# First measurements of chlorine 36 ($^{36}$Cl) wet deposition fluxes in the vicinity of Orano La Hague nuclear reprocessing plant in France

Deo-Gratias Sourabie, Didier Hebert, Lucilla Benedetti, Valery Guillou, Elsa Vitorge, Philippe Laguionie, Denis Maro

<figure><img src="image_1.png" /></figure>

## To cite this version:

Deo-Gratias Sourabie, Didier Hebert, Lucilla Benedetti, Valery Guillou, Elsa Vitorge, et al. First measurements of chlorine 36 ($^{36}$Cl) wet deposition fluxes in the vicinity of Orano La Hague nuclear reprocessing plant in France. Journal of Environmental Radioactivity, 2024, 278, pp.107470. 10.1016/j.jenvrad.2024.107470. hal-04608156

HAL Id: hal-04608156

https://hal.science/hal-04608156

Submitted on 12 Jun 2024

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

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<figure><img src="image_2.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
# First measurements of chlorine 36 ($^{36}$Cl) wet deposition fluxes in the vicinity of Orano La Hague nuclear reprocessing plant in France

Deo-Gratias Sourabie, Didier Hebert, Lucilla Benedetti, Valery Guillou, Elsa Vitorge, Philippe Laguionie, Denis Maro

<figure><img src="image_1.png" /></figure>

## To cite this version:

Deo-Gratias Sourabie, Didier Hebert, Lucilla Benedetti, Valery Guillou, Elsa Vitorge, et al., First measurements of chlorine 36 ($^{36}$Cl) wet deposition fluxes in the vicinity of Orano La Hague nuclear reprocessing plant in France. Journal of Environmental Radioactivity, 2024, 278, pp.107470. 10.1016/j.jenvrad.2024.107470. hal-04608156

HAL Id: hal-04608156

https://hal.science/hal-04608156v1

Submitted on 12 Jun 2024

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

<figure><img src="image_2.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
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# First measurements of chlorine 36 (³⁶Cl) wet deposition fluxes in the vicinity of Orano La Hague nuclear reprocessing plant in France.

Deo-Gratias Sourabie(1,2), Didier Hebert1*, Lucilla Benedetti², Valery Guillou², Elsa Vitorge³, Philippe Laguionie¹, Denis Maro¹

¹Institute for Radioprotection and Nuclear Safety (IRSN), PSE-ENV/STAAR/LERTA, Cherbourg-Octeville, 50130, France

deo-gratias.sourabie-capgemini@irsn.fr, didier.hebert@irsn.fr, philippe.laguionie@irsn.fr, denis.maro@irsn.fr

²Univ. Aix-Marseille, CNRS, IRD, INRAE, Coll. France, UM 34 CEREGE, Aix-en-Provence, 13545, France

³EDF – DPNT – DIPDE - DEE – Environment department, Villeurbanne, 69100, France
elsa.vitorge@edf.fr

## * Corresponding author:

E-mail address: didier.hebert@irsn.fr

Institute for Radiation protection and Nuclear Safety (IRSN)

Experimental Laboratory for Research and Expertise on Radionuclide Transfers in the Atmosphere

Rue Max Pol Fouchet

BP10- 50130 Cherbourg-Octeville

Tel: +33 (0)2 33 01 41 00

## Acknowledgements:

This work was supported by the French institute for radiation protection and nuclear safety (IRSN) and Electricite de France (EDF) under the umbrella of a research and development cooperation agreement on the safety of civil nuclear installations and their impact on health and the environment (IRSN LS21602 internal referencing). We would like to thank the LERTA team and Capgemini Engineering for their support in this work.
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# First measurements of chlorine 36 ($^{36}$Cl) wet deposition fluxes in the vicinity of Orano La Hague nuclear reprocessing plant in France.

Deo-Gratias Sourabie$^{(1,2)}$, Didier Hebert$^{1*}$, Lucilla Benedetti$^2$, Valery Guillou$^2$, Elsa Vitorge$^3$, Philippe Laguionie$^1$, Denis Maro$^1$

$^1$Institute for Radioprotection and Nuclear Safety (IRSN), PSE-ENV/STAAR/LERTA, Cherbourg-Octeville, 50130, France

deo-gratias.sourabie-capgemini@irsn.fr, didier.hebert@irsn.fr, philippe.laguionie@irsn.fr, denis.maro@irsn.fr

$^2$Univ. Aix-Marseille, CNRS, IRD, INRAE, Coll. France, UM 34 CEREGE, Aix-en-Provence, 13545, France

$^3$EDF – DPNT – DIPDE - DEE – Environment department, Villeurbanne, 69100, France
elsa.vitorge@edf.fr

## * Corresponding author:

E-mail address: didier.hebert@irsn.fr

Institute for Radiation protection and Nuclear Safety (IRSN)

Experimental Laboratory for Research and Expertise on Radionuclide Transfers in the Atmosphere

Rue Max Pol Fouchet

BP10-50130 Cherbourg-Octeville

Tel: +33 (0)2 33 01 41 00

## Acknowledgements:

This work was supported by the French institute for radiation protection and nuclear safety (IRSN) and Electricite de France (EDF) under the umbrella of a research and development cooperation agreement on the safety of civil nuclear installations and their impact on health and the environment (IRSN LS21602 internal referencing). We would like to thank the LERTA team and Capgemini Engineering for their support in this work.

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<figure><img src="image_3.png" /></figure>

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42 Summary:

43 Chlorine 36 ($^{36}$Cl) is a radionuclide of natural and anthropogenic origin, mainly used as a tracer in 44 geochemical studies. Owing to analytical constraints and its low environmental levels, knowledge of 45 $^{36}$Cl behavior in the environment is still very limited. In this study, we use environmental 46 measurements to report for the first time the wet deposition fluxes of $^{36}$Cl downwind an 47 anthropogenic source, the Orano nuclear reprocessing plant, which chronically emits $^{36}$Cl into the 48 environment. Measurements of $^{36}$Cl in rainwater samples at our study site were 1 to 2 orders of 49 magnitude above the environmental background. The isotope ratios $^{36}$Cl/Cl of the samples and the 50 $^{36}$Cl content in the rainwater averaged $2.3 \times 10^{-12}$ at.at$^{-1}$ and $1.7 \times 10^{8}$ at.l$^{-1}$ respectively. A decrease in 51 these levels was observed 20 km away from the study site, outside the plant's gas plume, indicating 52 that the marking of $^{36}$Cl on the study site is related to the plant discharges. Over the sampling period, 53 wet deposition fluxes at the study site averaged $3.4 \times 10^{3}$ at.m$^{-2}$s$^{-1}$, with significant values measured 54 when precipitations scavenge the plant's gas plume down onto our study site. Analysis of these 55 fluxes also revealed the presence of a significant rainout phenomenon in the study area. These 56 results provide new data on the wet deposition flux of $^{36}$Cl and will thus enable better assessment of 57 impact studies in a context of decommissioning or accidents involving nuclear power plants. 58

58

59 Key words:

60 Chlorine 36; Wet deposits; Nuclear fuel recycling; Dismantling nuclear power plants; Accelerator 61 Mass Spectrometry (AMS); Transfer in the environment.

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63
<figure><img src="image_3.png" /></figure>

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42 Summary:

43 Chlorine 36 ($^{36}$Cl) is a radionuclide of natural and anthropogenic origin, mainly used as a tracer in 44 geochemical studies. Owing to analytical constraints and its low environmental levels, knowledge of 45 $^{36}$Cl behavior in the environment is still very limited. In this study, we use environmental 46 measurements to report for the first time the wet deposition fluxes of $^{36}$Cl downwind an 47 anthropogenic source, the Orano nuclear reprocessing plant, which chronically emits $^{36}$Cl into the 48 environment. Measurements of $^{36}$Cl in rainwater samples at our study site were 1 to 2 orders of 49 magnitude above the environmental background. The isotope ratios $^{36}$Cl/Cl of the samples and the 50 $^{36}$Cl content in the rainwater averaged $2.3 \times 10^{-12}$ at.at$^{-1}$ and $1.7 \times 10^{8}$ at.l$^{-1}$ respectively. A decrease in 51 these levels was observed 20 km away from the study site, outside the plant's gas plume, indicating 52 that the marking of $^{36}$Cl on the study site is related to the plant discharges. Over the sampling period, 53 wet deposition fluxes at the study site averaged $3.4 \times 10^{3}$ at.m$^{-2}$s$^{-1}$, with significant values measured 54 when precipitations scavenge the plant's gas plume down onto our study site. Analysis of these 55 fluxes also revealed the presence of a significant rainout phenomenon in the study area. These 56 results provide new data on the wet deposition flux of $^{36}$Cl and will thus enable better assessment of 57 impact studies in a context of decommissioning or accidents involving nuclear power plants. 58

58

59 Key words:

60 Chlorine 36; Wet deposits; Nuclear fuel recycling; Dismantling nuclear power plants; Accelerator 61 Mass Spectrometry (AMS); Transfer in the environment.

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63
64 **1. Introduction**

With natural and anthropogenic origin, chlorine 36 ($^{36}$Cl) is a radioactive isotope (or radionuclide) of chlorine (Cl) with a lifetime of around 3.01 ± 0.02 x10$^5$ years (Phillips, 2000). It is a pure beta emitter ($\beta^-$), with low energy ($E_{max}$ = 708.6 keV) and low radiotoxicity (Bastviken et al., 2013). $^{36}$Cl is a cosmogenic radionuclide, meaning that it is naturally produced during nuclear interactions between primary and secondary cosmic ray particles with target element constituents of the terrestrial environment (Bastviken et al., 2013; Huggle et al., 1996; Stone et al., 1996; White and Broadley, 2001). $^{36}$Cl was massively introduced into the environment by neutron activation of $^{35}$Cl present in the sea as a result of nuclear testing in the Pacific. The high density of the energy released by these tests triggered major upward airflows, which carried some of the $^{36}$Cl produced into the atmosphere. This massive introduction of $^{36}$Cl is readily observable in the $^{36}$Cl measurements of ice cores, and the amount of $^{36}$Cl generated as a result of these tests is estimated at 1,000 years of natural production (Green et al., 2004; Heikkilä et al., 2009). However, it has recently been shown that the Cl fluxes induced by these tests have returned to natural levels in Europe (Johnston and McDermott, 2008).

Anthropogenic $^{36}$Cl is currently produced in nuclear reactor cores by the activation of stable Cl present as impurities in the fuel and in the plant's construction materials. $^{36}$Cl is therefore released into the atmosphere in the form of gaseous effluents during fuel reprocessing operations. $^{36}$Cl is also likely to be released into the atmosphere during the decommissioning of nuclear facilities (Le Dizès and Gonze, 2019; Llopart-Babot et al., 2022; Petrov and Pokhitonov, 2020; Sheppard et al., 1996). In abnormal or incidental situations (filters are assumed to be ineffective), $^{36}$Cl can also be released into the atmosphere in particulate form. Even when emitted in gaseous form, like other radionuclides, $^{36}$Cl can form ultrafine particles by nucleation or condense on atmospheric aerosols present in the environment (Budyka, 2000). Finally, $^{36}$Cl can be emitted into the atmosphere following a nuclear accident [Chernobyl example (Lazarev, 2003; Scheffel et al., 1999) and Fukushima (Ohta et al., 2023; Sasa et al., 2022)] or, on a smaller scale, as a result of a biomass combustion contaminated by nuclear industry emissions (White and Broadley, 2001).

Whether produced naturally or anthropogenically, $^{36}$Cl is rapidly eliminated from the atmosphere within a few weeks by precipitation or dry deposition (Phillips et al., 1988; Scheffel et al., 1999; Sourabie et al., 2023). Studies on $^{36}$Cl have been made possible mainly by advances in accelerator mass spectrometry, enabling environmental concentrations to be measured and the use of $^{36}$Cl for groundwater tracing (Braucher et al., 2018; Finkel et al., 2013; Merchel et al., 2011). Many studies have been carried out on wet deposits of $^{36}$Cl providing $^{36}$Cl wet deposition flux measurements around the globe (Johnston and McDermott, 2008; Pupier et al., 2016; Santos et al., 2004; Scheffel et al., 1999; Tosaki et al., 2012). However, these studies mainly focused on naturally produced $^{36}$Cl and didn't discriminate wet depositions from dry ones. In fact, compared to wet deposition, dry deposition of $^{36}$Cl is generally considered as non-significant but a recent study showed that dry deposition can contribute significantly to total $^{36}$Cl deposition (Sourabie et al., 2023). In addition, since chlorine is a micronutrient necessary for life, wet deposition can therefore be considered as the deposition of $^{36}$Cl in a bio assimilable form by living organisms.

