Modeling the release of radionuclides from irradiated LBE & Radionuclides in MEGAPIE Alexander Aerts & Jörg Neuhausen

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Neuhausen 1st IAEA workshop on challenges for coolants

1 Modeling the release of radionuclides from irradiated LBE & Radionuclides in MEGAPIE Alexander Aerts & Jörg Neuhausen 1st IAEA workshop on challenges for coolants in fast spectrum neutron systems IAEA, Vienna, July 5 th, 2017

2 Radionuclides in ADS design licensing * ADS system radionuclide inventory particle physics codes chemistry codes radionuclide behavior experimental analysis safety codes safety analysis 2

3 Radionuclides in ADS design licensing * ADS system radionuclide inventory particle physics codes chemistry codes radionuclide behavior experimental analysis safety codes safety analysis 3

4 MYRRHA ADS important chemical processes LBE cooled 100 MW accelerator driven system under development 6000 ton LBE 2.4 MW p + beam 4

5 Radionuclides in ADS design licensing * ADS system radionuclide inventory particle physics codes chemistry codes radionuclide behavior experimental analysis safety codes safety analysis 5

6 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? 6

7 potential dose impact by inhalation no retention in LBE assumed MYRRHA: 30 elements with potential dose > 5 msv (SO2, 1/10 3 lifetimes < f < 1/lifetime) Retention needs to be assessed for normal operation and accidents (water!) 7

8 Radionuclides in ADS design licensing * ADS system radionuclide c inventory particle physics codes chemistry codes radionuclide behavior experimental analysis safety codes safety analysis 8

9 Radionuclide behavior: retention by LBE Retention = not evaporating important phenomena that control retention of a radionuclide G/S adsorption precipitation dissolution gas phase reactions evaporation condensation 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 L/S adsorption deposition 9

10 Recommended vapour pressure correlations OECD-NEA HLM handbook (2015) 10

11 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) 11

Global approach to predict radionuclide release/chemistry in LBE MYrrha

oxygen, cover gas, corrosion products, initial impurities, RN, gas, condensed

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

quantum chemistry - extrapolation MYRRHA conditions - n, p, T, V (x,t) - O

radionuclides - chemical analysis: stable impurities Experimental results

12 Global approach to predict radionuclide release/chemistry in LBE MYrrha THermochemical model: MYTH thermochemical data ~1350 chemical species: Pb, Bi, oxygen, cover gas, corrosion products, initial impurities, RN, gas, condensed species - databases: HSC, FactSage, Barin, NIST, - other scientific literature dissolved species - Literature: analysis Pb-X, Bi-X phase diagrams, CALPHAD, - Po, I, Hg, Cd, Te, Se: evaporation data - O: EMF data polonium molecules - quantum chemistry - extrapolation MYRRHA conditions - n, p, T, V (x,t) - O control - cover gas impurities (O 2,H 2 O) Impurity inventory - neutronics: radionuclides - chemical analysis: stable impurities Experimental results Chemical composition - Evaporation, precipitation/dissolution - speciation MYRRHA safety analysis Source: 12

examples (1) Magnetite formation - Se, Te evaporation Some

agree well with experimental results Precipitation/dissolution

oxygen and dissolved iron Se Evaporation phenomena tellurium

13 examples (1) Magnetite formation - Se, Te evaporation Some thermochemical properties needed to be estimated Model predictions agree well with experimental results Precipitation/dissolution phenomena Magnetite formation in LBE: Reaction between dissolved oxygen and dissolved iron Se Evaporation phenomena tellurium molecules in the cover gas (MYTH) Te More validation needed for model predictions 13

14 MYTH examples (2) Po evaporation OECD recommended Henry constant correlation vs experimental data 14

15 Examples (2) Po evaporation OECD recommended Henry constant correlation vs experimental data Ok above 500 C Predicted release vs time at 400 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), Gonzalez et al., Radiochim. Acta 2014, 102(12),

16 Examples (2) Po evaporation Evaporation below 500 C in inert & reducing atmosphere Observed release vs time at 400 C in Ar long term release x 50 Transient release from surface oxide layer Gonzalez et al., J. Radioanal. Nucl. Chem 2014, 302(1), Gonzalez et al., J. Radioanal. Nucl. Chem 2016, 309(2),

17 Examples (2) Po evaporation Evaporation below 500 C in presence of water vapor Observed release vs time at 400 C in Ar/10%H 2 O % H 2 O x 2500 Surface oxide layer mediated release with increased volatilization due to water? PoO 2. H 2 O(g) dominant in the cover gas? Crucial effect, but lack of data to quantify Gonzalez et al., unpublished results,

