Modeling the release of radionuclides from irradiated LBE ... · Modeling the release of...

Modeling the release of radionuclides from

irradiated LBE

&

Radionuclides in MEGAPIE Alexander Aerts & Jörg Neuhausen

IAEA, Vienna, July 5th, 2017

1st IAEA workshop on challenges for coolants in fast spectrum neutron systems

Copyright © 2017 SCK•CEN

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ISC: Unrestricted Internal Use Source: [TBD]

Radionuclides in ADS

ADS system

radionuclide

inventory

radionuclide

behavior

*

safety

analysis

design

licensing

particle

physics

codes

safety

codes

chemistry

codes

experimental

analysis


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ADS system

radionuclide

inventory

radionuclide

behavior

*

safety

analysis

design

licensing

particle

physics

codes

safety

codes

chemistry

codes

experimental

analysis


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MYRRHA ADS – important chemical processes

LBE cooled 100 MW accelerator

driven system under development

6000 ton LBE

2.4 MW p+ beam


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ADS system

radionuclide

inventory

radionuclide

behavior

*

safety

analysis

design

licensing

particle

physics

codes

safety

codes

chemistry

codes

experimental

analysis


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ISC: Unrestricted Internal Use

radionuclide inventory of MYRRHA

Spallation and coolant activation products in LBE at end of life (40 EFPY)

+fuel pin leak -> mobile fission products released into LBE: I, Cs, Te, Mo, Pd, Ba,

others?


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MYRRHA: 30 elements with potential dose > 5 mSv (SO2, 1/103 lifetimes < f <

1/lifetime)

Retention needs to be assessed for normal operation and accidents (water!)

potential dose impact by inhalation

no retention in LBE assumed


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ADS system

c radionuclide

inventory

radionuclide

behavior

*

safety

analysis

design

licensing

particle

physics

codes

safety

codes

chemistry

codes

experimental

analysis


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Radionuclide behavior: retention by LBE

Retention = not evaporating

important phenomena that control retention of a radionuclide

evaporation

condensation

gas phase

reactions

G/S adsorption

L/S adsorption

deposition

precipitation

dissolution

Thermodynamic (equilibrium)

description requires:

Free energies of formation of solids

Partial free dissolution energies of

dissolved elements

Free energies of formation of gas

molecules

Free energies of adsorption


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Recommended vapour pressure correlations

OECD-NEA HLM handbook (2015)


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Limitations

Limited set of data, for small number of elements (>< ADS inventory)

Interactions between different elements/phases not fully accounted for

Not possible to assess for example

influence of oxygen control: interactions of impurity with dissolved oxygen,

Reactions with water vapour after accidental water ingress

Does not exploit maximally the large knowledge basis of scientific

literature

=> Limited use for safety assessments (licensing) complex installations (ADS,

HLM FR)


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Global approach to predict radionuclide release/chemistry in LBE

MYrrha THermochemical model: MYTH

Source:

gas, condensed species - databases: HSC,

FactSage, Barin, NIST,…

- other scientific

literature

polonium

molecules - quantum

chemistry

- extrapolation

dissolved species - Literature: analysis Pb-X, Bi-X phase

diagrams, CALPHAD, …

- Po, I, Hg, Cd, Te, Se: evaporation data

- O: EMF data

- n, p, T, V (x,t)

- O control

- cover gas impurities (O2,H2O)

- neutronics: radionuclides

- chemical analysis: stable

impurities

- Evaporation,

precipitation/dissolution

- speciation

Experimental

results

~1350 chemical species: Pb, Bi, oxygen, cover gas, corrosion products, initial impurities, RN, …

thermochemical data

MYRRHA conditions Impurity inventory

Chemical composition MYRRHA

safety

analysis


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Source: [TBD]

examples (1)

Magnetite formation - Se, Te evaporation

Source: [TBD]

Magnetite formation in LBE:

