STACY Code and its Application to the HTR-Module and HTTR

meinschaft 

Mitglied der Helmholtz-Gem 

Development of an Integrated Fission Product Release 

and Transport Code for Spatially Resolved Full-Core 

Calculations of V/HTRs 

A. Xhonneux 

Forschungszentrum Jülich, Germany 

Technical Meeting on Re-evaluation of Maximum Operating Temperatures 

g p g p 

and Accident Conditions for HTR Fuel and Structural Materials 

IAEA Headquarters,Vienna, June 10-12 2013

Overview 

• Overview of Fission Product Codes at FZJ 

• Introduction to STACY 

• Exemplary results for HTR-Module 

• Exemplary results for HTTR 

• Summary and outlook 

A. Xhonneux Technical Meeting on Re-evaluation of Maximum Operating Temperatures and Accident Conditions for 

2 

HTR Fuel and Structural Materials, Vienna,10-12 June 2013

Overview 







3 


Overview of Fission Product Codes at FZJ 

FP release rate from one FE 

(NOC and accident Conditions) 

•Fickean diffusion of FPs 

in defective and intact 

CPs / FEs 

•Recoil 

•SiC layer thinning 

Release from FEs and 

transport under 

accident conditions 

•FP transport in core 

due to convection 

•Deposition on reflector 

surfaces 

Fuel Performance 

• CP damage fractions 

• SiC layer thinning 

due to thermal 

decompostion 

o 

Deposition / penetration 

metallic surfaces 

(primary loop) 

• Some features have been implemented multiple times in the separate codes 

• Not complete to describe all phenomena under NOC and accident conditions 

STACY: Source Term Analysis l i Code d System 


4 


Former Approach for FP Release Calculation 

• 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 

„x“ cor re passes 

‣ Conservative approach 

‣ No spatial distribution of fission product release 

‣ More detailed calculation method necessary 

(Fuel temperature [°C] 

HTR-Module, VSOP) 


5 


Overview 







6 


Main Principles of STACY 

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

of individual tracer pebbles 

‣ Spatially resolved fission product release rates 

‣ More precise (less conservative) calculation of total release rate 

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

• VSOP: neutron flux and fluid temperature distributions under NOC 

• MGT: accident temperature distributions 

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


7 


Main Principles of STACY 

• 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 


8 


Former Fuel Shuffling Scheme in VSOP 


9 


Influence of Fuel Mixing on Burnup 

10 

9 

8 

7 

A] 

Burn nup [% FIM 

6 

5 

4 

3 

2 

1 

0 

Channel 1 

Channel 2 

Channel 3 

Channel 4 

Burnup Target 

15 x Channel 1 

15 x Channel 4 

1 3 5 7 9 11 13 15 

Number of completed core passes 

• In comparison to “VSOP batches”, tracer pebbles are not mixed 

• Tracer pebble is loaded to final storage if burnup target is 

reached, not after a predefined number of core passes 


10 


Screenshot of Tracer Pebbles within Eq. Core 

• 4,500 tracer fuel elements 

• Volumetric density of tracer fuel 

elements is constant 

• Colours indicate core pass number 


11 


Calculation of Fission Product Inventory 

• FRESCO-II: 

• Relative fission product release calculation with 

constant birth rate of fission product of interest 

• Neglecting space dependent d 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 


12 


I-131 Inventory of a Tracer Pebble 

core pass 

1.8 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 

entory 

Relative iod dine-131 inv 

1.6 

1.4 

1.2 

1.0 

0.8 

0.6 

0.4 

0.2 

0.0 

0 100 200 300 400 500 600 700 800 900 1000 

Irradiation time [EFPD] 

Inventory, Q = var., TNT 

Inventory, Q = const 


13 


I-131 Release Rate of a Tracer Pebble 

core pass 1 2 3 4 5 1 2 3 4 5 

1.8 

3.0E-12 30 

Relative iod dine-131 inve entory 

1.6 

1.4 

1.2 

1.0 

0.8 

0.6 

0.4 

0.2 

[mol/s] 

release rate 

Iodine 131 

2.5E-12 

2.0E-12 

1.5E-12 

1.0E-12 

5.0E-13 

0.0 

0 100 200 300 

0.0E+00 

0 100 200 300 



Inventory, Q = var., TNT 

Inventory, Q = const 

Rel. Rate = f(t), 15x inner, Q = var., TNT 

Rel. Rate = f(t), 15x inner, Q = const 


14 


Overview 







15 


Interatom Safety Analysis of HTR-Module (1) 

