Polymers under ionizing radiations: $Evidence\ of\ energy\ transfers\ towards\ radiation-induced\ defects$

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Polymers under ionizing radiations:

Evidence of energy transf ers towards radiation− induced def ects

M. Ferry, A. Ventura, S. Esnouf, E. Balanzat, Y. Ravache

To cite this version:

M. Ferry, A. Ventura, S. Esnouf, E. Balanzat, Y. Ravache. Polymers under ionizing radiations:

Evidence of energy transf ers towards radiation− induced defects. SHIM-ICACS(International

Symposium on Swift Heavy Ion in Matter - International Conference on Atomic Collision in Solids), Jul 2018, Caen, France. �cea-02339290�

Polymers under ionizing radiations:

Evidence of energy transfers towards

radiation-induced defects

M. Ferry1_{, A. Ventura}2_{, S. Esnouf}1

, E. Balanzat2, Y. Ngono-Ravache2

1 _{Den-Service d’Étude du Comportement des Radionucléides (SECR), CEA, Université}

Paris-Saclay, F-91191, Gif-sur-Yvette, France.

Introduction & context

From the industrial needs to

fundamental research

Polymers used in the electronuclear industry

| PAGE 3 1,3% 40,5% 16,3% 0,3% 10,1% 2,4% 18,1% 11% Polyurethane Chlorinated polymers Polyolefins Polyamides Cellulose Fluorinated polymers Ion-exchange resin Other polymers

Polymers in contact with radionuclides in the Intermediate Level Long Lived Waste

(IL-LLW) packages

Main risk associated with storage : gas emission (inflammation, corrosion…)

Estimate gas emission over at least 100 years (reversibility period)

Function of the irradiation conditions

Function of the polymer chemical structure (evolution with time & dose)

A deep geological disposal

ILW-LL package

To understand hydrogen emission mechanisms

Study of polyethylene as model polymer

| Page 5

“Simplest” polymer chemical structure before irradiation

Representative of polymers in IL-LLW packages

Presents the highest hydrogen radiation chemical yield

Whatever the irradiation conditions

Hydrogen is explosive/inflammable at high concentrations

Safety studies focused on H₂/PE couple

Need to understand H₂ emission mechanisms

PE chemical structure

CH₂

Effect of high doses on hydrogen release from PE

| Page 6 0 2 4 6 8 10 12 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Ions irradiation Gamma irradiation G (H 2 ) / G 0 (H 2 ) Dose [MGy]

Hypotheses to explain this decrease

1. Mass loss

2. ↘ hydrogen reservoir in the polymer

3. Energy transfers on the radiation-induced defects

-> Transfers of excitation, charges and radicals

Polyethylene irradiated under conditions

representative of storage

Important ↘ of the hydrogen release yield

when D ↗

Effect of high doses on hydrogen release from PE

| Page 7 0 2 4 6 8 10 12 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Ions irradiation Gamma irradiation G (H 2 ) / G 0 (H 2 ) Dose [MGy]

Hypotheses to explain this decrease

1. Mass loss

2. ↘ hydrogen reservoir in the polymer

3. Energy transfers on the radiation-induced defects

-> Transfers of excitation, charges and radicals

Polyethylene irradiated under conditions

representative of storage

Important ↘ of the hydrogen release yield

when D ↗

Materials containing benzene rings shown in literature to be very stable under

low LET ionizing radiation

Efficient at high LET too

Non conjugated bonds (C=C and C=O) also efficient

0 5 10 15 20 25 0.0 0.2 0.4 0.6 0.8 1.0 Cyclohexene formation in cyclohexane/benzene glasses Trans-vinylene formation in ethylene/styrene copolymers G (C = C ) / G (r e fe re n c e )

Molar aromatic content [%]

Evidences of energy transfers in copolymers

Schoepfle & Fellows, Ind. Eng. Chem. 23 (1931), 1396

Alexander & Charlesby, Proc. R. Soc. London, Ser. A 230 (1955), 136 Basheer & Dole, J. Polym. Sci.: Polym. Phys. Ed. 22 (1984), 1313

n

m

Partridge, J. Chem. Phys. 52 (1970), 2485

Slivinskas & Guillet, J. Polym. Sci.: Polym. Chem. Ed. 12 (1974), 1469 Ferry et al., J. Phys. Chem. B 117 (2013), 14497

| PAGE 9

Rivation, Cambon & Gardette, Nucl. Instrum. Methods Phys. Res., Sect. B 227 (2005), 357