Reaction between dissolved

oxygen and dissolved iron

Some thermochemical properties needed to be estimated

Model predictions agree well with experimental results

More validation needed for model predictions

Precipitation/dissolution

phenomena tellurium molecules in the cover gas (MYTH)

Te

Se

Evaporation phenomena


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MYTH examples (2)

Po evaporation

OECD recommended Henry constant correlation vs experimental data


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Examples (2)

Po evaporation

Predicted release vs time at 400 °C

OECD recommended Henry constant correlation vs experimental data

Ok above 500 °C

Analysis experimental data + quantum chemical calculations gas molecules

=> thermochemical model of MYRRHA: PbPo(g) and Po(g) dominant in the cover gas

Gonzalez et al., J. Nucl. Mater. 2014, 450(1-3), 299-303.

Gonzalez et al., Radiochim. Acta 2014, 102(12), 1083-1091.


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Examples (2)

Po evaporation

Evaporation below 500 °C in inert & reducing atmosphere

Transient release from surface oxide layer

x 50

Observed release vs time at 400 °C in Ar

long term

release

Gonzalez et al., J. Radioanal. Nucl. Chem 2014, 302(1), 195–200.

Gonzalez et al., J. Radioanal. Nucl. Chem 2016, 309(2), 597–605.


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Examples (2)

Po evaporation

Evaporation below 500 °C in presence of water vapor

Surface oxide layer mediated release with increased volatilization due to water?

PoO2.H2O(g) dominant in the cover gas?

Crucial effect, but lack of data to quantify

x 2500

Observed release vs time at 400 °C in

Ar/10%H2O

% H2O

Gonzalez et al., unpublished results, 2017.


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Examples (2)

Po evaporation

MYTH simulation with tellurium provides insight in polonium behavior

Tellurium evaporation from (Pb,Bi)oxide layer in presence of water vapour

Increased volatilization at low temperatures and formation of OH molecules

To do this for Po: thermochemical properties Po molecules needed, experimental

investigation mechanism + modeling


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Examples (3)

Iodine evaporation from LBE

Experimental results at low

temperature >> OECD correlations

Insufficient data in literature available

for estimation thermochemical

properties of dissolved iodine

Current approach: model fitted to

experimental results

Validation needed (independent

measurement techniques)

iodine molecules in the cover gas (MYTH)

iodine apparent Henry constant


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Examples (4)

Model prediction: enhanced iodine-cesium evaporation

Fuel pin rupture: Cs and I released into LBE simultaneously

Complete release into cover gas as CsI(g) predicted >>> OECD recommended

correlation

Kinetic effects?

Experimental validation needed


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RN retention by LBE in MYRRHA from MYTH model –

radiological impact

Spallation & activation source term only (no FP released)

No effects of oxide layer included!


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PART 2

Radionuclides in MEGAPIE


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The MEGAPIE experiment

ADS system

radionuclide

inventory

radionuclide

behavior

*

safety

analysis

design

licensing

particle

physics

codes

safety

codes

chemistry

codes

experimental

analysis

• A key experiment on the ADS

roadmap

• flowing LBE + 575 MeV protons

• Operated for 123 days at PSI in 2006

• MW power

• Tmax =350 °C

• Following slides: courtesy of Jörg

Neuhausen (PSI)


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Sampling

cover gas

monitoring

- sampling

- pressure measurement

- LBE bulk

- LBE-steel interface

- LBE-cover gas interface

post-irradiation

LBE sampling

• Major effort!


