1. LEADER Project Analysis of Representative DBC Events of the ETDR with RELAP5 and CATHARE Giacomino Bandini - ENEA/Bologna Genevieve Geffraye – CEA/Grenoble LEADER 4 th WP5 Meeting Karlsruhe, 22 November 2012

2. 2 Outline  Analyzed DBC Transients at EOC  ALFRED Modeling  Transient Results  Conclusions

3. 3 Analyzed Transients Main events and reactor scram threshold

4. 4 RELAP5 Modeling Feedwater Steam 521-8 531-8 551-8561-8 151 - 8 Feedwater Steam 521-8 531-8 551-8561-8 151 - 8 841-4 851-8 441-8 801-4 811-4831-4 815 401-8 841-4 - 801-4 811-4831-4 815 841-4 - 801-4 811-4831-4 815 611-8 841-4 - 801-4 811-4831-4 815 611- 711- 731- 741-4 751-8 761-4 621-4 641-4 771 781-8 601-4 661-4 611- 711-8 731-8 741-4 751- 761-4 621-4 641-4 771-8 781- 601-4 661-4 611- 711- 731- 741-4 751- 761-4 621-4 641-4 771- 781- 711- 731- 741-4 751- 761-4 621-4 641-4 771- 781 601-4 661-4 841-8 - 801-4 811-4831-4 815 841- - 801-8 811-8831-8 815 611- 841- - 801- 811-831- 411-8 611- 711- 731- 741-4 751- 761-4 621-4 641-4 771 781 711- 731- 741-4 751- 761-4 621-4 641-4 771- 781- 601-8 661-8 611- 711- 731- 741-8 751- 761-8 621-8 641-8 841-4 851-8 441-8 801-4 811-4831-4 815 401-8 841-4 - 801-4 811-4831-4 815 841-4 - 801-4 811-4831-4 815 611-8 841-4 - 801-4 811-4831-4 815 611- 711- 731- 741-4 751-8 761-4 621-4 641-4 771 781-8 601-4 661-4 611- 711-8 731-8 741-4 751- 761-4 621-4 641-4 771-8 781- 601-4 661-4 611- 711- 731- 741-4 751- 761-4 621-4 641-4 771- 781- 711- 731- 741-4 751- 761-4 621-4 641-4 771- 781 601-4 661-4 841-8 - 801-4 811-4831-4 815 841- - 801-8 811-8831-8 815 611- 841- - 801- 811-831- 411-8 611- 711- 731- 741-4 751- 761-4 621-4 641-4 771 781 711- 731- 741-4 751- 761-4 621-4 641-4 771- 781- 601-8 661-8 611- 711- 731- 741-8 751- 761-8 621-8 641-8 ALFREDNodalizationscheme with RELAP5 8MHXs 8 Secondary loops Primary circuit 8 IC loops Steam line Feedwater line 100 101102109 110 115 060061-8070 050 020 200 151-8 121-8 131-8 141 -8 220 230 210 100 101102109 110 115 060061-8070 050 020 200 151-8 121-8 131-8 141-8 220 230 210 100 101102109 110 180 060061-8070 050 020 200 151-8 121-8 131-8 141-8 220 230 210 Feedwater Steam 521-8 531-8 551-8561-8 151 - 8 Feedwater Steam 521-8 531-8 551-8561-8 151 - 8 841-4 851-8 441-8 801-4 811-4831-4 815 401-8 841-4 - 801-4 811-4831-4 815 841-4 - 801-4 811-4831-4 815 611-8 841-4 - 801-4 811-4831-4 815 611- 711- 731- 741-4 751-8 761-4 621-4 641-4 771 781-8 601-4 661-4 611- 711-8 731-8 741-4 751- 761-4 621-4 641-4 771-8 781- 601-4 661-4 611- 711- 731- 741-4 751- 761-4 621-4 641-4 771- 781- 711- 731- 741-4 751- 761-4 621-4 641-4 771- 781 601-4 661-4 841-8 - 801-4 811-4831-4 815 841- - 801-8 811-8831-8 815 611- 841- - 801- 811-831- 411-8 611- 711- 731- 741-4 751- 761-4 621-4 641-4 771 781 711- 731- 741-4 751- 761-4 621-4 641-4 771- 781-

5. 5 CATHARE Modeling ALFRED Nodalization scheme with CATHARE Primary circuit 2 Secondary loops (weight 4) 2 IC loops (weight 4)

6. 6 TD-1: Spurious reactor trip (1/3) (RELAP5 – CATHARE Comparison) Total reactivity and feedbacks ASSUMPTIONS:  Reactor scram at t = 0 s  Reactivity insertion of at least 8000 pcm in 1 s  Secondary circuits are available  constant feedwater flowrate RELAP5CATHARE

7. 7 TD-1: Spurious reactor trip (2/3) (RELAP5 – CATHARE Comparison) Core and MHX powers RELAP5CATHARE  Core decay power level in CATHARE is much higher than the one in RELAP5 in the initial phase of the transient  Power removal by secondary circuits reduces with reducing primary temperatures

