Proposal of movable reflector for fast reactor design

Transcription

1 Proposal of movable for fast reactor design authors: B. Vrban, J. Lüley, Š. Čerba, J. Haščík 1

2 CONTENT 1. Fast reactor development in Slovak republic 2. GFR 2400 design & specifications 3. Control rod worths & of neutron flux 4. Proposal of movable 5. Neutron traps with moderator materials 6. Calculation results 7. Applicability of proposed solutions 8. 2

3 INTRODUCTION Slovak republic is involved in Gen IV reactor R&D activities Mainly focused on Gas cooled fast reactor design ALLEGRO reactor unit may be placed in Slovakia ALLEGRO is a demonstrator unit of GFR 2400 power reactor 75 MW thermal power Without electricity generation The first core based on MOX fuel lower operational temperatures Next ceramic UPuC fuel should be utilized 3

4 INTRODUCTION GFR 2400 Model based on GoFastR (European FP7) UPuC fuel; W and Re liners, SiC cladding Inner Core PuC %; Outer Core PuC % Zr 3 Si 2 CSD +DSD - B 4 C (90% of 10 B) Primary coolant He - 7 MPa 3 x 800 MW th loops, indirect Brayton cycle Average coolant temp. ~700 C 4

5 INTRODUCTION GFR 2400 MW th 5

6 Normalized neutron flux density [cm -2.s -1 ] Slovak University of Technology in Bratislava INTRODUCTION 1.0E E E E E-04 GFR 2400 PGSFR E E E E E E-04 01E+00 10E E E+00 01E+04 10E E E+04 01E+08 Neutron energy [ev] 6

7 CONTROL ROD WORTH The control rod worth and amplification factors were calculated by SCALE system Identifier ρi e [pcm] i ρ CR [pcm] i A CR [-] ALL UP ± ALL DOWN ± ± 9 - DSD ± ± ± CSD ± ± ± CSD1R 809 ± ± ± CSD2R ± ± ± CSD ± ± ± CSD ± ± ± DSD ± ± ± DSD ± ± ± The total worth of all control rods is more than 37 $ 7

8 HOT SPOTS The large shadowing and anti-shadowing effects were found When all CR were fully inserted in a core, flux were identified. Local multiplication factors were calculated The total worth of all control rods is more than (DSD 13 β eff + CSD 24 β eff ) 8

9 PROPOSAL OF MOVABLE REFLECTOR The control rod systems are currently based on a common design concept Common mode failure: Gross core distortion (seismic events preventing absorbers motion) Distortion of the upper core, trapping absorber above the fissile zone Damage to the control rod drive housings preventing motion of one or more rod followers 9

10 PROPOSAL OF MOVABLE REFLECTOR Principally there are several methods of reactivity control Introducing additional absorbing material to the core Introducing an absorbing gas Introducing particles (powder) Flooding the core with an neutron absorbing liquid Introducing liquid absorbers into S/A Removing fuel or reshaping the core to form a less reactive assembly Increasing neutron leakage from the core, consequently reducing the reactivity of the core 10

11 PROPOSAL OF MOVABLE REFLECTOR Removing fuel or reshaping the core & Increasing neutron leakage from the core Ref: Westfall &Mayo: Neutronic Calculations of Fuel and Poison Drum Control of Refractory Metal Fast Spectrum Space Power Reactors, NASA,

12 PROPOSAL OF MOVABLE REFLECTOR Removing fuel or reshaping the core & Increasing neutron leakage from the core Ref: Super-safe, small and simple reactor, 4S, TOSHIBA Design, CRIEPI, Japan 12

13 MOVABLE REFLECTOR CONFIGURATIONS Three main configurations investigated: The six groups per six assemblies case The first ring withdrawal The first two rings withdrawal The 6x6 assemblies case 13

