Technical Meeting on Liquid Metal Reactor Concepts: Core Design and Structural Materials 12-14 JUNE 2013 IAEA HQ, VIENNA, AUSTRIA European LEad-Cooled TRAining reactor: structural materials and design issues S. Bortot, J. Ejenstam, M. Pukari, E. Suvdantsetseg, P. Szakalos, J. Wallenius Kungliga Tekniska Högskolan!
Outline! ELECTRA: European Lead-Cooled TRAining reactor! Why?! Where?! How?! Choice of materials! Fuel! Cladding, components and structures! Core design and modeling issues! Concluding remarks
ELECTRA: European Lead-Cooled TRAining reactor WHY?! Education and training facility! Test bed for LFR technology! Research on fast reactor dynamics! R&D on fuel recycle & manufacture
ELECTRA: European Lead-Cooled TRAining reactor WHERE?! ELECTRA-FCC to be built in Oskarshamn CLAB! ELECTRA: 0.5 MW LFR with (Pu,Zr)N fuel! OKG power plant premises OKG! Fuel cycle facilities for ELECTRA! Premises of CLAB interim storage CLAB
ELECTRA: European Lead-Cooled TRAining reactor HOW?! 0.5 MW LFR! 100 % natural convection! (Pu,Zr)N fuel! Core size 30 x 30 cm! Reactor vessel approximately 1 x 3 m! Tentative cost: 52 M, including FFC
Choice of materials FUEL - general! Only U free inert matrix fuels can provide the small core size necessary to achieve full heat removal by natural convection in an LFR! Several inetr matrix fuels exhibit good performance under irradiation:! PuO2-MgO (BOR-60)! (Pu,Am)O2-Mo (HFR)! (Pu,Zr,Y)O2 (Halden)! (Pu,Zr)N (BOR-60, JMTR, HFR, ATR)! Inert matrix nitride fuels offer the highest Pu density, hence small core size for ELECTRA
Choice of materials FUEL - properties 40 30 Thermal conductivity [W/m/k]! Thermal conductivity for (Pu 0.4,Zr 0.6 )N measured by VNIINM 20 10 0 (Pu 0.4,Zr 0.6 )N T [ C] 400 600 800 1000 1200 1400 1600! High temperature stability test carried out under vacuum, argon and nitrogen Weight loss (Pu 0.4,Zr 0.6 )N ZrN vacuum @ 2300 C 26.4% 1.9% argon @ 2300 C 2.7% 1.3% nitrogen @ 2200 C 1.7% 0.9%
Choice of materials FUEL manufacturing process! ZrN to be fabricated from metallic zirconium (to reduce impurities)! PuN to be fabricated from PuO2 (availability)! Mixing and heat treatment à solid solution! Process optimization carried out in collaboration with JAEA (Pu,Zr)N with 88% density! Less than 0.3 wt. % oxygen & carbon impurities achievable by using standard equipment! 2 fuel pins for test irradiation & fuel qualification to be fabricated at PSI
Choice of materials FUEL irradiation performance: CONFIRM! (Pu 0.3,Zr 0.7 )N fuel fabricated by PSI within CONFIRM; oxide source material! 20 % initial porosity CONFIRM! Irradiation to 10 % burnup in HFR! Linear rating: 43-46 kw/m! Gas release: < 5 % Xenon, 80 % Helium! Swelling: 0.9 % per percent Pu burnup! No internal corrosion
Choice of materials FUEL irradiation performance: BORA-BORA! Two-phase PuN-ZrN fuel fabricated by VNIINM! Metallic source material! 16 % initial porosity BORA-BORA! Irradiation in BOR-60 up to 19.4 % burnup! Linear rating: < 20 kw/m! Gas release: < 1 %! Swelling: < 0.1 % per percent Pu burnup! Internal corrosion: 15 microns; oxide phase observed in PIE
Choice of materials FUEL fabrication! 880 kg separated Pu, owned by OKG, in Sellafield! A Pu fuel fabrication lab is under commissioning in Chalmers! Capacity: one fuel pellet per day! In 2012 a Pu conversion facility was licensed, commissioned and operated in Studsvik! Capacity: 200 g Pu per day = one fuel pin for ELECTRA! Relicensing for ELECTRA fuel fabrication under discussion
Choice of materials CLADDING general 400 Stress [MPa]! Cladding creep rupture is a safety limiting design parameter in ELECTRA 300 200 100 T91 12R72 (15/15Ti)! Use of ELECTRA for transient tests requires high creep rupture strength! Austenitic steel selected 0 LMP [10 3 ] 19 20 21 22 23 24! Sandvik developed the 12R72 grade for Phénix in early 70 s Cr Ni Mn Mo Ti Si 15 15 1.8 1.2 0.5 0.4! Fabrication resumed for MYRRHA! Extensive set of creep data exists (200 000 hr)
Choice of materials CLADDING swelling: dose rate dependence! EoL dose for ELECTRA cladding tubes < 40 dpa! Swelling data for cold worked 15-15Ti indicate swelling threshold > 100 dpa 25 20 15 Swelling of Fe-16Cr-15Ni @ 50 dpa [%] 5x10-7 dpa/s! Dose rate dependence of swelling for austenitics is significant! Swelling larger at same dose for lower dose rates (Budylkin 2004) 10 16x10-7 dpa/s 5 Si fraction [wt %] 0 0 0.5 1.0 1.5! ELECTRA dose rate: 1 x 10-7 dpa/s! Swelling threshold to be confirmed
