1. Transient and equilibrium cycle characteristics on Paks uprated power units with 2 nd generation of Gadolinia fuel Imre Nemes Paks NPP Ltd. Hungary

2. General status of Paks Units Non-standard cycles because of incident on Unit 2 2003 Recovery works has finished on Unit 2, unit in operation since 1 January All units in normal order 108 % ( 1485 MWth, 500 MWe ) evaluated on Unit 4 in 2006 on Unit 1 in 2007 Power uprate in rest of units in next year (2008 )

3. Actually used fuel Fixed FA-s : 3.82 wt%, 12.3 mm pitch Followers : 3.82 wt%, 12.2 mm pitch, 2 mm shroud, Hf layer 90 ( 78+12 ) on 1375 MW units ( 4-year application of fixed assemblies 102 (90+12 ) on 1485 MW units ( poorer fuel cycle economy ) More economic fuel and cycle required

4. New fuel and cycle - Paks specific requirements Economic fuel cycle High enough reserve in limiting parameters –Uprated power on units – 1485 MWth, 500 MWe –Much less reserve in local limits –Limits are untouched : Max. assembly power6.58 – 0.37MW Max. pin power57 - 5.7kW Max. linear heat rate325 – 39W/cm Max. subchanel outlet temp. 326 – 7.5 C –Highly welcome, if parameter is monoton decreasing during cycle Moderate increase of max. burnup desired

5. Gd-2n fuel (for Paks) Geometry : Gd-2 fuel Avg. enr. 4.2 % Shroud : 1.5 mm for followers as well

6. Some features of this fuel K-inf vs. burnup curves for Gd-2n and 3.82 % enriched fuel Max. normalised pin power as a function of burnup for Gd-2n fuel

7. Method to provide 60 degree core symmetry SECTOR 1 SECTOR 2 Assembly with odd orientation Assembly with even orientation

8. Equilibrium cycle features / 1 Max. calculated burnups : Assembly 48.9 / 49.5 MWd/kgU Pin 52.7 MWd/kgU Pellet60.1 / 60.6 MWd/kgU FUEL DESCRIPTION 1ST C. 2ND C. 3RD C. 4TH C. 5TH C. Cycle 31 P 4.20 W 78 12.19 72 25.13 78 37.05 72 44.77 12 46.23 Q 4.20 F 6 14.62 12 26.90 6 38.08 12 47.40 0 0.00 Y 1.60 F 1 9.39 0 0.00 0 0.00 0 0.00 0 0.00 Cycle 32 P 4.20 W 72 11.98 78 25.32 72 36.93 78 45.03 12 46.64 Q 4.20 F 12 14.37 6 26.62 12 38.79 6 44.62 0 0.00 Y 1.60 F 0 0.00 1 17.87 0 0.00 0 0.00 0 0.00

9. Present and expected burnups AssemblyPinPellet Previous limit (MWd/kgU)49.005564 Actual limit (MWd/kgU)50.5056.7066.00 4.2 % Gd-fuel, transient and equilibrium cycles Max. burnup (MWd/kgU)AssemblyPinPellet Calculated maximum49.552.760.6 Engineering factor2.905.17 Calculated + eng. Factor52.4057.8067.60 Calculated + eng. Factor+reserve54.006070 Related to previous1.101.091.09 Related to new limit1.071.061.06

10. Equilibrium cycle features / 2

11. Boron letdown during eq. cycle

12. Max. pin power during eq. cycle

13. Max. linear heat rate during eq. cycle

14. Max. subchanel outlet temp. during eq. cycle

15. (quasy) LTA program Goal : test fuel assembly outlet temperature ( measured vs. predicted ) Finalise the model of outlet temperature measurement taking into accout coolant mixing features in assembly head Measure importance of follower containing Gd burnable poisson, compare to predicted Tool : 18 quasy LTA to Unit 4 of Paks, 12 fixed, 6 follower assemblies

16. Core arraengement for LTA program Gd fuel on positions : 18, 55 ( fixed ) 33 (followers ) Cycle 23 FUEL DESCRIPTION 1ST C. 2ND C. 3RD C. 4TH C. 5TH C. K 3.82 W 78 12.76 90 25.79 90 37.85 42 40.90 0 0.00 M 3.82 F 6 14.20 12 26.73 12 33.48 0 0.00 0 0.00 P 4.20 W 12 10.73 0 0.00 0 0.00 0 0.00 0 0.00 Q 4.20 F 6 14.33 0 0.00 0 0.00 0 0.00 0 0.00 X 2.40 F 0 0.00 1 22.49 0 0.00 0 0.00 0 0.00

17. Conclusions Gd – 2n fuel is seemed to satisfy Paks specific requirements Equilibrium cycle is determined Limiting parameters show relatively low value and monoton decreasing feature Max burnup is 6-7 % higher then the present one Reload for application of quasy LTA-s is prepared

18. Calculation codes Methodical calculations and CCS libraries : HELIOS 1.9 Core calculations : C-PORCA 6.2 –Number of axial layers : 41 for old 42 for new fuel