1. www.vuje.sk Reduction of Spent Fuel Volume by Optimisation of VVER- 440 Fuel Assembly AER Meeting, Working Group F Liblice, Czech Republic April 10 – 12, 2012 Pavol ČUDRNÁK Petr DAŘÍLEK Radoslav ZAJAC

2. 2 Content -Introduction – Brief History -Starting and Border Conditions -Results -Conclusion Reduction of Spent Fuel Volume by Optimisation of VVER-440 Fuel Assembly

3. 3 Introduction Reduction of Spent Fuel Volume by Optimisation of VVER-440 Fuel Assembly ASFEU project (2007 - 2013), part of program R&D Title of project: Increasing of the Slovak Republic Energy Safety Cod ITMS: 26220220077 Scientific activity: Space geometry discretisation of the Gd II VVER-440 fuel assembly and discretisation influence on neutron flux distribution and impact of Gd burnup The solution of one of the tasks is performed by HELIOS 1.10. This code is a commercial computer code and its usage by our partner FEI STU Bratislava has been questionable. For this reason a common office of STU & VUJE has been established in VUJE, Inc. in Trnava.

4. 4 Introduction Brief History of the VVER-440 Fuel Assembly in Slovakia Radial profiled VVER-440 fuel assemblies: used in Slovakia since 1999 - increasing of enrichment from 3.6 % U-235 to 3.82 % U-235 - four year fuel cycle Change of the 2 nd generation assemblies with Gd was performed in 2006 - increasing of enrichment to 4.25 % U-235 + 3.35 % Gd 2 O 3 The last development step is using of the 2 nd generation assembly called Gd-2R (4.87 % U-235 + 3.35 % Gd 2 O 3 ) - loaded last year in NPP Mochovce in the 1 st Unit - five year cycle Reduction of Spent Fuel Volume by Optimisation of VVER-440 Fuel Assembly

5. 5 Starting and Border Conditions Aim: Optimisation of Gd-2 assembly with burnable poisons Optimisation Basis: Gd-2 assemblies (4.25 % U-235 + 3.35 % Gd 2 O 3 ) and Gd-2R (4.87 % U-235 + 3.35 % Gd 2 O 3 ) All of the optimised assemblies included the same pin geometry, wrapper tube and also material composition of construction parts Pin enrichment and pin position in assembly was optimised only Reduction of Spent Fuel Volume by Optimisation of VVER-440 Fuel Assembly

6. 6 Starting and Border Conditions VVER-440 Gd-2 Fuel Assembly (4.25 % U-235 + 3.35 % Gd 2 O 3 ) Reduction of Spent Fuel Volume by Optimisation of VVER-440 Fuel Assembly

7. 7 Starting and Border Conditions VVER-440 Gd-2 Fuel Assembly (4.87 % U-235 + 3.35 % Gd 2 O 3 ) Reduction of Spent Fuel Volume by Optimisation of VVER-440 Fuel Assembly

8. 8 Main Aim: optimised VVER-440 assembly without a radical construction change to find: - Assembly with maximal multiplication ability and acceptable pin power peaking Subjects of Calculation: 1. Multiplication Coefficient for Infinite Lattice (k inf ) 2. Coefficient of Pin Power Peaking (k k ) Starting and Border Conditions Reduction of Spent Fuel Volume by Optimisation of VVER-440 Fuel Assembly

9. 9 Results Several tens of fuel assembly variants have been designed: -18 of them have been chosen and analysed - Variants of assemblies have been divided into 6 groups according to composition and characteristics Reduction of Spent Fuel Volume by Optimisation of VVER-440 Fuel Assembly

10. 10 Results Achieved Reduction of Spent Fuel Volume by Optimisation of VVER-440 Fuel Assembly Burnup [MWd/tHM]

11. 11 VVER-440 Gd-2 Fuel Assembly (4.924 % U-235 + 3.35 % Gd 2 O 3 ) Results Achieved Reduction of Spent Fuel Volume by Optimisation of VVER-440 Fuel Assembly 20+

12. 12 Reduction of Spent Fuel Volume by Optimisation of VVER-440 Fuel Assembly Results Achieved VVER-440 Gd-2 Fuel Assembly (4.792 % U-235 + 3.35 % Gd 2 O 3 ) 32

13. 13 Reduction of Spent Fuel Volume by Optimisation of VVER-440 Fuel Assembly Results Achieved VVER-440 Gd-2 Fuel Assembly (4.85 % U-235 + 3.35 % Gd 2 O 3 ) 33b

14. 14 Reduction of Spent Fuel Volume by Optimisation of VVER-440 Fuel Assembly Conclusion Up today: Fuel Assembly 4.792 % U-235 + 3.35 % Gd 2 O 3 -the most flat pin power distribution -five year cycle only Otimisation of fuel assembly is proceeding slowly Six year cycle: enriched fuel >5 % U-235 Growing burn-up reduces a spent fuel amount