Czechia Spent Fuel Characterization - Nucleus on... · 2019. 11. 18. · nuclear fuel in Czechia The storage is in sites of NPPs Multipurpose storage/transportation casks are used

Czechia Spent Fuel Characterization

J. Frybort

Czech Technical University in PragueState Office for Nuclear Safety

November 12, 2019

J. Frybort (CTU in Praue, SONS) Czechia Spent Fuel Characterization November 12, 2019 1 / 22

Contents

1 Nuclear Power in Czechia

2 Request for Characteristics and Techniques

3 Methods for Spent Fuel CharacterizationSpent Fuel CompositionCriticality Safety

4 Data and Knowledge Management

5 Conclusions and Summary


Nuclear Power in Czechia

Nuclear Reactors

Two nuclear power plants: NPPTemelın and NPP DukovanyNPP Temelın:

Two VVER-1000 V 320 reactorsCurrent capacity 2ˆ1055 MWe

NPP Dukovany:Four VVER-440 V 213 reactorsCurrent capacity 4ˆ510 MWe

Three experimental reactors: LVR-15,LR-0, and VR-1Only LVR-15 produces spent nuclearfuel, others are zero-power reactors



Spent Nuclear Fuel Production

There are estimates of total production of spent nuclear fuel foroperation of existing nuclear power plants (source RAWRA):

NPP Temelın approx. 3390 spent fuel assembliesNPP Dukovany approx. 14350 spent fuel assemblies

The nuclear capacity in Czechia should be expanded by newsources in the existing sitesProduction of spent nuclear fuels from these sources depends onparameters of the projectsEstimates of total spent fuel production is essential for planningstorage and disposal of spent fuel casksThe deep geological repository for the spent nuclear fuel shouldbe opened by 2065



Spent Nuclear Fuel Storage

There is only drystorage of spentnuclear fuel in CzechiaThe storage is in sitesof NPPsMultipurposestorage/transportationcasks are usedThere is continuousmonitoring of thecasks, but the drystorage does not allowvisual inspections


Request for Characteristics and Techniques

What Data Are Needed

Spent nuclear fuels are not reprocessed in CzechiaRequested data are limited to handling of the spent fuelassemblies after the end of irradiationThis includes dry storage and final disposalIt is necessary to be able to calculate residual decay heat, activity,and spent fuel compositionSpent fuel composition is essential for determination of radiationsources and criticality safety during the initial steps of spent fuelhandlingIt is getting increasing important to quantify uncertainties of theavailable calculations



Use of Requested Data

There is a spectrum of requested dataSpent fuel composition allows assessment of criticality safety ofnear reactor pool storage and spent fuel casks during handlingand transportationThere are limits of dose rate at 1 m distance from thetransportation cask, it cannot be evaluated without knowledge ofspent fuel compositionDesigning spent fuel casks and their loading patterns andevaluation of safe handling of the spent nuclear fuel requires alsotime evolution of decay heat after the end of fuel irradiation



Example of SKODA 1000/19 Cask

SKODA 1000/19 cask is used for spent VVER-1000 fuelassembliesSafety assessment of the cask required criticality safetycalculations including uncertainties, determination of decay heatand surface temperatures, and knowledge of production of gassesfor evaluation of the cask’s retention system


Methods for Spent Fuel Characterization

Computational Methods Available in Czechia

Being member of OECD/NEA allowsus to access large catalogue ofcalculation toolsInstitutions in Czechia also haveaccess to tools distributed in scope ofthe CAMP program of U.S. NRCAdditional tools like MCNPMonte-Carlo code for criticality andshielding calculations can beobtained via RSICC, but these aresubject of a feeExperimental data are parts of opendatabases like SFCOMPO andICSBEP


Methods for Spent Fuel Characterization Spent Fuel Composition

Tools for Spent Fuel Composition DeterminationThe typical mode for calculation of spent fuelcomposition is modeling of fuel depletion in2D environment with boundary conditions toform infinite lattice of identical assembliesSuch a task is regularly accomplished usingSCALE calculation tools developed by OakRidge National Laboratory (USA)SCALE capabilities:

fuel composition evolution based onORIGEN and CRAM methodsone-group data generation for the fuelevolutionfeatures flexible methods for self-shieldingallows generation of gamma and neutronsourcesintegrated shielding calculations

AP1000

VVER-1000



Limitations of Fuel Depletion Tools for VVER Reactors

VVER reactors with hexagonal fuel assembly and fuel pin latticeare operated in CzechiaPWR and BWR reactors have rectangular latticeAvailable tools usually have limitations regarding the hexagonallatticeExamples for SCALE tools:

NEWT neutron transport code does not have comparablecalculation acceleration capabilities for VVER reactorsORIGAMI tool does not allow calculation of individual pins inhexagonal latticerecent POLARIS code is currently not compatible with hexagonallattice



Validation of Depletion Tools

Fuel depletion tools must be validated, but it cannot be achievedin full by users (only correct usage)Experimental data are available from multiple sourcesMany open data can be accessed via SFCOMPO 2.0 database

SFCOMPO 2.0 is developed by the Nuclear Energy Agency inclose collaboration with Oak Ridge National LaboratoryIt is a great example of an international collaboration betweenORNL, NEA, and Universidad Politecnica de Madrid



