Reactivity Control of a Soluble-Boron-Free AP1000 Equilibrium Cycle

Transcription

1 Reactivity Control of a Soluble-Boron-Free AP1000 Equilibrium Cycle Mohd-Syukri Yahya and Yonghee Kim Korea Advanced Institute of Science and Technology (KAIST) Republic of Korea Nuclear Science and Technology Symposium (NST2016) Helsinki, Finland, 2-3 November 2016

2 Outline Motivation for a Soluble Boron Free (SBF) PWR Previous Studies on SBF PWR SBF AP1000 with BigT Absorber The BigT Absorber The Model BigT-loaded AP1000 Core Preliminary Results Core reactivity Radial power peaks Shutdown margin at EOC Conclusions & Future Works Soluble Boron Free PWR with the BigT Absorbers 2

3 Motivation for a Soluble Boron Free PWR Potential advantages of a soluble boron free (SBF) PWR: Elimination of boric-induced corrosion problems Simplification of reactor design, operation and maintenance Reduction of radioactive waste & doses to personnel e.g., tritium production from boron-lioh mixing for coolant ph control High & nearly constant negative MTC throughout cycle Source: Wikipedia 3

4 Noteworthy Past Works on SBF PWR A Galperin, M Segev & A Radkowsky (U-Negev Israel, 1986): SBF with Gadolinium BP CE-EPRI s Elimination of Soluble Boron for a New PWR Design (USA, 1989) EdF-CEA s Feasibility Studies of a Soluble Boron-Free 900-MWe PWR (France, 1998) Independent academic studies: JC Kim (Kyunghee, 1998): Nuclear Design Feasibility of SBF 600 MWe Core SY Kim (Hanyang, 2003): SBF 1300 MWe PWR with Pu-238 Added Fuel JR Mart (Oregon State, 2012): SBF Small Modular Reactor Available SBF SMR designs: Babcock & Wilcox s 125 MWe mpower KAERI s 90 MWe SMART Argentina s 27 MWe CAREM Westinghouse s 50 MWe IRIS-50 France DCNS s 160 MWe Flexblue Main takeaway points: Alternative control system must precisely be defined for a practical SBF PWR design SBF operation is less restrictive for a small PWR core There is no successful commercial SBF PWR as of today Soluble Boron Free PWR with the BigT Absorbers 4

5 KAIST s SBF PWR Approach Core management with mechanical rods and burnable absorbers (BAs), with borated water as secondary independent emergency trip Burnup reactivity swing kept sufficiently small (e.g. < 1,000 pcm) so as to minimize use of mechanical rods during normal operation SBF PWR operation with commercial BAs is, however, very difficult hence the needs for a new BA concept: Burnable absorber Integrated Guide Thimble (BigT) BigT-AHR (Azimuthally Heterogeneous Ring) BigT-fAHR (fixed AHR) BigT-Pad Soluble Boron Free PWR with the BigT Absorbers 5

6 Conceptual Strategy of an SBF PWR with the BigT Replace depleted BigT & shuffle assemblies during refueling batch-wise BigT geometries (BA thickness, span) to account for batch-wise reactivity variations due to burnup & xenon Core criticality management of the BigT-loaded SBF PWR can be realized as follows: offset super-criticality of fresh by sub-criticality of twice-burned assemblies maintain once-burned assemblies about critical Fresh Assembly Once-Burned Assembly Twice-Burned Assembly BigT-AHR B 4 C, thick 0.19 mm, span 50 BigT-AHR B 4 C, thick 0.44 mm, span 20 BigT-AHR B 4 C, thick 0.02 mm, span 65 Soluble Boron Free PWR with the BigT Absorbers 7

7 Scope of Study The objective define and evaluate a conceptual core design of an SBF PWR The calculation tools: Computer code: Serpent-2 Monte Carlo code Nuclear data: ENDF/B-VII.0 library The modeling simplifications assembly-wise batch-averaged compositions with six axial stacks (with bottom and top BigT cutbacks) of core-averaged axial temperature distributions minimize computing time while maintaining good accuracy for estimation of radial peaks & rod worth assume no significant axial effects which would invalidate general conclusions The search for equilibrium cycle was performed via repetitive depletion calculations until convergence 500 active & 100 inactive cycles, with 1,000,000 particles per cycle standard deviations of k-eff <5 pcm Soluble Boron Free PWR with the BigT Absorbers 7

8 The Model BigT-loaded SBF PWR The model SBF PWR was based on Westinghouse s AP1000 core 3,400 MWth reactor power for 490 effective full power days (EFPDs) 4.95-w/o, 95.5%TD UO 2 fresh assemblies In-in-out low-leakage loading pattern with batch-wise BigT-AHRs 52 fresh assemblies 52 once-burned assemblies 52 twice-burned assemblies The model AP1000 core 1 thrice-burned assembly The BigT- and IFBA-loaded fuel assembly Fresh Assembly Once-Burned Assembly Twice-Burned Assembly Thrice-Burned Assembly BigT-AHR B 4 C, thick 0.25 mm, span 30 BigT-AHR B 4 C, thick 0.25 mm, span 30 No BigT No BigT Soluble Boron Free PWR with the BigT Absorbers 9