The aim of this study is therefore to determine the only-wet deposition fluxes of $^{36}$Cl in fields close to the Orano La Hague plant, a chronic emitter of small quantities of $^{36}$Cl into the environment (GRNC, 1999). In fact, since Milton et al. (1994), no studies have been carried out on wet deposition of $^{36}$Cl in the vicinity of a chronic anthropogenic source. The isotopic ratio $^{36}$Cl/Cl in the atmosphere (gaseous and particulate fraction) 2 km away from the plant is 1 to 2 orders of magnitude higher than the natural background, suggesting that wet deposition fluxes of $^{36}$Cl in this area are greater than those generally reported in the literature (Sourabie et al., 2023). Following the study of $^{36}$Cl dry deposition
64 **1. Introduction**

65 With natural and anthropogenic origin, chlorine 36 ($^{36}$Cl) is a radioactive isotope (or radionuclide) of 66 chlorine (Cl) with a lifetime of around 3.01 ± 0.02 x10$^5$ years (Phillips, 2000). It is a pure beta emitter 67 ($\beta^-$), with low energy ($E_{max}$ = 708.6 keV) and low radiotoxicity (Bastviken et al., 2013). $^{36}$Cl is a 68 cosmogenic radionuclide, meaning that it is naturally produced during nuclear interactions between 69 primary and secondary cosmic ray particles with target element constituents of the terrestrial 70 environment (Bastviken et al., 2013; Huggle et al., 1996; Stone et al., 1996; White and Broadley, 71 2001). $^{36}$Cl was massively introduced into the environment by neutron activation of $^{35}$Cl present in 72 the sea as a result of nuclear testing in the Pacific. The high density of the energy released by these 73 tests triggered major upward airflows, which carried some of the $^{36}$Cl produced into the atmosphere. 74 This massive introduction of $^{36}$Cl is readily observable in the $^{36}$Cl measurements of ice cores, and the 75 amount of $^{36}$Cl generated as a result of these tests is estimated at 1,000 years of natural production 76 (Green et al., 2004; Heikkilä et al., 2009). However, it has recently been shown that the Cl fluxes 77 induced by these tests have returned to natural levels in Europe (Johnston and McDermott, 2008).

78 Anthropogenic $^{36}$Cl is currently produced in nuclear reactor cores by the activation of stable Cl 79 present as impurities in the fuel and in the plant's construction materials. $^{36}$Cl is therefore released 80 into the atmosphere in the form of gaseous effluents during fuel reprocessing operations. $^{36}$Cl is also 81 likely to be released into the atmosphere during the decommissioning of nuclear facilities (Le Dizès 82 and Gonze, 2019; Llopart-Babot et al., 2022; Petrov and Pokhitonov, 2020; Sheppard et al., 1996). 83 In abnormal or incidental situations (filters are assumed to be ineffective), $^{36}$Cl can also be released 84 into the atmosphere in particulate form. Even when emitted in gaseous form, like other 85 radionuclides, $^{36}$Cl can form ultrafine particles by nucleation or condense on atmospheric aerosols 86 present in the environment (Budyka, 2000). Finally, $^{36}$Cl can be emitted into the atmosphere 87 following a nuclear accident [Chernobyl example (Lazarev, 2003; Scheffel et al., 1999) and 88 Fukushima (Ohta et al., 2023; Sasa et al., 2022)] or, on a smaller scale, as a result of a biomass 89 combustion contaminated by nuclear industry emissions (White and Broadley, 2001).

90 Whether produced naturally or anthropogenically, $^{36}$Cl is rapidly eliminated from the atmosphere 91 within a few weeks by precipitation or dry deposition (Phillips et al., 1988; Scheffel et al., 1999; 92 Sourabie et al., 2023). Studies on $^{36}$Cl have been made possible mainly by advances in accelerator 93 mass spectrometry, enabling environmental concentrations to be measured and the use of $^{36}$Cl for 94 groundwater tracing (Braucher et al., 2018; Finkel et al., 2013; Merchel et al., 2011). Many studies 95 have been carried out on wet deposits of $^{36}$Cl providing $^{36}$Cl wet deposition flux measurements 96 around the globe (Johnston and McDermott, 2008; Pupier et al., 2016; Santos et al., 2004; Scheffel 97 et al., 1999; Tosaki et al., 2012). However, these studies mainly focused on naturally produced $^{36}$Cl 98 and didn't discriminate wet depositions from dry ones. In fact, compared to wet deposition, dry 99 deposition of $^{36}$Cl is generally considered as non-significant but a recent study showed that dry 100 deposition can contribute significantly to total $^{36}$Cl deposition (Sourabie et al., 2023). In addition, 101 since chlorine is a micronutrient necessary for life, wet deposition can therefore be considered as the 102 deposition of $^{36}$Cl in a bio assimilable form by living organisms.

103 The aim of this study is therefore to determine the only-wet deposition fluxes of $^{36}$Cl in fields close to 104 the Orano La Hague plant, a chronic emitter of small quantities of $^{36}$Cl into environment (GRNC, 105 1999). In fact, since Milton et al. (1994), no studies have been carried out on wet deposition of $^{36}$Cl in 106 the vicinity of a chronic anthropogenic source. The isotopic ratio $^{36}$Cl/Cl in the atmosphere (gaseous 107 and particulate fraction) 2 km away from the plant is 1 to 2 orders of magnitude higher than the 108 natural background, suggesting that wet deposition fluxes of $^{36}$Cl in this area are greater than those 109 generally reported in the literature (Sourabie et al., 2023). Following the study of $^{36}$Cl dry deposition
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flux on this site, the determination of ³⁶Cl wet deposition flux will therefore help to improve the
assessment of impact studies in a context of nuclear power plant decommissioning or accidents.

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## 2. Materials and methods

### 2.1. Study site and sampling

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Rainwater was sampled at the IRSN La Hague technical platform (IRSN Platform; 49°41'42.1"N, 1°52'24.2"W) located 2 km north of Orano La Hague plant (49°40'41.5"N, 1°52'30.7"W) in France and 2 km south of English Channel (Figure 1). ³⁶Cl is emitted concomitantly with krypton 85 (⁸⁵Kr), which serves as a tracer for the plant's atmospheric plume (Connan et al., 2014). As such, ⁸⁵Kr is measured continuously at the study site using a Berthold LB111 counter. Annual rainfall at the study site has averaged 643 mm over the past 10 years, with heavier precipitation in autumn. Rainwater was collected by an Eigenbrodt UNS130/E open-air rain collector equipped with an Eigenbrodt RS85 sensor, which only opens the water collector when precipitation was detected. This device ensures that all ³⁶Cl measured in rainwater mainly comes from wet deposits. A Watchdog 2000 series weather station was used to record rainfall at a frequency of 30 minutes throughout the sampling period. Samples were taken over an average period of two weeks, from July 16, 2021 to July 26, 2022; with a break in sampling from December 09, 2021 to February 22, 2022 due to a shutdown of the sampler.

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<figure><img src="image_4.png" /></figure>

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<caption>**Fig. 1.** Wind direction frequencies from May 17 to June 1, 2022 measured at the IRSN Platform.</caption>

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### 2.2. Sample processing and chlorine 36 measurement
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flux on this site, the determination of ³⁶Cl wet deposition flux will therefore help to improve the
assessment of impact studies in a context of nuclear power plant decommissioning or accidents.

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## 2. Materials and methods

### 2.1. Study site and sampling

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Rainwater was sampled at the IRSN La Hague technical platform (IRSN Platform; 49°41'42.1"N, 1°52'24.2"W) located 2 km north of Orano La Hague plant (49°40'41.5"N, 1°52'30.7"W) in France and 2 km south of English Channel (Figure 1). ³⁶Cl is emitted concomitantly with krypton 85 (⁸⁵Kr), which serves as a tracer for the plant's atmospheric plume (Connan et al., 2014). As such, ⁸⁵Kr is measured continuously at the study site using a Berthold LB111 counter. Annual rainfall at the study site has averaged 643 mm over the past 10 years, with heavier precipitation in autumn. Rainwater was collected by an Eigenbrodt UNS130/E open-air rain collector equipped with an Eigenbrodt RS85 sensor, which only opens the water collector when precipitation was detected. This device ensures that all ³⁶Cl measured in rainwater mainly comes from wet deposits. A Watchdog 2000 series weather station was used to record rainfall at a frequency of 30 minutes throughout the sampling period. Samples were taken over an average period of two weeks, from July 16, 2021 to July 26, 2022; with a break in sampling from December 09, 2021 to February 22, 2022 due to a shutdown of the sampler.

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<figure><img src="image_4.png" /></figure>

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<caption>Fig. 1. Wind direction frequencies from May 17 to June 1, 2022 measured at the IRSN Platform.</caption>

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### 2.2. Sample processing and chlorine 36 measurement
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Following sampling, the filtered samples underwent a series of chemical preparations to make them compatible with ³⁶Cl measurement by accelerator mass spectrometry and eliminate isobaric interferents such as sulfur 36 (Nakata and Hasegawa, 2011). Dissolved chlorine in rainwater is first precipitated to silver chloride by adding 1 mL of silver nitrate AgNO₃ 10% (analytical grade Emsure ACS, Merck) and 20 mL of nitric acid HNO₃ 70% (CMOS J.T.Baker, VWR). The precipitate is recovered by filtration through a polyethersulfone filter (Millipore Express Plus, 0.45µm, 47 mm, Merk) and transferred to a tube. 10 mL of ammonia NH₄OH 20% (Emplura, Merck) is used to dissolve the precipitate retained on the filter and 2 mL of saturated barium nitrate Ba(NO₃)₂ (analytical grade ACS, Alfa Aesar) is added to the sample tube. The addition of barium causes sulfur to precipitate out as barium sulfate (BaSO₃). The sample is filtered after 24 hours, then the operation is repeated twice with 1 mL of barium nitrate. After the third filtration of barium sulfate, 8 mL of nitric acid are added to the tube to re-precipitate dissolved chlorides. The samples are then cooled, shaken and centrifuged. The acid is removed, and the precipitate washed 3 times with ultrapure water (Merck Milli-Q, 18.2 MΩcm at 23°C) before being oven-dried at 40°C for 72h. After drying, the silver chloride precipitates were sent for measurement of ³⁶Cl and Cl. This measurement is performed by accelerator mass spectrometry (AMS) on the national instrument ASTER (Accelerator for earth sciences, environment and risks) (Finkel et al., 2013). The ratios ³⁶Cl/³⁵Cl and ³⁵Cl/³⁷Cl were obtained by normalization against the internal standard SM-CL-12 with an assigned ³⁶Cl/³⁵Cl value of (1.428 ± 0.021) x10⁻¹² (Merchel et al., 2011) and assuming a natural ³⁵Cl/³⁷Cl ratio of 3.127. The ³⁶Cl and Cl concentration of each sample is then calculated from the ratios ³⁶Cl/³⁵Cl, ³⁵Cl/³⁷Cl and the mass of doping solution (Na³⁵Cl; ³⁵Cl = 99.66%, Chemlab) added to the sample. These calculations are presented in detail in Bouchez et al. (2015).

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### 3. Results and discussion

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#### 3.1. Quality control

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To ensure the absence of contamination during sample preparation, reagent blanks were made. The ratio ³⁶Cl/³⁵Cl of our blanks (n = 3) averaged 1.6x10⁻¹⁵ which is close to the ratio ³⁶Cl/³⁵Cl of blanks measured by AMS at ASTER (1.3x10⁻¹⁵; Braucher et al., 2018). This allows us to ensure the absence of ³⁶Cl contamination during the processing of our samples.

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#### 3.2. Isotope ratios ³⁶Cl/Cl and ³⁶Cl content in rainwater

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**Table 1** shows the results of ³⁶Cl and Cl measurements on all our samples. The uncertainty corresponds to the instrumental uncertainty, comprising the measurement uncertainty, the uncertainty of the standard, the uncertainty of the mean of the calibration measurements and the systematic error of the machine. No sampling was carried out from August 24, 2021 to September 7, 2021 and from April 20, 2022 to May 3, 2022 due to low rainfall.

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Following sampling, the filtered samples underwent a series of chemical preparations to make them compatible with ³⁶Cl measurement by accelerator mass spectrometry and eliminate isobaric interferents such as sulfur 36 (Nakata and Hasegawa, 2011). Dissolved chlorine in rainwater is first precipitated to silver chloride by adding 1 mL of silver nitrate AgNO₃ 10% (analytical grade Emsure ACS, Merck) and 20 mL of nitric acid HNO₃ 70% (CMOS J.T.Baker, VWR). The precipitate is recovered by filtration through a polyethersulfone filter (Millipore Express Plus, 0.45µm, 47 mm, Merk) and transferred to a tube. 10 mL of ammonia NH₄OH 20% (Emplura, Merck) is used to dissolve the precipitate retained on the filter and 2 mL of saturated barium nitrate Ba(NO₃)₂ (analytical grade ACS, Alfa Aesar) is added to the sample tube. The addition of barium causes sulfur to precipitate out as barium sulfate (BaSO₃). The sample is filtered after 24 hours, then the operation is repeated twice with 1 mL of barium nitrate. After the third filtration of barium sulfate, 8 mL of nitric acid are added to the tube to re-precipitate dissolved chlorides. The samples are then cooled, shaken and centrifuged. The acid is removed, and the precipitate washed 3 times with ultrapure water (Merck Milli-Q, 18.2 MΩcm at 23°C) before being oven-dried at 40°C for 72h. After drying, the silver chloride precipitates were sent for measurement of ³⁶Cl and Cl. This measurement is performed by accelerator mass spectrometry (AMS) on the national instrument ASTER (Accelerator for earth sciences, environment and risks) (Finkel et al., 2013). The ratios ³⁶Cl/³⁵Cl and ³⁵Cl/³⁷Cl were obtained by normalization against the internal standard SM-CL-12 with an assigned ³⁶Cl/³⁵Cl value of (1.428 ± 0.021) x10⁻¹² (Merchel et al., 2011) and assuming a natural ³⁵Cl/³⁷Cl ratio of 3.127. The ³⁶Cl and Cl concentration of each sample is then calculated from the ratios ³⁶Cl/³⁵Cl, ³⁵Cl/³⁷Cl and the mass of doping solution (Na³⁵Cl; ³⁵Cl = 99.66%, Chemlab) added to the sample. These calculations are presented in detail in Bouchez et al. (2015).