8. 8 TD-1: Spurious reactor trip (2/2) (RELAP5 – CATHARE Comparison) Core temperatures (inlet, max outlet and max clad) RELAP5CATHARE  Initial temperature gradient on the fuel rod clad is about -10 °C/s  No risk for lead freezing since the feedwater temperature (335 °C) is above the solidification point of lead (327 °C)

9. 9 TD-3: Loss of AC power (1/4) (RELAP5 – CATHARE Comparison) Active core flowrate ASSUMPTIONS:  At t = 0 s  Reactor scram, primary pump coastdown, feedwater and turbine trip  At t = 1 s  DHR-1 system activation (4 IC loops) RELAP5CATHARE

10. 10 TD-3: Loss of AC power (2/4) (RELAP5 – CATHARE Comparison) Core temperatures Active core flowrate

11. 11 TD-3: Loss of AC power (3/4) (RELAP5 – CATHARE Comparison) Core decay, MHX and IC powers Primary lead temperatures

12. 12 TD-3: Loss of AC power (4/4) (RELAP5 – CATHARE Comparison) MAIN RESULTS:  No initial core flowrate undershoot  No significant clad temperature peak in the initial phase of the transient  After the initial transient the natural circulation in the primary circuit stabilizes around 1-2% of nominal value  Initial primary temperature decrease is over predicted by RELAP5 with respect to CATHARE due to differences in core decay power and steam release through safety relief valves  Primary temperature reduction in the long term is faster in RELAP5 calculation due to lack of mixing in the cold pool  cold lead at the MHX outlet flows towards core inlet without mixing in the cold pool above MHX outlet (different behavior in CATHARE with similar modeling)  Risk of freezing at MHX outlet is predicted by RELAP5 after about 2 hours, much earlier than with CATHARE  Similar DHR power removal (about 7 MW with 4 IC loops) is obtained by nearly halving the actual heat transfer surface of IC in CATHARE (much larger htc for steam condensation on the inner tube side)

13. 13 TD-7: Loss of primary pumps (1/3) (RELAP5 – CATHARE Comparison) Total reactivity and feedbacks RELAP5CATHARE ASSUMPTIONS:  At t = 0 s  All Primary pump coastdown  Reactor scram at t = 3 s on second scram threshold (Hot FA ΔT > 1.2 nominal value)  At t = 4 s  DHR-1 system activation (3 IC loops)

14. 14 TD-7: Loss of primary pumps (2/3) (RELAP5 – CATHARE Comparison) Core temperatures Active core flowrate

15. 15 TD-7: Loss of primary pumps (3/3) (RELAP5 – CATHARE Comparison) Core decay, MHX and IC powers Primary lead temperatures

16. 16 TO-1: FW temp. reduction (1/3) (RELAP5 – CATHARE Comparison) Primary lead temperature ASSUMPTIONS:  Loss of one preheater (FW temperature from 335 °C down to 300 °C in 1 s) + primary pump coastdown  reactor scram at t = 2 s on low FW temperature  4 IC loops in service for decay heat removal RELAP5CATHARE

17. 17 TO-1: FW temp. reduction (2/3) (RELAP5 – CATHARE Comparison) Primary lead temperatures Core decay, MHX and IC powers

18. 18 TO-1: FW temp. reduction (3/3) (RELAP5 – CATHARE Comparison) MAIN RESULTS:  No risk of lead freezing in the initial phase of the transient due to prompt reactor scram  Primary temperature reduction in the long term is faster in RELAP5 calculation due to lack of mixing in the cold pool  cold lead at the MHX outlet flows towards core inlet without mixing in the cold pool above MHX outlet (different behavior in CATHARE with similar modeling)  Risk of freezing at MHX outlet is predicted by RELAP5 after about 3 hours, much earlier than with CATHARE

19. 19 TO-1: FW flowrate +20% (1/3) (RELAP5 – CATHARE Comparison) Core and MHX powers Primary lead temperatures

20. 20 TO-1: FW flowrate +20% (2/3) (RELAP5 – CATHARE Comparison) Core temperatures Total reactivity and feedbacks

21. 21 TO-1: FW flowrate +20% (3/3) (RELAP5 – CATHARE Comparison) ASSUMPTIONS:  Feedwater flowrate +20% in 25 s MAIN RESULTS:  No significant perturbations on both primary and secondary sides  The system reaches a new steady-state condition in about 10 minutes without exceeding reactor scram set-points  The increase in power removal by secondary side is larger with RELAP5 with respect to CATHARE  higher perturbation on primary side with RELAP5

22. 22 Conclusions  In all analyzed DBC accidental transients, the protection system by reactor scram and by the prompt start-up of the DHR-1 for core decay heat removal is able to bring the plant in safe conditions in the short and long term  The core temperatures always remains well below the safety limits  No significant vessel wall temperature increase is predicted  The time to reach lead freezing at MHX outlet after start-up of DHR-1 system strongly depends on the assumptions taken on cold pool mixing  but in any case there is large grace time for countermeasures by operator actions