German Contribution to Item 2 of the Agenda “Status of ... - IAEA

Lehrstuhl für Reaktorsicherheit und –technik 

Univ.-Prof. Dr. rer. nat. Hans-Josef Allelein 

Institut für Energie- und Klimaforschung 

Nukleare Entsorgung und Reaktorsicherheit (IEK-6) 

German Contribution to Item 2 of the Agenda 

“Status of National & International GCR 

Programs” 

H.-J. Allelein et al.





Content 

I 

General Situation of Nuclear Energy in Germany 

II 

HTR activities in the Research Center Jülich and at 

LRST Aachen University 

III 

Outlook 

H.-J. Allelein 

TWG-GCR-23 

March 5-7, 2013, Vienna 

2





I 

General Situation of Nuclear Energy in 

Germany 


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General Situation of Nuclear Energy in Germany (1) 

• Decision in Oct. 2010 for lifetime extension 

8 years for seven plants censtructed before 1980 D 

14 years for ten younger plants 

• After Fukushima it was decided in June 2011 to shutdown 

these seven older plants plus Krümmel NPP. 

The other nine plants have to phase out, so that the last one 

will be shutdown in 2022. 

In general the situation for nuclear activities in Germany is 

difficult, in particular for HTR related ones. 


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• Following the actual German policy the remaining activities are 

focused on 

nuclear waste 

conservation of know-how and competence 

national R&D programs funded by the two Federal Ministries of 

Economics and Technology and of Education and Research, 

respectively 

with reference to HTR 

o 

o 

analytical activities (3d fluid mechanics, core behavior) 

experimental activities (fluid mechanics, dust behavior, 

graphite corrosion) 


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National projects or activities as parts of such ones 

• GRS, IKE Stuttgart University 

(anal.: fluid mechanics, core behavior) 

• LRST Aachen University and Technical University Dresden 

(exp. and anal.: investigations of dust behavior) 

• Research Center Jülich (RCJ) 

(anal.: fluid mechanics for pebbles and block type in 

different scales, core behavior) 


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International activities 

• EC Framework Programme (FP)-7 

(ARCHER, CARBOWASTE, GoFastR…) 

mainly analytical, different German partners 

• OECD-LOFC Project 

(Loss of Forced Coolant, Japanese HTTR, GRS and RCJ) 

• Co-operation between INET and RCJ 

• Working group on rework of AVR operation 

(caused by regional policy and RCJ board) 


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II 

HTR activities in the Research Center 

Jülich and at LRST Aachen University 

Test facilities INDEX and NACOK2 


New Models for fission product 

release, fuel management and dust 

issues 

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Scope of Activities 

Small scale 

experiments 

INDEX 

(high numbers) 

Integral experiments 

NACOK 2 

(detailed 

investigation) 

Code validation 

CFX 

(fluid mechanics 

HTRs) 

Code validation 

HCP 

(fluid mechanics 

HTRs) 


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h~300 

105 mm 





INDEX (small scale experiment) 

Laser 

IR camera 

TC 

Ø 95 

• Flow channel made of fused glass 

• Quadratic cross section (66x66mm) 

Induction coil 

(water cooled) 

camera 

Inlet of cooling water 

• Induction coil designed for 200g graphite 

• max. temperature pebble 1200°C 

pyrometer 

graphite sample 

induktive heatet 

up to 1200°C 

glas 

pyrometer 

• max. heating rate pebble 500°C/min 

Outlet of cooling water 

• First set up with single sphere (D=60mm) 

a=67 

• Later pebble bed, block elements 

flow chanel 

• TC, pyrometer, IR camera 

• Gas analytics (He, O 2 , CO 2 , CO) 

• Particle Imaging Velocimetry (2D / 3D) 

GAS (N2- 21°C) 


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INDEX 

First series: 

• single pebble 

• inductive heated single sphere 

• 700, 900, 1000, 1100, 1200°C 

• nitrogen flow 22 l/min 

• 2D PIV (classic) 

• flow field above the pebble 

• sequence of 200 pictures 

• measurements done in cold and hot state 


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max. pebble surface temperature / °C 





CFX: INDEX cool down experiment 

Temperature 

970 

800 

700 

Experiment 

Best Estimate 

Fine Grid 

600 

400 

[K] 

500 

400 

300 

200 

0 200 400 600 800 1000 1200 

time / s 


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INDEX 

Modifications in progress: 