### 3. Results and discussion

#### 3.1. Quality control

To ensure the absence of contamination during sample preparation, reagent blanks were made. The ratio ³⁶Cl/³⁵Cl of our blanks (n = 3) averaged 1.6x10⁻¹⁵ which is close to the ratio ³⁶Cl/³⁵Cl of blanks measured by AMS at ASTER (1.3x10⁻¹⁵; Braucher et al., 2018). This allows us to ensure the absence of ³⁶Cl contamination during the processing of our samples.

#### 3.2. Isotope ratios ³⁶Cl/Cl and ³⁶Cl content in rainwater

**Table 1** shows the results of ³⁶Cl and Cl measurements on all our samples. The uncertainty corresponds to the instrumental uncertainty, comprising the measurement uncertainty, the uncertainty of the standard, the uncertainty of the mean of the calibration measurements and the systematic error of the machine. No sampling was carried out from August 24, 2021 to September 7, 2021 and from April 20, 2022 to May 3, 2022 due to low rainfall.
<table><caption>**Table 1:** $^{36}$Cl measurements in rainwater samples from the study site; uncertainties is indicated by "±" in the table.</caption><thead><tr><th rowspan="2">Campaign no.</th><th rowspan="2">Start date</th><th rowspan="2">End date</th><th colspan="2">Rainfall</th><th rowspan="2">$^{36}\text{Cl}/\text{Cl}$</th><th rowspan="2">$^{36}\text{Cl}$</th></tr><tr><th>mm</th><th>mg.l<sup>-1</sup></th></tr></thead><tbody><tr><td>C1</td><td>16/07/2021</td><td>28/07/2021</td><td>56,1</td><td>3,0</td><td>2,4 ± 0,1</td><td>12,3 ± 1,7</td></tr><tr><td>C2</td><td>28/07/2021</td><td>09/08/2021</td><td>12,9</td><td>7,9</td><td>2,4 ± 0,1</td><td>32,3 ± 4,5</td></tr><tr><td>C3</td><td>09/08/2021</td><td>24/08/2021</td><td>7,5</td><td>4,6</td><td>1,1 ± 0,04</td><td>8,9 ± 1,3</td></tr><tr><td>C4</td><td>07/09/2021</td><td>21/09/2021</td><td>19,5</td><td>1,2</td><td>3,2 ± 0,1</td><td>6,8 ± 0,7</td></tr><tr><td>C5</td><td>21/09/2021</td><td>06/10/2021</td><td>74,6</td><td>11,0</td><td>0,7 ± 0,03</td><td>14,5 ± 2,9</td></tr><tr><td>C6</td><td>06/10/2021</td><td>19/10/2021</td><td>6,8</td><td>5,9</td><td>3,9 ± 0,1</td><td>39,2 ± 5,3</td></tr><tr><td>C7</td><td>19/10/2021</td><td>05/11/2021</td><td>80,2</td><td>13,2</td><td>0,3 ± 0,01</td><td>8,6 ± 0,9</td></tr><tr><td>C8</td><td>05/11/2021</td><td>23/11/2021</td><td>16,3</td><td>17,0</td><td>0,2 ± 0,01</td><td>6,2 ± 2,5</td></tr><tr><td>C9</td><td>23/11/2021</td><td>09/12/2021</td><td>86,2</td><td>13,1</td><td>0,5 ± 0,02</td><td>11,3 ± 1,2</td></tr><tr><td>C10</td><td>22/02/2022</td><td>08/03/2022</td><td>37,5</td><td>8,0</td><td>0,8 ± 0,04</td><td>11,6 ± 1,2</td></tr><tr><td>C11</td><td>08/03/2022</td><td>18/03/2022</td><td>13,9</td><td>3,1</td><td>5,4 ± 0,2</td><td>29,3 ± 3,2</td></tr><tr><td>C12</td><td>18/03/2022</td><td>05/04/2022</td><td>13,5</td><td>11,1</td><td>1,9 ± 0,1</td><td>36,8 ± 14,8</td></tr><tr><td>C13</td><td>05/04/2022</td><td>20/04/2022</td><td>24,3</td><td>7,6</td><td>0,7 ± 0,04</td><td>10,1 ± 1,1</td></tr><tr><td>C14</td><td>03/05/2022</td><td>17/05/2022</td><td>8,9</td><td>3,2</td><td>2,7 ± 0,1</td><td>15,3 ± 1,6</td></tr><tr><td>C15</td><td>17/05/2022</td><td>01/06/2022</td><td>21,5</td><td>1,3</td><td>3,8 ± 0,1</td><td>8,3 ± 0,9</td></tr><tr><td>C16</td><td>01/06/2022</td><td>15/06/2022</td><td>40,2</td><td>3,3</td><td>4,3 ± 0,2</td><td>24,4 ± 2,7</td></tr><tr><td>C17</td><td>15/06/2022</td><td>29/06/2022</td><td>17,8</td><td>6,4</td><td>2,4 ± 0,1</td><td>26,9 ± 2,9</td></tr><tr><td>C18</td><td>29/06/2022</td><td>13/07/2022</td><td>3,0</td><td>3,7</td><td>2,1 ± 0,1</td><td>13,4 ± 1,4</td></tr><tr><td>C19</td><td>13/07/2022</td><td>26/07/2022</td><td>6,7</td><td>1,8</td><td>5,3 ± 0,2</td><td>16,6 ± 2,3</td></tr></tbody></table>

Isotopic ratios $^{36}$Cl/Cl in rainwater samples ranged from 2.1x10$^{-13}$ to 5.4x10$^{-12}$ with an average of 2.3x10$^{-12}$ (median = 2.4x10$^{-12}$). The $^{36}$Cl/Cl isotopic ratio in rainwater is strongly influenced by the atmospheric Cl content of the aera. Since $^{36}$Cl is mainly produced by cosmic rays, in inland areas the stable Cl content is so low that the $^{36}$Cl/Cl ratio can reach 10$^{-13}$ whereas it is 10$^{-14}$ at the seaside (Johnston and McDermott, 2008). Despite the proximity of the sea 2 km from the study site, the $^{36}$Cl/Cl isotope ratios measured in our samples are 1 to 2 orders of magnitude higher than those of the natural environmental background (10$^{-13}$ - 10$^{-14}$), which is generally measured on sites far from anthropogenic sources of $^{36}$Cl (Table 2). However, the $^{36}$Cl/Cl ratio in our rainwater samples is of the same order of magnitude as those measured by Milton et al., (1994) neaby an anthropogenic source showing then the influence of Orano's plant discharges on the ratios measured. In fact, Milton et al., (1994) measured the highest $^{36}$Cl/Cl ratios reported in the literature at various distances from the Chalk River Nuclear Laboratory (CRL), with levels ranging from 1.6 to 30.8x10$^{-12}$. It is also quite interesting to notice that the $^{36}$Cl/Cl ratio in our rainwater samples is of the same order of magnitude as the ratio of 1.4x10$^{-12}$ measured by Sasa et al., (2022) in a monthly rainwater sample from Tsukuba during the month of the Fukushima nuclear power plant accident. Despite the distance of around 180 km from the accident site, this ratio was two orders of magnitude higher than those measured in monthly rainwater samples before and after this event (Sasa et al., 2022).
<table><caption>**Table 1:** $^{36}$Cl measurements in rainwater samples from the study site; uncertainties is indicated by "±" in the table.</caption><thead><tr><th rowspan="2">Campaign no.</th><th rowspan="2">Start date</th><th rowspan="2">End date</th><th colspan="2">Rainfall</th><th rowspan="2">$^{36}\text{Cl}/\text{Cl}$</th><th rowspan="2">$^{36}\text{Cl}$</th></tr><tr><th>mm</th><th>mg.l<sup>-1</sup></th></tr></thead><tbody><tr><td>C1</td><td>16/07/2021</td><td>28/07/2021</td><td>56,1</td><td>3,0</td><td>2,4 ± 0,1</td><td>12,3 ± 1,7</td></tr><tr><td>C2</td><td>28/07/2021</td><td>09/08/2021</td><td>12,9</td><td>7,9</td><td>2,4 ± 0,1</td><td>32,3 ± 4,5</td></tr><tr><td>C3</td><td>09/08/2021</td><td>24/08/2021</td><td>7,5</td><td>4,6</td><td>1,1 ± 0,04</td><td>8,9 ± 1,3</td></tr><tr><td>C4</td><td>07/09/2021</td><td>21/09/2021</td><td>19,5</td><td>1,2</td><td>3,2 ± 0,1</td><td>6,8 ± 0,7</td></tr><tr><td>C5</td><td>21/09/2021</td><td>06/10/2021</td><td>74,6</td><td>11,0</td><td>0,7 ± 0,03</td><td>14,5 ± 2,9</td></tr><tr><td>C6</td><td>06/10/2021</td><td>19/10/2021</td><td>6,8</td><td>5,9</td><td>3,9 ± 0,1</td><td>39,2 ± 5,3</td></tr><tr><td>C7</td><td>19/10/2021</td><td>05/11/2021</td><td>80,2</td><td>13,2</td><td>0,3 ± 0,01</td><td>8,6 ± 0,9</td></tr><tr><td>C8</td><td>05/11/2021</td><td>23/11/2021</td><td>16,3</td><td>17,0</td><td>0,2 ± 0,01</td><td>6,2 ± 2,5</td></tr><tr><td>C9</td><td>23/11/2021</td><td>09/12/2021</td><td>86,2</td><td>13,1</td><td>0,5 ± 0,02</td><td>11,3 ± 1,2</td></tr><tr><td>C10</td><td>22/02/2022</td><td>08/03/2022</td><td>37,5</td><td>8,0</td><td>0,8 ± 0,04</td><td>11,6 ± 1,2</td></tr><tr><td>C11</td><td>08/03/2022</td><td>18/03/2022</td><td>13,9</td><td>3,1</td><td>5,4 ± 0,2</td><td>29,3 ± 3,2</td></tr><tr><td>C12</td><td>18/03/2022</td><td>05/04/2022</td><td>13,5</td><td>11,1</td><td>1,9 ± 0,1</td><td>36,8 ± 14,8</td></tr><tr><td>C13</td><td>05/04/2022</td><td>20/04/2022</td><td>24,3</td><td>7,6</td><td>0,7 ± 0,04</td><td>10,1 ± 1,1</td></tr><tr><td>C14</td><td>03/05/2022</td><td>17/05/2022</td><td>8,9</td><td>3,2</td><td>2,7 ± 0,1</td><td>15,3 ± 1,6</td></tr><tr><td>C15</td><td>17/05/2022</td><td>01/06/2022</td><td>21,5</td><td>1,3</td><td>3,8 ± 0,1</td><td>8,3 ± 0,9</td></tr><tr><td>C16</td><td>01/06/2022</td><td>15/06/2022</td><td>40,2</td><td>3,3</td><td>4,3 ± 0,2</td><td>24,4 ± 2,7</td></tr><tr><td>C17</td><td>15/06/2022</td><td>29/06/2022</td><td>17,8</td><td>6,4</td><td>2,4 ± 0,1</td><td>26,9 ± 2,9</td></tr><tr><td>C18</td><td>29/06/2022</td><td>13/07/2022</td><td>3,0</td><td>3,7</td><td>2,1 ± 0,1</td><td>13,4 ± 1,4</td></tr><tr><td>C19</td><td>13/07/2022</td><td>26/07/2022</td><td>6,7</td><td>1,8</td><td>5,3 ± 0,2</td><td>16,6 ± 2,3</td></tr></tbody></table>

Isotopic ratios $^{36}$Cl/Cl in rainwater samples ranged from 2.1x10$^{-13}$ to 5.4x10$^{-12}$ with an average of 2.3x10$^{-12}$ (median = 2.4x10$^{-12}$). The $^{36}$Cl/Cl isotopic ratio in rainwater is strongly influenced by the atmospheric Cl content of the aera. Since $^{36}$Cl is mainly produced by cosmic rays, in inland areas the stable Cl content is so low that the $^{36}$Cl/Cl ratio can reach 10$^{-13}$ whereas it is 10$^{-14}$ at the seaside (Johnston and McDermott, 2008). Despite the proximity of the sea 2 km from the study site, the $^{36}$Cl/Cl isotope ratios measured in our samples are 1 to 2 orders of magnitude higher than those of the natural environmental background (10$^{-13}$ - 10$^{-14}$), which is generally measured on sites far from anthropogenic sources of $^{36}$Cl (Table 2). However, the $^{36}$Cl/Cl ratio in our rainwater samples is of the same order of magnitude as those measured by Milton et al., (1994) neaby an anthropogenic source showing then the influence of Orano's plant discharges on the ratios measured. In fact, Milton et al., (1994) measured the highest $^{36}$Cl/Cl ratios reported in the literature at various distances from the Chalk River Nuclear Laboratory (CRL), with levels ranging from 1.6 to 30.8x10$^{-12}$. It is also quite interesting to notice that the $^{36}$Cl/Cl ratio in our rainwater samples is of the same order of magnitude as the ratio of 1.4x10$^{-12}$ measured by Sasa et al., (2022) in a monthly rainwater sample from Tsukuba during the month of the Fukushima nuclear power plant accident. Despite the distance of around 180 km from the accident site, this ratio was two orders of magnitude higher than those measured in monthly rainwater samples before and after this event (Sasa et al., 2022).
196

