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EFIT-Pb Transient Analysis M. Schikorr, E. Bubelis EUROTRANS: DM1 WP1.5 : “Safety”

EFIT-Pb Transient Analysis M. Schikorr, E. Bubelis EUROTRANS: DM1 WP1.5 : “Safety” Bologna , 28-29 Mai 2008. Topics:.

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EFIT-Pb Transient Analysis M. Schikorr, E. Bubelis EUROTRANS: DM1 WP1.5 : “Safety”

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  1. EFIT-Pb Transient Analysis M. Schikorr, E. Bubelis • EUROTRANS: DM1 WP1.5 : “Safety” • Bologna , 28-29 Mai 2008 EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008

  2. Topics: 1. Recent EFIT-Pb SA design modifications leading to revised Core and Primary System Pressure Drops (Genova-April, Karlsruhe-April meetings, new Ansaldo document-May). • SIM-ADS Transient Results for EFIT-Pb : a. ULOF results (BOC, EOC) • DHRS mode operations • PLOHS EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008

  3. 1. EFIT Pressure Drops: Historical evolution • Initial Pressure drop estimates : DP_core ~ 0.6 bar, DP_prim. system ~ 1.0 bar, 2. 1st Iteration based on experimental PDS-XADS SA-inlet and SA-outlet pressure drops(Genova Meeting April 08), Pressure drop estimates : DP_core ~ 1.2 bar, DP_prim. system ~ 1.80 bar, 3. Most current pressure drop estimates after SA redesign by ANSALDO: DP_core ~ 0.75 bar, DP_prim. system ~ 1.41 bar, this will lead to a w_nat ~ 0.31 during ULOF(ss) EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008

  4. 1. EFIT Pressure Drops: as proposed by Ansaldo after SA redesign leading to lower SA inlet and outlet pressure drops. EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008

  5. 2. EFIT Pressure Drops: as proposed to be used in Transient Calcs. EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008

  6. EFIT-Pb: Avg and Peak Cladding and Fuel Temperatures at Nominal and ULOF-ss Plant Conditions for BOC and EOC based on new Pressure Drop data (1.42 bar) EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008

  7. EFIT-Pb: CZ1 Inner Zone Core averaged Avg. Pin BOL MgO-MOX fuel Static Calculations EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008

  8. EFIT-Pb: CZ2 Intermediate Zone Core averaged Avg. Pin BOL MgO-MOX fuel Static Calculations EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008

  9. EFIT-Pb: CZ3 Outer Zone Core averaged Avg. Pin BOL MgO-MOX fuel Static Calculations EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008

  10. EFIT-Pb: CZ1 Inner Zone Core averaged Avg. Pin EOC MgO-MOX fuel Static Calculations EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008

  11. EFIT-Pb: CZ2 Intermediate Zone Core averaged Avg. Pin EOC MgO-MOX fuel Static Calculations EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008

  12. EFIT-Pb: CZ3 Outer Zone Core averaged Avg. Pin EOC MgO-MOX fuel Static Calculations EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008

  13. Grid spacer calculation for EFIT-Pb EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008

  14. 1a. ULOF: BOL, Avg Pin, Peak Pin 1b. ULOF: EOC, Avg Pin, Peak Pin 1. EFIT-Pb ULOF Transient Cases Analysed using SIM-ADS Comparison to RELAP BOC calculations performed by ENEA and Ansaldo(ENEA: G. Bandini, P. Meloni, M. Polidori, ANSALDO: L. Mansini): EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008

  15. Proton Beam The EFIT Reactor Design: • EFIT is a pool-type reactor of about 400 MW power • Sub-critical reactor (Keff = 0.97) sustained by a spallation neutron source (beam proton energy 800 MeV and beam current 20 mA) • Reactor core with 3 U-free fuel zone with (Pu,MA)O2 in MgO matrix to improve the burning efficiency • Pure melt lead as primary coolant (lower cost and less activation products such as Polonium than LBE) • Core power is removed by forced circulation (4 pumps placed in the hot collector) through 8 steam generators with helical-coil tube bundle • 4 DHR heat exchangers are immersed in the annular cold pool between the inner vessel and the reactor vessel Pump Inner vessel Target Core heat exchanger Reactor vessel Figure Source: G. Bandini, P. Meloni, M. Polidori (ENEA - Bologna) EFIT Reactor Block EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008 4

