Vattenfall’s use of FRAPCON for PWR cycle-specific verification FRAPCON/FRAPTRAN User Group Mtg, Jeju, Korea 10 September 2017 Mattias Hemlin and David Schrire david.schrire@vattenfall.com Vattenfall Nuclear Fuel, SE-169 92 Stockholm, Sweden Confidentiality: None (C1) Vattenfall’s use of FRAPCON | D Schrire | 2017.09.10

Ringhals PWRs Overview Reactor type W 3-loop Core design 15x15, 12’, 157 FAs 17x17, 12’, 157 FAs Commercial operation May 1975 Sept 1981 Nov 1983 MW Th 2652 2775 2992 3135 2775 3292 Exit temp. (loop) °C 321 324 323 321  319 324 Fuel Vendor (Areva)/Westinghouse Fuel Type (previous/current) AFA-type all-M5 15 Upgrade (Opt Zirlo clad) HTP-type M5 clad RFA-2 (Opt Zirlo clad) Cycle Length 12 month Chemistry Control Constant pH (7.4) Constant pH (7.4)* SGR * Lower before SGR Vattenfall’s use of FRAPCON | D Schrire | 2017.09.10

Outline Ringhals PWRs - Operating conditions Cycle specific fuel rod design verification Westinghouse RFA-2 mid-life case Westinghouse RFA-2 EOL case PIE verification scope and results so far Conclusions Vattenfall’s use of FRAPCON | D Schrire | 2017.09.10

Cycle specific fuel rod design verification needs Verification requirements Vattenfall needs to confirm that all fuel rod design criteria are fulfilled for every core design (cycle) Calculations are done for all fuel rods in the core (both with and w/o Gd) for Rod internal pressure Maximum centerline temperature Permanent cladding strain Oxide thickness (peak) Cladding hydrogen content (peak)  Now using FRAPCON for in-house verification Verification in-house Previously only performed by fuel vendors Practical benefits of doing this in-house, e.g. Short turnaround time (e.g. for quick core redesign due to fuel damage, etc) Consistent methodology for all fuel types Independent code/methods  additional robustness  Vattenfall now started using FRAPCON for in-house verification Vattenfall’s use of FRAPCON | D Schrire | 2017.09.10

Cycle specific fuel rod design verification methodology Core simulation data The cycle specific input to FRAPCON is based on the 3-D core-follow and prediction calculations with Studsvik’s CMS system (CASMO-5/SIMULATE-3) Time-dependent reactor conditions for Linear heat generation rate (LHGR) Coolant pressure Coolant inlet temperature (for assembly) Coolant mass flux 12 axial nodes (LHGR, burnup and fn) at each time step (~10 per cycle)  Condensed to 3 axial profiles per cycle for FRAPCON (BOFP, MOC, EOFP) Specific power vs fn (fast) from bundle-average value at each node/time step Other input data The fuel rod input is based on the reload reports from the fuel vendors FRAPCON uses only 1 value per rod for enr. and Gd wt % for Gd rods Default values are currently used for the model options Vattenfall’s use of FRAPCON | D Schrire | 2017.09.10

Case study – Westinghouse RFA-2 mid-life case Background – selection of 2-cycle fuel rod High peak surface heat flux (SHF) at BOC2 (high Li)  Verify most aggressive conditions for Li-enhanced corrosion 2AH3 one of the hottest once-burnt assemblies in core at BOC D12 2nd hottest rod in assembly Selected for hot cell PIE Vattenfall’s use of FRAPCON | D Schrire | 2017.09.10

Case study – Westinghouse RFA-2 mid-life case Vattenfall’s use of FRAPCON | D Schrire | 2017.09.10

Case study – Westinghouse RFA-2 mid-life case Metallography at fuel-stack gap, maybe unrepresentative Vattenfall’s use of FRAPCON | D Schrire | 2017.09.10

Case study – Westinghouse RFA-2 EOL benchmark Assembly ID 0AH1 0AH3 0AH5 0AH8 EOL BU (4 cycles) 53.3 53.0 Vattenfall’s use of FRAPCON | D Schrire | 2017.09.10

Case study – Westinghouse RFA-2 EOL benchmark Vattenfall’s use of FRAPCON | D Schrire | 2017.09.10

Case study – Westinghouse RFA-2 EOL benchmark Rod selected for hot cell PIE Fresh bundle in 3rd cycle Vattenfall’s use of FRAPCON | D Schrire | 2017.09.10

Case study – Westinghouse RFA-2 EOLbenchmark 3rd and 4th cycle well above Vitanza threshold Vattenfall’s use of FRAPCON | D Schrire | 2017.09.10

Results – calculated vs measured FGR somewhat under-predicted  Very sensitive to LHR when above Vitanza threshold Spread in free volume  May be due to as-manufactured uncertainty Vattenfall’s use of FRAPCON | D Schrire | 2017.09.10