about 7200 kg, not enough for compromising the SLT condensation capabilities, even if reverse flow occurs during the first phases of the small LOCA transient.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