  16. The In-vessel Flow Paths during normal Heat Removal mode: Figure Source: G. Bandini, P. Meloni, M. Polidori (ENEA - Bologna) EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008

  17. EFIT-Pb : ULOF, BOC, RELAP results May 2008 Source:(G. Bandini)3 DHRS in operation, Power level remains at ~100% during transient Slide 1 What has changed since Madrid meeting: w_nat has decreased to ~ 30% from ~ 38% during ULOF(ss) due to revised prim. system pressure drops EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008

  18. EFIT-Pb : ULOF, BOC, RELAP results May 2008 Source:(G. Bandini)3 DHRS in operation, Power level remains at ~100% during transient Slide 2 EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008

  19. EFIT-Pb : ULOF, BOC, SIM-ADS results compared to RELAP May 2008 3 DHRS in operation, Power level remains at ~100% during transient Slide 1 EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008

  20. EFIT-Pb : ULOF, BOC, SIM-ADS results compared to RELAP 3 DHRS in operation, Power level remains at ~100% during transient Slide 2 EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008

  21. EFIT-Pb : ULOF, BOC, SIM-ADS results 3 DHRS in operation, Power level remains at ~100% during transient Slide 3 Conclusions: • Acceptable agreement between SIM-ADS and RELAP by assuming P_core ~ 100% during ULOF transient, and by making appropriate assumptions as regards inertial masses in the various primary system flow path volumes are made • Max clad temperatures of peak pin ~ 850 °C 18 seconds into ULOF due to flow undershoot down to ~ 10%, • For BOC conditions, minimum pin clad failure time > 30 minutes (acceptable !) • Need reactivity coefficients for EFIT-Pb to assess more realistic power response during ULOF transient EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008

  22. EFIT-Pb Reactivity Coefficient Data: Source : G.Glinatsis, „EFIT-MgO/Pb Core Design Reactivity Coefficients” Genova, April Meeting 2008 Coolant density Effect:  1% dens whole Active Core zones: (DK/K )/  1% dens = 0.00058  0.00002 Fuel Temperature Effect: T nom_fuel/zone 1800 K, BoL: Keff = 0.96147  0.00025; ( 0.96123  0.00027) BoC: Keff = 0.96207  0.00025; (0.96183  0.00025 ) EoC: Keff = 0.96227  0.00026; (0.96227  0.00026 ). This translates to: Coolant temp. coeff ~ + 0.65 pcm/°C Fuel temp. coeff ~ - 0.014 pcm/°C, or A_dopp ~ - 20 pcm Please somebody else verify above data calculations in term of [pcm/°C] ! EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008

  23. EFIT-Pb : ULOF, EOC, SIM-ADS calcs. compared to RELAP May 2008 (BOC), 3 DHRS in operation, realistic reactivity coefficients, power level >100% Slide 1 EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008

  24. EFIT-Pb : ULOF, EOC, SIM-ADS calcs. compared to RELAP 3 DHRS in operation, realistic reactivity coefficients, power level >100% Slide 2 ULOF Conclusions: • Power level > 100% during above ULOF transient due to ~ 0 Doppler coefficient and positive coolant coef. • Peak Fuel temperatures always remain < 1500 °C (not explicitly shown in above transparencies, thus no concern as regards possible MgO-MOX fuel evaporation expected ) • Max clad temperatures of peak pin ~ 870 °C 18 seconds into transient, EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008

  25. EFIT-Pb : ULOF, EOC, SIM-ADS calcs. compared to RELAP 3 DHRS in operation, realistic reactivity coefficients, power level >100% Slide 3 ULOF Conclusions cont: • For EOC conditions, minimum pin clad failure time ~ 80 sec because of flow undershoot down ~ 10% flow (acceptable ?????). Could expect peak pin clad leakages during this transient. Note: assumed 100% fission gas release in above calculations (very conservative !!, more realistic is probably ~ 70-80%) EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008

  26. DHRS operational mode (such as PLOHS): BOL Sequence of events: 1. Total Loss of primary heat sink (loss of all MHX) 2. Source shutdown; decay heat as heat source 3. 3 out of 4 DHRS systems function as heat sink 2. EFIT-Pb PLOH Transient using SIM-ADS Comparison to RELAP BOC calculations performed by ENEA and Ansaldo(ENEA: G. Bandini, P. Meloni, M. Polidori, ANSALDO: L. Mansini): EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008

