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P. Mikoláš e-mail: pavel.mikolas@skoda-js.cz ŠKODA JS a.s. Orlík 266, 31606 Plzeň Czech Republic

17th Symposium of AER Yalta, Ukraine, September 24-29, 2007 INFORMATION ABOUT AER WORKING GROUP A ON IMPROVEMENT, EXTENSION AND VALIDATION OF PARAMETRIZED FEW-FROUP LIBRARIES FOR VVER-440 AND VVER-1000. P. Mikoláš e-mail: pavel.mikolas@skoda-js.cz ŠKODA JS a.s. Orlík 266, 31606 Plzeň

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P. Mikoláš e-mail: pavel.mikolas@skoda-js.cz ŠKODA JS a.s. Orlík 266, 31606 Plzeň Czech Republic

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  1. 17th Symposium of AERYalta, Ukraine, September 24-29, 2007INFORMATION ABOUT AER WORKING GROUP A ON IMPROVEMENT, EXTENSION AND VALIDATION OF PARAMETRIZED FEW-FROUP LIBRARIES FOR VVER-440 AND VVER-1000 P. Mikoláš e-mail: pavel.mikolas@skoda-js.cz ŠKODA JS a.s. Orlík 266, 31606 Plzeň Czech Republic Information about WG A ...

  2. ABSTRACT • Joint AER WG A and WG B held their sixteenth meeting in Hrotovice (near NPP Dukovany), Czech Republic, during the period of 24-25 April 2007. • The objectives of the meeting, content of presentations and future activities are shortly described in this paper. Information about WG A ...

  3. INTRODUCTION • Joint AER Working Group A on „improvement, extension and validation of parameterized few-group libraries for VVER-440 and VVER-1000“ and AER Working group B on „core design“ held their sixteenth Meeting in Hrotovice during the period of 24-25, April 2007. • There were present altogether 14 participants from 8 member organizations (three states - List of participants is attached in the end of this paper) and read 10 presentations (List of presentations is also attached). • Objectives of the meeting of WG A: Issues connected with spectral calculations and few-groups libraries preparation. Information about WG A ...

  4. PRESENTATIONS • Four papers were presented in the frame of WG A Information about WG A ...

  5. Gy. Hegyi presented paper entitled:“Some new experience with ZR-6 measurements” • In the beginning of his paper he described: ·NURESIM (European Platform for NUclear REactor SIMulations), • - Areas of interest (Ø SP1 – Core physics Ø SP2 – ThermohydraulicsØ SP3 – Multiphysics Ø SP4 – Sensitivity and Uncertainty AnalysisØ SP5 – Integration), • -   Participants in the SP1 task:CEA, EDF,FZR, GRS, INRNE, JSI, Delft, KFKI, KTH, LUT, NRI, PSI + ASCOMP GMBH, UCL, Uni-KA, Upisa, UPM andVTT • - Organization Structure of NURESIM SP1 Core Physics (Including List of programmes involved and short description of APOLLO2 code with main components) Information about WG A ...

  6. Then he demonstrated:· Comparison of Zr-6 calculation with two codes APOLLO and KARATE Information about WG A ...

  7. - Simulation of a ZR-6 critical assembly measurement at room temperature was described • - Structure of calculations (Reference deterministic, Design and Monte-Carlo Reference) and Roadmap of Development, Validation and Qualification of Simulations Tools were presented Information about WG A ...

  8. Boron Coefficient ρ/CBThe experimental technique used for the boron coefficient ρ/CB was described.Results of comparisons: Information about WG A ...

  9. Conclusions: • The measurements (old & new?) are important • The validation is as important as the measurement itself • Further efforts are needed in these activities Information about WG A ...

  10. Pavel Mikoláš presented paper entitled: “Possibility of fuel cycles extension with up-rated power at Dukovany NPP “ • Possibility of fuel cycles extension with up-rated power at Dukovany NPP was shown. • Two ways were checked, the first is the enrichment increase in fuel of temporary FA and the other is FA design change. • Some basic characteristics of cycles with these changed FAs were also presented. Information about WG A ...

  11. 1. Introduction • Practically five years cycle has been achieved at NPP Dukovany in the last years. • However, the efficiency of fuel cycle can be improved if six years cycles are applied. • There are at least two ways how this goal could be achieved. • The simplest way is to increase fuel enrichment. • The second possibility is to change fuel assembly design. • In the paper presented, both possibilities were checked individually. Information about WG A ...

