1. 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

2. Content SPECTRA Model3 -SPECTRA/RELAP Model and Steady State Results5 -SPECTRA Model - Heat Transfer Correlations17 -SPECTRA Model - Reactivity Feedback18 -SPECTRA Model - SCRAM Signals20 Analyzed Transients21 -TR-4, Reactivity insertion, 250 pcm in 2 s22 -T-DEC1, Loss of all primary pumps, reactor trip fails27 -T-DEC5, Partial blockage of hottest fuel assembly32 Conclusions34 References35 Appendix A: Liquid Lead Properties36 2 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. 3 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. 4 NRG-22694/13.118781

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

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

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

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

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

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

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

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

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

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

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

16. Isolation Condenser RELAP Model and Steady State Results 16 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 17 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: 18 NRG-22694/13.118781

19. SPECTRA Model - Reactivity Feedback The constants in the reactivity feedback are: Component (slides 8, 9) -Doppler reactivity effect:K D = -566.0 SC-044/-055 -Axial fuel expansion:c fuel = -0.155 pcm/KSC-044/-055 -Coolant density:c cool = -0.268 pcm/KCV-044/-055 -Cladding expansion:c clad = +0.050 pcm/KSC-044/-055 -Wrapper expansion:c wrap = +0.026 pcm/KSC-064/-075 -Diagrid expansion:c dia = -0.152 pcm/KCV-020 -Pad expansion:c pad = -0.430 pcm/KCV-057 -Control rod, prompt:c rod = -0.218 pcm/KCV-021 -Control rod, delayed:neglected 19 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% 20 NRG-22694/13.118781

21. Analyzed Transients Transients: 1.TR-4Reactivity insertion, 250 pcm in 2 s. Model: 8 identical loops combined into one, no IC 2.TO-1, TO-3Loss of FW pre-heater on 1 loop (TO-3: +all primary pumps stop) Model: 1+3+4 identical loops, IC working on 4 loops 3.TO-4, TO-620% increase of FW flow (TO-6: +all primary pumps stop) Model: 8 identical loops combined into one, no IC 4.T-DEC1Loss of all primary pumps. Reactor trip fails. Model: 8 identical loops combined into one, no IC 5.T-DEC3Loss of SCS. Reactor trip fails. Model: 3+5 identical loops, IC working on 3 loops 6.T-DEC-4Loss of off-site power. Reactor trip fails. Model: 3+5 identical loops, IC working on 3 loops 7.T-DEC5Partial blockage of hottest assembly. Model: 8 identical loops combined into one, no IC 8.T-DEC6SCS failure Model: 8 identical loops combined into one, no IC green: done red: still to be done 21 NRG-22694/13.118781

22. TR-4Reactivity 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, SPECTRAReactor power, TR-4, RELAP5 [3] 22 NRG-22694/13.118781

23. TR-4Reactivity 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, SPECTRAReactor and SG power, TR-4, RELAP5 [3] 23 NRG-22694/13.118781

24. TR-4Reactivity 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, SPECTRAFuel temperatures, TR-4, RELAP5 [3] 24 NRG-22694/13.118781

25. TR-4Reactivity 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, SPECTRACoolant temperatures, TR-4, RELAP5 [3] 25 NRG-22694/13.118781

26. TR-4Reactivity 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, SPECTRAReactivities, TR-4, RELAP5 [3] 26 NRG-22694/13.118781

27. T-DEC1Loss 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, SPECTRACore inlet flow, T-DEC1, RELAP5 [3] 27 NRG-22694/13.118781

28. T-DEC1Loss 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, SPECTRAReactor power, T-DEC1, RELAP5 [3] 28 NRG-22694/13.118781

29. T-DEC1Loss 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, SPECTRAFuel temperatures, T-DEC1, RELAP5 [3] 29 NRG-22694/13.118781

30. T-DEC1Loss 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, SPECTRACoolant temperatures, TR-4, RELAP5 [3] 30 NRG-22694/13.118781

31. T-DEC1Loss 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, SPECTRAReactivities, TR-4, RELAP5 [3] 31 NRG-22694/13.118781

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. 32 NRG-22694/13.118781

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, SPECTRACladding temperatures, T-DEC5, SPECTRA 33 NRG-22694/13.118781

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. 34 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. 35 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. 36 NRG-22694/13.118781

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

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

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

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