18 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 18

19 Examples (3) Iodine evaporation from LBE Experimental results at low temperature >> OECD correlations iodine molecules in the cover gas (MYTH) Insufficient data in literature available for estimation thermochemical properties of dissolved iodine iodine apparent Henry constant Current approach: model fitted to experimental results Validation needed (independent measurement techniques) 19

20 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 20

21 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! 21

22 PART 2 Radionuclides in MEGAPIE 22

The MEGAPIE experiment ADS system A key experiment on the ADS roadmap * flowing LBE + 575

licensing T max =350 C radionuclide behavior particle physics codes chemistry codes

23 The MEGAPIE experiment ADS system A key experiment on the ADS roadmap * flowing LBE MeV protons radionuclide inventory Operated for 123 days at PSI in 2006 MW power design licensing T max =350 C radionuclide behavior particle physics codes chemistry codes experimental analysis Following slides: courtesy of Jörg Neuhausen (PSI) safety analysis safety codes 23

24 Sampling cover gas monitoring - sampling - pressure measurement post-irradiation LBE sampling - LBE bulk - LBE-steel interface - LBE-cover gas interface Major effort! 24

Cover gas monitoring Pressure increase during operation by hydrogen and helium consistent with nuclear code predictions MYTH predictions suggest release as H 2 (g) or H 2

25 Cover gas monitoring Pressure increase during operation by hydrogen and helium consistent with nuclear code predictions MYTH predictions suggest release as H 2 (g) or H 2 O(g) Xe, Kr are released, reasonable agreement with nuclear code predictions Little released mercury detected but quantification difficult Traces of polonium < astatine 25

26 Post-irradiation LBE analysis gamma spectra before separation steel interface cover gas interface bulk 26

27 Post-irradiation LBE analysis: lanthanides 173 Lu, 148 Gd, 146 Pm 173 Lu estimated total activity [GBq] bulk 22 6 LBE/steel interface predicted activity [GBq] % of predicted amount 7 ± ± 18 Sum 203 ± ± 20 inhomogeneous -> interface : bulk ratio = 9 : 1 Resonable agreement with calculated inventory (64%) MYTH predictions in agreement: Ln oxide formation 27

28 Post-irradiation LBE analysis: iodine 129 I ( 36 Cl) 129 I estimated total activity [Bq] predicted activity [Bq] % of predicted amount bulk ± LBE/steel interface (37 ± 20) ± 23 LBE cover gas interface (14 1) x 10-3 Absorber (38 2) x 10-2 (44 2) x 10-4 Sum 3997 ± ± 23 Inhomogeneous: incorporation into surface layer Reasonable agreement with calculated inventory (factor 2) Difficult to assess likely chemical state 28

29 Post-irradiation LBE analysis: polonium 208 Po, 209 Po, 210 Po 208 Po (Bq/g) 209 Po (Bq/g) 210 Po (Bq/g) chem. anal ± ± ± FLUKA MCNPX Homogeneous no enrichment Resonable agreement with calculated inventory MYTH predictions in agreement 29

30 Conclusions 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 30

31 Acknowledgements: The authors thank the Belgian Government for supporting the MYRRHA project. This project has received funding from the Euratom research and training programme under grant agreement No (MYRTE).?

32 Copyright SCK CEN PLEASE NOTE! This presentation contains data, information and formats for dedicated use ONLY and may not be copied, distributed or cited without the explicit permission of the SCK CEN. If this has been obtained, please reference it as a personal communication. By courtesy of SCK CEN. SCK CEN Studiecentrum voor Kernenergie Centre d'etude de l'energie Nucléaire Belgian Nuclear Research Centre Stichting van Openbaar Nut Fondation d'utilité Publique Foundation of Public Utility Registered Office: Avenue Herrmann-Debrouxlaan 40 BE-1160 BRUSSELS Operational Office: Boeretang 200 BE-2400 MOL 32

33 Pb, Bi and O solution properties HLM handbook OECD

34 Solubility data in OECD HLM handbook (2015) 34

35 Limitations Limited set of data, for small number of elements (>< ADS inventory) 35

36 Limitations Does not exploit maximally the large knowledge basis of scientific literature Thermodynamic properties of dissolution 36

37 Limitations Does not exploit maximally the large knowledge basis of scientific literature Thermodynamic properties of dissolution 37

38 Lutetium in MYTH model Lu oxidized and phase separated under normal operating conditions (oxygen controlled LBE) 38

39 What does MYRRHA thermochemical model say about hydrogen? Hydrogen will be converted to water vapor at equilibrium in oxygen controlled LBE: H 2 (g) + O(lbe) = H 2 O(g) But: reaction slow below 400 C -> release as H 2 (g) (MEGAPIE < 350 C) Minor fraction of H could be incorporated in solid spallation product hydroxides. 39

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