Dose assessment for workers at mercury recycling of sludge and scale from natural gas production

Dose assessment for workers at mercury recycling of sludge and scale from natural gas production Hartmut Schulz IAF - Radioökologie GmbH. Karpatenstraße 20 01326 Dresden Wolfgang Mothes GMR Gesellschaft für Metallrecycling mbh, Naumburger Str. 24 04229 Leipzig

Dose assessment for workers at mercury recycling of sludge and scale from natural gas production About Scale and Sludge Radiological measurements and dose assessment at the recycling of mercury and the immobilisation of the residues Radiological measurements and dose assessment at the disposal of immobilised residues at a landfill 2

NORM: Scale and Sludge containing Mercury What is the topic near Leipzig gas production plant Transport Recycling of Mercury landfill radioactive immobilisates Mercury Marketing 3

Typical scale in tubings Scale thickness up to 5 mm Scale mass 4 to 10 kg per 10 m tubing 2 to 5 tons in 5 km length of pipeline 0-8 %mass percent mercury 4

Mercury drops in a typical sludge 8-15 %mass percent mercury but also up to 30% possible The mercury drops contain always Pb-210 typical values: 5-10 Bq/g (/gram mercury) 5

5 Relevant radionuclides in the residues (sludge and scale) U-238 decay series: Ra-226, Pb-210, Po-210 Th-232 decay series: Ra-228, Th-228 U-238 < 1 Bq/g Th-232 < 1 Bq/g Practically of minor importance After 30 years practically no Ra-228 and Th-228 in the residues! 6

A(Ra-228) A(Th-228) after 4 years years 7

450 400 350 Typical radionuclide compositions at the beginning and after 20 years At the beginning [Bq/g] 300 250 200 150 100 50 0 0 100 200 300 400 500 600 Ra-226 [Bq/g] Pb-210 [Bq/g] Ra-228 [Bq/g] Th-228 [Bq/g] 350 300 250 [Bq/g] 200 150 after 20 years Pb-210 [Bq/g] Ra-228 [Bq/g] Th-228 [Bq/g] 100 50 0 0 100 200 300 400 500 600 Ra-226 [Bq/g] 8

500 450 400 Radionuclide compositions after 50 and 100 years after 50 years [Bq/g] 350 300 250 200 150 100 50 Pb-210 [Bq/g] Ra-228 [Bq/g] Th-228 [Bq/g] 0 0 100 200 300 400 500 600 Ra-226 [Bq/g] 600 500 after 100 years [Bq/g] 400 300 200 Ra-226 Pb-210 Pb-210 [Bq/g] Ra-228 [Bq/g] Th-228 [Bq/g] 100 0 0 100 200 300 400 500 600 Ra-226 [Bq/g] 9

Distribution of Radionuclides in a gas production pipe (length 5 km) bottom [m] surface 10

Activity ratios from the bottom to the surface (gas production pipe 5 km length) bottom [m] surface 11

density and thickness of scale in a gas production pipe Thickness [mm] Thickness Density [g/cm³] Density [g/cm³] bottom [m] surface 12

Gamma dose rates of barrels with residues (Scales from hydrocleaning, high pressure cleaning or waterblasting, 2000 bar) 20 15 10 5 0 80 barrels, mass 14 t Häufigkeit Mean value gamma dose rate: 8,8 µsv/h mean value Ra-226: 30 Bq/g 0 4 8 12 16 20 24 28 32 36 40 44 48 [µsv/h] 13

Ra-226 distribution in barrels with sludge 60 50 experimental frequency Ra-226 lognormal distribution 172 barrels with sludge, Frequency 40 30 Mean value Ra-226: 10,9 Bq/g Median: 3,8 Bq/g Mass: 17 tons 20 10 0 0 4 8 12 16 20 24 28 32 36 40 44 48 [Bq/g] 14

Pb-210 distribution in barrels with sludge 30 experimental frequency Pb-210 lognormal distribution 172 barrels with sludge, Mass: 17 tons 20 Mean value Pb-210: 22,5 Bq/g Frequency 10 0 Median: 9,8 Bq/g 0 4 8 12 16 20 24 28 32 36 40 44 48 In average specific Pb-210 activity of sludge larger than that of Ra-226 [Bq/g] 15

Typical activity ranges in Sludge and Scale Ra-226 up to 150 5-500 Der Vortrag kann auf der IAF Webseite Ra-228 30 1-350 www.iaf-dresden.de heruntergeladen weden Th-228 depending on age depending on age Pb-210 Po-210 Sludge [Bq/g] up to 500 (depending on age) Scale [Bq/g] 1-500 depending on age Specific activities of U-238 und Th-232 mostly below 1 Bq/g. 16