197

198

<table><caption>**Table 2:** $^{36}$Cl measurements in rainwater reported in the literature.</caption><thead><tr><th>Date</th><th>Site</th><th><sup>36</sup>Cl/Cl (x10<sup>-15</sup>)</th><th>at.l<sup>-1</sup> (x10<sup>6</sup>)</th><th>Source</th></tr></thead><tbody><tr><td>1979</td><td>La Jolla, United States</td><td>58</td><td>2.5</td><td>(Finkel et al., 1980)</td></tr><tr><td>1988</td><td>Several sites in Israel</td><td>1.8 - 50</td><td>0.34 - 125</td><td>(Herut et al., 1992)</td></tr><tr><td>1991-1992</td><td>St. Mary's County, United States</td><td>3.8 - 568</td><td>1.2 (average)</td><td>(Hainsworth et al., 1994)</td></tr><tr><td>1999-1993</td><td>Several sites around Chalk River Nuclear Laboratories, Canada*</td><td>(1.6 - 30.8) x10<sup>3</sup></td><td>9.5 - 2.6 x10<sup>5</sup></td><td>(Cornett et al., 1997; Milton et al., 1994)</td></tr><tr><td>1999-2000</td><td>Seville, Spain</td><td>4 - 300</td><td>0.12 - 22.7</td><td>(Santos et al., 2004)</td></tr><tr><td>2004-2007</td><td>Tsukuba, Japan</td><td>13 - 116</td><td>0.28 - 1.76</td><td>(Tosaki et al., 2012)</td></tr><tr><td>2010-2011</td><td>Several sites in Europe</td><td>21 - 746</td><td>1.63 - 9.92</td><td>(Johnston and McDermott, 2008)</td></tr><tr><td>2010-2011</td><td>Tsukuba, Japan</td><td>18 - 1420</td><td>0.1 - 18.3</td><td>(Sasa et al., 2022)</td></tr><tr><td>2012-2013</td><td>Montiers, France</td><td>177</td><td>3.2</td><td>(Grapeloup et al., 2023)</td></tr><tr><td>2012-2014</td><td>Montiers, France</td><td>40 - 900</td><td>0.8 - 8.9</td><td>(Pupier et al., 2016)</td></tr><tr><td>2021-2022</td><td>La Hague, France*</td><td>217 - 5486</td><td>62 - 390</td><td>This study</td></tr></tbody></table>

199

*Sites with a nearby anthropogenic source of $^{36}$Cl (< 3 km)

200

201

202

203

204

205

206

207

208

209

210

211

212

213

214

In the present study, $^{36}$Cl levels in collected rainwater ranged from 6.2 ± 2.5x10⁷ to 3.9 ± 0.5x10⁸ at.l⁻¹ with an average of 1.7 ± 0.2x10⁸ at.l⁻¹ (median = 1.3 ± 0.1x10⁸ at.l⁻¹). The levels of $^{36}$Cl in our rainwater samples remain mostly 1 to 2 orders of magnitude above the natural background, which is of the order of 10⁶ at.l⁻¹. This natural background value is the one generally measured in rainwater by various authors at sites around the world (Table 2). However, a content of 125.10⁶ at.l⁻¹ similar to the average content of our samples was measured by Herut et al (1992). Finding no correlation with site location, rainfall amount, topography or distance from the sea, Herut et al. (1992) attributed the higher $^{36}$Cl content to the presence of storms, which considerably increased the drawdown of atmospheric $^{36}$Cl during sampling. Several authors also report variability in $^{36}$Cl content in rainwater, depending on latitude and season (Hainsworth et al., 1994; Tosaki et al., 2012). Natural production of $^{36}$Cl is indeed latitudinally dependent, with higher production near the geomagnetic poles (Masarik and Beer, 1999; Poluianov et al., 2016). Similarly, when the tropopause rises in spring, stratospheric $^{36}$Cl is introduced into the troposphere. At the same time, more cosmic rays enter the troposphere, and the fraction of cosmogenic $^{36}$Cl produced in the troposphere increases (Hainsworth et al., 1994). However, this variability cannot be observed on our results because anthropogenic sources of $^{36}$Cl
196

197

198

<table><caption>**Table 2:** ³⁶Cl measurements in rainwater reported in the literature.</caption><thead><tr><th>Date</th><th>Site</th><th>³⁶Cl/Cl (x10<sup>-15</sup>)</th><th>at.l<sup>-1</sup> (x10<sup>6</sup>)</th><th>Source</th></tr></thead><tbody><tr><td>1979</td><td>La Jolla, United States</td><td>58</td><td>2.5</td><td>(Finkel et al., 1980)</td></tr><tr><td>1988</td><td>Several sites in Israel</td><td>1.8 - 50</td><td>0.34 - 125</td><td>(Herut et al., 1992)</td></tr><tr><td>1991-1992</td><td>St. Mary's County, United States</td><td>3.8 - 568</td><td>1.2 (average)</td><td>(Hainsworth et al., 1994)</td></tr><tr><td>1999-1993</td><td>Several sites around Chalk River Nuclear Laboratories, Canada*</td><td>(1.6 - 30.8) x10<sup>3</sup></td><td>9.5 - 2.6 x10<sup>5</sup></td><td>(Cornett et al., 1997; Milton et al., 1994)</td></tr><tr><td>1999-2000</td><td>Seville, Spain</td><td>4 - 300</td><td>0.12 - 22.7</td><td>(Santos et al., 2004)</td></tr><tr><td>2004-2007</td><td>Tsukuba, Japan</td><td>13 - 116</td><td>0.28 - 1.76</td><td>(Tosaki et al., 2012)</td></tr><tr><td>2010-2011</td><td>Several sites in Europe</td><td>21 - 746</td><td>1.63 - 9.92</td><td>(Johnston and McDermott, 2008)</td></tr><tr><td>2010-2011</td><td>Tsukuba, Japan</td><td>18 - 1420</td><td>0.1 - 18.3</td><td>(Sasa et al., 2022)</td></tr><tr><td>2012-2013</td><td>Montiers, France</td><td>177</td><td>3.2</td><td>(Grapeloup et al., 2023)</td></tr><tr><td>2012-2014</td><td>Montiers, France</td><td>40 - 900</td><td>0.8 - 8.9</td><td>(Pupier et al., 2016)</td></tr><tr><td>2021-2022</td><td>La Hague, France*</td><td>217 - 5486</td><td>62 - 390</td><td>This study</td></tr></tbody></table>

199

*Sites with a nearby anthropogenic source of ³⁶Cl (< 3 km)

200

201

202

203

204

205

206

207

208

209

210

211

212

213

214

In the present study, ³⁶Cl levels in collected rainwater ranged from 6.2 ± 2.5x10⁷ to 3.9 ± 0.5x10⁸ at.l⁻¹ with an average of 1.7 ± 0.2x10⁸ at.l⁻¹ (median = 1.3 ± 0.1x10⁸ at.l⁻¹). The levels of ³⁶Cl in our rainwater samples remain mostly 1 to 2 orders of magnitude above the natural background, which is of the order of 10⁶ at.l⁻¹. This natural background value is the one generally measured in rainwater by various authors at sites around the world (Table 2). However, a content of 125.10⁶ at.l⁻¹ similar to the average content of our samples was measured by Herut et al (1992). Finding no correlation with site location, rainfall amount, topography or distance from the sea, Herut et al. (1992) attributed the higher ³⁶Cl content to the presence of storms, which considerably increased the drawdown of atmospheric ³⁶Cl during sampling. Several authors also report variability in ³⁶Cl content in rainwater, depending on latitude and season (Hainsworth et al., 1994; Tosaki et al., 2012). Natural production of ³⁶Cl is indeed latitudinally dependent, with higher production near the geomagnetic poles (Masarik and Beer, 1999; Poluianov et al., 2016). Similarly, when the tropopause rises in spring, stratospheric ³⁶Cl is introduced into the troposphere. At the same time, more cosmic rays enter the troposphere, and the fraction of cosmogenic ³⁶Cl produced in the troposphere increases (Hainsworth et al., 1994). However, this variability cannot be observed on our results because anthropogenic sources of ³⁶Cl
overcome natural production of ³⁶Cl influenced by latitude and season. The variability observed between the different campaigns in our study is therefore rather influenced by rainfall and Orano's releases of ³⁶Cl into the atmosphere in the vicinity of the study site.

The ³⁶Cl levels measured in our samples remain lower than those of Ohta et al. (2023), who estimated ³⁶Cl levels in rainwater at 4.7x10¹⁰ at.l⁻¹ in the 6 weeks following the Fukushima accident. The ³⁶Cl levels measured in our samples also remain lower than those measured 250 m from the CRL, which reached 2.6x10¹¹ at.l⁻¹ (Milton et al., 1994). It should be noted however that these levels measured in rainwater by Milton et al. (1994) were linked to CRL discharges of ³⁶Cl. In fact, measurements taken away from the CRL were strongly related to the distance from the point of discharge. Levels in rainwater were around 2.6x10⁹ at.l⁻¹ at 3 km, 5.6x10⁷ at.l⁻¹ at 10 km and 9.5x10⁶ at.l⁻¹ at 140 km. Nevertheless, this reduction in concentrations was not linear and depended strongly on speed and wind direction. Drawing a parallel with our study and the distance between our study site and the Orano plant (2 km), rainwater sampling was carried out at the IRSN Laboratory (IRSN Lab; 49°38'04.8"N, 1°38'45.6"W) located 20 km away from the IRSN Platform, synchronized with the sampling period running from May 17 to June 1 2022, using an automatic rain collector. As shown in **Figure 1**, wind direction during this period was predominantly south-westerly.

The position of the IRSN Lab, around 20 km from the IRSN Platform and outside the gas plume over the period under consideration, enabled us to estimate changes in ³⁶Cl levels outside the influence of Orano plant's gaseous emissions. **Table 3** compares the results obtained from this rainwater sample with those obtained from the IRSN Platform. Rainfall at IRSN Lab was 15 mm over the period in consideration, which is of the same order of magnitude as that measured at IRSN platform (21 mm). But, the ³⁶Cl content in the rainwater sampled at the IRSN laboratory is an order of magnitude lower than that taken at the IRSN Platform indicating that the marking of ³⁶Cl on IRSN platform is related to the release of ³⁶Cl by the nearby plant. However, since observation period showing the data in Table 3 is limited, there are still some uncertainties about the representativity of this experiment. It is nevertheless interesting to note that both, the ³⁶Cl/Cl ratio and the ³⁶Cl concentration in the IRSN laboratory rainwater sample are like those in sites away from anthropogenic sources of ³⁶Cl.

<table><caption>**Table 3:** Comparison of ³⁶Cl levels in rainwater collected at the study site (IRSN Platform) and at the IRSN Laboratory (IRSN Lab).</caption><thead><tr><td>Sample</td><td><sup>36</sup>Cl/Cl</td><td><sup>36</sup>Cl (at.l<sup>-1</sup>)</td></tr></thead><tbody><tr><td>Rainwater IRSN Lab</td><td>2,9.10<sup>-14</sup></td><td>4,2 ± 0,6.10<sup>6</sup></td></tr><tr><td>Rainwater IRSN Platform</td><td>3,8.10<sup>-12</sup></td><td>8,3 ± 0,9.10<sup>7</sup></td></tr></tbody></table>

### 3.3. Chlorine 36 wet deposition flux

It is difficult to monitor changes in ³⁶Cl wet deposition relying only on concentrations measured in rainwater. Wet deposition should therefore be expressed in terms of wet deposition flux, in order to standardize all campaigns on this basis and make a more objective comparison. Wet deposition fluxes ($F_w$, at.m⁻²s⁻¹) of ³⁶Cl were determined from equation (Eq.1) commonly used by various authors in the literature (Hainsworth et al., 1994) :

$$F_w = \frac{[^{36}\text{Cl}] \times P}{d} \quad (\text{Eq.1})$$
overcome natural production of ³⁶Cl influenced by latitude and season. The variability observed between the different campaigns in our study is therefore rather influenced by rainfall and Orano's releases of ³⁶Cl into the atmosphere in the vicinity of the study site.

