PALAMA

SAFIR2014 interim seminar Ville Tulkki VTT Technical Research Centre of Finland

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Contents

PALAMA Brief review

Focus subject for presentation: Uncertainty in fuel performance modelling, its representation in codes of other fields (e.g. reactor dynamics, system

codes) and development of fuel simulation methods applicable in situations of limited

information

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PALAMA

PALAMA (PolttoAineen Laaja-Alainen MAllinnus) is a four-year project focused on fuel behaviour studies Approximately 3 person-years per year Strong international co-operation (Halden Reactor Project, IRSN, Quantum

Technology) Also links to other fields of reactor analysis

A. Arkoma, VTT-R-06565-12

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PALAMA subjects

Work done in PALAMA can be roughly classified into four categories Fuel behaviour

Studies on basic phenomena such as cladding behaviour during RIA and abnormal operation conditions, cladding oxidation, Gd fuel behaviour, effects of load following operation on fuel performance

Statistical analysis Development of methods for statistically analysing fuel behaviour during

normal and transient situations Multiphysics

Combination of fuel behaviour codes to thermal hydraulic and reactor physics tools

Validation and benchmarks Creation of validation system SPACE International benchmarks FUMEX-III, WGFS RIA

benchmark, Uncertainty Analysis in best estimate Modelling UAM

J. Kättö

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Uncertainty

Uncertainty of the input and models and their effect to the uncertainty of the results are an important topic of research Tells us how certain we can be of analysis results

Several international programmes on the subject OECD/NEA Uncertainty Analysis in best estimate Modelling (UAM) studying

uncertainty propagation through whole calculation chain BEMUSE focusing on uncertainty in system codes

For instance, gap conductance is one of the main contributors to cladding temperature during transients Common input base value in non-fuel specific applications 3000 W/m2K,

variation 30 % Represents fresh fuel, yet not everything happens with a new core

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Gap conductance according to fuel performance code ENIGMA

Base value and variation

E. Syrjälahti, VTT-R-08464-11

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Issue with methods used

To compound the problem, it would appear that the traditional methods for uncertainty analysis do not in general work with fuel behaviour Linearity and/or additivity assumed Many interconnected phenomena in fuel, neither of the assumptions holds Different modes of operation activating at various points of rod life E.g. cladding initially creeps inwards due to pressure differential, then

outwards as it is being pushed by expanding fuel pellet Higher-order effects studied with variance decomposition

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T. Ikonen

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Transferring information on variance forward

Fuel models used in codes of other fields of reactor analysis often very simple As-fabricated geometry, no link between thermal and

mechanical behaviour No accurate physical response, no ability to use

correctly detailed information on uncertainties etc Amount of information to predict fuel behaviour at

burnup is large Conditions from beginning of life to moment of

interest needed to be known Often such information is not available Thus even best fuel models do not help if we cannot

initialize them correctly

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Qualitative problem and our proposed solution

Fuel behaviour codes Complex interconnected

models Provide best estimate

results Physics as we understand

them Require lots of case-by-

case information not necessarily available

Fuel models in general use Simple, static heat elements Provide some approximate

results Physics not well

represented Do not require new

information for each simulation case

System for improved fuel modelling New integrated fuel

model FINIX to bring physical response to transients Method for describing

fuel state with as little information as possible

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FINIX fuel behaviour model and interface for multiphysics applications

Provides thermomechanically coupled solution to transient heat transfer inside fuel rod Correlations from open literature Variety of boundary conditions possible

Implementable at source code level to other codes Depends on external programs to provide boundary

conditions Such as heat transfer from cladding surface to coolant Simple correlations available for applications which do

not provide such information Model verification and initial benchmarking done

Validation and further model development in the latter half of PALAMA

T. Ikonen, VTT-R-00730-13

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Taking burnup into account

Determination of minimum amount of information needed to parameterize fuel state at given burnup Parameterization once per fuel

and reactor type from experimental data or fuel performance modelling Inherently statistical approach

End users initialize FINIX by deciding on burnup used in their own simulations

E. Syrjälahti, VTT-R-08464-11

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Status of the system

First version of FINIX completed Accurate temperate distribution and heat transfer inside fuel rod

In 2013 implementation to Serpent and TRAB-3D/HEXTRAN Initial test of implementation and of ability to model fuel at burnup with chosen

method Other applications for FINIX and further model and method development

based on feedback, interest and user experience

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Summary

PALAMA is 4-year project centered on fuel behaviour studies Focus of this presentation was the new solution for improved fuel

modelling in arbitrary applications which is under development FINIX fuel model for improved physical description of the fuel Method for initializing fuel at burn-up

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Thanks are due to

PALAMA team 2011–2012 Asko Arkoma Antti Daavittila Anitta Hämäläinen Timo Ikonen Seppo Kelppe Joonas Kättö Anna Nieminen Jan-Olof Stengård Elina Syrjälahti Ville Tulkki Tuomas Viitanen

International IRSN France Halden Reactor Project Quantum Technology Sweden

Domestic Reference Group 3 KOURA KÄÄRME NEPAL SAFIR2014

You

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