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Cover gas monitoring

Pressure increase during

operation by hydrogen and

helium consistent with nuclear

code predictions

MYTH predictions suggest

release as H2(g) or H2O(g)

Xe, Kr are released, reasonable

agreement with nuclear code

predictions

Little released mercury

detected but quantification

difficult

Traces of polonium < astatine


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Post-irradiation LBE analysis

gamma spectra before separation

bulk

cover gas

interface

steel

interface


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Post-irradiation LBE analysis: lanthanides

173Lu estimated

total activity

[GBq]

predicted

activity

[GBq]

% of

predicted

amount

bulk 22 6

321

7 ± 2

LBE/steel

interface 181 58 57 ± 18

Sum 203 ± 64 64 ± 20

173Lu, 148Gd, 146Pm

inhomogeneous -> interface : bulk ratio = 9 : 1

Resonable agreement with calculated inventory (64%)

MYTH predictions in agreement: Ln oxide formation


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129I (

36Cl)

Inhomogeneous: incorporation into surface layer

Reasonable agreement with calculated inventory (factor 2)

Difficult to assess likely chemical state

Source: [TBD]

Post-irradiation LBE analysis: iodine

129I estimated

total activity

[Bq]

predicted

activity

[Bq]

% of

predicted

amount

bulk 295 18

8560

3.4 ± 0.2

LBE/steel interface (37 ± 20)102 43 ± 23

LBE cover gas interface 1.2 0.1 (14 1) x 10-3

Absorber (38 2) x 10-2 (44 2) x 10-4

Sum 3997 ± 2018 47 ± 23


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208Po, 209Po, 210Po

Homogeneous – no enrichment

Resonable agreement with calculated inventory

MYTH predictions in agreement

Source: [TBD]

Post-irradiation LBE analysis: polonium

208Po

(Bq/g)

209Po

(Bq/g)

210Po

(Bq/g)

chem. anal. 1.63 ± 0.14 × 106 1.04 ± 0.08 × 104 5.04 ± 0.39 × 107

FLUKA 3.28 × 106 1.63 × 104 1.61 × 108

MCNPX 1.42 × 106 2.68 × 104 1.53 × 108


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In safety assessments for licensing of LBE/Pb cooled ADS and FR, accurate

prediction of retention of radionuclides by LBE/Pb is crucial

Recommended data in OECD handbook allow limited assessments only

SCK-CENs approach (MYTH model) allows global equilibrium analysis and has been

very successful in several cases

But for a number critical radionuclides (e.g. polonium, iodine) the availability of

fundamental data and understanding of mechanisms is still insufficient for

quantitative predictions

Thermochemical (equilibrium) model needs coupling to system/CFD code

Dedicated collaborative R&D programmes should be set up to fill the gaps

Chemical analyses of the integral MEGAPIE experiment remain the most important

experience feedback to qualitatively check model predictions

Source: [TBD]

Conclusions

…?

Acknowledgements: The authors thank the Belgian Government for

supporting the MYRRHA project.

This project has received funding from the Euratom

research and training programme 2014-2018 under

grant agreement No 662186 (MYRTE).


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Copyright © 2017 - SCKCEN

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SCK•CEN

Studiecentrum voor Kernenergie

Centre d'Etude de l'Energie Nucléaire

Belgian Nuclear Research Centre

Stichting van Openbaar Nut

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Foundation of Public Utility

Registered Office: Avenue Herrmann-Debrouxlaan 40 – BE-1160 BRUSSELS

Operational Office: Boeretang 200 – BE-2400 MOL


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Pb, Bi and O solution properties HLM handbook OECD 2015


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Solubility data in OECD HLM handbook (2015)


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Limitations

Limited set of data, for small number of elements (>< ADS inventory)


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Limitations

Does not exploit maximally the large knowledge basis of scientific literature

Thermodynamic properties of dissolution


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Limitations

Does not exploit maximally the large knowledge basis of scientific literature

Thermodynamic properties of dissolution


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Lutetium in MYTH model

• Lu oxidized and phase separated under normal operating conditions (oxygen controlled LBE)


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What does MYRRHA thermochemical model say about

hydrogen?

Hydrogen will be converted to water vapor at equilibrium

in oxygen controlled LBE: H2(g) + O(lbe) = H2O(g)

But: reaction slow below 400 °C -> release as H2(g) (MEGAPIE < 350 °C)

Minor fraction of H could be incorporated in solid spallation product

hydroxides.

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