• Normal operating conditions 

• FP release calculation of one representative 

fuel element 

• Codes being applied: 

‣ SLIPPER for condensable fission i products 

(cesium, strontium, silver species) 

‣ STADIF for noble gases and iodine species 

• Accident conditions 

• Rudimentary calculation of fission product 

inventory distribution at start of the accident 

• Code being applied: 

‣ FRESCO-I for all nuclides 

(e.g. cesium, strontium, silver and iodine species) 


16 


Interatom Safety Analysis of HTR-Module (2) 

• Application of so-called Trumpet Curve for coated particle failure fraction 

1.0E-03 

Co oated particle 

failure frac ction 

1.0E-04 

Fresh fuel element 

Fuel element (50% target burnup) 

Fuel element (100% target burnup) 

1.0E-05 

1000 1100 1200 1300 1400 1500 1600 

Fuel temperature [°C] 


17 


Comparison of Main Parameters 

• Neutron flux and fuel temperature distribution 

in good agreement 

• Influence of cone modeling and realistic pebble flow 

pattern on parameters negligible 

further use of model without cone and parallel 

pebble flow 

VSOP model of HTR-Module incl. cone 


18 


Fission Product Release Fractions during DLOFC 

1.0E-04 

10E-05 

1.0E 05 

Re 

elative releas 

se fraction 

1.0E-06 

1.0E-07 

1.0E-08 

08 

FRESCO-I 

(Interatom) 

STACY 

1.0E-09 

1.0E-10 

0 20 40 60 80 100 120 140 160 180 200 

Accident time [h] 

FRESCO-I, Cs-137 FRESCO-I, I-131 FRESCO-I, Sr-90 

FRESCO-I, Cs-137 FRESCO-I, I-131 FRESCO-I, Sr-90 

STACY, Cs-137 STACY, I-131 STACY, Sr-90 

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

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


19 


Comparison of STACY and Interatom Results 

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

Design 

Nuclide STACY SLIPPER 


STACY 

Expected 

SLIPPER 


Cs‐137 2.67×10 3 5.9×10 4 6.76×10 2 3.0×10 4 

I‐131 51×10 5.1×10 7 38×10 3.8×10 6 13×10 1.3×10 7 95×10 9.5×10 5 

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

Design 

Expected 

Nuclide 

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

STACY FRESCO‐I STACY FRESCO‐I STACY FRESCO‐I STACY FRESCO‐I 





Cs‐137 2.62x10 ‐5 8.44x10 ‐5 4.76x10 ‐6 8.44x10 ‐5 7.81x10 ‐6 5.09x10 ‐5 6.01x10 ‐7 8.98x10 ‐6 

I‐131 5.31x10 ‐55 2.86x10 ‐55 2.05x10 ‐55 1.16x1016x10 ‐55 4.96x10 ‐66 9.13x10 ‐66 3.24x10 ‐66 1.12x1012x10 ‐66 

1 

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


2 

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



20 


Comparison of STACY and Interatom Results 

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

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 


21 


Influence of Core Pass Number on Fuel Temp. 

mperature DLOFC [°C] 

Max. fuel te 

1650 

1600 

1550 

1500 

1450 

1400 

VSOP, nominelle NZL 

ZIRKUS, nominelle NZL 

VSOP, +10% NZL 

ZIRKUS, +10 % NZL 

VSOP, +10 % NZL, -10 % WL, -10 % WK 

1350 

5 6 7 8 9 10 11 12 13 14 15 

Core pass number 

Source of ZIRKUS data : Bernnat W., Feltes W., Model for reactor physics calculation for HTR pebble bed modular reactors, Nuclear Engineering and Design 222 (2003) 


22 


Influence of Core Pass Number on Cs-137 Release 

lease rate [m mol/s] 

