Faucher, Margaux

Ferraro, Diego

Leppänen, J.

Mancusi, D.

Sanchez-Espinoza, V.

Valtavirta, V.

Zoia, A.

English

In recent years, there has been a growing interest in developing high-fidelity reactor physics calculations, for both stationary and transient (operational and accidental) behavior. In this context, the H2020 McSAFE project represents a collaborative effort led by 12 institutions from 7 EU countries to provide reliable and efficient numerical tools for the simulation of generation 2 and 3 light water reactors (LWR). In order to meet this challenge, several new major features are under development for Monte Carlo codes to be able to simulate non-stationary neutron transport with and without thermal-hydraulic feedbacks. Within this framework, in the present work a series of transient scenarios with reactivity insertions due to control rod movement for a 3D PWR Minicore benchmark are proposed and analyzed. Simulations are obtained based on the Serpent and TRIPOLI-4 ® Monte Carlo codes, where kinetic capabilities have been recently (and independently) developed. The respective results are compared to each other in order to assess the accuracy of non-stationary simulations on realistic configurations. Running times, convergence and foreseen requirements are also briefly discussed. </p

Mancusi, Davide

Zoia, Andrea

Valtavirta, Ville

Leppänen, Jaakko

Sanchez-Espinoza, Victor Hugo

VTT Research System

Serpent and TRIPOLI-4® transient calculations comparisons for several reactivity insertion scenarios in a 3D PWR minicore benchmark