Radon Generation of Dry Scales Exhalation box in a closed tubing 25.000 Bq/m³ [ hours ] of radon could be reached Schichtdicke [ thickness ] Ra-226 [ Exhalationsrate exhalation ] [ Exhalationsrate exhalation ] [ diffusion Diffusionskonstante parameter ] [mm] [Bq/g] [Bq/(m² s)] [Bq/(m² h)] [m²/s] 2,7 440 0,0068 25 5,5 10-18 17

Radon Generation of Sludge Practically radon exhalation of sludge of minor importance Why? Radon Oil-Water distribution coefficient (K d ) is rather large! K d Diesel / Water 39,8 ± 4 Benzine / Water 52,3 ± 6 Air / Water 4 K d = c c Oil W Bq l Bq l 18

Mercury recycling process Sludge and/or Scale 90-95 mass% waste Evaporation and condensation for extraction of raw-mercury dry mineral radioactive residues of the recycling process raw mercury Multi-level purification 5-10 mass% Marketing 19

Preparatory work Preparatory work Taking over the NORM residues Transport of NORM (ADR 7) from somewhere to Leipzig Reception and Inspection control in Leipzig Temporary Storage of NORM Compilation of Charges for the production process (de-mercurisation) Radiation Protection yes, not considered yes, not considered 20 yes yes no

Ongoing work Vacuothermal de-mercurisation RP yes Immobilization of the dry residues RP yes Disposal at a landfill RP yes 21

Take-over room 22

Storage of sludge and scale 23

Plant for de-mercurisation 24

Storage of dry mineral residue after the de-mercurisation process 25

Equipment for making the immobilisates (about 1:1 mixture of NORM residues and geo-polymer) 26

Radiological measurements for dose assessment Radon measurements Gamma rate measurements Dust measurements (α- and γ- spectroscopy) Radionuclide analyses (α- and γ-spectroscopy) 27

Radon concentration in taking-over storage 200 150 average over 3 weeks: 20 Bq/m³ Radon concentration comparable to that of the atmosphere 32 28 24 [Bq/m³] 100 20 16 [ C] 12 50 8 4 0 20.6.10 22.6.10 24.6.10 26.6.10 28.6.10 30.6.10 2.7.10 4.7.10 6.7.10 8.7.10 10.7.10 0 Taking over storage Temperature 28

[Bq/m³] 3000 2500 2000 1500 1000 500 Radon concentration in the storage weekend 34 average over 3 weeks: 855 Bq/m³ 32 average during work: 200 Bq/m³ 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 [ C] 0 0 21.6.10 22.6.10 23.6.10 24.6.10 25.6.10 26.6.10 27.6.10 28.6.10 29.6.10 30.6.10 1.7.10 2.7.10 3.7.10 4.7.10 5.7.10 6.7.10 7.7.10 8.7.10 9.7.10 10.7.10 storage temperature 29

Why elevated Radon concentrations? Residues after the de-mercurisation are almost dry, no volatile organic compounds, emanation factor E: 0,2-0,6 specific Ra-226-activity fairly high stored in big bags Not radon tight 30

Radon concentration in production plant 300 250 200 average over 3 weeks: 30 Bq/m³ closed system and ventilation 38 36 34 32 30 28 26 24 [Bq/m³] 150 100 50 22 20 18 16 14 12 10 8 6 4 2 [ C] 0 0 20.6.10 21.6.10 22.6.10 23.6.10 24.6.10 25.6.10 26.6.10 27.6.10 28.6.10 29.6.10 30.6.10 1.7.10 2.7.10 3.7.10 4.7.10 5.7.10 6.7.10 7.7.10 8.7.10 9.7.10 10.7.10 11.7.10 production plant emperature 31

Radon concentration in immobilisation room 600 500 average over 3 weeks: 109 Bq/m³ average during work: 28 Bq/m³ Efficient ventilation system 30 28 26 24 22 400 20 [Bq/m³] 300 weekend weekend 18 16 14 12 [ C] 200 10 8 100 6 4 2 0 0 22.7.10 23.7.10 24.7.10 25.7.10 26.7.10 27.7.10 28.7.10 29.7.10 30.7.10 31.7.10 1.8.10 2.8.10 3.8.10 4.8.10 5.8.10 6.8.10 7.8.10 8.8.10 9.8.10 10.8.10 doing immobilisation immobilisation room temperature 32

work taking-over, compiling charges handling in the storage Summary: Radon exposure Exposure time [h] Radon concentration [Bq/m³] Dose [msv] 100 20 0,01 200 200 0,12 de-mercurisation 1200 30 0,11 immobilisation 300 28 0,03 sum 1800 0,27 33