Cs-137 rel 

6.0E-10 

5.0E-10 

4.0E-10 

3.0E-10 

2.0E-10 

1.0E-10 

55 Durchläufe core passes 



10 10 Durchläufe core passes 

15 15 Durchläufe 

core passes 

Kurve Curve maximaler of max. releases Freisetzungsraten 

0.0E+00 

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 

Accident time [h] 

Calculation with STACY 


23 


Overview 







24 


Fission product release calculation of HTTR 

• Improvements in fission product release code: 

• Fickean diffusion within (hollow) cylindrical bodies 

• Usage of Monte-Carlo method to randomize particle failure 

• Usage of burnup calculation to determine nuclide inventories instead of 

using simplified analytical equation 

→ Spatial resolved fission product release rates 

(so far, only block‐wise) 

• Burnup calculation with SERPENT 

• Monte-Carlo neutronics code incl. burnup calculation 

• Developed at VTT Technical Research Centre 

• Applied to HTTR, HTR-10, Konvoi (1300 MW class) 

etc. at FZJ 


25 


Serpent Model of HTTR 

Layer 2: 1: 4: 5: 6: 7: 3: 9: 8: Top Fuel Bottom reflector 

layer 

reflector 


26 


Cesium-137 release rates after 660 days 

Example:Layer 2 (blocks containing fuel only) 

-150 

-100 

5.64044E-11 

5.61247E-11 

5.61489E-11 

[mol/s] 

5.69754E-11 

5.56938E-11 

-50 

5.60440E-11 

6.64296E-11 

6.63254E-11 

5.51433E-11 

6.99919E-11 

Positio on 2 

0 

5.61235E-11 7.00011E-11 6.98107E-11 5.60894E-11 

6.64607E-1164607E 6.57313E-11 

11 

5.61670E-11 7.05264E-11 6.98409E-11 5.52424E-11 

6.98319E-11 

50 

5.55644E-11 

6.58100E-11 

6.55939E-11 

5.58302E-11 

5.55661E-11 

5.61413E-11 

5.58089E-11 5.58945E-11 

100 

5.55622E-11 

• Temperature input by JAEA 

• Fission product 150 

-150 calculation -100 -50 of one 0 representative 50 100 compact 150 per fuel block 

Position 1 

during “standard operation plan” of 660 days 


27 


Cesium-137 release rates under NOC 

Relative Cesium-13 37-release fraction 

1.0E-01 

1.0E-02 

1.0E-03 

1.0E-04 

1.0E-05 

1.0E-06 

HT‐Phase 

FRESCO-II, Layer1 




STACY, Layer 1 




0 110 220 330 440 550 660 

Time [d] 


28 


Overview 






29 


Summary 

• 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, MGT-3D and the burnup code TNT to enable detailed 

spatially resolved fission product release calculations 

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

living i nuclides are higher h respectively lower in comparison to 

former calculation methods 

• STACY has been coupled to the backbone of the HTR Code 

Package (currently being tested) 


30 


Outlook 

• Fission product release of Cs-137, Sr-90, I-131, Ag-110m of 

HTR-10 (ARCHER Project) 

• VSOP model simulating running-in-phase is based on HTR-10 

model being developed as a contribution to CRP 5 

(prediction of first criticality) 

• Calibration of control rods (2D VSOP model) 

• Modeling of fluid mechanics in VSOP (THERMIX) 

• Development of irregular fuel shuffling scheme 


31 


Thermal power during running-in phase HTR-10 

10 

9 

8 

Measured 

7 

Pow wer [MW] 

6 

5 

4 

3 

Condensed 

power 

history 

2 

1 

0 

0 500 1000 1500 

Operation days 

Source: Fu LI, The HTR-10, operation performance and data collected, IAEA Consultancy Meeting, Vienna, 5-7 December 2011 


32 


Calculated reactivity values by using VSOP 

• Calculated reactivity values during operation and zero power phase 

• Fine-tuning of the reactivity k eff = 1.0 would be easily possible with the 

control rods margins 

operation 

zero power 

phase 


33 


Comparison of FRESCO-I and STACY 


34

STACY Code and its Application to the HTR-Module and HTTR

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