  12. 2.Fuel assembly with higher enrichment • Enrichment of 4.95 w% of U235 in some of fuel pins in a fuel assembly is supposed. • The other characteristics (it means excluding enrichment) are the same as for fuel assembly of Gd-2 or Gd-2M for up-rated power. • It seems to be clear that this maximal enrichment can not be applied in all fuel pins because in this case pin power non-uniformity would be very high (more than 1.15), which would be a problem from the point of view of pin power factor in the core. • Therefore, enrichment is lower in some pins and one from possible solutions with only three different enrichments with pin power non/uniformity of 1.072 has been found. • These fuel assemblies have been loaded into core in transient end equilibrium cycles of Dukovany NPP for up-rated power (cycles 27th to 34th of Unit III) and basic characteristics of these cycles are shown in Tables 1. • It is seen that fuel cycles prolongation has been achieved, but this prolongation may not be sufficient for six-year cycle. Information about WG A ...

  13. 3. New fuel assembly design • The other possibility how to extend the fuel cycle (and how potentially achieve six year cycle) is the application of fuel assembly with an improved design. • The first one is higher mass content of uranium in a fuel assembly. This can be achieved by two ways: • First, to remove central hole in fuel pellet and • Second, to enlarge fuel pellet diameter • In our checking, both conditions were applied together. Other characteristics are the same as for FA for up-rated power (Gd-2M). • The next possibility is to enlarge pin pitch. • It has been applied too. Information about WG A ...

  14. 3. New fuel assembly design (cont.) • The “last” possibility is to “omit” FA shroud. • This is practically not realistic, in any way; some other structural parts must be introduced in a FA; in our simplified model, • Thickness of FA shroud was lowered in two steps, namely from 1.5 mm on 1.0 mm and then on 0.5 mm. The basic characteristics of these cycles for up-rated power are shown in Table 5 showing that possibilities of fuel assemblies with this improved design in enlargement of fuel cycles are very promising. Information about WG A ...

  15. 4. Discussion • The values shown in Tables 1 and 5 cannot be supposed to be quite real because pin power non-uniformity is to high and different loadings must be found. • Also, probably loading with lower number of fresh FA would be found instead of simple enlargement of the fuel cycle. • Nevertheless, it seems to be clear that FA have still potential in the sense of fuel cycle economy. Information about WG A ...

  16. 5. Conclusions • Although only preliminary analyses described in the paper have been performed, • it can be concluded that temporary design of VVER-440 FA is not optimal (as it is well known) and it exists great potential how to increase FA reactivity, which is a necessary condition in achieving full six years loading strategy. • (Potential in lowering core neutron leakage is practically exhausted as is also the possibility in reducing neutron absorption in construction parts of a FA.) Information about WG A ...

  17. TablesTable 1 Cycles length with FAs with higher enrichment Information about WG A ...

  18. Table 5Cycles length with different FAs types Information about WG A ...

  19. V. Krýsl and J. Šůstek presented paper entitled:„Influence of Hf plate on integral and differential efficiency of CR” • In their paper the efficiency of control rods (CRs) at the end of cycle (EOC) during the last few EDU NPP cycles has been investigated. • When comparing behaviour of the last cycles of EDU NPP, different behaviour of the differential efficiency of CR was observed. Information about WG A ...

  20. Two possible causes of this phenomenon were supposed: • Lower burn-up of the lower part of the CRs, which are during the cycle out of the zone; consequently at the end of the cycle fuel with lower burn-up is inserted into the zone • Using of the Hafnium (Hf) plates in the coupler of CRs • Material specification of FA was provided Information about WG A ...

  21. Basic Calculations: • Basic archives calculation was provided by MOBY-DICK programme following data of the EDU DATABASE, cycle 1-20, unit 3 • Cycles 17-21 with constant nominal power, with CR position 214 and 250 cm, for examination of influence of burn-up of the lower part of the regulatory CR • Alternative calculation of the cycle 17 and 18 where CR with Hf plate (which were inserted into positions of non-regulatory CRs) with fictive CR without Hf plate were replaced, followed by the calculation of the cycle 19, in which these FA were in regulatory positions Information about WG A ...

  22. Calculations of the CR Efficiency: • As a method of the determination of the efficiency of CRs was used gradual insertion of CRs at the end of the cycle, with constant concentration of Xe and Sm. Integral reactivity is direct output of calculations, differential reactivity was calculated by differentiation of the integral reactivity. Scale of the differential reactivity was multiplied by 10, for better contrast. Also difference between integral reactivities (for height of CRs 214 and 250 cm) is shown. As we can see, this difference increases with number of cycle. Information about WG A ...

