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Swedish contributions to the safety of ASTRID reactor: multi-grant project at KTH

Swedish contributions to the safety of ASTRID reactor: multi-grant project at KTH.

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Swedish contributions to the safety of ASTRID reactor: multi-grant project at KTH

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  1. Swedish contributions to the safety of ASTRID reactor: multi-grant project at KTH Diana Caraghiaur1, Augusto Hernandez Solis1, Ranjan Kumar1, Sebastian Raub1, Pavel Kudinov1, Weimin Ma, Nathalie Marie2, Christophe Journeau2, Laurent Trotignon2, Frédéric Bertrand2 and SevostianBechta1 1 - Division of Nuclear Power Safety at Royal Institute of Technology (KTH) 2 - French Alternative Energies and Atomic Energy Commission - Commissariat à l'énergieatomique et aux énergies alternatives (CEA), Cadarache ESNII+ summer school, KTH, Stockholm, May 20, 2014

  2. VR framework grants to support first long term direct collaboration between France and Sweden in nuclear energy • The purpose is to strengthen nuclear research and to stimulate the development of Jules Horowitz Research Reactor (JHR) and sodium-cooled prototype reactor (ASTRID): • Multi-grant projects: 60 MKr, in two calls with deadlines in 2011 and 2013 • PhD students/Postdocs: - Work at CEA, Cadarache- Enrolled in Sweden and do a Swedish PhD/Postdoctoral project- Both Swedish and French supervisors

  3. VR Multi-Project Grants in Nuclear Energy Research • 3 multi-grant projects funded by the Swedish Research Council in the spring of 2012 (projects in collaboration with CEA, France – French Alternative Energies and Atomic Energy Commission): • DEMO-JHR (coordinator: Prof. Christophe Demazière, Chalmers): 3 PhD projectsincluding 1 at KTH: DEPTHS, Development of Procedures of Thermal-Hydraulic Simulations for JHR • ASTRID corephysics and diagnostics (coordinator; Prof. Imre Pázsit, Chalmers): 4 PhD projects including 1 at KTH: ALDESA, Acoustic Leak DEtection in Sodium Applications • ASTRID safety(coordinator: Prof. Sevostian Bechta, KTH): 1 PhD + 3 post-docprojects.

  4. VR Multi-Project Grants in Nuclear Energy Research (2) • 2nd VR call project of 2014: • DrStaffanJacobssonSvärd, Uppsala universitet: Assessing fuel behavior in the sodium-cooled fast reactor ASTRID, 2.5 MSEK • Prof. Janne Walenius, KTH: two PhD projects on Thermodynamic assessments of relevance for fuel-cladding interaction and on Modelling of fission product transport in MOX fuel, 6 MSEK • Prof. ImrePazsit, Chalmers: Neutronicmodeling of control rod withdrawal, 2.5 MSEK

  5. ASTRID-Safety multi-grant project at KTH Aimed at safety improvement of ASTRID SFB including severe accident prevention and mitigation WP1 – Corium retention • 1 PhD student, 4 years • WP2 – Simulation of an early phase of a severe accident 1 post-doc, 2 years WP3 – Probabilistic safety analysis • 1 post-doc, 2 years WP4 – Analysis of severe accident scenarios with simplified models • 1 post-doc, 2 years

  6. WP1: Corium retention • PhD student: Sebastian Raub • Supervisors: Pavel Kudinov (KTH) and Christophe Journeau (CEA) • WP is aimed at integration of CEA and KTHexperience in LWR and SFB safety andimprovement of severe accident management(SAM) of ASTRID reactor

  7. Research tasks Contribution into ASTRID core catcher with the studies of: - melt fragmentation in sodium coolant and corium debris bed formation, - long term coolability of corium debris by sodium natural convection Application of models and tools developed in LWR safety for analysis of to usage for Sodium The current approach is building on KTH-Expertise in Severe Accidents in a typical Swedish Light Water Reactor. The mathematical underpinning of existing Software Tools, developed at KTH is analyzed for assumptions and deductive steps are no longer valid or need adjustment due to the shift from water to liquid sodium and their respective sets of physical properties. Incorporate the adjustments into the existing code structure Evaluate modified Code Find under which range of parameters and boundary conditions the code will perform according to expectations ( debris mass flow into coolant pool, debris temperature, etc) Add Improvements to existing Code Package Possibilities include enhanced heat transfer and vapor production capabilities, as well as debris heap settling and