KITopen

1 Institute for Neutron Physics and Reactor Technology (INR)www.kit.eduKIT – The Research University in the Helmholtz Association3 VTT Technical Research Centre of Finland2 Den-Service d’Etudes des Réacteurs et de Mathématiques Appliquées (SERMA), CEASerpent and TRIPOLI-4® transient calculations comparisons for several reactivity insertion scenarios in a 3D PWR minicore benchmarkDiego Ferraro1, Margaux Faucher2, D. Mancusi2, A. Zoia2, V. Valtavirta3, J. Leppänen3 and V. Sanchez-Espinoza1M&C 2019Portland, Oregon, US, August 25 – 29, 20192Presentation Overview Introduction & motivation: the McSAFE: high-fidelity Horizon 2020 multiphysics project Proposed verification scheme: Benchmark and scenarios Main results comparison and analysis Conclusions & further workD. Ferraro et al – M&C201931.1 – Introduction & motivation Increasing effort to develop highly accurate multi-physics approaches for nuclear reactor analysis of complex phenomenology.  Increasing demand from designers, operators, regulators and other stakeholders. Several projects around the world oriented to provide high-fidelity results  improvement of local phenomena calculation & provide reference solutions). Under this framework, the McSAFE project started in 2017 under Horizon 2020 (EU):McSAFE: High –Performance Montecarlo Methods for SAFEtyDemonstration: Cooperation between code developers, methods developers and industry stakeholders. 12 partners from 9 countries around EU and an extended community of users around world.Introduction Results & discussion Summary & OutlookProblem & ModelD. Ferraro et al – M&C201941.2 – Introduction & motivation Global  McSAFE goal “move towards high fidelity calculations for steady state, burnup and transient calculations” Several MC codes involved within McSAFE for the diverse applications In this work we focus on Serpent and TRIPOLI-4 for transients calculations How to do this  RIA-type scenarios based on a detailed 3D benchmark for a 3x3 PWR Minicore are proposed. Scenarios start from critical state and undergo a series of reactivity excursions transients through control rod (CR) withdrawals.Introduction Results & discussion Summary & OutlookProblem & Model Scope of this work: Analyze and compare combined capabilities (and identify potential bottlenecks or issues) Analyze performance and requirements (identify VR techniques required for a full scope case)D. Ferraro et al – M&C201952.1 – PWR Minicore transientsIntroduction Results & discussion Summary & OutlookProblem & ModelsProblem We need a well stated benchmark suitable for MC transient calculations  Not an easy task: most oriented to Nodal diffusion codes or out of scope for this stage (full core PWR or not suitable scenarios).  Here the UAM 3-D 15x15 FA PWR Minicore1 is used as basis:1Benchmarks for Uncertainty Analysis in Modelling (UAM) for the Design, Operation and Safety Analysis of LWRs - Volume II:Specification and Support Data for the Core Cases (Phase II )For this problem, rated power (141MWth) and TH fields for fuel pins and coolant are proposed  RIA based transient scenarios are proposed.Reflector Reflector Reflector Reflector ReflectorReflector U ReflectorReflector R ReflectorReflector ReflectorReflector Reflector Reflector Reflector ReflectorUUU UUUUFuel assembly FR pitch ~1.44 cmMinicore arrayLateral, Top & bottom reflector modelU= UnroddedR= RoddedD. Ferraro et al – M&C201962.2 – PWR Minicore transient scenarios Five scenarios are proposed:Introduction Results & discussion Summary & OutlookProblem & ModelsScenarios# Name Main descriptionTime scope1 AStart from critical state. Withdrawal of CR at constant velocity 40 cm/s from 0.2 to 1.2s. Further insertion at same velocity from 1.2 to 2.2 s0 to 5 s with 50 bins (0.1 s each)2 BStart from critical state. Withdrawal of CR at constant velocity 40 cm/s from 0.2 to 1.2s. Further insertion at same velocity from 1.2 to 2.2 s. Repeat procedure starting at 2.4s.3 CStart from critical state. Withdrawal of CR at constant velocity 40 cm/s from 0.2 to 1.2s. Further insertion at same velocity from 3 to 4 s4 D.1Start from critical state. Withdrawal of CR at constant velocity 40 cm/s from 0.2 to 1.2s.5 D.2Start from critical state. Withdrawal of CR at constant velocity 40 cm/s from 0.2 to 1.2s, but considering simplified TH feedback at fuel level:Additional energy from steady state (E) deposited into the fuel for each time bin, increasing temperature of each fuel level node (with 10 axial levels) as :𝐸𝑡𝑖𝑚𝑒 𝑏𝑖𝑛𝑖,𝑗 𝑛𝑜𝑑𝑒= 𝑚𝑓𝑢𝑒𝑙𝑖,𝑗 𝑛𝑜𝑑𝑒𝑐𝑝∆𝑇𝑡𝑖𝑚𝑒 𝑏𝑖𝑛𝑖,𝑗 𝑛𝑜𝑑𝑒For each scenario global and pin by pin powers are analyzed and compared CRtCRtCRtCRtCRtD. Ferraro et al – M&C201972.3 – PWR Minicore 3D Models Introduction Results & discussion Summary & OutlookProblem & ModelsModel Independent 3-D models were developed:x-y cutx-z cut (not-scale)  Developed independently Transient handling implementation approach depends on code.  