1. Development of a RELAP5-3D thermal-hydraulic model for a Gas Cooled Fast Reactor D. Castelliti, C. Parisi, G. M. Galassi, N. Cerullo (San Piero A Grado Nuclear Research Group ) DIMNP – University of Pisa - ITALY 2006 RELAP5-3D © Users Seminar Holiday Inn SunSpree Resort – West Yellowstone – USA 16 – 18 August 2006

2. Contents Introduction Introduction ETDR Thermal-Hydraulic Nodalization ETDR Thermal-Hydraulic Nodalization Main Results Main Results  Steady State  Transient Conclusions Conclusions

3. Introduction [1/3] GCFR, a Gen IV system developed by a wide international consortium (NNC, CEA, CIRTEN, Framatome, JRC-IE, NRG, PSI, Univ. of Delft, etc.) GCFR, a Gen IV system developed by a wide international consortium (NNC, CEA, CIRTEN, Framatome, JRC-IE, NRG, PSI, Univ. of Delft, etc.) Huge efforts required for testing materials, component, plants layout Huge efforts required for testing materials, component, plants layout Need to have a testing facility  ETDR Need to have a testing facility  ETDR Need to have numerical tool and a model for proposed experimental analyses Need to have numerical tool and a model for proposed experimental analyses

4. Introduction [2/3] Different features of GCFR system vs. present NPPs technology Different features of GCFR system vs. present NPPs technology  Helium coolant  Direct Brayton cycle  Fast Neutron Flux  Fuel geometry Needs reliable to have a reliable flexible and flexible system code for experiments planning and analyses RELAP5-3D ©

5. Introduction [3/3] Proposed ETDR layout as testing facility for GCFR system: Proposed ETDR layout as testing facility for GCFR system:  Testing start-up and demo cores (different temperatures ranges)  Testing fuel and structural materials  Analyzing system dynamic behavior  Asses Codes Qualification

6. ETDR TH Nodalization [1/2] 722 722 Nodes 836 836 Junctions 401 401 Heat Structures 4635 4635 Mesh Points

7. ETDR TH Nodalization [2/2] Core modeled by two hydraulic channels Core modeled by two hydraulic channels  Average channel  Hot channel MULTID component used for MHX for an improved estimation of Heat Transfer Coefficient (HTC not imposed) MULTID component used for MHX for an improved estimation of Heat Transfer Coefficient (HTC not imposed) Blower modeled by PUMP component  use of benchmark homologous curves Blower modeled by PUMP component  use of benchmark homologous curves Heat structures simulated for all components Heat structures simulated for all components Model qualified according to benchmark data Model qualified according to benchmark data

8. Qualification [1/2] - Volume-Height Curve

9. Qualification [2/2] - Steady State Results ParameterValueReferenceError System flow rate 32.18 Kg/s 32.00 Kg/s 0.56 % 0.56 % Average channel flow rate 0.60 Kg/s N/AN/A Hot channel flow rate 0.58 Kg/s N/AN/A Pressure (top of the vessel) 6.92 MPa 7.00 MPa 1.14 % Total mass of coolant 450.28 Kg N/AN/A Total mass of coolant without DHR 351.60 Kg N/AN/A Core inlet temperature 262.5 °C 260.0 °C 0.96 % Core average exit temperature 561.7 °C 560.0 °C 0.30 % Exit temp. In average channel 560.6 °C N/AN/A Exit temp. In hot channel 613.2 °C N/AN/A Maximum clad temp. In avg. channel 623.0 °C N/AN/A Maximum clad temp. In hot channel 685.0 °C N/AN/A Maximum fuel temp. In avg. channel 944.0 °C N/AN/A Maximum fuel temp. In hot channel 1067.0 °C N/AN/A Main blower head 8399 m 2 /s 2 8565 m 2 /s 2 1.94 % Main blower torque -2025.5 Nm -2036.4 Nm 0.53 % Main heat exchanger heat transfer area 157.32 m 2 157.00 m 2 0.2 % Main heat exchanger heat transfer coefficient 2261.8 W/(m 2 K) 1648.0 W/(m 2 K) 37.2 % Reactor power 50 MW 0 %0 %0 %0 % Core pressure drop -0.42 bar -0.41 bar 2.44 % Main blower pressure drop 0.5147 bar N/AN/A

10. LOFA Results [1/7] - Blower Velocity

11. LOFA Results [2/7] - Primary pressure

12. LOFA Results [3/7] - DHR mass flow - helium side Open DHR valves

13. LOFA Results [4/7] – DHR mass flow – water side

14. LOFA Results [5/7] - Hot channel Clad temperature

15. LOFA Results [6/7] - Power trend in DHR HX (provided run-down curve)

16. LOFA Results [7/7] Two transient-cases analyzed Two transient-cases analyzed 1.provided run-down curve 2.calculated run-down curve DHR Valves open in 170 s from LOFA in 1 st case, and in 600 s in 2 nd case DHR Valves open in 170 s from LOFA in 1 st case, and in 600 s in 2 nd case Second transient less severe than first one Second transient less severe than first one  lower pressure peak  lower cladding temperature peak Natural Circulation occurs at: Natural Circulation occurs at:  370 s first case  870 s in second case (from LOFA) No differences can be found after 1700 s from LOFA for both transients No differences can be found after 1700 s from LOFA for both transients Equilibrium conditions reached after 2600 s from LOFA Equilibrium conditions reached after 2600 s from LOFA

17. Conclusions RELAP5-3D © confirmed to be a valid and a reliable tool for the development of GCFR technology RELAP5-3D © confirmed to be a valid and a reliable tool for the development of GCFR technology Model developed can be applied and tested for other transients Model developed can be applied and tested for other transients Further data needed for extensive qualification Further data needed for extensive qualification Future works: Future works:  Improvements of MHX model using cylindrical geometry MULTID  Add 0D and 3D NK feedback