  8. First ideas about modeling 3 Major Modules: Flow in Porous Media/Evaporation: Solves Ergun’s Filtration equation for flow in a packed bed Solves Phase continuity with flow Does not attempt heat transfer calculations  Heat Release goes completely in evaporation Flow in the coolant pool: Solves Equation of continuity and Turbulent Equation of Momentum, using the k – ε turbulence model Melt Particle Motion and Depositon: Lagrangian model for each particle Particles do not interact Velocity vector of particles consists of 2 parts Velocity field for liquid phase with corrections for buoyancy force Random vector with Gaussian probability distribution, magnitude of variance tied to turbulence Provides corrections to the flow fields due to: • pressure differentials • density changes • Phase changes Provides flow fields for both phases • Provides flow fields for both phases • Provides drag force on particles • Debris Bed From by particle depositon

  9. WP2: Simulation of an early phase of a severe accident • Postdoctoral researcher: Augusto Hernandez-Soliz • Supervisors: Weimin Ma (KTH) Laurent Trotignon, Pierre Gubernatis(CEA) WP is focused on further developmentof SIMMER-III code for the initial phase of SA with core melting and relocation

  10. Motivation • The core design of ASTRID hadposedmany challenges for the modeling of neutronic and TH phenomena | PAGE 10

  11. ASTRID fuel pins • Unprotected Transient of Power (UTOP) • We are focused on simulating what happens at the fuel pin at the begining of an accident • State-of-the art safety analysis relies on computer codes (e.g. SAS-SFR, SIMMER) in order to understand what happens during an unexpected reactor transient 8,5 mm Fissile zone of fuel rods: 0,4 kg of fuel + 0,1 kg of steel Relatively high internal pressure (100b) Fuel assambly(271 rods): 95 kg of fuel + 53 kg of steel SNa  1/3 Sth

  12. Fuel behaviourduring a TOP • The power transient (initial or induced) causes a rapidheating of the fuel, creating a cavityinside the pin. Degradationisdriven by the melting of UO2, and due to the dilatation and rapidpressurization of the cavity up to mechanicalfailure • On such a sequence, we look to represent thesocalledearly stage of the primary phase of the transient, i.e.: • At the pin level: Fuel heating and meelting, evolution and pressure of the cavity up to cladding rupture and ejection of molten fuel to Na • Transient of Power | PAGE 12

  13. Solution scheme Transition (1° rupture of can wall) Initiating event Initiating (primary) stage Secondary stage Irradiation Transition stage SIMMER III or IV : 1 or 2 mesh per assembly • SAS one-pin h= point-kinetic Current scheme • Point kinetics • Limitations on handling CFV coregeometry • Cannothandle multi-pin modeling per channel, • (i.e. one average pin/channel) Drawbacks SIMMER-III* Multi-classes in // and Multi-pins + DPIN • SIMMER III or IV : 1 or 2 mesh per assembly GERMINAL New scheme Cathare : TH of the reactor loop Neutronics = PARIS Point-kinetic OR spatial | PAGE 13

  14. SIMMER-III code • The code thatwillbeused in thisproject corresponds to the SIMMER-III (V. 3E) code • Developed by KIT (Germany), JNC (Japan) and CEA Cadarache to study the consequence of core disruptive accidents in SFRs | PAGE 14

  15. Detailed PIN-I model of the SIMMER-III code • The best possible way to model a fuel pin canbefound in DPIN-1: • Can handleannular pellets • A mesh of 11 nodescanbedefined for the pellet in order to model accuratelytemperature profiles Pcav DPIN-1 (<11 grids) Grid (<11) Cp(Ti), ri,li, Porositiesei Local concentrations of FPs Cavity= Pcav(PU02+PPF), Tcav. Thermal-hydraulics of UO2 are not modeled in the cavity Simplifiedmechanical model of the fuel | PAGE 15