Choice of materials CLADDING corrosion! Max cladding temperature under nominal operation: 830 K (540 C) GESA-FeCrAlY Austenitic steel GESA-FeCrAlY + T91! Alumina (or silica) protection necessary for operation beyond 8000 hours! Al-bearing bulk steel has low creep resistance! GESA protection of austenitic steels is applicable today for short cladding tubes if limited number is to be produced! GESA was tested on 15-15Ti in LBE at 600 C for up to 8000 hours! ELECTRA cladding: 50 cm x 400 pieces
Choice of materials HEAT EXCHANGERS! F/M steels preferred due to lower thermal expansion! Bulk Fe10CrAl-RE under development in collaboration with Sandvik! 10 000 hours tests of Fe10CrXAl-RE in lead performed at 550 C & 10-7 wt.% Oxigen 200 nm Fe10Cr6Al-RE 10 000 h @ 550 C! 6 wt.% Al ensures thin (0.1 micron), stable and protective alumina scale formation! Al content under optimization (welding issues)! Thermal ageing tests are carried out to investigate potential for embrittlement
Core design and modeling issues CORE CONFIGURATION! (Pu 0.4,Zr 0.6 )N fuel, ~ 70 kg Pu from spent UOX! 397 fuel pins, D clad = 12.6 mm! Active core dimensions: ~ 30 x 30 cm! Shutdown and reactivity compensation using 12 rotating B 4 C drums.! Linear rating: ~4 kw/m! Core life: 14 full power years 10 B4C/steel drums! Burnup: ~ 5% fission in actinides! Maximum dose: 30-40 dpa
Core design and modeling issues CONTROL SYSTEM DESIGN! Single drum rotation should not lead to cladding creep rupture! SAS4A transient over-power simulation indicates limit of reactivity insertion at 1.7$ (450 pcm), for a rate of 1$/s.! Total reactivity loss compensation: > 5000 pcm! 12 drums necessary! Similar to Russian space reactor concept (TOPAZ/Yenisey)
Core design and modeling issues SAFETY PARAMETERS Parameter BOL EOL βeff 270 pcm 240 pcm KDoppler ~ 0 ~ 0 αpb (core) -0.4 pcm/k -0.4 pcm/k αpb (global) -1.8 pcm/k -2.5 pcm/k Pb void (core) -3600 pcm -3600 pcm αaxial -0.4 pcm/k -0.4 pcm/k αradial -1.5 pcm/k -1.3 pcm/k! Very hard neutron spectrum! Zero Doppler feedback! Large leakage! Negative coolant temperature coefficient! Large negative axial temperature feedback! Coolant temperature coefficient more negative at EOL, in spite of 8% Am in the fuel
Core design and modeling issues CHALLENGING IN MODELING: REPRODUCTION TIME! Effective neutron reproduction time affected by presence of large, nonabsorbing reflector (lead)! 67% of all neutrons leak into the reflector! 26% of leaked neutrons return to core!! Deterministic calculations face problems related to convergence of (adjoint) flux in reflector! Cross sections for adjoint Monte Carlo not available at KTH! Two options:! Time dependent Monte Carlo (MCNP5) à Λ = 61±2 ns (dynamic repr. time)! Perturbation with 1/v absorber (Serpent) à Λ = 80±2 ns (static repr. time)
Core design and modeling issues CHALLENGING IN MODELING: AXIAL EXPANSION IN SAS4A/SASSYS-1! SAS4A permits to model axial dependence of axial expansion worth, using an axial distribution of fuel worth! Change in reactivity = sum of changes in fuel density x fuel worth! Increase of core height not taken into account! In small cores, a significant error arises! ELECTRA:! density = -2% -> k = -1760 pcm! H = +2% -> k = + 530 pcm
Core design and modeling issues CHALLENGING IN MODELING: NATURAL CIRCULATION! BELLA benchmarked towards SAS4A for 0.1$ reactivity insertion! Maximum power and temperatures agree reasonably well.! Temperatures decrease faster in BELLA! Significant discrepancy in natural convection flow rate
Concluding remarks! A small LFR may be designed to operate on 100% natural convection! Sandvik s 12R72 grade of 15-15Ti delivers high creep resistance! GESA treatment potentially ensures adequate corrosion protection! Bulk Fe10CrXAl-RE considered for heat exchangers! Open issues:! Dose rate dependence of swelling in austenitic cladding materials! Al-limit for weldability of FeCrAl-RE steels! Modeling of ELECTRA transients reveals major challenges:! Neutron reproduction time! Axial expansion coefficient! Natural convection flow rates
Technical Meeting on Liquid Metal Reactor Concepts: Core Design and Structural Materials 12-14 JUNE 2013 IAEA HQ, VIENNA, AUSTRIA Thank you for your kind attention!