Andriolo, L.

Gianfelici, S.

Lemasson, D.

Marchetti, M.

Massone, M.

Poumerouly, S.

Rineiski, A.

English

KITopen

Transient 3D simulations for the ASTRID reactor: preliminary results for the ULOF Initiation PhaseInternational Conference FR 22, 19-22 April 2022, ViennaS. Gianfelici, M. Massone, A. Rineiski, M. Marchetti, L. Andriolo, D. Lemasson, S. PoumeroulyTRANSIENT 3D SIMULATIONS FOR THE ASTRID REACTOR:PRELIMINARY RESULTS FOR THE ULOF INITIATION PHASEInternational Conference on Fast Reactors and Related Fuel Cycles FR22: Sustainable Clean Energy for the Future, 19-22 April 2022, ViennaTransient 3D simulations for the ASTRID reactor: preliminary results for the ULOF Initiation PhaseInternational Conference FR 22, 19-22 April 2022, ViennaThe ASTRID reactor• ASTRID (Advanced Sodium Technological Reactor for Industrial Demonstration)• Gen-IV SFR pool-type reactor of 1500 MWth designed for industrial scale demonstration• CFV (Low Void worth Core) core design– negative full void coefficient– good fuel burnup performances– intrinsic safety features improve behavior during transients2Parameter ValueNominal thermal power 1500 MWCore inlet/outlet temperature 400/550 °CMass flow rate through the fuel SAs 7206 kg/sInner/outer fissile height 60/90 cmInner/lower fertile height 20/30 cmInner/outer sodium plenum 40/30 cmVoid reactivity effect, core at equilibrium -0.5 $ (-184 pcm)CFV core parametersTransient 3D simulations for the ASTRID reactor: preliminary results for the ULOF Initiation PhaseInternational Conference FR 22, 19-22 April 2022, ViennaThe ASTRID reactor• Two zones, inner and outer, with different active region heights and fuel enrichments.• Sodium plenum zone above the active region, aiming at the reduction of the sodium voiding feedback coefficient.• Inner core subassemblies with an intermediate fertile zone, which limits the power peaking factor and improves thebreeding ratio.• Three different types of absorber rods: control and shutdown rods (RBC), diverse control and shutdown rods(RBD) and floating safety rods (DCS-P).• Core material relocation tubes.3CFV core, horizontal and vertical Transient 3D simulations for the ASTRID reactor: preliminary results for the ULOF Initiation PhaseInternational Conference FR 22, 19-22 April 2022, ViennaSIMMER-III and SIMMER-IV codes• SIMMER-III and SIMMER-IV codes, 2D and 3D tools with multi-phase, multi-velocity-field and multi-component fluid-dynamic framework coupled with a structure and a neutronic model.4• Capable to simulate reactivity excursionsand possible recriticalities due to fuelrelocation.• Originally developed for severe accidentsanalyses in SFRs.• With the increasing availability ofcomputational power, a transition from 2Dto full 3D simulations is to be expected,with a more realistic representation of thereactor core and components.• A 3D SIMMER-IV steady state, followed byan ULOF transient, has been modelled forASTRID. The results were compared withthe data obtained with previous 2D models.SIMMER code structureTransient 3D simulations for the ASTRID reactor: preliminary results for the ULOF Initiation PhaseInternational Conference FR 22, 19-22 April 2022, ViennaSIMMER nodalizations• Cartesian (XYZ) and axial symmetric (RZΘ) options availableto model the 2D and 3D meshes• In our 2D simulation, axially symmetric (RZ) setup was used.Different subassembly groups are approximated usingdifferent 2D rings.• 3D setup with cartesian (XYZ) geometry. Each subassemblyis modelled individually with 2 dedicated meshes.52D SIMMER-III rings3D SIMMER-IV model: hexagonal subassemblies are approximated with 2 cartesian meshes Transient 3D simulations for the ASTRID reactor: preliminary results for the ULOF Initiation PhaseInternational Conference FR 22, 19-22 April 2022, ViennaSIMMER modelsSIMMER-III 2D:• Axial-symmetric 2D model,44 radial and 93 axialmeshes.• The core of 18 SA rings, 11fuel rods and 7 control andsafety rods.SIMMER-IV 3D:• Fluid-dynamics mesh iscomposed by 27×54×76cells in XYZ geometry• Cells in the corners areemployed to model the twopumps and the two IHXs6Transient 3D simulations for the ASTRID reactor: preliminary results for the ULOF Initiation PhaseInternational Conference FR 22, 19-22 April 2022, ViennaSIMMER modifications• A 3D model with neutronics and thermohydraulic models enabled is still a verychallenging task from a computational standpoint, even in a parallel environment.• KIT has developed a correction set that replaces the original SIMMER transportsolver, based on DANTSYS, with the PARTISN code, which features parallelizationcapabilities.• Parallelization has been introduced also in the cross-section generation and self-shielding procedure.• Multi-group cross-section collapsing technique is implemented to condense, at everytime step, an 11-groups cross-sections library, usually used at KIT for SFRcalculations, into 4-groups one.• The neutron flux convergence criteria have been eased in cells with very low fluxvalues, e.g. at neutronics domain corners.7Transient 3D simulations for the ASTRID reactor: preliminary results for the ULOF Initiation PhaseInternational Conference FR 22, 19-22 April 2022, ViennaULOF core power and reactivity• Initial decrease to around 80% of the nominal value in the first 20 s of the ULOFtransient for both 2D and 3D cases.