• optimizing setup for dust 

experiments 

• new fused glass flow channel 

• ports for additional instrumentation 

(particle measurement by APS, 

SMPS) 

• new exhaust for particle loaded gas 

• moveable induction coil 


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NACOK2- Set-up Run 

• 5 segments (upgradeable) 

• ceramic flow channel 

• base plate 

• one ceramic block with holes 

• windows 

• simple “chimney” set up 

• strait, open gas inlet 

• open exhaust 

• 24 thermo couples 

• ultra sonic flow meter 

• 2D PIV 


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T [°C] 



1400 



Temperatures 

TRC Zone 1 

TRC Zone 2 

1200 

TRC Zone 3 

TRC Zone 4 

TRC Zone 5 

1000 

Zone 1 solid 

Zone 1 Gas 

Zone 2 Window 

800 

Zone 3 Wall 

Zone 4 Wall 

Zone 5 Wall 

600 

400 

Block center bottom 

Block center middle 

Block center top 

Block edge top 

200 

0 

35 40 45 50 55 60 

Dt [h] 


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NACOK2- Pebble Bed 1000°C 

• simple “chimney” set up 

• heating rate 30°C/h 

• 8 layers of ceramic pebbles 

• 200 total with half spheres 

• T max = 1000°C (upper pebble layer) 

• gas flow variation: 20, 30, 40 m³/h 

• four sets of PIV measurements at: 

1. 20 m³/h, 1000°C (layer 8) 

2. 30 m³/h, same furnace temperature 

→ T drop 

3. 30 m³/h, 1000°C (layer 8) 

4. 40 m³/h, 1000°C (layer 8) 

• 120 h experimental time 


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T [°C] 



1200 

1100 

1000 

900 

800 

Temperatures 



Zone 1 solid 

1. Layer (1,1) 

1. Layer (2,2) 

1. Layer (3,3) 

1. Layer (4,4) 

1. Layer (5,5) 

5. Layer (3,1) 

5. Layer (3,3) 

8. Layer (3, 3.5) 

Zone 2 wall 

Zone 3 wall 

700 

Zone 4 wall 

Zone 5 wall 

600 

500 

400 


1 2 3 4 

35 40 45 50 55 60 65 70 75 

Dt [h] 

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PIV at 1000°C, flow rate 20m³/h 

gas flow 

20m³/h 


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CFX: Simulation of the 1 st Pebble Experiment 

Resulting mass flow 

21.7 m³/h 


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temperature / °C 





Transient for the 1st NACOK2 test with ceramic pebbles 

1200 

in air 

center of the top layer 

1000 

800 

600 

MGT-3D, but only 2D 

MGT-3D simulation (2D-Modell) 

Experiment 

400 

200 

max. deviation: 75,07°C 

0 

11-6-12 0:00 12-6-12 0:00 13-6-12 0:00 14-6-12 0:00 15-6-12 0:00 16-6-12 0:00 

time 


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NACOK2 

Modifications in progress: 

• optimizing setup for graphite experiments 

• gas tight closed system (pneumatic valves 

with exhaust gas cooler at outlet) 

• gas support N 2 , He, air, CO 2 , gas mixtures 

up to 50 m³/h 

• gas analytics He, O 2 , CO 2 , CO in flow 

channel and heating zone 

• pressure measurement in every segment 


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HTR Code Package (HCP) 

Objective: "Design, implementation and validation of software for the simulation of 

V/HTRs applying the latest programming techniques and standards." 


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STACY 

… Source Term Analysis Code System 

SHUFLE … Software for Handling Universal Fuel 

Elements 

STAR 

… Source Term Aerosol Resuspension 

(for graphite dust transport, deposition and 

resuspension) 


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„x“ core passes 

Temperature [°C] 





Former Approach for FP Release Calculation 

(Fuel temperature [°C] 

HTR-Module, VSOP) 

• FRESCO-II: Fission product release calculation for one or several 

representative fuel element(s) 

• Time averaged release rate of sphere is multiplied with the total 

number of fuel elements to determine core release rate 

− 

− 

− 

Conservative approach 

No spatial distribution of fission product release 

More detailed calculation method necessary for best estimate 

calculations particularly with regard to design basis and beyond 

design basis accidents 

1200 

1000 

800 

600 

400 

200 

0 

0 250 500 750 1000 1250 

Time [d] 


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Main Principles of STACY (1) 

