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LEADER, Task 5.5 ETDR Transient Analyses with SPECTRA Code LEADER Project JRC, Petten, February 26, 2013 M.M. Stempniewicz stempniewicz@nrg.eu NRG-22694/13.118781. Content. SPECTRA Model 3 SPECTRA/RELAP Model and Steady State Results 5 SPECTRA Model - Heat Transfer Correlations 17

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  1. LEADER, Task 5.5 ETDR Transient Analyses withSPECTRA Code LEADER ProjectJRC, Petten, February 26, 2013M.M. Stempniewiczstempniewicz@nrg.euNRG-22694/13.118781

  2. Content • SPECTRA Model 3 • SPECTRA/RELAP Model and Steady State Results 5 • SPECTRA Model - Heat Transfer Correlations 17 • SPECTRA Model - Reactivity Feedback 18 • SPECTRA Model - SCRAM Signals 20 • Analyzed Transients 21 • TR-4, Reactivity insertion, 250 pcm in 2 s 22 • T-DEC1, Loss of all primary pumps, reactor trip fails 27 • T-DEC5, Partial blockage of hottest fuel assembly 32 • Conclusions 34 • References 35 • Appendix A: Liquid Lead Properties 36 NRG-22694/13.118781

  3. SPECTRA Model • A model of the ETDR, ALFRED reactor design [1] was prepared for the SPECTRA code [2]. • Nodalization of the SPECTRA model was assumed very similar to the nodalization applied for RELAP analyses at ENEA [3]. Some simplifications in the number of nodes were made whenever possible. • The model consists of: • Primary system (liquid lead) • Steam Generators and secondary system loops (8 steam/water loops) • Isolation Condensers • The EOC conditions were assumed. For modelling the gap, fuel swelling of 0.149 mm was assumed (initial gap size 0.150 mm), following RELAP model. NRG-22694/13.118781

  4. SPECTRA Model • The model was prepared such that the 8 loops can be combined into one or split into several (up to 8) loops, if needed. • This is done using # and $, for example: • * Multiplicity • 102#21 $.0 * No. of loops • Automatic replacement of # → loop No. and $ → number of identical loops, creates the desired model version. • The model was tested by running steady state calculations and comparing results with the resuts obtained at ENEA using RELAP5 [3]. • Comparison of SPECTRA and RELAP results is given below. A good agreement is obtained. NRG-22694/13.118781

  5. Fuel ElementsSPECTRA Model and Steady State Results NRG-22694/13.118781

  6. Fuel ElementsRELAP Model and Steady State Results NRG-22694/13.118781

  7. Reactor CoreSPECTRA Model and Steady State Results NRG-22694/13.118781

  8. Reactor CoreRELAP Model and Steady State Results NRG-22694/13.118781

  9. Primary SystemSPECTRA Model and Steady State Results NRG-22694/13.118781

  10. Primary SystemRELAP Model and Steady State Results NRG-22694/13.118781

  11. Steam GeneratorSPECTRA Model and Steady State Results NRG-22694/13.118781

  12. Steam GeneratorRELAP Model and Steady State Results NRG-22694/13.118781

  13. Secondary LoopSPECTRA Model and Steady State Results NRG-22694/13.118781

  14. Secondary LoopRELAP Model and Steady State Results NRG-22694/13.118781

  15. Isolation CondenserSPECTRA Model and Steady State Results NRG-22694/13.118781

  16. Isolation CondenserRELAP Model and Steady State Results NRG-22694/13.118781

  17. SPECTRA Model - Heat Transfer Coefficient Correlations • If a liquid metal is to be applied in SPECTRA calculations, the HTC correlations must be defined in input. The following correlations have been used: • Ushakov correlation - reference [4]: here x = P/D • Reactor Core: Ushakov, with P/D=1.32 • Steam Generator: Ushakov, with P/D=1.4182 NRG-22694/13.118781

  18. SPECTRA Model - Reactivity Feedback • The reactivity feedback includes: • Doppler reactivity effect: • Axial fuel expansion: • Coolant density: • Cladding expansion: • Wrapper expansion: • Diagrid expansion: • Pad expansion: • Control rod: NRG-22694/13.118781 18

  19. SPECTRA Model - Reactivity Feedback • The constants in the reactivity feedback are: • Component • (slides 8, 9) • Doppler reactivity effect: KD = -566.0 SC-044/-055 • Axial fuel expansion: cfuel = -0.155 pcm/K SC-044/-055 • Coolant density: ccool = -0.268 pcm/K CV-044/-055 • Cladding expansion: cclad = +0.050 pcm/K SC-044/-055 • Wrapper expansion: cwrap = +0.026 pcm/K SC-064/-075 • Diagrid expansion: cdia = -0.152 pcm/K CV-020 • Pad expansion: cpad = -0.430 pcm/K CV-057 • Control rod, prompt: crod = -0.218 pcm/K CV-021 • Control rod, delayed: neglected NRG-22694/13.118781