  27. Nitrogen Header Cooling air Chimney Air Vapour Condenser Oil Vapour Separator Condensed Oil Drum Condensed Oil EFIT Reactor Safety-Related DHR Loop Boiling Oil Inner vessel Reactor vessel DHR Dip Cooler The Decay Heat Removal (DHR) System of EFIT-Pb • The DHR system is conceived for inherently safe decay heat removal and passive mode actuation • 4 independent loops partially filled with organic oil, that dissipate the decay heat to the atmosphere by natural convection circulation • Each loop consists of a dip cooler immersed in the cold pool where the oil partially vaporize and an air-vapor condenser with stack chimney and interconnecting piping • Oil boiling point is determined by superimposed pressure of an inert gas • In normal operation the oil is below its boiling point and the DHR removes only heat losses from SGs and inner vessel (few 100 kW) to keep cold the upper part of the reactor vessel Figure Source: G. Bandini, P. Meloni, M. Polidori (ENEA - Bologna) EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008

  28. The In-vessel Flow Paths during the Decay Heat Removal mode: Figure Source: G. Bandini, P. Meloni, M. Polidori (ENEA - Bologna) EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008

  29. How long does it take until the complicated natural convection flow pattern in EFIT-Pb is established ? ENEA / ANSALDO have performed SIMMER III and RELAP calculations trying to obtain a first estimate of the time it will take until heat removal via natural circulation through the DHRS dip coolers is established. See presentation by G. Bandini, P. Meloni, M. Polidori, „Assessment of Decay Heat Removal by Natural Circulation in the EFIT Reactor” during THIRS meeting in Karlsruhe April 14-16 2008. 3. RELAP needed some modifications in pressure drop coefficients to simulate the time delay effect. SIM-ADS needs similar adjustments. DHRS Mode Issues: EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008

  30. Core Decay Heat Removal in Natural Circulation RELAP and SIMMER III Code Result Comparison to PLOHS Core and DHR Mass Flow Rate Core Decay and DHR Power • Both codes (SIMMER and RELAP) predict efficient removal of decay power after about 2000 s • Mass flow rates through the core and DHR well compare in the medium term • Code results differ in the initial transient owing to the different modeling Figure Source: G. Bandini, P. Meloni, M. Polidori (ENEA - Bologna) EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008

  31. Core Decay Heat Removal in Natural Circulation SIM-ADS, RELAP and SIMMER III Code Result Comparison to PLOHS • w_nat ~ 9% during DHRS mode • ~ 2000 sec full nat. convection flow established • SIM-ADS predicts overshoot in heat removal of DHRS HX compared to RELAP and SIMMER • ~ 4000 sec removal of heat in balance with decay heat • What limits heat removal in DHRS HX to ~ 20 MW ??? EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008

  32. We need to decide if the thermal inertia of the nominal heat flow path as encountered during ULOF transient (i.e natural convection response after primary pump shutdown) with a flow undershoot down to ~ 10% nominal flow (or even less) shall be accepted as reference and then be used during all the transients with similiar primary system plant response. We need to decide if the thermal inertia of the DHRS heat flow paths as encountered during a PLOH or ULOH as predicted by SIMMER III (and adjusted to in RELAP and in SIM-ADS) shall be accepted as the reference response of the primary system (i.e., it takes about 2000 sec until full DHRS nat. convection flow is establihed). The response of the DHRS and MHX heat exchanger to various transients needs to be checked by the various codes as SIM-ADS predicts an overshoot in the DHRS HX heat removal during the PLOHS transient. Definition of the secondary side conditions of the DHRS HX : T_inlet = 392 °C ?? T_inlet = 404 °C ??, T_sat = ???, what are pressure conditions P= 11.5 bar ???, consistency with oil property tables ??, what tables ?? Conclusion:To continue and fianlize our EFIT-PB transient anlysis: EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008

  33. PHLOS Transient: RELAP5 Results (1) Core and DHR Mass Flow Rate Core Decay and DHR Power Reactor trip • Reactor trip is calculated by RELAP5 at 46 s • After some initial oscillations (free level movements) core and DHR mass flow rates becomes stable and the DHR attains maximum performance (20 MW for 3 loops in operation) after about 700 s EUROTRANS WP1.5 Safety Meeting : Bologna, May 28-29, 2008 18 THIRS Workshop, Forschungszentrum Karlsruhe, Germany, April 14-16, 2008

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