Defects formed during irradiation of polyethylene

Methodology developed

To assess energy transfers

towards radiation-induced

defects

Polyethylene(s) with controlled « defects »

| Page 11

Study of very well controlled polyethylene(s)

Addition of specific groups with controlled:

-Concentrations

-Position of insertion (backbone or on side-chains)

Polyethylenes commercially found

Polyethylenes syntheses

UCCS/CIMAP collaboration ICS/CIMAP collaboration PE perfect chemical structure CH₂ CH₂ n

Organic material and radionuclides (RN)

in the ILLW packages :

a

and

b

/

g

emitters

Emitters simulation

b/g emitters : g irradiations using

60_{Co and} 137_{Cs sources (0.3 to 0.7}

kGy.h-1₎

a emitters :

-Irradiations of simulation, using C and Ar ions (≈ 500 kGy.h-1_{,at GANIL, Caen,}

France or at GSI, Darmstadt, Germany)

Underlying mechanisms to be better

understood

Which parameters allow a decrease in the gas emission?

| PAGE 12

α

β

γ

Irradiations under conditions representative of

those in nuclear waste containers

E_i ≈ 1 MeV (PE) 2,5 MeV.mg-1_.cm2 0,0005 cm 0,002 MeV.mg-1_.cm2 0,37 cm 0,002 MeV.mg-1_.cm2 14 cm

Set-ups depending on the irradiation

conditions

Closed ampoules

-Gamma and High Energy GANIL line

Specific devices

-Medium Energy GANIL line -M-Branch GSI line

Modifications induced by irradiation

followed by

High resolution gas mass spectrometry FTIR

Irradiation and tracked-changes

Energy transfers on ketone (>C=O) bonds

Main defect under oxidative atmosphere

G(H

₂

) ↘ more effective in PE under radio-oxidation than in copolymers with

C=O defects chemically inserted in the backbone

Indication of the contribution of the secondary defects (carboxylic acids…) | Page 15 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0 2 4 6 8 10 12 0.0 0.2 0.4 0.6 0.8 1.0 1.2 G (H 2 ) / G 0 (H 2 )

C=O weight content

(ethylene-carbon monoxide) copolymer irradiated under vaccum*

PE irradiated under oxidative atmosphere

Dose [MGy]

Slivinskas & Guillet, J. Polym. Sci.: Polym. Chem. Ed. 12 (1974), 1469 Lacoste & Carlsson, J. Polym. Sci. Part A: Polym. Chem. 30 (1992), 493

y

O

z _n

Conversion dose <=> [C=O]

Energy transfers on vinylene (C=C) bonds

Main defect under inert atmosphere

PE containing C=C bonds

Saturation effect at high concentrations

Activity per protective bond ↘

-Dilution effect

↘ of G(H

₂

) in both cases

Equivalent up to [C=C] ≈ 0.2 mol.kg-1

in PE, i.e. ≈ 2 MGy

At higher doses, other defects have to be taken into account

| Page 16

Perfect PE irradiated at high dose PE containing C=C bonds

Inert atmosphere at low LET

Ventura et al., J. Phys. Chem. B 120 (2016), 10367 Ventura, PhD thesis (2013)

y

n z

Energy transfers on vinylene (C=C) bonds

Main defect under inert atmosphere: LET

AT high LET using SHI

Trans-vinylenes are the

predominant protective bond up to

[C=C] ≈ 0.6 mol.kg-1 _{in PE, i.e. ≈}

10 MGy

Protection less effective using SHI than

g

-rays

In track recombination before migration

Non-homogeneous

radiation-induced C=C bonds repartition using SHI

| Page 17

Perfect PE irradiated at high dose PE containing C=C bonds

Inert atmosphere using SHI

Ventura et al., J. Phys. Chem. B 120 (2016), 10367 Ventura, PhD thesis (2013)

y

n z

LET effect

| Page 18

Esters in the backbone

Confirmation of LET effect on in-chain ester polymers

↘ of G(H₂) more important per ester unit using low LET irradiation

At high LET, non-scavengeable energy trapped in ion tracks

-Excited and ionized molecules concentration too high to allow migration -In-track recombinations

Scavengeable energy fraction

About ≈ 2/3 for g-rays <=> about ≈ 1/2 for SHI

0 20 40 60 80 100 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Low LET (g-rays) High LET (SHI)