  20. SPECTRA Model - SCRAM Signals • SCRAM signals incorporated into the model: • Neutron flux > 120% • Average assembly ΔT > 1.2×nominal • Hot assembly ΔT > 1.2×nominal • Low primary floe W < 90% NRG-22694/13.118781

  21. Analyzed Transients • Transients: • TR-4 Reactivity insertion, 250 pcm in 2 s. Model: 8 identical loops combined into one, no IC • TO-1, TO-3 Loss of FW pre-heater on 1 loop (TO-3: +all primary pumps stop) Model: 1+3+4 identical loops, IC working on 4 loops • TO-4, TO-6 20% increase of FW flow (TO-6: +all primary pumps stop) Model: 8 identical loops combined into one, no IC • T-DEC1 Loss of all primary pumps. Reactor trip fails. Model: 8 identical loops combined into one, no IC • T-DEC3 Loss of SCS. Reactor trip fails. Model: 3+5 identical loops, IC working on 3 loops • T-DEC-4 Loss of off-site power. Reactor trip fails. Model: 3+5 identical loops, IC working on 3 loops • T-DEC5 Partial blockage of hottest assembly. Model: 8 identical loops combined into one, no IC • T-DEC6 SCS failure Model: 8 identical loops combined into one, no IC green: done red: still to be done NRG-22694/13.118781

  22. TR-4 Reactivity insertion, 250 pcm in 2 s • Scenario: • Reactivity of 250 pcm (0.8375 $) is inserted in 2 seconds. • Reactor trip (SCRAM signal) is disabled. • Core power reaches 970 MW and decreases to about 500 MW. Corresponding peak in RELAP5 is 870 MW, with decrease to about 450 MW. • Reactor power, TR-4, SPECTRA Reactor power, TR-4, RELAP5 [3] NRG-22694/13.118781

  23. TR-4 Reactivity insertion, 250 pcm in 2 s • Long term core power behavior: • After the initial transient the core power slowly reduces and stabilizes slightly below 400 MW, with the same power removed by SG-s. • SG power increases slowly due to temperature increase at SG inlet on the primary side. Steam outlet temperature increases on the secondary side (constant FW flow rate). • Reactor and SG power, TR-4, SPECTRA Reactor and SG power, TR-4, RELAP5 [3] NRG-22694/13.118781 23

  24. TR-4 Reactivity insertion, 250 pcm in 2 s • Fuel temperatures: • The fuel peak temperature reaches a maximum value close to 2700°C (2600°C in RELAP) in the initial part of the transient and then slowly decreases to about 2400°C. • Maximum fuel temperature is higher in Spectra and exceeds for a short period the melting temperature (MOX melting point ~2673°C). This is a consequence of higher peak power and the SPECTRA/RELAP difference will be investigated in the future. • Fuel temperatures, TR-4, SPECTRA Fuel temperatures, TR-4, RELAP5 [3] NRG-22694/13.118781 24

  25. TR-4 Reactivity insertion, 250 pcm in 2 s • Coolant temperatures: • After an initial jump of about 40 °C the core outlet temperature slowly increases following the temperature increase at core inlet. • The maximum core outlet temperature stabilizes at about 620°C (about 600°C in RELAP). • Coolant temperatures, TR-4, SPECTRA Coolant temperatures, TR-4, RELAP5 [3] NRG-22694/13.118781 25

  26. TR-4 Reactivity insertion, 250 pcm in 2 s • Reactivities: • The inserted reactivity is mainly counterbalanced by negative Doppler and fuel expansion feedbacks induced by fuel temperature increase • Total reactivity reaches a maximum of about 190 pcm (175 pcm in RELAP) at 2 s and then reduces according to negative feedbacks. • Reactivities, TR-4, SPECTRA Reactivities, TR-4, RELAP5 [3] NRG-22694/13.118781 26

  27. T-DEC1 Loss of All Primary Pumps • Scenario: • Coastdown of all primary pumps. • The secondary circuits remain in operation in forced circulation • Reactor trip (SCRAM signal) is disabled. • After an initial small core flow rate undershot natural circulation stabilizes in the primary circuit a little above 5000 kg/s. • Core inlet flow, T-DEC1, SPECTRA Core inlet flow, T-DEC1, RELAP5 [3] NRG-22694/13.118781 27

  28. T-DEC1 Loss of All Primary Pumps • The core power initially reduces due to negative reactivity feedbacks and then stabilizes at about 240 MW (about 210 MW in RELAP5), in equilibrium with SG power. • The SG power initially decreases due to reduced primary flow and then increases with the lead temperature increase at the SG inlet. • Reactor power, T-DEC1, SPECTRA Reactor power, T-DEC1, RELAP5 [3] NRG-22694/13.118781 28