  23. Examples of Results:Fig. 3 Integral and differential efficiency of CRs, B3C19, EOC (SFR38ZRH, with Hf plate) Information about WG A ...

  24. Fig. 4 Integral and differential efficiency of CRs, B3C19, EOC (SUR38ZRH, without Hf plate) Information about WG A ...

  25. Conclusion: • A Hafnium plate in coupler part of CA causes different differential efficiency of control rod. Information about WG A ...

  26. Sándor Patai-Szabó presented paper entitled: “Impact of Gamma Smearing on Pin Power Distribution” nUsual approach in codes: whole of the fission energy deposited in the fuel pin, where fission happened nActually about 9-10 % of fission energy deposited in other parts of the assembly and in the moderator nComponents of energy release due to fission, from ENDFB 6.8, without neutrinos were also shown. nGamma energy is about 7 % nAnalysis of the spatial distribution is possible with HELIOS code in coupled neutron-gamma transport calculation nOutput parameter of HELIOS is kinetic energy of gammas deposited by scattering and absorption nFuel assemblies with and without gadolinium were examined in infinite lattice of assemblies Information about WG A ...

  27. Gamma energy deposited in assembly and moderator: Information about WG A ...

  28. n80 % of gamma energy deposited in fuel pin, but in other pins than it was produced. The pin power distributions will be a bit different. Taking into account spatial gamma distribution is called ”gamma smearing”.  • Fuel assemblies investigated: nProfiled 3,82 % assembly with 1,23 cm pin pitch nGd-2 fuel, 4.25 % enrichment, 6 pins with Gd2O3 nModified Gd assembly, containing 3 pins with Gd2O3 Information about WG A ...

  29. Example of results: Comparison of energy release (without and with “gamma smearing”) Information about WG A ...

  30. Information about WG A ...

  31. nIn realistic situations the gamma transport between different assemblies can be more significant nThe determinant parameter is the (whole) power of neighbouring assembly n Using a simple assumption the gamma power from neighbouring assembly was added to the investigated assembly, influence on neighbouring assembly can bee checked Information about WG A ...

  32. Conclusions: nThe usual approach is conservative in assemblies without gadolinium, the difference is negligible nThe increase in pins containing gadolinium is significant, but the pin power is very low in these pins – they are negligible nDuring burn-up the pin power in these pins increases, but as the gadolinium burns out, the difference between usual approach and gamma smearing becomes negligible nEffect of neighbourhood is significant, refinement of investigation is necessary nResults should be checked by other codes (e.g. MCNP) nConsidering the fuel pins containing gadolinium: Should the thermo-hydraulics analyses take into account the higher pin power or not? Information about WG A ...

  33. CONCLUSION • Four papers were presented on WG A devoted tasks, which are important. • More effort should be concentrated on special effects, like historical dependences of cross sections or / and boundary conditions. Information about WG A ...

  34. APPENDIXList of presentationsWG A • A-1: György Hegyi (MTA KFKI AEKI): • Some new experience with ZR6 measurements • A-2: Pavel Mikoláš (ŠKODA JS a.s.): • Possibility of fuel cycles extensions with up-rated power on NPP Dukovany • A-3: Václav Krýsl (ŠKODA JS a.s.), Josef Šůstek (ŠKODA JS a.s.): • Influence of a hafnium plate on integral and differential efficiency of control rod • A-4: Sándor Patai-Szabó (TS Enercon Ltd.): • Impact of Gamma Smearing on Pin Power Distribution Information about WG A ...

  35. WG B • B-1: István Pós (Paks NPP): • Study of the application of Finite Element method for 2-and 3-dimensional diffusion calculations • B-2: György Hegyi (MTA KFKI AEKI): • New challenges in core calculations • B-3: Petr Dařílek (VÚJE, a.s.): • Informal information about high power at VVER-440 • B-4: Radim Vočka (ÚJV Řež, a.s.) • Macrocode ANDREA: state of development for VVER-1000 reactors • B-5: Juraj Breza (VÚJE, a.s), Ctibor Strmenský (VÚJE a.s.): • Gd benchmark calculations in VUJE • B-6: Josef Bajgl (Dukovany NPP), Miroslav Lehmann (ÚJV Řež, a.s.): • Optimisation of VVER-440 core loadings - Common and Special Tasks Information about WG A ...

  36. List of participants Information about WG A ...

  37. Information about WG A ...

  38. Information about WG A ...

  39. Information about WG A ...

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