G 0 (H 2 ) / G 0 (H 2 ) HD P E Aliphatic content [wt %] y O O z _n

LET and defects position effects

| Page 19

G(H

₂

) ↘ with C=O and C=C bonds

Energy transfers effective whatever the double bond type

Radiation protection effect more effective at low LET than at high LET

In-track radicals recombination

Chang & LaVerne, J. Polym. Sci.: Part A: Polym. Chem. 38 (2000),1656

0.01 0.1 1 10 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0

Perfect PE (this work) PE with C=O defects (this work) PE with C=C defects (this work) PE from literature* g-rays H He C G (H 2 ) [10 -7 mol.J -1 ] LET [MeV.mg-1.cm2]

LET and defects position effects

| Page 20

G(H

₂

) ↘ with C=O and C=C bonds

Energy transfers effective whatever the double bond type

Radiation protection effect more effective at low LET than at high LET

In-track radicals recombination

Chang & LaVerne, J. Polym. Sci.: Part A: Polym. Chem. 38 (2000),1656

0.01 0.1 1 10 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0

Perfect PE (this work) PE with C=O defects (this work) PE with C=C defects (this work) PE from literature g-rays H He C G (H 2 ) [10 -7 mol.J -1 ] LET [MeV.mg-1.cm2] ?

LET and defects position effects

| Page 21

G(H

₂

) ↘ with C=O and C=C bonds

Energy transfers effective whatever the double bond type

Radiation protection effect more effective at low LET than at high LET

In-track radicals recombination

Differences in PE with defects due to defects position

Case for PE with C=C defects : defects in the backbone with lower G(H₂)

Chang & LaVerne, J. Polym. Sci.: Part A: Polym. Chem. 38 (2000),1656

0.01 0.1 1 10 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0

Perfect PE (this work) PE with C=O defects (this work) PE with C=C defects (this work) PE from literature g-rays H He C G (H 2 ) [10 -7 mol.J -1 ] LET [MeV.mg-1.cm2] ?

Application for the industrial cases

| Page 22 0 2 4 6 8 10 12 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Ions irradiation Gamma irradiation G (H 2 ) / G 0 (H 2 ) Dose [MGy]

Radiation protection effective and due to

energy transfers

Better radiation protection at low LET

than under SHI

Whatever the defect studied

Two phenomena

Ion-track density effect

Non-homogeneous repartition of the defects

PE irradiated under SHI and g-rays under oxidative atmosphere

CH₂ CH₂ CH₂ CH₂ C CH₂ CH₂ CH₂ CH₂ CH₂ CH₂ CH₂ O

Conclusion

In the deep underground repository context

Energy transfers decrease the hydrogen release Positive effects on safety purpose

-Up to now, G₀(H₂) ~ 4.10-7 _mol.J-1 _{used in the nuclear safety cases}

=> Very conservative value

Update possible with detailed explanations

From a fundamental point of view

Efficiency depends on the protective group of the material

-Its nature

-Its concentration

-Its position (backbone or on side-chain)

LET effect

-Energy transfers probably less effective in the track core -Effect of the density and repartition of the protective bonds

| PAGE 26

Gervais & Bouffard, Nucl. Instrum. Methods Phys. Res., Sect. B 88 (1994), 355

Ion beams to simulate α irradiations ?

Why SHI instead of α ?

LET equivalent to radionuclides-emitted α Higher penetration range

Homogeneous irradiation under several

microns (case of PE)

0.01 0.1 1 10 100 10 100 1000 10000 C Ne Ar He TEL (ke V/µ m) Energie (MeV/A) JANNuS SME - GANIL M3 Branch - GSI HE - GANIL α particle 40 µm 160 µm _{870 µm} 7830 µm

Combined effects of position and LET

y O O z n n m O O Esters in the backbone Side-chain ester

In-chain defects more effective than side-chain ester

1/3 energy scavenged by side-chain esters

2/3 energy scavenged by esters in the backbone

=> Same repartition than C-C transfers (2/3) and C-H transfers (1/3) in PE*

=> 1/3 of non scavengeable energy

In-chain defects

Energy scavenged by in-chain effect ↘ when LET ↗ But part of energy migrates out of the ions tracks

-Better ↘ with in-chain defects at high LET than with side-chain protection

*_{Partridge, J. Chem. Phys. 52 (1970), 2485}

0 20 40 60 80 100 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

In-chain defects under g-rays Side-chain defects under g-rays In-chain defects using SHI

G 0 (H 2 ) / G 0 (H 2 ) HD P E Aliphatic content [wt %]