Summary: gamma rate measurements taking-over [µsv/h] storage [µsv/h] production plant [µsv/h] equipment for immobilisation [µsv/h] 0,24 0,98 0,33 0,42 taking-over [msv] storage [msv] production plant [msv] equipment for immobilisation [msv] 0,014 0,118 0,238 0,076 34

Summary: external exposure work Exposure time [h] Gamma dose rate [nsv/h] Dose [msv] taking-over, compiling charges 100 240 0,014 handling in the storage 200 980 0,118 de-mercurisation 1200 330 0,238 immobilisation 300 420 0,076 sum 1800 0,45 35

Inhalation of Dust We quantify the dust deposition by measuring the total activity of the used masks!! Most effective and accurate method!! Example: 10 days of deposition worker Very often dominating together with Po-210 Ra-226 [Bq] Ra-228 [Bq] Th-228 [Bq] Pb-210 [Bq] 1 0,6 0,15 0,14 1,4 2 1,7 0,4 0,44 4,4 36

Exposure due to Inhalation of Dust worker exposure time [h] Dose without mask [msv] Dose with mask [msv] 1 1800 0,24 0,024 2 1800 0,74 0,074 Without masks one could easily get an exposure exceeding 1 msv/year!! 37

Total doses for de-mercurisation and immobilisation work taking-over, compiling charges handling in the Exposure time [h] External exposure [msv] Inhalation radon and dust [msv] Total Dose [msv] 100 0,014 0,014 0,028 200 0,118 0,128 0,246 storage de-mercurisation 1200 0,238 0,16 0,398 immobilisation 300 0,076 0,042 0,118 sum 1800 0,45 0,34 0,79 Due to radiation protection measures total exposure dose < 1 msv/year for workers 38

Immobilization with geo-polymer dry mineral radioactive residues of the recycling process Immobilization of the residues by addition of a polymer (geo-polymer) mixing ratio: about 1 : 1 Up to 250 kg in a 120 l barrel ready for disposal 39

Characteristics of the Immobilisate made with geo-polymer Long term stability, Like Hardened Concrete, weather-proof old mortar similar to geo-polymer concrete negligible elution of harmful substances (radionuclides, heavy metals, arsenic) No Exposure via the water path 40

Elution of Immobilisates Sample Ra-226 Ra-228 Th-228 Pb-210 Po-210 [Bq/g] [Bq/g] [Bq/g] [Bq/g] [Bq/g] 1 18 8,85 9,1 3,2 3,2 2 61 11,4 15 80 80 Eluate Ra-226 Ra-228 Th-228 Pb-210 Po-210 [Bq/l] [Bq/l] [Bq/l] [Bq/l] [Bq/l] 1 <0,02 <0,008 <0,02 <0,02 0,018 2 <0,09 0,015 <0,01 0,12 0,005 Eluate has a quality comparable to that of mineral water concerning concentration of radionuclides no exposure along the water path 41

Advantage of the Immobilisate made with geopolymer Negligible low exhalation of radon No formation of dust at handling, transportation and disposal No elution of radionuclides after disposal!! No internal exposition External Exposition due to Gamma Radiation is the only Exposure Pathway 42

According to 98 of the German Radiation Protection Ordinance the de-mercurised residues are released The criterion is: The effective dose should not exceed 1 msv/year (reference value for persons of the population). The values of the specific activities of the relevant radionuclides play practically no role! 43

Transport to the landfill near Leipzig Recycling of Mercury landfill radioactive immobilisates Mercury 44

Barrels filled with immobilisates ready for the transport to the landfill 45

Transport: Radioactive, ADR 7 46

Radiological characteristics of a typical loading to be disposed 30 25 48 barrels, mass: 11,1 tons Mean values 20 Ra-226: 12,2 Bq/g Pb-210: 19,0 Bq/g [Bq/g] 15 10 5 Ra-226 Pb 210 Gamma dose rate: 3,8 µsv/h 0 0 2 4 6 [µsv/h] 47

Gamma dose rate in the driver s cab µsv/h 0,58 48

Transport on street to the landfill Distance to the landfill 13 km Driving time: 15 minutes Gamma dose rate in the driver s cab: 0,3-0,6 µsv/h landfill 15 transportations per year to the landfill Exposure dose of the driver: <2 µsv/year 49

Work at the landfill Handling and storing the barrels: 15 minutes Distance of the worker to the barrels 3-5 meters Gamma dose rate: <0,3 µsv/h landfill Exposure dose of the worker at the landfill: <2 µsv/year 50

Summary Despite the fact, that we are dealing with rather elevated specific activities of the relevant radionuclides, the exposure doses can be kept low by applying necessary Radiation Protection measures. The immobilisation of de-mercurised sludge and scale has the great advantage, that a very stable deposition of hazardous residues can be achieved. 51