1. Italian National Agency for New Technologies, Energy and Environment Advanced Physics Technology Division Via Martiri di Monte Sole 4, 40129 Bologna, Italy EUROTRANS - DM1 WP 1.5 Meeting 6th FRAMEWORK PROGRAM EURATOM Management of Radioactive Waste Massimiliano Polidori, Giacomino Bandini, Paride Meloni Analysis of EFIT Protected and Unprotected Accidental Transients with PARCS/RELAP5 Coupled Code Forschungszentrum Karlsruhe, 27-28 November, 2008

2. EUROTRANS DM1 – WP 1.5 Progress Meeting, Forschungszentrum Karlsruhe, November 27-28, 2008 2 Outline Description of the Codes The RELAP5 Model of EFIT The PARCS Model and Assumption of EFIT Analysis of Protected Transients Spurious Beam Trip 1 sec Analysis of Unprotected Transients Loss of Flow (ULOF) Loss of Heat Sink (ULOH) ULOF + ULOH Beam Overpower from Hot Full Power (HFP) Beam Overpower from Hot Zero Power (HZP) Conclusions

3. EUROTRANS DM1 – WP 1.5 Progress Meeting, Forschungszentrum Karlsruhe, November 27-28, 2008 3 PARCS/RELAP Coupled Code Our State-of-the-Art code to simulate the Neutronic-T/H coupled phenomena for safety purpose is: PARCS v1.01 – 3D Neutronic coarse mesh code that solves the 2- group diffusion equation in cartesian geometry, modified to treat fast spectrum and external neutron source. RELAP5 mod 3.2.2  – Thermal-Hydraulic 1D code modified to treat heavy liquid metal (lead, LBE) PVM GI RELAP5 PARCS Fuel/Coolant Temperature and Density, Void Fraction,..  Cross Section Neutron Flux Reactor Power

4. EUROTRANS DM1 – WP 1.5 Progress Meeting, Forschungszentrum Karlsruhe, November 27-28, 2008 4 The RELAP5 Model of EFIT RELAP5 Noding Scheme Primary system layout by D1.26 of ANSALDO (November 2007) Gagging at core inlet according to SIM- ADS Active Core Region is represented by rings in according with the designed layout. Ring 1 – 18 FA (Inner Zone) Ring 2 – 24 FA (Inner Zone) Ring 3 – 30 FA (Interm Zone) Ring 4 – 36 FA (Interm Zone) Ring 5 – 42 FA (Outer Zone) Ring 6 – 30 FA (Outer Zone) GAP behavior at BOC according to FZK- SIMADS analysis (114 μm). It is considered also the target and bypass (reflector) regions with their own thermal power deposition.

5. EUROTRANS DM1 – WP 1.5 Progress Meeting, Forschungszentrum Karlsruhe, November 27-28, 2008 5 The PARCS Model and Assumption of EFIT PARCS Mesh Dimension At Cold (20°C) Conditions: Width = 8.27 cm Height = 9.55 cm EFIT Core Layout At Nominal Power: Width = 8.33 cm Height = 9.62 cm

6. EUROTRANS DM1 – WP 1.5 Progress Meeting, Forschungszentrum Karlsruhe, November 27-28, 2008 6 The PARCS Model and Assumption of EFIT Axial View of EFIT Core Layout Axial Nodal Correspondance PARCSRELAP5

7. EUROTRANS DM1 – WP 1.5 Progress Meeting, Forschungszentrum Karlsruhe, November 27-28, 2008 7 The PARCS Model and Assumption of EFIT - XSEC XSEC Formalism in PARCS Tfuel 400°C750°C1100°C Tcoolant 400°COOO 440°CO 550°COO XSEC Data Set to Find the Derivative Cross Sections at BOC Conditions Omogenized Collapsed in 2 groups (0.079 MeV Cutting Energy) Normalization of  f to achieve the desired Power in each Zone (not each Ring) k eff  0. 960778 at nominal power condition

