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VTT TECHNICAL RESEARCH CENTRE OF FINLAND LTD
PANCHOPhysics and Chemistry of Nuclear Fuel
SAFIR2018 Interim SeminarVille Tulkki
202/05/2017 2
PANCHO
Project investigating various aspects of nuclear fuel behaviour
Development of own fuel codeand
associated automatedvalidation system
Fuel behaviourduring
accidents
Improved understandingof fuel pellet and
cladding properties
302/05/2017 3
Safety relevance of these studies
Safety barriers:
Containment building
Primary circuit
Fuel cladding
Fuel pellet
4402/05/2017
FINIX fuel module
On-going development of own fuelmoduleCompetence developmentSource code level understandingFlexibility of use
Integration with Serpent,Hextran, Trab-3D
Redesigned data structures andinterface for enhanced couplingcapabilitiesTime-independent plasticdeformation modlesNew heat transfer models forbetter stability in steady stateconditions
Development continuesFission gas release, claddingoxidation, failure criterion…
T. Ikonen et al.: EPJ Nuclear Sci. Technol. 2, 37 (2016)
5502/05/2017
Automated validation system
All codes need an extensivevalidationComparison between codepredictions and experimentsAutomated system to run newcode version and compare tocases in the database
6602/05/2017
Accident behaviour
Nuclear fuel behaviour duringpostulated accident conditionsstudied within internationalresearch projects
IAEA CRP FUMACOECD/NEA RIA BenchmarkPhase II
Training of scientistsValidation of toolsInternational collaboration
7702/05/2017
IAEA CRP Fuel Modelling in AccidentConditions
Focus on loss of coolantaccidentsIntegral and single-effectexperiments studied
Halden LOCA experimentsAEKI cladding burst experiments
Validation of new version ofFRAPTRAN code
Erroneous behaviourdiscovered and reported todeveloper
Cases included in validationdatabase and will be used inFINIX validation
8802/05/2017
Reactivity Initiated Accidents
OECD’s RIA Benchmark seriesAims to determine the currentstate of the art in understandingof RIAsThermohydraulic boundaryconditions demonstrated tocause a lot of uncertainty
SCANAIRDeveloped by IRSN formodelling RIA in PWRs
Long-term work at VTT toinclude BWR relevantmodels
BWR cladding modelsBWR thermal hydraulicsthrough GENFLO coupling
9902/05/2017
Pellet chemistry
Spent fuel contains close to allelements of the periodic tableChemical conditions inside thepellet matrix affect how theseelements behaveSome are volatile and/orchemically aggressive
Source of radioactive release,cause of stress corrosioncracking of cladding tube
Continuation of fuel matrixleaching project
ThO2 pelletDevelopment of chemistryanalysis module in anassociated project
Doctoral study grant fromFortum Foundation
101002/05/2017
Evolution of Th concentrations indissolution experiments
Chemistry module used todemonstrate the buffering effectof UMoO6 to urania pelletoxygen potential at high burnup
H. Loukusa et al. / Journal of Nuclear Materials 481(2016) 101-110
E. Myllykylä et al. J Radioanal Nucl Chem (2017)311:225–235
111102/05/2017
Mechanical
Fuel vendors constantly developcladding materials for improvedperformanceMechanical properties influencethe fuel response to changingconditions
E.g. pellet-cladding interactionrestricts the rate of change inpowerImproved understanding helps toplan operations
Development of viscoelasticmodel to describe claddingcreep response to changingconditions
Demonstration of the suitabilityof the methodology withmodern claddings
Adaptation of LCSP creepmodel to zirconium alloysInitialization of experimentalinvestigations of cladding tubeproperties
1202/05/2017 12
Verification of creep models
Viscoelastic model shown toperform well in describingtransient testsLCSP model models long termbehaviourIn future, combination of the two
1302/05/2017 13
Mechanical testing
CREBELLO deviceCapable of creep testing with varyingstresses and biaxiality ratiosOnline measurement of tubularsample’s length and diameter
Varying biaxiality and stress changesinvestigated in PANCHO
1%Nb cladding material
1402/05/2017 14
First tests
1502/05/2017 15
1602/05/2017 16
Summary
PANCHO focuses on nuclear fuel behaviourDevelopment of own capabilities
FINIX fuel code and validation systemOne D.Sc (Tech) in 2015; two foreseen this year
Validation and extension of tools for Finnish needsSCANAIR for BWR applicationsAssessment of new versions of FRAPCON and FRAPTRAN
Combining experimental and modelling workStudying pellet chemistry and cladding tube mechanical properties
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