  29. T-DEC1 Loss of All Primary Pumps • Fuel temperatures: • Peak and average fuel temperatures reduce according to the decrease of core power level. • The maximum fuel temperature stabilizes at about 1700˚C (1400˚C in RELAP). • Fuel temperatures, TDEC1, SPECTRA Fuel temperatures, T-DEC1, RELAP5 [3] NRG-22694/13.118781 29

  30. T-DEC1 Loss of All Primary Pumps • Coolant temperatures: • Initial lead temperature increase at core outlet max calculated value near 700°C at 15 s • Max core outlet temperature stabilizes just above 600 °C • The core inlet temperature slowly decreases and stabilizes at about 340°C • Coolant temperatures, TR-4, SPECTRA Coolant temperatures, TR-4, RELAP5 [3] NRG-22694/13.118781 30

  31. T-DEC1 Loss of All Primary Pumps • Reactivities: • The inserted reactivity is mainly counterbalanced by negative Doppler and fuel expansion feedbacks induced by fuel temperature increase • Total reactivity reaches a maximum of about 190 pcm (175 pcm in RELAP) at 2 s and then reduces according to negative feedbacks. • Reactivities, TR-4, SPECTRA Reactivities, TR-4, RELAP5 [3] NRG-22694/13.118781 31

  32. T-DEC5 Partial Blockage of Hottest Fuel Assembly • Scenario: • Partial blockage of the hottest fuel assembly. • Inlet junction (JN-001, slide 7) assumed to be blocked • Blockages considered: • 50% • 60% • 70% Coolant temperatures, T-DEC5, SPECTRA • 80% • 90% • Reactor trip (SCRAM signal) is disabled. NRG-22694/13.118781 32

  33. T-DEC5 Partial Blockage of Hottest Fuel Assembly • With 90% blockage (decrease of inlet flow area by a factor of 10, or increase of resistance factor by a factor of 100): • maximum fuel temperature is ~2430 K, (~2160˚C) • maximum clad temperature is ~940 K, (~670˚C) • coolant exit temperature is ~1060 K (790˚C) • Fuel temperatures, T-DEC5, SPECTRA Cladding temperatures, T-DEC5, SPECTRA NRG-22694/13.118781 33

  34. Conclusions • Results of several transients analyzed for the ETDR, ALFRED reactor design were shown and compared to the results of RELAP calculations from ENEA. • Steady state results obtained with SPECTRA and RELAP are in very good agreement. • Some discrepancies are observed for transient simulations. These discrepancies will be investigated in the future. NRG-22694/13.118781

  35. References • [1] E. Bubelis, K. Mikityuk, "PLANT DATA FOR THE SAFETY ANALYSIS OF THE ETDR (ALFRED)", TEC058-2012, Revision: 0 (Draft), Issued by PSI/KIT (including contributions from ANSALDO, ENEA, EA, CEA, SRS), 30.04.2012. • [2] M.M. Stempniewicz, “SPECTRA Sophisticated Plant Evaluation Code for Thermal-Hydraulic Response Assessment, Version 3.60, August 2009, Volume 1 – Program Description, Volume 2 – User’s Guide, Volume 3 – Subroutine Description, Volume 4 - Verification and Validation”, NRG K5024/10.101640, Arnhem, April 24, 2009. • [3] G. Bandini, “Design and safety analysis of ALFRED - Accident Analyses Overview”, 3rd LEADER International Workshop, Bologna, 6-th - 7-th September. • [4] P.A. Ushakov, A.V. Zhukov, M.M. Matyukhin, “Heat transfer to liquid metals in regular arrays of fuel elements”, High Temperature, 15, pp. 868-873, 1977. NRG-22694/13.118781

  36. Appendix A: Liquid Lead Properties • If a liquid metal is to be applied in SPECTRA calculations, the properties of liquid metal must be supplied by the user. The properties of liquid lead were obtained flow: • “Handbook on Lead-bismuth Eutectic Alloy and Lead Properties, Materials Compatibility, Thermal-hydraulics and Technologies”, OECD/NEA Nuclear Science Committee. ISBN 978-92-64-99002-9, 2007 • The required properties include: • Saturation pressure • Liquid properties, including: • Density • Specific heat • Thermal conductivity • Viscosity • Speed of sound • Vapor properties are not defined, i.e. sodium vapor cannot be encountered in calculations with the present model. NRG-22694/13.118781

  37. Liquid Lead Properties, Psat(T), h(T) (a) Above: values tabulated for SPECTRA (b) Below: source data NRG-22694/13.118781

  38. Liquid Lead Properties, ϱ(T), cp(T) (a) Above: values tabulated for SPECTRA (b) Below: source data NRG-22694/13.118781

  39. Liquid Lead Properties, k(T), μ(T) (a) Above: values tabulated for SPECTRA (b) Below: source data NRG-22694/13.118781

  40. Liquid Lead Properties, σ(T), c(T) (a) Above: values tabulated for SPECTRA (b) Below: source data NRG-22694/13.118781

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