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

TECHNOLOGY FOR BUSINESS