• Calculation of CP failure fractions and FP release rates of a large 

number of individual tracer pebbles 

− 

− 

Spatially resolved fission product release rates 

Best estimate calculation of total release rate from core 

• Usage of stand-alone codes as an intermediate step: 

− 

VSOP: neutron flux and fluid temperature distributions 

under normal operation conditions 

− MGT: accident temperature distributions 

• Fuel shuffling is modeled so far after stream tube model in VSOP 

(later on SHUFLE will be used) 


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Main Principles of STACY (2) 

• Tracer pebbles are added to the core according to a given distribution with 

the help of a random number generator 

• For each tracer pebble, an individual burnup and radial temperature profile 

calculation is performed 

• Simulation of FP release rate and CP damage fraction for each individual 

tracer pebble 

• Combining results to spatially resolved FP release distributions by 

determining average release rate of tracer pebbles within each region 

• FP release of tracer pebbles is representative for core in case distribution 

of tracer elements over core volume is representative 


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Calculation of Fission Product Inventory 

• FRESCO-II: 

− Relative fission product release calculation with 

constant birth rate of fission product of interest 

− Neglecting space dependent neutron fluxes 

− Birth rate during accident is neglected 

• STACY: 

− Coupling of STACY with newly developed burnup 

code TNT 

− Including precise calculation of inventory in fission 

product release calculation 

− Still condensed birth and removal rate 


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I-131 Inventory of a Tracer Pebble 


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Spatial distribution of I-131 Release Rates 


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Fission Product Release Fractions during DLOFC 


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Comparison of STACY and Interatom Results (1) 

Equilibrium core: Output power specific release values [Bq/(MW th ∙h)] 

Nuclide 

STACY 

Design 

SLIPPER 

(Interatom) 

STACY 

Expected 

SLIPPER 


Cs-137 2.7×10 3 5.9×10 4 6.8×10 2 3.0×10 4 

I-131 5.1×10 7 3.8×10 6 1.3×10 7 9.5×10 5 

1 

: N. N. :Aktivitätsfreisetzung und Strahlenexposition bei der HTR-Modul-Kraftwerksanlage Teil I: Bestimmungsgemäßer Betrieb, 

HTR-Modul Kraftwerk Konzeptbegutachtungsunterlagen, Band 4, Siemens Interatom, 1987 


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DLOFC: Cumulative relative release fraction of core inventory after 200 h 

Design 

Expected 

Nuclide 

STACY 

+90°C Nom. temperature +90°C Nom. temperature 

FRESCO-I 


STACY 

FRESCO-I 


STACY 

FRESCO-I 


STACY 

FRESCO-I 


Cs-137 2.6x10 -5 8.4x10 -5 4.8x10 -6 8.4x10 -5 7.8x10 -6 5.1x10 -5 6.0x10 -7 9.0x10 -6 

I-131 5.3x10 -5 2.9x10 -5 2.1x10 -5 1.2x10 -5 5.0x10 -6 9.1x10 -6 3.2x10 -6 1.1x10 -6 

DLOFC … 

Depressurized Loss of Forced Cooling accident 

2 

: N. N.: Aktivitätsfreisetzung und Strahlenexposition bei der HTR-Modul-Kraftwerksanlage Teil II: Störfälle, 

HTR-Modul Kraftwerk Konzeptbegutachtungsunterlagen, Band 4, Siemens Interatom, 1988 


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STACY results in comparison to Interatom results (STACY / Interatom): 

Equilibrium core: Output power specific release values [Bq/(MW th ∙h)] 

• Iodine-131: Order of magnitude higher 

• Cesium-137: Factor of 20 lower 

(mainly affected by modified modeling and not by revised 

difusion coefficient for Sic) 

DLOFC: Cumulative relative release fraction of core inventory after 200 h 

• Iodine-131: Factor of 2 higher 

• Cesium-137: Factor of 3 (design) to 6 (expected) lower 


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Summary for STACY 

• Original codes have been modernized and merged to form one consistent 

code module STACY 

• STACY has been extended and coupled with the code system VSOP and 

burn up code TNT to enable detailed spatially resolved fission product 

release calculations 

• Fission product release rate of short-living respectively long-living nuclides 

are higher respectively lower in comparison to former calculation methods 


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Motivation for a New Fuel Shuffling Approach 

• Fuel tube model is limited with respect to new 

functionalities 

• Flow tube model requires an additional grid, which 

is not preferred in HTR Code Package (HCP) 

