1. Transmutation and ADS Safety EUROTRANS WP1.5 Meeting, Nov 27-28, Karlsruhe Simulation of EFIT Steam Generator Tube Rupture Accident (U-10) M. Flad, S. Wang, W. Maschek Forschungszentrum Karlsruhe, IKET, Postfach 3640 D-76201 Karlsruhe

2. Transmutation and ADS Safety EUROTRANS WP1.5 Meeting, Nov 27-28, Karlsruhe Content - Introduction - EFIT Reactor - EFIT SG Characteristics - SGTR Event - Validation of SIMMER on HLM/water Interaction - Simulation of EFIT SGTR Event - Modeling Set Up - Results - Discussion - Outlook - Summary

3. Transmutation and ADS Safety EUROTRANS WP1.5 Meeting, Nov 27-28, Karlsruhe Introduction The European Facility for Industrial Transmutation (EFIT) is developed to transmute long-lived actinides from spent fuel on an industrial scale. Main Characteristics: 386 MW th ADT Pb cooled (400 °C – 480 °C) two-loop design (no intermediate loop) 4 pumps / 8 internal heat exchangers pumps located in hot leg core with MA actinide load (positive void worth) HP-HT HX EFIT reactor The feasibility of the EFIT design has to be proven In case of a steam generator tube rupture (SGTR) accident high pressurized water blasts into the HLM pool evoking several risks: water/steam dragged into the core (reactivity insertion) potential of primary coolant sloshing CCI shockwave (damage propagation) pressurization of cover gas These features lead to simplified design and drastically reduced construction costs.

4. Transmutation and ADS Safety EUROTRANS WP1.5 Meeting, Nov 27-28, Karlsruhe EFIT SG Characteristics thermal power of core386 MW th core inlet temperature400 °C core outlet temperature480 °C primary coolant pumps 4 number of SG 8 specifications of each SG power50 MW number of tubes 91 inner diameter14.2 mm outer diameter17.5 mm length of tube~ 26 m feeding line pressure152 bar SG inlet pressure147 bar SG outlet pressure140 bar conditions at tube inletsub-cooled (335 °C) conditions at tube outletsuperheated vapor (450 °C) SG inventory56 kg (31 kg liquid, 25 kg vapor) mass flow rate/tube resp. velocity0.3 kg/s (inlet: 3.4 m/s, outlet: 43.3 m/s) SGTR break: supposed to happen at end of straight part - most conservative case fluid at almost inlet conditions (sub-cooled / saturated water): relative high density lowest starting position (residual stress from bending process) immersion heater

5. Transmutation and ADS Safety EUROTRANS WP1.5 Meeting, Nov 27-28, Karlsruhe SG Tube Rupture Event Conditions: pressure in SG tube:147 bar pressure in HLM: ~ 6 bar sub-cooled water:335 °C 630 kg/m 3 rupture type:Guillotine crack tubes ruptured1 Consequences: discharge rate of water pressure (energy) of CCI vapor production / relocated HLM impact on structures / propagation sloshing of HLM sloshing induced cover gas ingress penetration depth of water/steam pressurization of cover gas Simulation of SGTR event: HLM/water interaction needs to be validated ruptured SG tubes

6. Transmutation and ADS Safety EUROTRANS WP1.5 Meeting, Nov 27-28, Karlsruhe SIMMER Validation on HLM / Water Interaction Sibamoto experiments: injection of HLM into water injection of water into HLM Under severe accident conditions in sodium cooled fast reactors hot fuel and steel get in contact with cold sodium (FCI) which has to be modeled and simulated. The SIMMER code has been validated on FCI problems by successful recalculation of numerous experiments with UO2 or fuel simulants and sodium or water. For validating the code on HLM / water interaction the Sibamoto experiments have been chosen. Data from experiments: either vapor production or penetration of water/steam into LBE. Simulations with SIMMER reproduces satisfactorily penetration history of set of 5 experiments after modification of input parameter. Example: Simulation of Sibamoto experiment

7. Transmutation and ADS Safety EUROTRANS WP1.5 Meeting, Nov 27-28, Karlsruhe SIMMER Validation on HLM / Water Interaction (continued) SGTR Experiment at TALL Facility (KTH): low pressure injection of water (< 10 bar) into LBE single SG tube geometry (scale 1:1) used for SGTR and SGTL accidents lifetime history of water droplet in flowing LBE ICE Experiment in CIRCE facility, Russian experiment, … Results of experiments shall be used for further validation of SIMMER code. SGTR Bundle Experiment (FZK): high pressure injection of vapor (240 bar) into Pb SG tube bundle geometry (19 pins, scale 1:4) penetration history / HLM/water interaction / many quantities under construction / experiments: summer 2009 LIFUS-5 Test Facility (ENEA): high pressure injection of water (~ 200 bar) into LBE (Pb) SG tube bundle geometry (20 pins, scale 1:1) HLM/water interaction / no penetration history / many quantities first tests performed (2006, 2007)