9 The Search for Equilibrium Cycle Transition core SBF core Equilibrium cycle search via repetitive depletion calculations until convergence (500 active & 100 inactive cycles, with 1,000,000 particles per cycle: st-dev ±5 pcm) Soluble Boron Free PWR with the BigT Absorbers 9

10 Reactivity Depletion of the Equilibrium Cycle 1,850 pcm 310 EFPDs Burnup reactivity swing (BRS) for a practical SBF PWR should be small, e.g. < 1,000 pcm BRS of BigT-loaded SBF AP1000 ~1,850 pcm (this is quite promising) Soluble Boron Free PWR with the BigT Absorbers 11

11 Assembly Power Profile of the Equilibrium Cycle Fresh (4.95%) 0 EFPD 310 EFPDs 490 EFPDs Onceburned Thriceburned Twiceburned Peak assembly power Soluble Boron Free PWR with the BigT Absorbers 13

12 Pin Power Profile of Hottest Assembly 0 EFPD Max pin power = EFPDs Max pin power = Soluble Boron Free PWR with the BigT Absorbers 13

13 Other Core Neutronic Parameters EFPDs 0* FTC (HFP), pcm/k MTC (HFP), pcm/k *clean core (no Xenon) = Soluble Boron Free PWR with the BigT Absorbers 13

14 Most Severe Shutdown Margin of the Equilibrium Cycle BigT-AHR requires new control rod cm absorber rod, i.e. ~20% smaller in radius loss of rod worth due to size reduction, rod shadowing & flux interference Employ rodding patterns of AP1000 First Core (AP1000 Design Control Doc, 2011) Reactivity effects Parameters at 310 EFPDs (pcm) Reactivity insertion (HFP to HZP) Ag-In-Cd (AIC) rod Natural B 4 C rod Total power defect 1,725 1,725 Void content (1) Total control rod requirement 1,775 1,775 Estimated rod worth (HZP) 1 All rods inserted less most reactive stuck rod 6,566 7,528 (2) Less 10% 5,909 6,775 Worst stuck rod worth 1,361 2,403 Shutdown margin Calculated margin [(2) (1)] 4,134 5,000 Required shutdown margin 1, , Total rod worth implicitly includes the rod insertion allowance 2 Reference: NDR Yonggwang NPP Unit 1 Cycle 12 (1999) 14

15 Cold Shutdown Concern Unrodded core reactivity 0 EFPD (pcm) 310 EFPDs (pcm) 490 EFPDs (pcm) At hot full power (HFP), eq. Xenon 3,909 1, At hot zero power (HZP), eq./no Xenon 5,599 / 5,602 3,603 / 6,444 1,888/4,918 At cold zero power (CZP), no Xenon 11,623 11,422 10,128 Unrodded core reactivity change 0 EFPD (pcm) 310 EFPDs (pcm) 490 EFPDs (pcm) From HFP to HZP, eq. Xenon 1,690 1,725 1,837 From HZP to CZP, no Xenon 6,021 4,978 5,209 Note: Xenon worth at HZP 3 2,841 3,030 Rodded core reactivity (no Xenon) 0 EFPD (pcm) 310 EFPDs (pcm) 490 EFPDs (pcm) At HZP, with Ag-In-Cd black rods -1,451-1,482-4,124 At CZP, with Ag-In-Cd black rods 5,954 5,414 3,285 At HZP, with natural B 4 C black rods -3,572-3,486-6,102 At CZP, with natural B 4 C black rods 4,377 4,167 2,143 At CZP, with 99 w/o B 4 C black rods 2,667 3,048 1,052 Rod worth (no Xenon) 0 EFPD (pcm) 310 EFPDs (pcm) 490 EFPDs (pcm) At HZP, with Ag-In-Cd black rods 7,053 7,926 9,042 At CZP, with Ag-In-Cd black rods 5,669 6,008 6,843 At HZP, with natural B 4 C black rods 9,174 9,930 11,021 At CZP, with natural B 4 C black rods 7,245 7,255 7,982 At CZP, with 99 w/o B 4 C black rods 8,956 8,374 9,075 Note: rod worth increases with burnup & from CZP to HZP 15

16 Conclusions & Future Works Our approach requires only minor modification to existing technology Batch-wise BigT-AHR absorbers, which are replaced during refueling Smaller Ag-In-Cd or natural B 4 C rods May easily be retrofitted to commercial PWRs Emergency boron injection system during safe cold shutdown Preliminary analyses imply a promising solution to an SBF PWR design Reactivity swing ~1,850 pcm Fairly consistent albeit bit high radial power peaks Sufficiently high shutdown margin (>4,000 pcm) Future works: Further optimizations on BigT designs & loading pattern of the SBF PWR Detailed 3D modeling of the SBF PWR core Quantifications of other vital neutronic core parameters Soluble Boron Free PWR with the BigT Absorbers 15

17 Thank You 17