JEFF 3.1.1 NDL Axial dependency of temperature and density for fuel and coolant Control rod movement For coupled D.2. case (only Serpent)  Python scriptD. Ferraro et al – M&C2019Serpent 2 TRIPOLI-4®x-y cutx-z cut (not-scale) 82.4 – Global behavior reference The most simple comparison possible  Point kinetics!  A simplified point kinetic model1 was developed for these scenarios using kinetic parameters from Serpent (obtained in critical calculations):Introduction Results & discussion Summary & OutlookProblem & ModelsGlobal comparisonሶ𝑃 =𝜌 − 𝛽Λ𝑃 +෍𝑖=18𝐶𝑖 𝜆𝑖 Eq. 1ሶ𝐶𝑖 =𝛽𝑖Λ𝑃 − 𝐶𝑖𝜆𝑖Eq. 2ሶ𝑇𝑓𝑢𝑒𝑙 = 𝑃 − 𝑃0 𝐾 Eq. 3𝜌 = 𝜌𝐶𝑅 𝑡 + 𝛼𝑡(𝑇𝑓𝑢𝑒𝑙 − 𝑇𝑓𝑢𝑒𝑙0)Eq. 41Eq 1 to 4 solved using Wasora code: https://www.seamplex.com/wasora/ Fuel temperature feedback coefficient was calculated using Serpent critical model (only for case D.2) CR worth was also calculated using Serpent critical model and converted to reactivity vs timeD. Ferraro et al – M&C201993.1 – Results comparisonScenario A (no TH feedback) Scenario and global power from Serpent, TRIPOLI-4® and PK comparison:Introduction Results & discussion Summary & OutlookProblem & ModelsScenario A Good and consistent global behavior for this RIA-kind transient  Some differences (PK overshoot, probably due to leakage in real 3D case)D. Ferraro et al – M&C20191.0E+081.5E+082.0E+082.5E+083.0E+083.5E+080.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0Power [W]Time [s]Transient Power evolution  (Scenario A - no TH feedback)Power calculated by SerpentNominal PowerPoint Kinetics + Serpent constants (IFP)Power calculated by TRIPOLIScenario ACRt103.2 – Results comparisonScenario B (no TH feedback)  Scenario A duplicated Scenario and global power from Serpent, TRIPOLI-4® and PK comparison:Introduction Results & discussion Summary & OutlookProblem & ModelsScenario B Good and consistent global behavior for this repeated transient consistent for both codes Some differences (PK overshoot)Scenario BD. Ferraro et al – M&C20191.0E+081.5E+082.0E+082.5E+083.0E+083.5E+084.0E+080.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0Power [W]Time [s]Transient Power evolution  (Scenario B - no TH feedback)Power calculated by SerpentNominal PowerPoint Kinetics + Serpent constants (IFP)Power calculated by TRIPOLICRt113.3 – Results comparisonScenario C (no TH feedback)  Scenario A with flat top Scenario and global power from Serpent, TRIPOLI-4® and PK comparison:Introduction Results & discussion Summary & OutlookProblem & ModelsScenario C Good and consistent global behavior for this flat top transient Precursors buildup OK  Delayed neutrons OK Some differences (PK overshoot)Scenario CD. Ferraro et al – M&C20191.0E+082.0E+083.0E+084.0E+085.0E+086.0E+087.0E+088.0E+080.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0Power [W]Time [s]Transient Power evolution  (Scenario C - no TH feedback)Power calculated by SerpentNominal PowerPoint Kinetics + Serpent constants (IFP)Power calculated by TRIPOLICRt123.4 – Results comparisonScenario D.1 (no TH feedback)  Scenario A without CR insertion Scenario and global power from Serpent, TRIPOLI-4® and PK comparison:Introduction Results & discussion Summary & OutlookProblem & ModelsScenario D.1 Good and consistent global behavior for this supercritical transient for both codes Some cumulative differences What should we expect with TH feedback?Scenario D.1D. Ferraro et al – M&C20191.0E+083.0E+085.0E+087.0E+089.0E+081.1E+091.3E+090.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0Power [W]Time [s]Transient Power evolution  (SC D.1 - no TH feedback)Power calculated by SerpentNominal PowerPoint Kinetics + Serpent constants (IFP)Power calculated by TRIPOLICRt133.5 – Results comparisonScenario D.2 (D.1 + simplified TH feedback) Scenario and global power from Serpent and PK comparison:Introduction Results & discussion Summary & OutlookProblem & ModelsScenario D.2 Good global behavior for this supercritical transient  Feedback on TH fields is working properly!   Some differences (PK overshoot, to be further analyzed)1.0E+081.5E+082.0E+082.5E+083.0E+083.5E+080.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0Power [W]Time [s]Transient Power evolution (Scenario D.2 - simplified  TH feedback)Power calculated by Serpent - with TH feedbackNominal PowerPoint Kinetics + Serpent constants (IFP)TH feedback is working properly!!D. Ferraro et al – M&C2019Scenario D.2CRtAdiabatic feedback143.5 – Some remarks on results differences Perturbation analysis of the proposed scenarios (PK model):Introduction Results & discussion Summary & OutlookProblem & ModelsFurther remarksD. Ferraro et al – M&C20191.0E+081.5E+082.0E+082.5E+083.0E+083.5E+084.0E+084.5E+085.0E+085.5E+080.