8. Transmutation and ADS Safety EUROTRANS WP1.5 Meeting, Nov 27-28, Karlsruhe Simulation of EFIT SGTR Accident Modeling Setup SIMMER-III (2D) / R-Z / 26 x 52 cells Pb flow: 400 – 480 °C, 33500 kg/s, flow established by B.C. 8/8 core, 1/8 SG flow path twofold (3/4, 1/4); B.C. inflow = outflow SG: thin-walled cylinder (1 SG geometry) v(Pb) = -0.5 m/s, no access for vapor SGT: thin-walled cylinder, (1 SGT geom.) inventory: H 2 O at inlet cond. (mass cons.) B.C.: 15.2 MPa, 335 °, orifice at tube inlet discharge rate ~1.0 kg/s (0.6 kg/s/tube) Core: 7+4 rings (geometry, vol. fractions), heat source model (375 MW, power prof. ) Δp core = 0.7 bar, radial orificing Vessel: geometry, rounded shape

9. Transmutation and ADS Safety EUROTRANS WP1.5 Meeting, Nov 27-28, Karlsruhe Possible flow paths for discharged vapor / displaced Pb: through the SG (not for the simulation model) through the cold pool through the core flow governed by pressure and flow resistances starting conditions very important Using option “pump model off” allows/requires crucial test: Given: mflow inlet, T in, orifices, P th, p outlet, levels, etc. Get: mflow core, Δp core, T out, mflow out, pool levels Pb accumulation in cold/hot system? At steady state: set B.C. to Pb outflow = Pb inflow Results of Simulation (1)

10. Transmutation and ADS Safety EUROTRANS WP1.5 Meeting, Nov 27-28, Karlsruhe Results of Simulation (2) SGT and Discharge: tube in 2-d as thin-walled cylinder orifice from simulation of SG at steady-state cross section and mass inventory kept initial mass substituted by liquid water feeding conditions: 152 bar / 335 °C; const counter pressure heavily changing discharge has to be calibrated Ansaldo: 0.6 kg/s/tube (no information about reliability) discharge aimed to be 1.0 kg/s (resulting value: 1.08 kg/s) 2nd coolant under discharge conditions: decompression: partly vaporizing already inside the tube further expansion to pool pressure: rapid vaporization surviving droplets dragged along survive only for a short time

11. Transmutation and ADS Safety EUROTRANS WP1.5 Meeting, Nov 27-28, Karlsruhe Results of Simulation (3) Liquid water: According to the results water is rapidly vaporized (decompression); surviving droplets are strictly limited to the cold pool and stay sufficiently far away from the core inlet plane. Steam ingress into the core: With updated model parameters (Sibamoto exp.) and refined modeling a slight steam ingress into the core is predicted: vapor is mostly directed upwards to the cover gas region, but about 10-15 wt% of the discharged water passes through the core as steam vapor reaches the core intermittently leading to a core void of 4 % (at maximum) corresponding void worth in the range of 300 – 500 pcm different modeling approaches back these results

12. Transmutation and ADS Safety EUROTRANS WP1.5 Meeting, Nov 27-28, Karlsruhe Results of Simulation (4) Volume fraction plots for vapor (gas) for SGTR accident simulation

13. Transmutation and ADS Safety EUROTRANS WP1.5 Meeting, Nov 27-28, Karlsruhe Results of Simulation (5) Volume fraction plots for vapor (gas) for SGTR accident simulation (active core zone)

14. Transmutation and ADS Safety EUROTRANS WP1.5 Meeting, Nov 27-28, Karlsruhe Discussion of Results The consequences of a failure of one SG tube in EFIT are assessed with the following conditions: guillotine cut of tube (not the typical crack form) discharge rate 1.08 kg/s (80 % higher than Ansaldo value) water at inlet conditions (rupture plane: x ~ 3.5 m, coolant: x = 0 m) initial mass defined to be fully liquid no coast-down function of secondary coolant feeding line front-end consideration of rupture problem model does not allow rising of steam within SG primary coolant flow along tube fully maintained during SGTR event Under conservative assumptions a steam ingress into the core is predicted leading to a maximum core void of ~4 % (roughly 300-500 pcm). Liquid water is not introduced into the core.

15. Transmutation and ADS Safety EUROTRANS WP1.5 Meeting, Nov 27-28, Karlsruhe Summary The rupture of one tube within an EFIT SG is numerically simulated using the SIMMER-III code (2-d). The results based on various improvements (updated parameters, more detailed modelling) gives a refined picture of the consequences of an SGTR accident. A steam ingress into the core is predicted based on a number of conservative assumptions. According to the results a total core void of 4 % (maximum) is to be expected (roughly 300-500 pcm). Due to the decompression water is quickly vaporized; droplets of liquid water stay sufficiently away from the core inlet plane. Code validation efforts on this field are extremely important with respect to a CCI event. However, sufficient HLMC/water interaction experiments are lacking providing a high pressure injection for SG geometry. New data input is expected from the SG tube bundle experiments at FZK supposed to start in summer 2009.