SFCOMPO 2.0 VVER Data

The SFCOMPO 2.0 database contains datafor AGR, BWR, CANDU, MAGNOX, PWR,RBMK, VVER-440, and VVER-1000 reactorsThere are experimental data for 12 BWR and16 PWR reactorsWe can found there 4 measurements forVVER-1000 and 3 for VVER-440 reactorsIt is more correct to look for individualsamplesThere are 249 BWR samples, 308 PWRsamples, 20 VVER-1000 samples, and 47VVER-440 samplesThere are no experimental decay heat datafor VVER reactors



Spent Fuel Composition Calculation Validation

State Office for Nuclear Safetyrequires validation of tools forsafety calculationsSerpent2 capabilities for spentfuel composition determinationwere evaluated in 2018


Methods for Spent Fuel Characterization Criticality Safety

Tools for Spent Fuel Composition Criticality Safety

Criticality safety calculations connected with spent fuels must becarried out for all steps of handling with the spent fuel assembliesSpent fuel assemblies in Czechia are first stored in pools next toreactor vessels and then transferred into dry storage until futurepermanent disposalIt is necessary to maintain subcriticality of the spent fuel pools forall potential configurationsSimilarly, subcriticality must be guaranteed for handling andespecially transportation of spent fuel storage casksUncertainty of the criticality calculations must be quantified basedon the available benchmark experimentsThere is a deficiency in fission products’ data



Database for Criticality Safety Validation

International Criticality Safety Benchmark Evaluation Project(ICSBEP) contains criticality safety benchmark specifications thathave been derived from experiments that were performed atvarious critical facilities around the worldThe 2019 edition contains 574 evaluations with benchmarkspecifications for 4973 critical, near-critical or subcriticalconfigurationsVVER reactors are part of LEU-COMP-THERM (LCT)benchmarks:

LEU: low-enriched uraniumCOMP: compositionTHERM: thermal system

There are 73 benchmark experiments for square lattice and 26sets for hexagonal lattice



Calculation of ICSBEP Benchmarks

Serpent2 capabilities for criticality calculations were evaluatedwith various types of nuclear data: ENDF/B-VII.1, ENDF/B-VIII.0,JEF-2.2, and JEFF-3.3Total 687 configurations were prepared for 39 sets of benchmarkcasesThere is an official Serpent2 validation set containing 507configurations, 180 configuration were added during this studyBoth square and hexagonal lattice configurations were chosenVVER related LCT 5, 7, 15, 19, 21, 26, 28, 30, 36, 53, 61, 64, 70,75, 79, 85, 86, 87, 94 are in the studyNot all benchmark experiment are similarly reliable



Serpent2 and MCNP Agreement

Agreement between Serpent2 and MCNP results was evaluated

0.995

1.000

1.005

1.010LC

T01

LCT

02

LCT

05

LCT

06

LCT

07

LCT

08

LCT

09

LCT

10

LCT

11

LCT

17

LCT

28

LCT

35

LCT

39

LCT

42

LCT

79

aver

age

mul

tiplic

atio

n fa

ctor

MCNP-ENDF/B-VII.1MCNP-ENDF/B-VIII.0

Serpent-ENDF/B-VII.1Serpent-ENDF/B-VIII.0

Serpent-JEFF-3.3Serpent-JEF-2.2


Data and Knowledge Management

Data ManagementThe most detailed data regarding spent nuclear fuel has CEZcompany operating the Czech NPPsThe complete depletion history is known for each individual fuelassemblyAll the key aspects of spent nuclear fuels must be reconstructedby depletion calculationsA vast database of operational data is maintained by UJV(Nuclear Research Institute)There is an in-house ANDREA nodal code for planning and safetyevaluation of fuel loadingsThe database allows easy comparison of different ANDREA andmacroscopic data versionsSpent fuel characteristics are determined by SCALE calculationsThere is good cooperation with Czech universities and operationaldata are available for students’ research


Data and Knowledge Management

Data Availability

Radiactive Waste Repository Authority is responsible for researchand development of Czech deep geological spent fuel repositoryDepletion history comes from CEZ companyDepartment of Nuclear Reactors of Czech Technical University inPrague supports RAWRA with research activitiesDatabase of spent fuel characteristics was developed in2015/2016, importance of key material impurities was analyzedComplex analysis of the proposed repository was conducted in2017/2018More research is planned for 2020


Conclusions and Summary


Spent fuel characterization relies dominantly on calculationsWe are using mostly SCALE calculation package for fuel depletionand MCNP/Serpent2 programs for criticality safety and radiationtransferIt is necessary to have validated tools for safety analysesIt would help us to see better support of hexagonal lattices for allkinds of calculationsUncertainty qualification cannot be achieved without databases ofmeasurement of irradiated fuel samples and critical experimentsWe would like to see expansion of experiments with fissionproducts to allow more realistic evaluation of the burnup-creditapproach



Thank you for your attention


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Czechia Spent Fuel Characterization - Nucleus on... · 2019. 11. 18. · nuclear fuel in Czechia The storage is in sites of NPPs Multipurpose storage/transportation casks are used