• More elaborated approaches, like Discrete 

Element Method (DEM) are too time consuming for 

being used in a multi-physics code package 

• New approach is required for HCP 

Software for Handling of Universal FueL Elements 


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Requirements for Fuel Shuffling Code 

• Fuel management of spherical and prismatic block type fuel elements 

• 2D/3D-geometry, cartisan and dylindrical coordinates 

• Manually and automatically repositioning of fuel elements 

• XML based input concept (e.g. shuffling scheme) 

• Usage of HCP data model (e.g. fuel element and mesh object) 

• High level of source code reusability 

• Acceptable simulation time with respect to other code modules 

• Extendible on future demands 


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New Aspects of SHUFLE 

• Modelling of discharge tube 

• Differing flow velocities in azimuthal direction 

• Space dependent filling factor / densification of pebble bed 

• Tracking of single batches (multi fuel pass fuel strategy) 

• Simulation of conical pebble heap(s) 

• More precise modelling of stagnant zones 

1030°C 

900°C 

935°C 

Fig.: Fuel temperature distribution [2] 

Fig.: Stagnant zones [1] 

[1] Yang, X.: Experimental Investigation on Feasibility of Two-Region-Designed Pebble-Bed High-Temperature Gas-Cooled Reactor, INET, 2008 

[2] Verfondern, K.: Numerische Untersuchung der 3-dimensionalen stationären Temperatur- und Strömungsverteilung im Core eines Kugelhaufen-Hochtemperaturreaktors, 1984 


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Pebble Flow in SHUFLE 

• The laminar flow paths of fuel pebbles in SHUFLE are simulated by propagating 

smaller voids which are created at the core bottom when discharging pebbles 

• SHUFLE processes flow lines measured experimentally of created by a code based 

on real physics (e.g. DEM) 

• Main purpose is to display fuel movement in larger framework (e.g. HCP) 

Fig.: Measured flow paths [1] 

Fig.: Silo drainage [2] 

[1] Yang, X.: Experimental Investigation on Feasibility of Two-Region-Designed Pebble-Bed High-Temperature Gas-Cooled Reactor, INET, 2008 

[2] Kamrin K., Rycrof C., Bazant M., The stochastic flow rule: a multi-scale model for granular plasticity, MIT. Cambridge, 2007 


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Validation Setup 

• ANABEK test facility (Siemens-Interatom) 

• Pebble bed surface is covered with marked test spheres 

• Pebble bed is shuffled as long as marked spheres are within the vessel 

• Result: residence time distribution (RTD) 

„test spheres“ 


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Simulation Results (Residence Time Distribution) 


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Summary for SHUFLE 

• The HTR Code Package (HCP) requires a detailed fuel shuffling approach 

based on its data model => SHUFLE 

• The new code SHUFLE is able to fill the gap between sophisticated codes 

(e.g. DEM) and rudimentary models (e.g. stream tube model) 

• It was shown that residence time distributions from the ANABEK test 

facility were accurately simulated by SHUFLE 

• SHUFLE will become part of the HCP 


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Implementation of dust module STAR 

Modelling of Staub- (dust): 

Transport 

• convective dust exchange between meshes 

• interaction of dust concentration with deposition and resuspension 

Ablagerung (deposition) 

• implementation of theoretical / semi-empirical correlations 

• modeling of dust behavior on the surface for adhesive forces 

Resuspension 

• implementation of the quasi-static Rock‘n Roll model 


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STAR 

• the STAR code was developed for the simulation of dust behavior in HTR 

• first application for an estimate of the source term due to dust for 

depressurization of the HTR-Module 

• rough assessment of activity released with the INES scale: 

• Level 3 event for design basis accident (DBA) 

• Level 4 event (unfavorable assumptions) for beyond DBA 

Future work: 

• improved simulation of dust in confinement (project ARCHER) 

• further validation / improvement of STAR with focus on conditions 

representative for HTR (project TARGET) 


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III 

Outlook 


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Current German activities funded until 2015 

Main objectives to be achieved until then 

• availability of the first HTR Code Package (HCP) version 

• extension of the experimental data base for fluid mechanics and 

graphite dust behaviour, e.g. for MGT-3D 

• capability of performing predictive calculations for block-type fuel 

HTR 


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German Contribution to Item 2 of the Agenda “Status of ... - IAEA

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