The ³⁶Cl levels measured in our samples remain lower than those of Ohta et al. (2023), who estimated ³⁶Cl levels in rainwater at 4.7x10¹⁰ at.l⁻¹ in the 6 weeks following the Fukushima accident. The ³⁶Cl levels measured in our samples also remain lower than those measured 250 m from the CRL, which reached 2.6x10¹¹ at.l⁻¹ (Milton et al., 1994). It should be noted however that these levels measured in rainwater by Milton et al. (1994) were linked to CRL discharges of ³⁶Cl. In fact, measurements taken away from the CRL were strongly related to the distance from the point of discharge. Levels in rainwater were around 2.6x10⁹ at.l⁻¹ at 3 km, 5.6x10⁷ at.l⁻¹ at 10 km and 9.5x10⁶ at.l⁻¹ at 140 km. Nevertheless, this reduction in concentrations was not linear and depended strongly on speed and wind direction. Drawing a parallel with our study and the distance between our study site and the Orano plant (2 km), rainwater sampling was carried out at the IRSN Laboratory (IRSN Lab; 49°38'04.8"N, 1°38'45.6"W) located 20 km away from the IRSN Platform, synchronized with the sampling period running from May 17 to June 1 2022, using an automatic rain collector. As shown in **Figure 1**, wind direction during this period was predominantly south-westerly.

The position of the IRSN Lab, around 20 km from the IRSN Platform and outside the gas plume over the period under consideration, enabled us to estimate changes in ³⁶Cl levels outside the influence of Orano plant's gaseous emissions. **Table 3** compares the results obtained from this rainwater sample with those obtained from the IRSN Platform. Rainfall at IRSN Lab was 15 mm over the period in consideration, which is of the same order of magnitude as that measured at IRSN platform (21 mm). But, the ³⁶Cl content in the rainwater sampled at the IRSN laboratory is an order of magnitude lower than that taken at the IRSN Platform indicating that the marking of ³⁶Cl on IRSN platform is related to the release of ³⁶Cl by the nearby plant. However, since observation period showing the data in Table 3 is limited, there are still some uncertainties about the representativity of this experiment. It is nevertheless interesting to note that both, the ³⁶Cl/Cl ratio and the ³⁶Cl concentration in the IRSN laboratory rainwater sample are like those in sites away from anthropogenic sources of ³⁶Cl.

<table><caption>**Table 3:** Comparison of ³⁶Cl levels in rainwater collected at the study site (IRSN Platform) and at the IRSN Laboratory (IRSN Lab).</caption><thead><tr><td>Sample</td><td><sup>36</sup>Cl/Cl</td><td><sup>36</sup>Cl (at.l<sup>-1</sup>)</td></tr></thead><tbody><tr><td>Rainwater IRSN Lab</td><td>2,9.10<sup>-14</sup></td><td>4,2 ± 0,6.10<sup>6</sup></td></tr><tr><td>Rainwater IRSN Platform</td><td>3,8.10<sup>-12</sup></td><td>8,3 ± 0,9.10<sup>7</sup></td></tr></tbody></table>

### 3.3. Chlorine 36 wet deposition flux

It is difficult to monitor changes in ³⁶Cl wet deposition relying only on concentrations measured in rainwater. Wet deposition should therefore be expressed in terms of wet deposition flux, in order to standardize all campaigns on this basis and make a more objective comparison. Wet deposition fluxes ($F_w$, at.m⁻²s⁻¹) of ³⁶Cl were determined from equation (Eq.1) commonly used by various authors in the literature (Hainsworth et al., 1994) :

$$F_w = \frac{[^{36}\text{Cl}] \times P}{d} \quad (\text{Eq.1})$$
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With [³⁶Cl] the sample's ³⁶Cl content (at.l⁻¹), P the campaign rainfall (l.m⁻²) and d the campaign duration (s).

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As shown in **Figure 2**, wet deposition fluxes of ³⁶Cl at our study site range from 3.3 ± 0.4x10² and 8.3 ± 1.7x10³ at.m⁻²s⁻¹ with an average of 3.4 ± 0.5x10³ at.m⁻²s⁻¹ (median = 3.2 ± 1.3x10³ at.m⁻²s⁻¹). As described above, ⁸⁵Kr serves as a tracer for the atmospheric plume at the Orano plant and is therefore measured continuously at the study site. This continuous measurement makes it possible to determine the periods when the plume is present over the study site. In order to assess the importance of the plume scavenging on ³⁶Cl deposition fluxes, the percentage of the plume subject to leaching has been calculated for all campaigns.

<figure><img src="image_5.png" /></figure>

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<caption>**Fig. 2.** Wet deposition fluxes of ³⁶Cl and percentages of rain events over the duration of the plume's presence, determined using krypton 85 measurements at the study site.</caption>

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The Cl wet deposition flux ranges from 1.6 ± 0.1x10¹⁴ and 1.4 ± 0.1x10¹⁶ at.m⁻²s⁻¹ with an average of 3.1 ± 0.5x10¹⁵ at.m⁻²s⁻¹ (median = 1.6 ± 0.2x10¹⁵ at.m⁻²s⁻¹) (Figure 3).
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With [³⁶Cl] the sample's ³⁶Cl content (at.l⁻¹), P the campaign rainfall (l.m⁻²) and d the campaign duration (s).

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As shown in **Figure 2**, wet deposition fluxes of ³⁶Cl at our study site range from 3.3 ± 0.4x10² and 8.3 ± 1.7x10³ at.m⁻²s⁻¹ with an average of 3.4 ± 0.5x10³ at.m⁻²s⁻¹ (median = 3.2 ± 1.3x10³ at.m⁻²s⁻¹). As described above, ⁸⁵Kr serves as a tracer for the atmospheric plume at the Orano plant and is therefore measured continuously at the study site. This continuous measurement makes it possible to determine the periods when the plume is present over the study site. In order to assess the importance of the plume scavenging on ³⁶Cl deposition fluxes, the percentage of the plume subject to leaching has been calculated for all campaigns.

<figure><img src="image_5.png" /></figure>

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<caption>**Fig. 2.** Wet deposition fluxes of ³⁶Cl and percentages of rain events over the duration of the plume's presence, determined using krypton 85 measurements at the study site.</caption>

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The Cl wet deposition flux ranges from 1.6 ± 0.1x10¹⁴ and 1.4 ± 0.1x10¹⁶ at.m⁻²s⁻¹ with an average of 3.1 ± 0.5x10¹⁵ at.m⁻²s⁻¹ (median = 1.6 ± 0.2x10¹⁵ at.m⁻²s⁻¹) (Figure 3).
<figure><img src="image_6.png" /><figcaption>Fig. 3. Cl wet deposition flow on the study site.</figcaption></figure>

The linear regression lines between these wet deposition fluxes ($^{36}$Cl and Cl) as a function of rainfall are shown in Figure 4.

<figure><img src="image_7.png" /><figcaption>Fig. 4. Correlation coefficient and linear regression line for (A) wet deposition flux of $^{36}$Cl as a function of precipitation; (B) wet deposition flux of Cl as a function of precipitation.</figcaption></figure>

Based on the linear regression lines for wet deposition fluxes as a function of precipitation, it can be seen that the deposition flux of $^{36}$Cl appears to be less dependent on rainfall than that for Cl.

This no doubt explains why Cl wet deposition fluxes are particularly high for campaigns with the highest rainfall (examples of campaigns n° 5, 7 and 9). On the other hand, the wet deposition flux of $^{36}$Cl on the IRSN Platform is linked to the $^{36}$Cl content in the air at the time of precipitations. This is
<figure><img src="image_6.png" /><figcaption>Fig. 3. Cl wet deposition flow on the study site.</figcaption></figure>

The linear regression lines between these wet deposition fluxes ($^{36}$Cl and Cl) as a function of rainfall are shown in Figure 4.

<figure><img src="image_7.png" /><figcaption>Fig. 4. Correlation coefficient and linear regression line for (A) wet deposition flux of $^{36}$Cl as a function of precipitation; (B) wet deposition flux of Cl as a function of precipitation.</figcaption></figure>

Based on the linear regression lines for wet deposition fluxes as a function of precipitation, it can be seen that the deposition flux of $^{36}$Cl appears to be less dependent on rainfall than that for Cl.

This no doubt explains why Cl wet deposition fluxes are particularly high for campaigns with the highest rainfall (examples of campaigns n° 5, 7 and 9). On the other hand, the wet deposition flux of $^{36}$Cl on the IRSN Platform is linked to the $^{36}$Cl content in the air at the time of precipitations. This is
confirmed by the fact that the presence of <sup>85</sup>Kr (attesting the presence of <sup>36</sup>Cl emitted by Orano on the study site) during a rainy episode increases the quantity of <sup>36</sup>Cl deposited. This can be observed in the wet deposition fluxes of <sup>36</sup>Cl measured in campaigns n°5, 7 and 9. The particularly high wet deposition fluxes of <sup>36</sup>Cl in campaigns n°1, 2 and 16 cannot, however, be explained by the presence of the plume <sup>36</sup>Cl. The deposition fluxes measured in these 3 campaigns cannot therefore be explained by the washout alone. Apart from the washout, the wet deposition fluxes measured over these campaigns can only be explained by the presence of a <sup>36</sup>Cl drawdown in the cloud or rainout in addition to the washout. We already know that following liquid discharges of <sup>36</sup>Cl into the sea near the IRSN Platform, atmospheric <sup>36</sup>Cl of marine origin was measured on the IRSN Platform in the absence of the gaseous plume from Orano plant (Sourabie et al., 2023). However, these liquid discharges of <sup>36</sup>Cl have different frequencies from atmospheric discharges and the quantities are not measured. Based on marine dispersion models, we also know that radionuclide dispersion following liquid discharges from Orano La Hague can extend over kilometers (Fiévet et al., 2020). Even if it is a weak possibility, as it happens for Cl, <sup>36</sup>Cl can also be incorporated into the cloud many kilometers upstream of the study site, and then washed down by precipitation. The presence of wet deposition by rainout in addition to wet deposition by washout would thus explain the significant deposition fluxes found in campaigns n°1, 2 and 16. It could also explain the differences observed in <sup>36</sup>Cl content on IRSN Platform and at IRSN Lab. However, unlike Cl, the incorporation of <sup>36</sup>Cl into the cloud depends on the quantities of <sup>36</sup>Cl discharged into the sea by Orano plant which are subjected to strong variations in space and time.

Apart from a few studies focusing exclusively on the wet deposits of <sup>36</sup>Cl, notably that of Hainsworth et al. (1994), the majority of studies on wet deposition of <sup>36</sup>Cl use rainwater samplers subjected to dry deposition during non-rainy periods. Nevertheless, the wet deposition fluxes of <sup>36</sup>Cl determined at our study site are generally an order of magnitude higher than those measured by Santos et al. (2004) in Seville (from 5 to 1250 at.m<sup>-2</sup>s<sup>-1</sup>); by Keywood et al. (1998) in Australia (15 at.m<sup>-2</sup>s<sup>-1</sup> on average); by Tosaki et al. (2012) in Tsukuba (between 8 and 173 at.m<sup>-2</sup>s<sup>-1</sup>); by Pupier et al. (2016) and Grapeloup et al. (2023) at Montier-sur-Saulx (from 45 to 396 at.m<sup>-2</sup>s<sup>-1</sup>); by Hainsworth et al. (1994) in Maryland (38 at.m<sup>-2</sup>s<sup>-1</sup> on average); by Knies et al. (1994) in West Lafayette (between 10 and 180 at.m<sup>-2</sup>s<sup>-1</sup>); by Johnston and McDermott (2008) at sites across Europe (between 11 and 153 at.m<sup>-2</sup>s<sup>-1</sup>); and by Scheffel et al. (1999) on sites spread across the globe (between 25 and 755 at.m<sup>-2</sup>s<sup>-1</sup>).

The wet deposition fluxes of <sup>36</sup>Cl measured at our site are however equivalent to the dry deposition fluxes of <sup>36</sup>Cl on grass previously measured at the same site over the same period of time by Sourabie et al (2023). Indeed, the average wet deposition flux of <sup>36</sup>Cl measured in this study (3.1x10<sup>3</sup> at.m<sup>-2</sup>s<sup>-1</sup>) is similar to the average dry deposition flux of <sup>36</sup>Cl on grass (2.3x10<sup>3</sup> at.m<sup>-2</sup>s<sup>-1</sup>). Although largely above natural background levels, these environmental levels of <sup>36</sup>Cl do not present any radiological risk to the environment or humans. Concerning Cl wet deposition fluxes, due to the proximity of the sea, they are higher than those determined by Pupier et al. (2016) 390 km from the sea (0.07 to 1.32x10<sup>15</sup> at.m<sup>-2</sup>s<sup>-1</sup>) and by Tosaki et al. (2012) 50 km from the sea (0.27 to 2.00x10<sup>15</sup> at.m<sup>-2</sup>s<sup>-1</sup>).

