Status of accident analysis for HCPB

1. Status of accident analysis for HCPB X. Jin, L.V. Boccaccini, R. Meyder Garching, 9th Oct. 2006 Meeting on Safety assessment for EU TBM

2. TCWS vault HCS + CPS Port Cell Plasma Chamber T Building TES PIE • A double-ended pipe break in the TBM cooling loop in a large diameter pipe (ID=100mm) of the primary loop discharging coolant in the TCWS vault during plasma burn. • The coolant inventory is lost and the heat removal capability of the HCS goes to zero in short time.

3. Ex-vessel LOCA using RELAP5 MOD3.2 Double-ended pipe break in the TBM cooling loop in a large diameter pipe (DN100, Di=98.3mm, Da=114.3mm) during plasma burn (270KW/m²). Valve cross section: Vlve606 pipe break: 0.015178m² (=2*pipe area) Pressure vessel (PV) vlve 702: 0.0002513m²

4. Pressure results for ex-vessel LOCA • time constant 1.05s (p=2.96MPa) • at 2.4s p< 1MPa • at 10s p g 0 (time for ramp of HTC in the next calculation)

5. Heat up of the FW (and TBM) TCWS vault HCS + CPS Port Cell 270KW/m² Hot spot 500KW/m² T Building TES

6. Break of the FW TCWS vault HCS + CPS Port Cell Plasma Chamber T Building TES

7. Case A • A trigger system able to shut down the plasma in 100s is assumed and doesn’t fail. • In this case, only the failure of the FW channels (now filled with a mixture of He/air at about 0.1 MPa) is considered as following failure; it opens a by pass from the TCWS to the VV with air penetration in VV. Be/air reaction at the FW surface occurs. • A loss of off-site power occurs, which is equivalent to a loss of heat sink in the TBM cooling system; it also means that the VV cooling system is in the natural convection mode. • After differential pressure inversion the gases (air, He) in the VV and in TBM flow towards outside through the TBM cooling loop bypass and tritium and dust can be transported from the gas stream and released in the external zones.

8. TBM-Model for study of temperature (air oxidation) Cut from EM_TBM (pol*tor*rad=740*1270*750) Boundary conditions: • Surface heat flux 500/270KW/m² • FW cooling 330°C, 5000W/m²K • Cooling plate 450°C, 3000W/m²K • Radial power distribution • Radiation MF back side to 135°C • Radiation after plasma off from Be-cover to blanket FW surface temperature* • Radiation from BU back plate to MF3 • Be reaction rate** • After heating power factor * FIGURE VII.3.3.1-5 G84RI601-07-10 R1.0 ** G81RI1003-08-08W0.1

9. Case A/3,4,5 (Other possibilities tbd)

10. FW2 FW3 FW4 FW5 FW6 1290 1057 824 591 358 125 Temperature (°C) interface 760 Plasma side surface 0 90 180 270 360 450 Time (s) 100s Be-cover Case A 100s delay (500KW/m²)

11. Case B • The detection of the ex-vessel LOCA fails to trigger the Fusion Power Shutdown System (FPSS); the plasma reaction runs until the beryllium cover of the first wall reaches 1290 °C. This is the melting temperature of beryllium and leads to inherent plasma shut down. • In this case it is assumed a complete failure of the FW integrity with penetration of air in the VV. • In addition it is assumed that a major plasma disruption is triggered by the entering air but without failure of water confinement in the shielding blanket or divertor system. • A loss of off-site power coincides with the disruption, which is equivalent to a loss of heat sink in the TBM cooling system; it also means that the VV cooling system is in the natural convection mode. • Box structures containing lithium orthosilicate and beryllium pebbles can loose their integrity. This means that air can enter the TBM box reacting with the Be pebbles. • After differential pressure inversion the gases (air, He) in the VV and in TBM flow towards outside through the TBM cooling loop bypass and tritium and dust can be transported from the gas stream and released in the external zones.

12. Case B/3,4,5,6,7

13. FW2 FW3 FW4 FW5 FW6 1290 1057 824 591 358 125 Temperature (°C) 896 interface Plasma side surface 0 90 180 270 360 450 Time (s) 212s Be-cover Case B 212s delay to Be melting point (270Kw/m²)

14. 980 856 732 608 484 360 1290 1090 890 690 490 290 Temperature (°C) Temperature (°C) 0 4.8 9.6 14.4 19.2 24 Time (h) 0 170 340 510 680 850 Time (s) Case B/7 0.1MPa air in pebble bed (“unrestricted air access” model) Pebble bed temperatures, enlarged Pebble bed temperatures, 24h after plasma off

15. Case C • In addition it is assumed that a major plasma disruption is triggered by the entering air with failure of water confinement in the shielding blanket or divertor system. • A loss of off-site power coincides with the disruption, which is equivalent to a loss of heat sink in the TBM cooling system; it also means that the VV cooling system is in the natural convection mode. • Box structures containing lithium orthosilicate and beryllium pebbles can loose their integrity. This means that a mixture of air/steam (tbd) can enter the TBM box reacting with the Be pebbles. • After differential pressure inversion the gases (air, steam) in the VV and in TBM flow towards outside through the TBM cooling loop bypass and tritium and dust can be transported from the gas stream and released in the external zones.

16. m H2 Case C Be/steam, assumption for ANSYS calculation TBM pebble bed 0.2m³ Be+H2O->BeO+H2-370KJ/mol steam diffuses into TBM pebble bed pmax=60KPa, in=0.005mol/s Porosity por=0.67 Steam pressure in pebble bed p=nRT/[0.2*(1-por)], R=8.314J/molK

17. Case C Be/steam reaction 172g H2 generated after 5h, extrapolation to 1day 825.6g H2, 4days 3.3Kg H2 (tbd). 0.236g H2 generated after 5h, extrapolation to 1day 1.133g H2, 4days 4.53g H2 (tbd).

18. tbd • Case A/3 ramp of power for plasma shut down in 100s? • Case A/6, B/8 After differential pressure inversion the gases (air, He) in the VV and in TBM flow towards outside through the TBM cooling loop bypass and tritium and dust can be transported from the gas stream and released in the external zones. • Case B/3 reference temperature uses EUROFER melting point instead of Be melting point? • Case C/7-8 Box structures containing lithium orthosilicate and beryllium pebbles can loose their integrity. This means that a mixture of air/steam (tbd) can enter the TBM box reacting with the Be pebbles. After differential pressure inversion the gases (air, steam) in the VV and in TBM flow towards outside through the TBM cooling loop bypass and tritium and dust can be transported from the gas stream and released in the external zones.