  16. Objectives of the project • Attempts to model the motion of the molten fuel inside the cavity have been carried out in DPIN-2 • Altough not verysuccesfully • Therefore, the main idea of the projectis to improve the DPIN-1 model of SIMMER-III • By trying to implement a time-dependent and axial in-fuel model within the cavity, where the thermal-hydraulicseffects are takenintoaccount • Retro-engineering canbeperformedbased on the in-fuel • motion models of other codes (such as SAS-SFR) cavity | PAGE 16

  17. Sensitivityanalysis in SAS-SFR • In order to do retro-engineering from SAS-SFR into SIMMER-III, the most important model parametersshouldbeknown in advance in order to simplify the work • The aimis to rank the importance of the different input parameterstowards a certain output • Statisticalmethodscanbeused for suchsensitivityanalysis (SA) | PAGE 17

  18. Somesensitivityanalysisresultsobtainedwith SAS-SFR TOP Fuel conductivity (1-Sigma = 1%), Normal PDF Maximum axial clad. temp. after 100 calculations | PAGE 18

  19. Some sensitivity analysis results obtained with SAS-SFR (2) TOP Porosity (1-Sigma = 1%), Normal PDF Maximum axial clad. temp. after 100 calculations | PAGE 19

  20. Somesensitivityanalysisresultsobtainedwith SAS-SFR (3) TOP Gap Heat Transfer Coeff. (1-Sigma = 1%), Normal PDF Maximum axial clad. temp. after 100 calculations MOST DOMINANT PARAMETER | PAGE 20

  21. Future plans SAS-SFR SIMMER-III • Build a general vision of the SAS-SFR approach + phenomena • In-fuel motion model • Thermo-mechanicalcavity model • Understand the SIMMER-III approach of fuel pin degradationmodeling • Pin Model • EJECT • DEFORM • Pin Model • SPIN • DPIN • Computeselected CABRI tests (TOP) • E5/E7 • LT2/PF2 • Improved DPIN-I • In-fuel motion model | PAGE 21

  22. WP3: PSA of ASTRID system design • Postdoctoral researcher: Ranjan Kumar • Supervisors: Pavel Kudinov (KTH) Frederic Bertrand (CEA) • WP is aimed at Dynamic PSA of ASTRID Decay Heat Removal System taking into account failed component recovery

  23. ASTRID DHR Systems • ASTRID has a significant boiling margin in normal operation (more than 300°C) together with a high thermal inertia of the primary system (advantage over PWR). • Decay heat removal systems mainly use • air as a cold source and they are based on forced and natural convection, which • allows passive mode of systems operation. • DHR system must be practically free from the loss of the decay heat removal function. Probabilistic Safety Assessment of ASTRID DHR Systems

  24. PSA Research Objectives • To evaluateCoreDamage Frenquencyfor current ASTRID DHR systems design and analyse potential accident scenarios withconsideration of recovery of failed items. • To perform PSA of current design of ASTRID DHR systemstakingintoaccountbothprobabilistic and deterministicapproaches. • To demonstrate and improve the design for practicallyfailure free DHR function. Probabilistic Safety Assessment of ASTRID DHR Systems

  25. Schematic Diagram of ASTRID DHR System • ASTRID DHR systemsconsist of four types of DHR systems: • 4 loops of S1 used in normal and accident conditions (100% for first 3 days) • 2 active loops of S2 (2 x 100%) • 2 passive loops of S3 (2x 100%) • 2 loops in the bottom of the reactor vessel S4(2x 50%) Probabilistic Safety Assessment of ASTRID DHR Systems

  26. Grace Periodfor Components Recovery • Figure shows the long term sodium temperature calculations taking into account the DHR system operation. • Grace period depends on the sequences of failure and their effects on the sodium temperature rise. S2/S3 S4 Probabilistic Safety Assessment of ASTRID DHR Systems

  27. CEA-KTH aproach:A PSA Level-1 Method with Repairable Components • A PSA Level-1 Method with Repairable Componentsisproposed and implementedby exploiting the grace period using partial dynamic Event Tree and Fault Tree (To be presented in ESREL2014 conference) C1-C5 are either OK or NOT OK based on usersdefineddecouplingcriteria Probabilistic Safety Assessment of ASTRID DHR Systems