8. EUROTRANS DM1 – WP 1.5 Progress Meeting, Forschungszentrum Karlsruhe, November 27-28, 2008 8 Steady-State Nominal Power Conditions It doesn't make sense a direct comparison between the two model due to the different hypothesis unless to consider that RELAP5 stand-alone refers to 1 HOT FA instead of those could be considered the "HOT FAs" in RELAP5/PARCS, i.e. 18(CZ1-RING1), 30(CZ2-RING3), 42(CZ3-RING5). Weighting the lead outlet temperatures of each ring for the numbers of relative FAs, we obtain the same outlet average temperatures in each core zone obtained by RELAP5 stand-alone 482°C (same mass flowrates). (*) The temperature of RELAP S.A. refers to the Average Pin of Hot FA.

9. EUROTRANS DM1 – WP 1.5 Progress Meeting, Forschungszentrum Karlsruhe, November 27-28, 2008 9 T/H-Neutronic Coupled Simulations TRANSIENT ANALYZED FOR PB-COOLED EFIT DESIGN WITH RELAP5/PARCS NumberTransientDescriptionBOC PROTECTED TRANSIENTS P-10Spurious beam trip beam trip for 1s (and 10s intervals) XOXO UNPROTECTED TRANSIENTS U-1ULOF Total loss of forced circulation in primary system (4 pumps) X600 U-2UTOP500 pcm jump in reactivity at HFPO U-4 DECULOH Total loss of secondary loops (4 loops) X1100 U-5 DECULOF + ULOH Total loss of forced circulation and secondary loops X2100 U-11 Beam Overpower Jump to 120% at HFP X1000 U-12 Beam Overpower Jump to 120% at HZP X1000

10. EUROTRANS DM1 – WP 1.5 Progress Meeting, Forschungszentrum Karlsruhe, November 27-28, 2008 10 Spurious beam trip of 1 sec Fission and Total Exchanged Power Reactivity the prompt and strong power drop following the source switch-off agrees with what is expected for a sub-critical reactor dominated by the prompt neutrons of source this transients is too fast to appreciate a change in SGs thermal power exchange thermal feedback, due to the fast cooling of the fuel, is responsible for a slight increase of the reactivity and a consequent peak of the fission power at the accelerator restart Switch-off and switch-on in 1ms

11. EUROTRANS DM1 – WP 1.5 Progress Meeting, Forschungszentrum Karlsruhe, November 27-28, 2008 11 Lower and Upper Plenum Temperature Fuel, Clad and Lead Max Temperature RING - 3 Spurious beam trip of 1 sec -4°C in the Upper Plenum after about 10s No variation of Inlet Core temperature also after 600s of transients Jump of fuel max temperature of 164°C Jump of clad and outlet lead temperature of 16°C

12. EUROTRANS DM1 – WP 1.5 Progress Meeting, Forschungszentrum Karlsruhe, November 27-28, 2008 12 Fission and Total Exchanged Power Reactivity All the primary pumps stop at 100 s, the accelerator remain at the same flux level Small peak of power of 11 MWth after which return at the same initial level 376 MWth SGs reduced their exchange capability for 25s, until the natural circulation is started Core mass flowrate undershoot to the 30% Peak of reactivity of 130 pcm due mainly to the positive effect of coolant temperature Unprotected Loss of Flow

13. EUROTRANS DM1 – WP 1.5 Progress Meeting, Forschungszentrum Karlsruhe, November 27-28, 2008 13 Lower and Upper Plenum Temperature Fuel, Clad and Lead Max Temperature Unprotected Loss of Flow RING - 3 Outlet plenum temperature maximum value of 631°C, stable at 621°C Inlet core temperature overcooling at 359°C Fuel temperature peak to 1390°C with a jump of 177°C Clad temperature peak up to 790°C