14 SYSTEM WITH MODERATING MATERIAL To enhance the worth of withdrawal neutron spectral shifting by moderation material in form of neutron traps was investigated Proposed neutron traps inspired by simple and robust VVER- 440 control rod design In normal operation the movable S/As are in their upper positions In the case of emergency the movable assemblies are dropped to the lower edge of the fuel part and the original material is replaced by neutron traps 14

15 SYSTEM WITH MODERATING MATERIAL In VVER-440 the neutrons are slow-down in CR inner cavity which is filled by water coolant. The slow-down neutrons are then trapped in the boron steel absorber (2% B natural, 20% Cr, 16% Ni) 15

16 Faculty of Electrical Engineering and Infromation Technology THE CHOICE OF MODERATOR MATERIALS Three different 10 B enrichments in boron steel were studied (Bnat, B70% and B90%) The width of hexagonal boron steel absorber is twice as it is in VVER-440 case Several moderators were chosen: Modertor Abundance of Density Melting isotopes [g.cm -3 ] temperature [K] ZrH 1.5 Natural ZrH 2.0 Natural LiH Natural LiH Enriched 7 Li BeO Natural MgO Natural Li 2 O Enriched 7 Li SiC Natural

17 Δς [pcm] Slovak University of Technology in Bratislava RESULTS The results of 6x6 configuration The withdrawal without the use of neutron trap is 1744 pcm (48.5 pcm per one assembly) Six groups per six assemblies withdrawal AD MgO 6x6 AD Li2O 6x6 AD SiC 6x6 AD BeO 6x6 AD ZRH15 6x6 AD ZRH20 6x6 AD LiHenr 6x6 AD LiHnat 6x6 Bnat B70 B90 10 B enrichment in boronsteel absorber 17

18 RESULTS LMF analysis for BeO case confirmed increased efficiency No significant differences between B70 and B90 cases The hot spot areas were shifted deeper to the core LMFs for the BeO moderator and Bnat, B70 and B90 case 18

19 Δς [pcm] Slovak University of Technology in Bratislava Faculty of Electrical Engineering and Infromation Technology RESULTS The results of first ring configuration The worth of first ring withdrawal without the use of neutron trap reaches 3115 pcm which correspond to 34 pcm per single S/A The first ring withdrawal AD MgO R1 AD Li2O R1 AD SiC R1 AD BeO R1 AD ZRH15 R1 AD ZRH20 R1 AD LiHenr R1 AD LiHnat R1 Bnat B70 B90 10 B enrichment in boronsteel absorber 19

20 Δς [pcm] Slovak University of Technology in Bratislava Faculty of Electrical Engineering and Infromation Technology RESULTS The removal of first two rings The worth of this configuration without the use of neutron traps is 5562 pcm which correspond to 29.5 pcm for one removed assembly. The first and second rings withdrawal AD MgO R1R2 AD Li2O R1R2 AD SiC R1R2 AD BeO R1R2 AD ZRH15 R1R2 AD ZRH20 R1R2 AD LiHenr R1R2 AD LiHnat R1R Bnat B70 B90 10 B enrichment in boronsteel absorber 20

21 PRACTICAL APPLICATION System is useful in a case when CR are trapped in/above the core Additional space needed in axial direction Both under and above the core Parts of movable can be controlled independently Electromagnetic field can be used to handle movable assemblies in their upper position Activation of the system can be based on thermal fuse Bimetal thermostat or melting fuse Heat pipes/sink to transfer a heat from source to thermal fuse 21

22 CONCLUSION Application of movable seems to be useful Reflector 6x6 configuration shows the best results Additional space in axial direction is needed The of moderator materials in the simple neutron trap shows good increase of the efficiency of movable The best results were achieved for hydrogen moderators ZrH x and LiH, although possible tritium production and molecule dissociation is a serious concern From the non-hydrogen moderators the most promising results are in BeO case BeO the high thermal conductivity and high melting point, photo neutrons Achieved results may be easily extrapolated to another fast reactor core designs 22

23 Thank you for your attention Questions? 23