• After this point, sodium boiling starts to influence the transient and the evolution ofthe two calculations diverge significantly.8• The sodium boiling andrewetting behavior in the innercore sodium plenum leads toreactivity oscillations.• In 2D geometry the reactivityswings are much wider,reaching values above zero andso leading to wider powerswings.Transient 3D simulations for the ASTRID reactor: preliminary results for the ULOF Initiation PhaseInternational Conference FR 22, 19-22 April 2022, ViennaULOF core power and reactivity• Reactivity and power trendsheavily influenced by the sodiumboiling and rewetting• Sodium vapor volume evaluated inthe sodium plenum area and in thecore• Steep increase in vapor formationat 24 s leads to a first reactivityswing.• Voiding/condensation evolution in3D is more gradual and thereactivity swings are lesspronounced compared to 2Dduring the initiation phase.9Transient 3D simulations for the ASTRID reactor: preliminary results for the ULOF Initiation PhaseInternational Conference FR 22, 19-22 April 2022, ViennaULOF Pin and SA failure• 3D SIMMER calculation– First pin failure: 39.3 s after ULOF start– First can wall failure: 64.3 s after ULOF start– After 72.5 s, the last considered time in the 3D calculation, 8 subassemblies in theouter core zone show pin failures, of which 2 with can wall failures. These failures arelocated in the SAs of the outer core, where the power is higher due to Beginning OfLife (BOL) core configuration.– No fuel melting is observed.• 2D SIMMER calculation– First pin failure: 44.15 s after ULOF start– First can wall failure: 62.1 s after ULOF start• Comparing the 2D and 3D discretizations, an event such as a can wall failure involves all ofthe SAs discretized in one ring of the bidimensional model, instead of a limited number ofSAs in the 3D model.10Transient 3D simulations for the ASTRID reactor: preliminary results for the ULOF Initiation PhaseInternational Conference FR 22, 19-22 April 2022, ViennaULOF Pin and SA failure• At 67.1 s from ULOF start (60 s)the can-wall fails on the right side.• The sodium vapor enters thesecond outer core ring, increasingthe sodium vapor volume in theactive zone and pushing the liquidsodium in the sodium plenum.• Subsequent reactivity insertionand a final power peak iscalculated.• Compared to the 3D, in 2D ringsgeometry the insertion of sodiumvapor in the active core zone fromone mesh to the other has amuch stronger impact on thereactivity feedbacks and on theglobal reactivity.11Transient 3D simulations for the ASTRID reactor: preliminary results for the ULOF Initiation PhaseInternational Conference FR 22, 19-22 April 2022, ViennaConclusions• With the availability of new computers and techniques, a 3D model calculation has been set up and used as basisfor steady state and ULOF transient analyses for the ASTRID reactor. The results obtained have been comparedto previous 2D calculations to assess effects of 2D and 3D modelling on the evolution of the transient.• Due to the computational power required, modifications to the code have been applied with the aim of speeding upthe calculation. Nonetheless, the computation of such a case is still very challenging: the simulation of about 72.5 sof ULOF transient, steady state included, has taken almost one year of computation using 32 processors.• However, the preliminary results show interesting differences between 2D and 3D results, especially regarding thesodium boiling and rewetting behavior, which greatly affects the reactivity swing and thus the power evolutionduring the ULOF transient.• The results demonstrate the applicability of SIMMER-IV to full vessel SFRs for the simulation of ULOF initiationphase. This applicability was up to now restricted by the very high computation costs and very long simulationtimes, and full vessel SFR models for transient analyses at KIT were mainly performed with the 2D SIMMER-IIIcode. These limitations have been eased recently with modification and optimization of the code.• The established model and code versions offer a basis for further SIMMER-IV code and 3D ASTRID modeloptimizations. They may help to accelerate 3D calculations further, thus opening ways for routine application of 3Dmodels for the initiation phase and for investigation of SIMMER-IV applicability to 3D simulations of later phases ofULOF, such as transition to full core melting and mechanical energy release under hypothetical accidentconditions.12Transient 3D simulations for the ASTRID reactor: preliminary results for the ULOF Initiation PhaseInternational Conference FR 22, 19-22 April 2022, ViennaThank you for yourkind attention!

Transient 3D simulations for the ASTRID Reactor: Preliminary Results for the ULOF initiation phase

https://publikationen.bibliothek.kit.edu/1000150065/149177088

Transient 3D simulations for the ASTRID Reactor: Preliminary Results for the ULOF initiation phase

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