14. EUROTRANS DM1 – WP 1.5 Progress Meeting, Forschungszentrum Karlsruhe, November 27-28, 2008 14 Fission and Total Exchanged Power Reactivity Unprotected Loss of Heat Sink All the secondary pumps stops at 100 s, the accelerator remain at the same flux level The power level remain the same, Core mass flowrate slightly decrease DHR system (3 out of 4 units) reaches full operation (21 MW) after 280s Coolant temperature positive effect and Fuel temperature negative effect

15. EUROTRANS DM1 – WP 1.5 Progress Meeting, Forschungszentrum Karlsruhe, November 27-28, 2008 15 Lower and Upper Plenum Temperature Fuel, Clad and Lead Max Temperature Unprotected Loss of Heat Sink RING - 3 All the temperature increase and they can go on if nothing happen DHR mass flowrate increase just after the pumps trip Delta Temperature over the DHR 20°C DHR Temperature and Mass Flowrate

16. EUROTRANS DM1 – WP 1.5 Progress Meeting, Forschungszentrum Karlsruhe, November 27-28, 2008 16 Fission and Total Exchanged Power Reactivity ULOF + ULOH The superposition of the effects come true! Seems that the reactivity inserted could reach the 0 or a negative value.

17. EUROTRANS DM1 – WP 1.5 Progress Meeting, Forschungszentrum Karlsruhe, November 27-28, 2008 17 Lower and Upper Plenum Temperature Fuel, Clad and Lead Max Temperature ULOF + ULOH RING - 3 Fuel temperature peak 1410°C than 1930° after 2000s of transient Lead temperature at outer ring 3 reach 1510°C The transient is ended by time step card, but seems that should crash in few more seconds

18. EUROTRANS DM1 – WP 1.5 Progress Meeting, Forschungszentrum Karlsruhe, November 27-28, 2008 18 Power Evolution Beam Overpower to 120% from HFP Reactivity Source overpower of +20% at 100 s without recovery action Peak of power of 75 MWth (20%) after which the core power have no variation SGs increase their performances and DHR start to work after 600s of transient As expected it is the fuel reactivity that have the major worth with a peak of 30 pcm

19. EUROTRANS DM1 – WP 1.5 Progress Meeting, Forschungszentrum Karlsruhe, November 27-28, 2008 19 Fuel, Clad and Lead Temperature Beam Overpower to 120% from HFP RING - 3 Lower and Upper Plenum Temperature Fuel temperature peak 1375°C than 1410° at the end of transient Clad temperature 565°C Lead temperature at outer ring 3 reach 539°C

20. EUROTRANS DM1 – WP 1.5 Progress Meeting, Forschungszentrum Karlsruhe, November 27-28, 2008 20 Power Evolution Beam Overpower to 120% from HZP Reactivity Source overpower from 0 level to +120% at 0s without recovery action Instantaneous jump of power at about 450 MWth SGs increase their performances and DHR start to work after 600s of transient Overpower at HFP vs HZP without difference regarding the reactivity inserted

21. EUROTRANS DM1 – WP 1.5 Progress Meeting, Forschungszentrum Karlsruhe, November 27-28, 2008 21 Beam Overpower to 120% from HZP RING - 3 Lower and Upper Plenum Temperature Fuel, Clad and Lead Max Temperature Fuel temperature peak 1375°C than 1410° at the end of transient Clad temperature 570°C after 1500s Lead temperature at outer ring 3 reach 544°C after 1500s

22. EUROTRANS DM1 – WP 1.5 Progress Meeting, Forschungszentrum Karlsruhe, November 27-28, 2008 22 Conclusions The analyses of the thermalhydraulics-neutronics behavior of the EFIT reactor have been conducted with the coupled code RELAP5/PARCS. Nominal steady state conditions achieved with the coupled model are in line with those calculated by RELAP5 stand-alone, taking into account the large modelling differences over the core. In the transients analyzed the feedback effects are quite negligible as expected unless we consider an accident that take into account a partial or total coolant voiding. All the unprotected transient analyzed shows that no major challenging situation are expected for the materials in accidental conditions and that there is a lot of time to recover those situations.