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0Power [W]Time [s]Transient Power evolution  (Scenario B - no TH feedback)Power calculated by SerpentNominal PowerPoint Kinetics + Serpent constants (IFP)Power calculated by TRIPOLIPoint Kinetics + Serpent constants (IFP) nominal + 10 pcmPoint Kinetics + Serpent constants (IFP) nominal - 10 pcmPoint Kinetics + Serpent constants (IFP) nominal + 15 pcmPoint Kinetics + Serpent constants (IFP) nominal - 15 pcm1.0E+083.0E+085.0E+087.0E+089.0E+081.1E+091.3E+091.5E+090.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0Power [W]Time [s]Transient Power evolution  (Scenario D.1 - no TH feedback)Power calculated by SerpentNominal PowerPoint Kinetics + Serpent constants (IFP)Power calculated by TRIPOLIPoint Kinetics + Serpent constants (IFP) nominal + 10 pcmPoint Kinetics + Serpent constants (IFP) nominal - 10 pcmPoint Kinetics + Serpent constants (IFP) nominal + 15 pcmPoint Kinetics + Serpent constants (IFP) nominal - 15 pcm Slight differences on reactivity have a clear impact in the long-term power evolution (cumulative). TH feedback will have a stabilizing effect on the discrepancies. Impact on further steps?CRtScenario D.1CRtScenario B153.6 – Towards high-fidelitySpatially resolved tallies for scenario A Fission Power example (Serpent 2):D. Ferraro - 8th SUMGIntroduction Results & discussion Summary & OutlookProblem & ModelsTowards high-fidelity Highly detailed (i.e. pin-by-pin) results feasible Total neutron flux example (TRIPOLI-4®)163.7  – Requirements and performanceThe computational costs and performance comparison Compared computational costs for Serpent and TRIPOLI-4®D. Ferraro - 8th SUMGIntroduction Results & discussion Summary & OutlookProblem & ModelsConvergence and performance Highly detailed (i.e. pin-by-pin) results require high amount of resources Consistent performance for both codesParameter / Scenario A B C D1Serpent1Active neutron histories 1.00E+07 1.00E+07 1.00E+07 1.00E+07Processors 1000 1000 1000 1000Running wallclock time [min] 393 412 482 593Average stdev [%] 1 sigma 0.65 0.68 0.96 1.26Max stdev [%] 1 sigma 1.1 1.2 1.7 3.4FOM [ (1/( sigma2T) ] 6.0E-02 5.3E-02 2.3E-02 1.1E-02TRIPOLI-4Active histories 1.00E+08 1.00E+08 8.00E+07 4.00E+07Processors 1000 1000 1000 1000Running wallclock time [min] 1006 1103 1388 1254Average stdev [%] 1 sigma 0.46 0.47 0.55 0.85Max stdev [%] 1 sigma 0.68 0.68 0.78 1.09FOM [ (1/(sigma2 T) ] 4.8E-02 4.2E-02 2.4E-02 1.1E-021 Run in hybrid MPI/OMP in cluster based on nodes with 2x10 intel Xeon processors E5-2660 v3 @ 2.6 GHz2 Run in pure MPI in cluster based on nodes with 2x14-cores Intel Broadwell @ 2.4GHz (AVX2)174 – Conclusions and further work The McSAFE is a high-fidelity project aimed at developing high-fidelity calculations, including transient analysis A detailed 3D benchmark for a 3x3 PWR Minicore is proposed as basis to develop a series of scenarios (RIA-type) Results obtained & compared with the Serpent 2 and TRIPOLI-4® MC codes  first code-to-code comparison for such RIA type transient simulations For all transient scenarios results from TRIPOLI-4® and Serpent 2 are in good agreement First step towards the verification and performance analysis.  Further work:• Coupling with TH subchannel codes (SUBCHANFLOW)• Proper verification (code-to-code) and validation with experimental dataD. Ferraro et al – M&C2019Introduction Results & discussion Summary & OutlookProblem & Models184 – Further work (under development)D. Ferraro et al – M&C2019Serpent model SCF model (coolant-centered)Full paper submitted to ANE (May 2019): “Serpent/SUBCHANFLOW pin-by-pin coupled transient calculations for a PWR minicore” - D. Ferraro et al.• Given the good obtained results, further coupling (master-slave) was developed with SERPENT+SUBCHANFLOW (COBRA-based subchannel thermalhydraulics).• First verification results already available for Serpent+SCF (consistent behavior)Introduction Results & discussion Summary & OutlookProblem & ModelsTRIPOLI/SUBCHANFLOW also under development8508759009259509751000102510501075110011251150117512001.0E+081.5E+082.0E+082.5E+083.0E+083.5E+084.0E+084.5E+085.0E+080 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5Temperature [K]Fission Power [W]Time [s]Total Fission Power RIA Scenario - extraction at 35 cm/sFuel Temperature Average [K]  - extraction at 35 cm/sStatistical error bars at 2 Sigma19www.kit.eduQuestions? Thank you for your attention!!! M&C 2019Portland, Oregon, US, August 25 – 29, 201920Additional information D. Ferraro et al – M&C201901002003004005000 5 10 15 20 25 30 35 40 45Rho [pcm]Extraction [cm]CR reactivity  SerpentCR reactivity TRIPOLI4Error bars at 2 SigmaCodeBoron concentration [ppm]keff (+/- 1 )Reactivity difference with Serpent [pcm]Serpent 1480 (adjusted) 1.00006  +/ 2e-5 -TRIPOLI-4 1493 (adjusted) 0.99995 +/ -5e-5 -11TRIPOLI-4 1480 1.00124 +/ -17 e-5 117Static reactivity comparison between TRIPOLI and Serpent 

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Serpent and TRIPOLI-4® transient calculations comparisons for several reactivity insertion scenarios in a 3D PWR minicore benchmark

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