Although rarely used, wet deposition can also be described through deposition flux expressed over the duration of precipitation. Wet deposition fluxes of <sup>36</sup>Cl over the duration of precipitation refer to the amount of <sup>36</sup>Cl washed down at the time of precipitations, rather than over the total duration of the campaign. Wet deposition fluxes of <sup>36</sup>Cl expressed over the duration of precipitations (F'<sub>w</sub> ; at.m<sup>-2</sup>s<sup>-1</sup>) were determined from equation (Eq.2):

$$F'_{w} = \frac{[^{36}\text{Cl}] \times P}{d'} \quad (\text{Eq.2})$$
confirmed by the fact that the presence of <sup>85</sup>Kr (attesting the presence of <sup>36</sup>Cl emitted by Orano on the study site) during a rainy episode increases the quantity of <sup>36</sup>Cl deposited. This can be observed in the wet deposition fluxes of <sup>36</sup>Cl measured in campaigns n°5, 7 and 9. The particularly high wet deposition fluxes of <sup>36</sup>Cl in campaigns n°1, 2 and 16 cannot, however, be explained by the presence of the plume <sup>36</sup>Cl. The deposition fluxes measured in these 3 campaigns cannot therefore be explained by the washout alone. Apart from the washout, the wet deposition fluxes measured over these campaigns can only be explained by the presence of a <sup>36</sup>Cl drawdown in the cloud or rainout in addition to the washout. We already know that following liquid discharges of <sup>36</sup>Cl into the sea near the IRSN Platform, atmospheric <sup>36</sup>Cl of marine origin was measured on the IRSN Platform in the absence of the gaseous plume from Orano plant (Sourabie et al., 2023). However, these liquid discharges of <sup>36</sup>Cl have different frequencies from atmospheric discharges and the quantities are not measured. Based on marine dispersion models, we also know that radionuclide dispersion following liquid discharges from Orano La Hague can extend over kilometers (Fiévet et al., 2020). Even if it is a weak possibility, as it happens for Cl, <sup>36</sup>Cl can also be incorporated into the cloud many kilometers upstream of the study site, and then washed down by precipitation. The presence of wet deposition by rainout in addition to wet deposition by washout would thus explain the significant deposition fluxes found in campaigns n°1, 2 and 16. It could also explain the differences observed in <sup>36</sup>Cl content on IRSN Platform and at IRSN Lab. However, unlike Cl, the incorporation of <sup>36</sup>Cl into the cloud depends on the quantities of <sup>36</sup>Cl discharged into the sea by Orano plant which are subjected to strong variations in space and time.

Apart from a few studies focusing exclusively on the wet deposits of <sup>36</sup>Cl, notably that of Hainsworth et al. (1994), the majority of studies on wet deposition of <sup>36</sup>Cl use rainwater samplers subjected to dry deposition during non-rainy periods. Nevertheless, the wet deposition fluxes of <sup>36</sup>Cl determined at our study site are generally an order of magnitude higher than those measured by Santos et al. (2004) in Seville (from 5 to 1250 at.m<sup>-2</sup>s<sup>-1</sup>); by Keywood et al. (1998) in Australia (15 at.m<sup>-2</sup>s<sup>-1</sup> on average); by Tosaki et al. (2012) in Tsukuba (between 8 and 173 at.m<sup>-2</sup>s<sup>-1</sup>); by Pupier et al. (2016) and Grapeloup et al. (2023) at Montier-sur-Saulx (from 45 to 396 at.m<sup>-2</sup>s<sup>-1</sup>); by Hainsworth et al. (1994) in Maryland (38 at.m<sup>-2</sup>s<sup>-1</sup> on average); by Knies et al. (1994) in West Lafayette (between 10 and 180 at.m<sup>-2</sup>s<sup>-1</sup>); by Johnston and McDermott (2008) at sites across Europe (between 11 and 153 at.m<sup>-2</sup>s<sup>-1</sup>); and by Scheffel et al. (1999) on sites spread across the globe (between 25 and 755 at.m<sup>-2</sup>s<sup>-1</sup>).

The wet deposition fluxes of <sup>36</sup>Cl measured at our site are however equivalent to the dry deposition fluxes of <sup>36</sup>Cl on grass previously measured at the same site over the same period of time by Sourabie et al (2023). Indeed, the average wet deposition flux of <sup>36</sup>Cl measured in this study (3.1x10<sup>3</sup> at.m<sup>-2</sup>s<sup>-1</sup>) is similar to the average dry deposition flux of <sup>36</sup>Cl on grass (2.3x10<sup>3</sup> at.m<sup>-2</sup>s<sup>-1</sup>). Although largely above natural background levels, these environmental levels of <sup>36</sup>Cl do not present any radiological risk to the environment or humans. Concerning Cl wet deposition fluxes, due to the proximity of the sea, they are higher than those determined by Pupier et al. (2016) 390 km from the sea (0.07 to 1.32x10<sup>15</sup> at.m<sup>-2</sup>s<sup>-1</sup>) and by Tosaki et al. (2012) 50 km from the sea (0.27 to 2.00x10<sup>15</sup> at.m<sup>-2</sup>s<sup>-1</sup>).

Although rarely used, wet deposition can also be described through deposition flux expressed over the duration of precipitation. Wet deposition fluxes of <sup>36</sup>Cl over the duration of precipitation refer to the amount of <sup>36</sup>Cl washed down at the time of precipitations, rather than over the total duration of the campaign. Wet deposition fluxes of <sup>36</sup>Cl expressed over the duration of precipitations (F'<sub>w</sub> ; at.m<sup>-2</sup>s<sup>-1</sup>) were determined from equation (Eq.2):

$$F'_{w} = \frac{[^{36}\text{Cl}] \times P}{d'} \quad (\text{Eq.2})$$
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With [³⁶Cl] the sample's ³⁶Cl content (at. l⁻¹), P the campaign rainfall (l.m⁻²) and d' the total rainfall duration (s).

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As shown in **Figure 5**, ³⁶Cl wet deposition fluxes reported to precipitations duration range from 1.0 ± 0.4x10⁴ and 2.0 ± 1.4x10⁵ at.m⁻²s⁻¹ with an average of 7.4 ± 1.9x10⁴ at.m⁻²s⁻¹ (median = 7.5 ±1.7x10⁴ at.m⁻²s⁻¹). As a reminder, rainfall at the study site is acquired at a frequency of 30 minutes. The duration of rainfall is therefore calculated by multiplying the number of chronicles in which rainfall was measured by the duration of the chronicle (30 minutes).

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<figure><img src="image_8.png" /></figure>

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<caption>**Fig. 5.** Rainfall duration and wet deposition flux of ³⁶Cl over rainfall duration.</caption>

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Overall, the wet deposition fluxes of ³⁶Cl expressed over the duration of precipitation (d') is 1 to 2 orders of magnitude greater than that reported to the entire duration of campaign (d) and dry deposition fluxes of ³⁶Cl on grass previously measured at the same site over the same period of time by Sourabie et al (2023). This reflects the amount of chlorine 36 that is captured and delivered to the ground by raindrops. However, it can be noticed that this flux varies between the different campaigns. For example, the ³⁶Cl F'w of campaign n°2 is an order of magnitude higher than that of campaign n°8 despite their similar rainfall. The absence of plume washout during these two campaigns shows that wet deposition by rainout is neither systematic nor constant over time. The differences observed between these campaigns without plume washout may be related to differences in the cloud generation process, but this is unlikely to explain the large flux difference between campaigns n°2 and n°8. Due to the large uncertainties on rainout, it is quite difficult to distinguish between rainout and washout in ³⁶Cl wet deposition for campaigns with presence of ⁸⁵Kr during rain events. However, based on our measurements, we think that in the presence of the plume, ³⁶Cl wet deposition by washout is greater than that by rainout. However, the relatively punctual presence of the plume at our site (on average 10% of the time) and the high rainfall in the region make rainout a significant contributor to ³⁶Cl wet deposition on our site.
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With [³⁶Cl] the sample's ³⁶Cl content (at. l⁻¹), P the campaign rainfall (l.m⁻²) and d' the total rainfall duration (s).

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As shown in **Figure 5**, ³⁶Cl wet deposition fluxes reported to precipitations duration range from 1.0 ± 0.4x10⁴ and 2.0 ± 1.4x10⁵ at.m⁻²s⁻¹ with an average of 7.4 ± 1.9x10⁴ at.m⁻²s⁻¹ (median = 7.5 ± 1.7x10⁴ at.m⁻²s⁻¹). As a reminder, rainfall at the study site is acquired at a frequency of 30 minutes. The duration of rainfall is therefore calculated by multiplying the number of chronicles in which rainfall was measured by the duration of the chronicle (30 minutes).

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<figure><img src="image_8.png" /><figcaption>**Fig. 5.** Rainfall duration and wet deposition flux of ³⁶Cl over rainfall duration.</figcaption></figure>

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Overall, the wet deposition fluxes of ³⁶Cl expressed over the duration of precipitation (d') is 1 to 2 orders of magnitude greater than that reported to the entire duration of campaign (d) and dry deposition fluxes of ³⁶Cl on grass previously measured at the same site over the same period of time by Sourabie et al (2023). This reflects the amount of chlorine 36 that is captured and delivered to the ground by raindrops. However, it can be noticed that this flux varies between the different campaigns. For example, the ³⁶Cl F'w of campaign n°2 is an order of magnitude higher than that of campaign n°8 despite their similar rainfall. The absence of plume washout during these two campaigns shows that wet deposition by rainout is neither systematic nor constant over time. The differences observed between these campaigns without plume washout may be related to differences in the cloud generation process, but this is unlikely to explain the large flux difference between campaigns n°2 and n°8. Due to the large uncertainties on rainout, it is quite difficult to distinguish between rainout and washout in ³⁶Cl wet deposition for campaigns with presence of ⁸⁵Kr during rain events. However, based on our measurements, we think that in the presence of the plume, ³⁶Cl wet deposition by washout is greater than that by rainout. However, the relatively punctual presence of the plume at our site (on average 10% of the time) and the high rainfall in the region make rainout a significant contributor to ³⁶Cl wet deposition on our site.
353 **4. Conclusions**

354 Through 19 experimental campaigns, ³⁶Cl was measured in rainwater for the first time downwind of
355 the Orano La Hague plant, a chronic emitter of small quantities of ³⁶Cl into the environment. The
356 levels of ³⁶Cl measured in rainwater, of the order of 10⁸ at.l⁻¹, were 1 to 2 orders of magnitude above
357 the natural background, demonstrating the influence of the plant's discharges on our site. The study
358 of wet deposition fluxes of ³⁶Cl showed the importance of ³⁶Cl deposition when the plant plume is
359 washed out by precipitation, but also highlighted the presence of wet deposition by rainout of ³⁶Cl.
360 However, these results remain specific to our study site and are linked to the proximity of chronic
361 discharge sources (atmospheric and marine). Moreover, these environmental levels of ³⁶Cl do not
362 present any radiological risk. Nevertheless, these results will serve to improve our knowledge on the
363 fate of ³⁶Cl in the environment. They will also enable better assessment of impact studies in a context
364 of decommissioning or nuclear power plant accidents, so that dosimetric impact can be better
365 considered and associated uncertainties reduced. These results could moreover serve as an
366 experimental basis for the development and validation of wet deposition models for ³⁶Cl.

367

368 **References:**

369 Bastviken, D., Svensson, T., Sandén, P., Kylin, H., 2013. Chlorine cycling and fates of 36Cl in terrestrial environments. Swedish Nuclear Fuel and Waste Management Co.

371 Bouchez, C., Pupier, J., Benedetti, L., Deschamps, P., Guillou, V., Keddadouche, K., Aumaître, G., Arnold, M., Bourlès, D., 2015. Isotope Dilution-AMS technique for 36Cl and Cl determination in low chlorine content waters. Chem. Geol. 404, 62–70.

374 https://doi.org/10.1016/j.chemgeo.2015.03.022

375 Braucher, R., Keddadouche, K., Aumaître, G., Bourlès, D.L., Arnold, M., Pivot, S., Baroni, M., Scharf, A., Rugel, G., Bard, E., 2018. Chlorine measurements at the 5MV French AMS national facility ASTER: Associated external uncertainties and comparability with the 6MV DREAMS facility.

378 Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. At. 420, 40–45.

379 https://doi.org/10.1016/j.nimb.2018.01.025

380 Budyka, A.K., 2000. Phase transformations of iodine and other volatile radionuclides in free atmosphere. J. Aerosol Sci., European Aerosol Conference 2000 31, 480–481.

382 https://doi.org/10.1016/S0021-8502(00)90493-2

383 Connan, O., Solier, L., Hébert, D., Maro, D., Lamotte, M., Voiseux, C., Laguionie, P., Cazimajou, O., Le Cavelier, S., Godinot, C., Morillon, M., Thomas, L., Percot, S., 2014. Near-field krypton-85

385 measurements in stable meteorological conditions around the AREVA NC La Hague
386 reprocessing plant: estimation of atmospheric transfer coefficients. J. Environ. Radioact. 137,
387 142–149. https://doi.org/10.1016/j.jenvrad.2014.07.012

388 Cornett, R.J., Andrews, H.R., Chant, L.A., Davies, W.G., Greiner, B.F., Imahori, Y., Koslowsky, V.T., Kotzer, T., Milton, J.C.D., Milton, G.M., 1997. Is 36Cl from weapons' test fallout still cycling in the atmosphere? Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. At.,

391 Accelerator Mass Spectrometry 123, 378–381. https://doi.org/10.1016/S0168-

392 583X(96)00733-1

393 Fiévet, B., Bailly du Bois, P., Voiseux, C., Godinot, C., Cazimajou, O., Solier, L., De Vismes Ott, A., Cossonnet, C., Habibi, A., Fleury, S., 2020. A comprehensive assessment of two-decade radioactivity monitoring around the Channel Islands. J. Environ. Radioact. 223–224, 106381.