  28. Top Event A RepairableFaultTree in Proposed PSA level I G1 FDEP G2 G3 (withrecovery) (withoutrecovery) G4 « Recovery of failed items canreduce up to 54% the chance of top eventfailure » G1 & G3 : Seriesgates G2 & G3: Parallelgates λ: failure rate μ: recovery/repair rate Probabilistic Safety Assessment of ASTRID DHR Systems

  29. DynamicSafetyAssessment of ASTRID DHR system • PyCATSHOO (PythonicObject Oriented Hybrid Stochastic Automata) method models a system with interacting probabilistic and deterministic variables explicitly. • The modeling and analysis using PyCATSHOO is currently undergoing on ASTRID DHR system. PyCATSHOO model of ASTRID DHR systems in which the hybridautomata D1, D2, D3, and POOL communicate real-timelyamongthemselvesthrough message box (coloured) about their state such as randomfailure (probabilistic) of DHR systems and sodiulmtemperaturerise (deterministic) in pool Probabilistic Safety Assessment of ASTRID DHR Systems

  30. WP4: Analysis of severe accident scenarios • Postdoctoral researcher: Diana Caraghiaur • Supervisors: Pavel Kudinov (KTH) Nathalie Marie and Frédéric Bertrand (CEA) • WP aimed at assessment of expansion phase of a SFR FCI with simplified models

  31. Motivation Coremelting • fuel-coolant interaction • => coolantvaporisation • power excursion • => fuel vaporisation mechanisticmodelling simplifiedmodelling mechanicalenergy release due to vapour expansion understandingthe phenomena limitation of vesselloadings

  32. Phenomena of fuel-coolant interaction • Molten fuel-sodium interaction createsfavourable conditions for fine fuel fragmentation • This leads to drasticincrease of heattransfer surface area, and thus, the amount of heatrapidlytransferredfrom the fuel to the (more volatile) sodium • In consequence, a large amount of sodium vapourisproduced in a short time • The specific volume of sodium gasisabout 3000 times largerthan the specific volume of liquid sodium • The increase in volume produces pressure in the enclosed volume of fuel assembly, reactorcore or primaryvessel • The mechanicalenergyisreleased, whichcanendanger the surrounding structures

  33. Fine fragmentation – a prerequisite for energetic FCI! • A large subcooling of sodium • The interfacialtemperaturebetweenmolten fuel and sodium canbebelow the meltingtemperature of fuel • Fragmentation canbe due to formation of a solidcrust on the surface of fuel droplet. The crustisruptured due to an internal pressure build up Illustration of fragments obtainedfrom interaction of a single moltenmetaldropletpenetrating a sodium pool, Zhang et al, 2009 …the largest fragment shows that the inside of the lowerhemisphereisempty. The diameter of the hemisphereisalmostequal to the initial droplet. The appearance of lower part clearly shows to be the solidcrustproducedupon contact with sodium.. Illustration of parameterswhich influence the molten fuel droplet fragmentation due to solidification

  34. Simplified model • Complement to mechanictictools. The mechanistictoolis not yetavailable for SFR FCI, thus the simplified model canbe the onlytool for the design of ASTRID • Fastcalculation of parameters of interest – mechanicalenergy release and pressure evolution • Possibility of conducting large parametricstudies • Easy adaptation to various FCI configuration (variousscales, design evolution, etc.) • Bettertreatment of epistemicuncertainties • Consists of: • Heattransferfrom fuel to sodium (associatedwithfragmented fuel) • Energy conservation in the sodium (one- or two-phase) • Equation of state (one- or two-phase) • Constraints (acoustic and inertial) Example of schematicrepresentation of the system at t=0

  35. Model results for different sizes of fuel droplets Geometryused for calculations, applicable to simulate CORECT 2 experiments. Z(t) represents the interface between the interaction zone and the cold liquid sodium column

  36. Future plans • Sensitivitystudies on fragmentation using CORECT 2 tests • Reactor case application for the ASTRID project at differentscales for varioustypicalbounding configurations • Implementation of the tool in the PROCOR CEA severe accident platform

  37. Concluding remarks The ASTRID – safety projects are in progress but it is already visible that this collaboration is quite successful It is not only example of international collaboration - between France and Sweden, but also interdisciplinary one - between safety of LWRs and SFRs

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