396 https://doi.org/10.1016/j.jenvrad.2020.106381

397 Finkel, R., Arnold, M., Aumaître, G., Benedetti, L., Bourlès, D., Keddadouche, K., Merchel, S., 2013.

398 Improved 36Cl performance at the ASTER HVE 5MV accelerator mass spectrometer national
353 **4. Conclusions**

354 Through 19 experimental campaigns, ³⁶Cl was measured in rainwater for the first time downwind of
355 the Orano La Hague plant, a chronic emitter of small quantities of ³⁶Cl into the environment. The
356 levels of ³⁶Cl measured in rainwater, of the order of 10⁸ at.l⁻¹, were 1 to 2 orders of magnitude above
357 the natural background, demonstrating the influence of the plant's discharges on our site. The study
358 of wet deposition fluxes of ³⁶Cl showed the importance of ³⁶Cl deposition when the plant plume is
359 washed out by precipitation, but also highlighted the presence of wet deposition by rainout of ³⁶Cl.
360 However, these results remain specific to our study site and are linked to the proximity of chronic
361 discharge sources (atmospheric and marine). Moreover, these environmental levels of ³⁶Cl do not
362 present any radiological risk. Nevertheless, these results will serve to improve our knowledge on the
363 fate of ³⁶Cl in the environment. They will also enable better assessment of impact studies in a context
364 of decommissioning or nuclear power plant accidents, so that dosimetric impact can be better
365 considered and associated uncertainties reduced. These results could moreover serve as an
366 experimental basis for the development and validation of wet deposition models for ³⁶Cl.

367

368 **References:**

369 Bastviken, D., Svensson, T., Sandén, P., Kylin, H., 2013. Chlorine cycling and fates of 36Cl in terrestrial environments. Swedish Nuclear Fuel and Waste Management Co.

371 Bouchez, C., Pupier, J., Benedetti, L., Deschamps, P., Guillou, V., Keddadouche, K., Aumaître, G., Arnold, M., Bourlès, D., 2015. Isotope Dilution-AMS technique for 36Cl and Cl determination in low chlorine content waters. Chem. Geol. 404, 62–70.

374 https://doi.org/10.1016/j.chemgeo.2015.03.022

375 Braucher, R., Keddadouche, K., Aumaître, G., Bourlès, D.L., Arnold, M., Pivot, S., Baroni, M., Scharf, A., Rugel, G., Bard, E., 2018. Chlorine measurements at the 5MV French AMS national facility ASTER: Associated external uncertainties and comparability with the 6MV DREAMS facility.

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383 Connan, O., Solier, L., Hébert, D., Maro, D., Lamotte, M., Voiseux, C., Laguionie, P., Cazimajou, O., Le

384 Cavelier, S., Godinot, C., Morillon, M., Thomas, L., Percot, S., 2014. Near-field krypton-85 measurements in stable meteorological conditions around the AREVA NC La Hague reprocessing plant: estimation of atmospheric transfer coefficients. J. Environ. Radioact. 137, 142–149. https://doi.org/10.1016/j.jenvrad.2014.07.012

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388 Cornett, R.J., Andrews, H.R., Chant, L.A., Davies, W.G., Greiner, B.F., Imahori, Y., Koslowsky, V.T., Kotzer, T., Milton, J.C.D., Milton, G.M., 1997. Is 36Cl from weapons' test fallout still cycling in the atmosphere? Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. At., Accelerator Mass Spectrometry 123, 378–381. https://doi.org/10.1016/S0168-583X(96)00733-1

388 Cornett, R.J., Andrews, H.R., Chant, L.A., Davies, W.G., Greiner, B.F., Imahori, Y., Koslowsky, V.T., Kotzer, T., Milton, J.C.D., Milton, G.M., 1997. Is 36Cl from weapons' test fallout still cycling in the atmosphere? Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. At., Accelerator Mass Spectrometry 123, 378–381. https://doi.org/10.1016/S0168-583X(96)00733-1

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393 Fiévet, B., Bailly du Bois, P., Voiseux, C., Godinot, C., Cazimajou, O., Solier, L., De Vismes Ott, A., Cossonnet, C., Habibi, A., Fleury, S., 2020. A comprehensive assessment of two-decade radioactivity monitoring around the Channel Islands. J. Environ. Radioact. 223–224, 106381.

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397 Finkel, R., Arnold, M., Aumaître, G., Benedetti, L., Bourlès, D., Keddadouche, K., Merchel, S., 2013.

398 Improved 36Cl performance at the ASTER HVE 5MV accelerator mass spectrometer national
399 facility. Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. At., Proceedings of the Twelfth International Conference on Accelerator Mass Spectrometry, Wellington, New Zealand, 20-25 March 2011 294, 121-125. https://doi.org/10.1016/j.nimb.2012.05.019

402 Finkel, R.C., Nishiizumi, K., Elmore, D., Ferraro, R.D., Gove, H.E., 1980. 36Cl in polar ice, rainwater and seawater. Geophys. Res. Lett. 7, 983-986. https://doi.org/10.1029/GL007i011p00983

404 Grapeloup, C., Cornu, S., Giraud, X., Pupier, J., Team, A., Guillou, V., Ciffroy, P., Cabana, B.L., Couegnas, C., Hatté, C., Benedetti, L., 2023. 36Cl, a new tool to assess soil carbon dynamics. Sci. Rep. 13, 15085. https://doi.org/10.1038/s41598-023-41555-x

407 Green, J.R., Cecil, L.D., Synal, H.-A., Santos, J., Kreutz, K.J., Wake, C.P., 2004. A high resolution record of chlorine-36 nuclear-weapons-tests fallout from Central Asia. Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. At., Proceedings of the Ninth International Conference on Accelerator Mass Spectrometry 223-224, 854-857.

411 https://doi.org/10.1016/j.nimb.2004.04.157

412 GRNC, 1999. GRNC, Groupe Radioécologie Nord Cotentin, Work group no.1 report: inventory of radioactive waste from nuclear installations. [WWW Document]. URL http://www.gep-nucleaire.org/norcot/gepnc/sections/travauxgep/premiere_mission5339/volume_1_publie_en/view (accessed 2.16.23).

416 Hainsworth, L.J., Mignerey, A.C., Helz, G.R., Sharma, P., Kubik, P.W., 1994. Modern chlorine-36 deposition in southern Maryland, U.S.A. Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. At. 92, 345-349. https://doi.org/10.1016/0168-583X(94)96032-1

419 Heikkilä, U., Beer, J., Feichter, J., Alfimov, V., Synal, H.-A., Schotterer, U., Eichler, A., Schwikowski, M., Thompson, L., 2009. ³⁶Cl bomb peak: comparison of modeled and measured data. Atmospheric Chem. Phys. 9, 4145-4156. https://doi.org/10.5194/acp-9-4145-2009

422 Herut, B., Starinsky, A., Katz, A., Paul, M., Boaretto, E., Berkovits, D., 1992. 36Cl in chloride-rich rainwater, Israel. Earth Planet. Sci. Lett. 109, 179-183. https://doi.org/10.1016/0012-821X(92)90082-7

425 Huggle, D., Blinov, A., Stan-Sion, C., Korschinek, G., Scheffel, C., Massonet, S., Zerle, L., Beer, J., Parrat, Y., Gaeggeler, H., Hajdas, W., Nolte, E., 1996. Production of cosmogenic 36Cl on atmospheric argon. Planet. Space Sci. 44, 147-151. https://doi.org/10.1016/0032-0633(95)00085-2

429 Johnston, V., McDermott, F., 2008. The distribution of meteoric Cl-36 in precipitation across Europe in spring 2007. Earth Planet. Sci. Lett. 275, 154-164. https://doi.org/10.1016/j.epsl.2008.08.021

432 Keywood, M.D., Fifield, L.K., Chivas, A.R., Cresswell, R.G., 1998. Fallout of chlorine 36 to the Earth's surface in the southern hemisphere. J. Geophys. Res. Atmospheres 103, 8281-8286. https://doi.org/10.1029/97JD03125

435 Knies, D.L., Elmore, D., Sharma, P., Vogt, S., Li, R., Lipschutz, M.E., Petty, G., Farrell, J., Monaghan, M.C., Fritz, S., Agee, E., 1994. 7Be, 10Be, and 36Cl in precipitation. Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. At. 92, 340-344. https://doi.org/10.1016/0168-583X(94)96031-3

439 Lazarev, V., 2003. The cosmogenic and anthropogenic 36Cl in the environment. Technische Universität München.

441 Le Dizès, S., Gonze, M.A., 2019. Behavior of 36Cl in agricultural soil-plant systems: A review of transfer processes and modelling approaches. J. Environ. Radioact. 196, 82-90. https://doi.org/10.1016/j.jenvrad.2018.10.011

444 Llopart-Babot, I., Vasile, M., Dobney, A., Boden, S., Bruggeman, M., Leermakers, M., Qiao, J., Warwick, P., 2022. On the determination of 36Cl and 129I in solid materials from nuclear decommissioning activities. J. Radioanal. Nucl. Chem. https://doi.org/10.1007/s10967-022-08327-9

448 Masarik, J., Beer, J., 1999. Simulation of particle fluxes and cosmogenic nuclide production in the Earth's atmosphere. J. Geophys. Res. Atmospheres 104, 12099-12111. https://doi.org/10.1029/1998JD200091
399 facility. Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. At., Proceedings of the Twelfth International Conference on Accelerator Mass Spectrometry, Wellington, New Zealand, 20-25 March 2011 294, 121-125. https://doi.org/10.1016/j.nimb.2012.05.019

402 Finkel, R.C., Nishiizumi, K., Elmore, D., Ferraro, R.D., Gove, H.E., 1980. 36Cl in polar ice, rainwater and seawater. Geophys. Res. Lett. 7, 983-986. https://doi.org/10.1029/GL007i011p00983

404 Grapeloup, C., Cornu, S., Giraud, X., Pupier, J., Team, A., Guillou, V., Ciffroy, P., Cabana, B.L., Couegnas, C., Hatté, C., Benedetti, L., 2023. 36Cl, a new tool to assess soil carbon dynamics. Sci. Rep. 13, 15085. https://doi.org/10.1038/s41598-023-41555-x

407 Green, J.R., Cecil, L.D., Synal, H.-A., Santos, J., Kreutz, K.J., Wake, C.P., 2004. A high resolution record of chlorine-36 nuclear-weapons-tests fallout from Central Asia. Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. At., Proceedings of the Ninth International Conference on Accelerator Mass Spectrometry 223-224, 854-857.

411 https://doi.org/10.1016/j.nimb.2004.04.157

412 GRNC, 1999. GRNC, Groupe Radioécologie Nord Cotentin, Work group no.1 report: inventory of radioactive waste from nuclear installations. [WWW Document]. URL http://www.gep-nucleaire.org/norcot/gepnc/sections/travauxgep/premiere_mission5339/volume_1_publie_en/view (accessed 2.16.23).

416 Hainsworth, L.J., Mignerey, A.C., Helz, G.R., Sharma, P., Kubik, P.W., 1994. Modern chlorine-36 deposition in southern Maryland, U.S.A. Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. At. 92, 345-349. https://doi.org/10.1016/0168-583X(94)96032-1

419 Heikkilä, U., Beer, J., Feichter, J., Alfimov, V., Synal, H.-A., Schotterer, U., Eichler, A., Schwikowski, M., Thompson, L., 2009. ³⁶Cl bomb peak: comparison of modeled and measured data. Atmospheric Chem. Phys. 9, 4145-4156. https://doi.org/10.5194/acp-9-4145-2009

422 Herut, B., Starinsky, A., Katz, A., Paul, M., Boaretto, E., Berkovits, D., 1992. 36Cl in chloride-rich rainwater, Israel. Earth Planet. Sci. Lett. 109, 179-183. https://doi.org/10.1016/0012-821X(92)90082-7

425 Huggle, D., Blinov, A., Stan-Sion, C., Korschinek, G., Scheffel, C., Massonet, S., Zerle, L., Beer, J., Parrat, Y., Gaeggeler, H., Hajdas, W., Nolte, E., 1996. Production of cosmogenic 36Cl on atmospheric argon. Planet. Space Sci. 44, 147-151. https://doi.org/10.1016/0032-0633(95)00085-2

429 Johnston, V., McDermott, F., 2008. The distribution of meteoric Cl-36 in precipitation across Europe in spring 2007. Earth Planet. Sci. Lett. 275, 154-164. https://doi.org/10.1016/j.epsl.2008.08.021

432 Keywood, M.D., Fifield, L.K., Chivas, A.R., Cresswell, R.G., 1998. Fallout of chlorine 36 to the Earth's surface in the southern hemisphere. J. Geophys. Res. Atmospheres 103, 8281-8286. https://doi.org/10.1029/97JD03125

435 Knies, D.L., Elmore, D., Sharma, P., Vogt, S., Li, R., Lipschutz, M.E., Petty, G., Farrell, J., Monaghan, M.C., Fritz, S., Agee, E., 1994. 7Be, 10Be, and 36Cl in precipitation. Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. At. 92, 340-344. https://doi.org/10.1016/0168-583X(94)96031-3

439 Lazarev, V., 2003. The cosmogenic and anthropogenic 36Cl in the environment. Technische Universität München.

441 Le Dizès, S., Gonze, M.A., 2019. Behavior of 36Cl in agricultural soil-plant systems: A review of transfer processes and modelling approaches. J. Environ. Radioact. 196, 82-90. https://doi.org/10.1016/j.jenvrad.2018.10.011

444 Llopart-Babot, I., Vasile, M., Dobney, A., Boden, S., Bruggeman, M., Leermakers, M., Qiao, J., Warwick, P., 2022. On the determination of 36Cl and 129I in solid materials from nuclear decommissioning activities. J. Radioanal. Nucl. Chem. https://doi.org/10.1007/s10967-022-08327-9

448 Masarik, J., Beer, J., 1999. Simulation of particle fluxes and cosmogenic nuclide production in the Earth's atmosphere. J. Geophys. Res. Atmospheres 104, 12099-12111. https://doi.org/10.1029/1998JD200091
451 Merchel, S., Bremser, W., Alfimov, V., Arnold, M., Aumaître, G., Benedetti, L., Bourlès, D.L., Caffee, M., Fifield, L.K., Finkel, R.C., Freeman, S.P.H.T., Martschini, M., Matsushi, Y., Rood, D.H., Sasa, K., Steier, P., Takahashi, T., Tamari, M., Tims, S.G., Tosaki, Y., Wilcken, K.M., Xu, S., 2011. Ultra-trace analysis of 36Cl by accelerator mass spectrometry: an interlaboratory study. *Anal. Bioanal. Chem.* 400, 3125–3132. https://doi.org/10.1007/s00216-011-4979-2
452
453
454
455
456 Milton, G.M., Andrews, H.R., Causey, S.E., Chant, L.A., Cornett, R.J., Davies, W.G., Greiner, B.F., Koslowsky, V.T., Imahori, Y., Kramer, S.J., McKay, J.W., Milton, J.C.D., 1994. Chlorine-36 dispersion in the Chalk River area. *Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. At.* 92, 376–379. https://doi.org/10.1016/0168-583X(94)96037-2
456
457
458
459
460 Nakata, K., Hasegawa, T., 2011. Improvement of pre-treatment method for 36Cl/Cl measurement of Cl in natural groundwater by AMS. *Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. At.* 269, 300–307. https://doi.org/10.1016/j.nimb.2010.11.022
463
464
465 Ohta, T., Fifield, L.K., Palcsu, L., Tims, S.G., Pavetich, S., Mahara, Y., 2023. Record of 3H and 36Cl from the Fukushima nuclear accident recovered from soil water in the unsaturated zone at Koriyama. *Sci. Rep.* 13, 19672. https://doi.org/10.1038/s41598-023-46853-y
466
467
468
469 Petrov, B.F., Pokhitonov, Yu.A., 2020. Content of Long-Lived Radionuclides of Carbon-14 and Chlorine-36 in Reactor Graphite and in the Biosphere (Is there a Problem with Carbon-14 and Chlorine-36 when It Comes to the Processing of Reactor Graphite?). *Radiochemistry* 62, 138–140. https://doi.org/10.1134/S106636222001018X
470
471
472 Phillips, F.M., 2000. Chlorine-36, in: Cook, P.G., Herczeg, A.L. (Eds.), *Environmental Tracers in Subsurface Hydrology*. Springer US, Boston, MA, pp. 299–348. https://doi.org/10.1007/978-1-4615-4557-6_10
473
474
475 Phillips, F.M., Mattick, J.L., Duval, T.A., Elmore, D., Kubik, P.W., 1988. Chlorine 36 and tritium from nuclear weapons fallout as tracers for long-term liquid and vapor movement in desert soils. *Water Resour. Res.* 24, 1877–1891. https://doi.org/10.1029/WR024i011p01877
476
477
478 Poluianov, S.V., Kovaltsov, G.A., Mishev, A.L., Usoskin, I.G., 2016. Production of cosmogenic isotopes 7Be, 10Be, 14C, 22Na, and 36Cl in the atmosphere: Altitudinal profiles of yield functions. *J. Geophys. Res. Atmospheres* 121, 8125–8136. https://doi.org/10.1002/2016JD025034
479
480
481 Pupier, J., Benedetti, L., Bouchez, C., Bourlès, D., Leclerc, E., Thiry, Y., Guillou, V., 2016. Monthly record of the Cl and 36Cl fallout rates in a deciduous forest ecosystem in NE France in 2012 and 2013. *Quat. Geochronol.* 35, 26–35. https://doi.org/10.1016/j.quageo.2016.04.002
482
483
484
485
486 Santos, F.J., López-Gutiérrez, J.M., García-León, M., Schnabel, C., Synal, H.-A., Suter, M., 2004. Analysis of 36Cl in atmospheric samples from Seville (Spain) by AMS. *Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. At.*, Proceedings of the Ninth International Conference on Accelerator Mass Spectrometry 223–224, 501–506. https://doi.org/10.1016/j.nimb.2004.04.094
487
488
489
490 Sasa, K., Ochiai, Y., Tosaki, Y., Matsunaka, T., Takahashi, T., Matsumura, M., Sueki, K., 2022. Chlorine-36 deposition at Tsukuba, Japan, after the Fukushima Daiichi Nuclear Power Plant accident. *Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. At.* 532, 73–77. https://doi.org/10.1016/j.nimb.2022.10.003
491
492
493 Scheffel, C., Blinov, A., Massonet, S., Sachsenhauser, H., Stan-Sion, C., Beer, J., Synal, H.A., Kubik, P.W., Kaba, M., Nolte, E., 1999. 36Cl in modern atmospheric precipitation. *Geophys. Res. Lett.* 26, 1401–1404. https://doi.org/10.1029/1999GL900249
494
495
496 Sheppard, S.C., Johnson, L.H., Goodwin, B.W., Tait, J.C., Wuschke, D.M., Davison, C.C., 1996. Chlorine-36 in nuclear waste disposal—1. Assessment results for used fuel with comparison to 129I and 14C. *Waste Manag.* 16, 607–614. https://doi.org/10.1016/S0956-053X(97)00001-9
497
498
499
500 Sourabie, D.-G., Hebert, D., Benedetti, L., Vitorge, E., Lourino-Cabana, B., Guillou, V., Maro, D., 2023. First quantitative constraints on chlorine 36 dry deposition velocities on grassland: Comparing measurements and modelling results. *J. Environ. Radioact.* 268–269, 107264. https://doi.org/10.1016/j.jenvrad.2023.107264
451 Merchel, S., Bremser, W., Alfimov, V., Arnold, M., Aumaître, G., Benedetti, L., Bourlès, D.L., Caffee, M., Fifield, L.K., Finkel, R.C., Freeman, S.P.H.T., Martschini, M., Matsushi, Y., Rood, D.H., Sasa, K., Steier, P., Takahashi, T., Tamari, M., Tims, S.G., Tosaki, Y., Wilcken, K.M., Xu, S., 2011. Ultra-trace analysis of 36Cl by accelerator mass spectrometry: an interlaboratory study. *Anal. Bioanal. Chem.* 400, 3125–3132. https://doi.org/10.1007/s00216-011-4979-2

456 Milton, G.M., Andrews, H.R., Causey, S.E., Chant, L.A., Cornett, R.J., Davies, W.G., Greiner, B.F., Koslowsky, V.T., Imahori, Y., Kramer, S.J., McKay, J.W., Milton, J.C.D., 1994. Chlorine-36 dispersion in the Chalk River area. *Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. At.* 92, 376–379. https://doi.org/10.1016/0168-583X(94)96037-2

460 Nakata, K., Hasegawa, T., 2011. Improvement of pre-treatment method for 36Cl/Cl measurement of Cl in natural groundwater by AMS. *Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. At.* 269, 300–307. https://doi.org/10.1016/j.nimb.2010.11.022

463 Ohta, T., Fifield, L.K., Palcsu, L., Tims, S.G., Pavetich, S., Mahara, Y., 2023. Record of 3H and 36Cl from the Fukushima nuclear accident recovered from soil water in the unsaturated zone at Koriyama. *Sci. Rep.* 13, 19672. https://doi.org/10.1038/s41598-023-46853-y

466 Petrov, B.F., Pokhitonov, Yu.A., 2020. Content of Long-Lived Radionuclides of Carbon-14 and Chlorine-36 in Reactor Graphite and in the Biosphere (Is there a Problem with Carbon-14 and Chlorine-36 when It Comes to the Processing of Reactor Graphite?). *Radiochemistry* 62, 138–140. https://doi.org/10.1134/S106636222001018X

470 Phillips, F.M., 2000. Chlorine-36, in: Cook, P.G., Herczeg, A.L. (Eds.), *Environmental Tracers in Subsurface Hydrology*. Springer US, Boston, MA, pp. 299–348. https://doi.org/10.1007/978-1-4615-4557-6_10

473 Phillips, F.M., Mattick, J.L., Duval, T.A., Elmore, D., Kubik, P.W., 1988. Chlorine 36 and tritium from nuclear weapons fallout as tracers for long-term liquid and vapor movement in desert soils. *Water Resour. Res.* 24, 1877–1891. https://doi.org/10.1029/WR024i011p01877

476 Poluianov, S.V., Kovaltsov, G.A., Mishev, A.L., Usoskin, I.G., 2016. Production of cosmogenic isotopes 7Be, 10Be, 14C, 22Na, and 36Cl in the atmosphere: Altitudinal profiles of yield functions. *J. Geophys. Res. Atmospheres* 121, 8125–8136. https://doi.org/10.1002/2016JD025034

479 Pupier, J., Benedetti, L., Bouchez, C., Bourlès, D., Leclerc, E., Thiry, Y., Guillou, V., 2016. Monthly record of the Cl and 36Cl fallout rates in a deciduous forest ecosystem in NE France in 2012 and 2013. *Quat. Geochronol.* 35, 26–35. https://doi.org/10.1016/j.quageo.2016.04.002

482 Santos, F.J., López-Gutiérrez, J.M., García-León, M., Schnabel, C., Synal, H.-A., Suter, M., 2004. Analysis of 36Cl in atmospheric samples from Seville (Spain) by AMS. *Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. At.*, Proceedings of the Ninth International Conference on Accelerator Mass Spectrometry 223–224, 501–506. https://doi.org/10.1016/j.nimb.2004.04.094

487 Sasa, K., Ochiai, Y., Tosaki, Y., Matsunaka, T., Takahashi, T., Matsumura, M., Sueki, K., 2022. Chlorine-36 deposition at Tsukuba, Japan, after the Fukushima Daiichi Nuclear Power Plant accident. *Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. At.* 532, 73–77. https://doi.org/10.1016/j.nimb.2022.10.003

491 Scheffel, C., Blinov, A., Massonet, S., Sachsenhauser, H., Stan-Sion, C., Beer, J., Synal, H.A., Kubik, P.W., Kaba, M., Nolte, E., 1999. 36Cl in modern atmospheric precipitation. *Geophys. Res. Lett.* 26, 1401–1404. https://doi.org/10.1029/1999GL900249

494 Sheppard, S.C., Johnson, L.H., Goodwin, B.W., Tait, J.C., Wuschke, D.M., Davison, C.C., 1996. Chlorine-36 in nuclear waste disposal—1. Assessment results for used fuel with comparison to 129I and 14C. *Waste Manag.* 16, 607–614. https://doi.org/10.1016/S0956-053X(97)00001-9

497 Sourabie, D.-G., Hebert, D., Benedetti, L., Vitorge, E., Lourino-Cabana, B., Guillou, V., Maro, D., 2023. First quantitative constraints on chlorine 36 dry deposition velocities on grassland: Comparing measurements and modelling results. *J. Environ. Radioact.* 268–269, 107264. https://doi.org/10.1016/j.jenvrad.2023.107264
501 Stone, J.O., Allan, G.L., Fifield, L.K., Cresswell, R.G., 1996. Cosmogenic chlorine-36 from calcium

502 spallation. Geochim. Cosmochim. Acta 60, 679–692. https://doi.org/10.1016/0016-

503 7037(95)00429-7

504 Tosaki, Y., Tase, N., Sasa, K., Takahashi, T., Nagashima, Y., 2012. Measurement of the 36Cl deposition

505 flux in central Japan: natural background levels and seasonal variability. J. Environ. Radioact.

506 106, 73–80. https://doi.org/10.1016/j.jenvrad.2011.11.010

507 White, P.J., Broadley, M.R., 2001. Chloride in Soils and its Uptake and Movement within the Plant: A

508 Review. Ann. Bot. 88, 967–988. https://doi.org/10.1006/anbo.2001.1540

509

510
501 Stone, J.O., Allan, G.L., Fifield, L.K., Cresswell, R.G., 1996. Cosmogenic chlorine-36 from calcium

502 spallation. Geochim. Cosmochim. Acta 60, 679–692. https://doi.org/10.1016/0016-

503 7037(95)00429-7

504 Tosaki, Y., Tase, N., Sasa, K., Takahashi, T., Nagashima, Y., 2012. Measurement of the 36Cl deposition

505 flux in central Japan: natural background levels and seasonal variability. J. Environ. Radioact.

506 106, 73–80. https://doi.org/10.1016/j.jenvrad.2011.11.010

507 White, P.J., Broadley, M.R., 2001. Chloride in Soils and its Uptake and Movement within the Plant: A

508 Review. Ann. Bot. 88, 967–988. https://doi.org/10.1006/anbo.2001.1540

509

510