J.P. Bolívar 1) and R. García-Tenorio 2) OCCUPATIONAL EXPOSURES AND DISTRIBUTION OF NATURAL RADIONUCLIDES IN THE PHOSPHORIC ACID PRODUCTION BY THE WET PROCESS (SPAIN) J.P. Bolívar 1) and R. García-Tenorio 2) Department of Applied Physics, University of Huelva (Spain) Department of Applied Physics II, University of Seville (Spain) 9th European ALARA Network Workshop. Augsburg, 18 – 21 October 2005

MAIN OBJETIVES To study the fluxes and distribution of natural radionuclides in the industrial process of phosphoric acid production, in Huelva (Spain). To evaluate the radiological impact of this industrial activity on the workers.

LOCATION OF THE FACTORIES Huelva Town Odiel river Fertilizer plants Tinto river Odiel river MINING AREA 50 km Tinto river NATURE RESERVE Complex-2 Industrial

Tinto river Common river mouths Discharge PR point Odiel river Phosphate rock (PR) + Sulphuric acid (SA) Phosphoric acid (PA) + Phosphogypsum (PG) Phosphogypsum active piles Tinto river Odiel river Common river mouths Discharge PR point Fertilizer plants Salt marshes Huelva town Restored piles

Concentrated Phosphoric acid Phosphate Rock CONCENTRATION FILTRATION MILLING ACID ATTACK Phosphogypsum: into piles WATER Sulphuric acid P2O5 recycling (22%) Production acid (27% P2O5 ) Concentrated Phosphoric acid (54 % P2O5 ) PR ~ 2·106 Tm PA SA PG ~ 3·106 Tm ANNUALLY CONSUMPTION - PRODUCTION Sedimentary PR 238U ~ 1.5·103 Bq/kg; 232Th ~ 30 Bq/kg

PHOSPHATE ROCK (P R) Table 1 Table 2 Milling step. Activity concentrations (Bq/kg) Sample type 238U 226Ra 228Ra Raw PR 1840 ± 130 1560 ± 80 22 ± 2 Buk milled PR 1640 ± 90 1722 ± 90 20 ± 2 Optimum size PR 1630 ± 90 1780 ± 90 40K 16 ± 2 Table 1 Attack step. Activity concentrations in pulps (Bq/kg) Sample type 238U 226Ra 228Ra Liquid 1340 ± 90 5 ± 1 < 1.1 Solid 450 ± 30 760 ± 35 14 ± 2 40K 8 ± 2 14 ± 3 Table 2

Table 3 Table 4 Filtration step. Activity concentrations (Bq/kg) Sample 238U 226Ra 228Ra PG before washing 810 ± 50 880 ± 40 14 ± 2 PG after first washing 460 ± 30 1040 ± 50 15 ± 2 PG after second washing 450 ± 30 1000 ± 50 17 ± 2 PG to be stored 310 ± 20 900 ± 50 Table 3 Concentration step. Activity concentrations (Bq/kg) Sample 238U 226Ra 228Ra P2O5 (32%) 1300 ± 70 4 ± 1 < 1 P2O5 (54%) 1830 ± 180 8 ± 1 Table 4

Concentrations (Bq/kg) Concentrations (Bq/kg) Concentrations (Bq/kg) HOT POINTS Concentrations (Bq/kg) Fraction 238U 230Th 226Ra 210Pb Liquid 2100 1250 7.5 45 Solid 2000 4300 Sludges precipitated in the tanks where phosphoric acid is stored Table A Concentrations (Bq/kg) Fraction 238U 230Th 226Ra 210Pb Liquid 1250 250 4.5 85 Solid 900 1300 1400 Sludges floating in the tanks where phosphoric acid is stored Table B Concentrations (Bq/kg) Fraction 238U 230Th 226Ra 210Pb Prayon Filter 300 2300 3400 Milling Filter 1000 1200 2100 1100 PG from pipes 2000 830 1400 Scales and filters from the filtration step collected during maintenance Table C

Dosimetric study inside the Factories External irradiation: gamma - beta Internal irradiation 222Rn + daugthers In progress Ready Indirect route ingestion Internal irradiation dust inhalation In progress

EXTERNAL GAMMA DOSE RATES External gamma dose rates (mGy/y) inside the factories above background Morocco Kola Fertilizer stores Inside a DAP store 0.25 Milling zone Inside phosphorites silo 2.20 0.60 1 meter beside silo 0.35 1.50 1 meter away milled rock pile 0.40 -- Mill operator cabin 0.45 1 meter away rock dust pipes 0.80 Attack zone Above compartments 3 and 4 of reactor 0.90 0.95 At 2 meters over reactors 4 and 5 0.10 Above compartments 4 and 5 of reactor

Table 6 External gamma dose rates (mGy/y) inside the factories above background Morocco Kola Filtration zone (ABOVE the filter, not accessible to the workers) At 1 m between the pulp entrance and the 1st washing 6.75 4.20 At 1 meter of the 1st washing 9.20 8.95 At 1 meter between the 1st and 2nd washing 6.40 4.90 At 1 meter of the 2nd washing 8.65 9.90 Filtration zone ( AROUND the filter, accessible to workers) Between the pulp entrance and 1st washing 1.50 1.05 Between the 1st and 2nd washing 1.20 Between the 2nd and 3rd washing Concentration zone At 2 meters of the concentration zone 0.10 -- Above the production acid decantation pool 1.85 Other places Chemical laboratory 0.00 Control process room Old control process room Table 6

Distance factory - piles ~ 1 km PG PILES IN OPERATION Huelva town Restored piles Regulating water reservoir Pipes pumping waters Piles  Factories Pumping station Pipes pumping waters Factories  Piles Perimetral wall Perimeter Channel Tinto river Distance factory - piles ~ 1 km

Dosimetric study in PG piles External irradiation: gamma - beta Internal irradiation 222Rn+daugthers Preliminary results Ready Indirect route ingestion Internal irradiation dust inhalation Preliminary results

Enhanced external dose rates in active PG piles Point Dose rate (mGy/yr) 1 2.69 10 1.20 2 1.23 11 1.24 3 1.05 12 1.06 4 2.13 13 1.38 5 1.31 14 1.47 6 15 7 1.63 16 1.51 8 1.08 17 1.25 9 1.52 18 0.85

Δexternal doses (mGy/year) ACTIVE PHOSPHOGYPSUM PILES Entrance Occupational factors < 0.2 Δexternal doses (mGy/year) Entrance 2.70 Perimetral wall 1.40 Pumping station ~ 0 Surrounding soils

222Rn exhalation rates in phosphogypsum piles Point Exh. rate Uncert. Mean St. Desv. Range of values: 55 - 2300 Bq m-2 h-1 Average: 613 ± 286 Bq m-2 h-1

222Rn in the piles PG Piles Huelva town 13,1 ± 1,6 12,6 ± 2,0 Hour 5 10 15 20 25 30 35 1 3 7 9 11 13 17 19 21 23 Activity 222 Rn (Bq/m ) Exteriores Huelva Exteriores Balsas Hour Huelva town outdoors PG Piles PG Piles Huelva town 13,1 ± 1,6 12,6 ± 2,0 Average values for Six months

Equipments used for samplings SAMPLING OF “TOTAL SUSPENDED PARTICLES” (TSP) Equipments used for samplings in both PG piles and the background Area Thershold = 150 µg m-3 Average = 50 µg m-3 TSP concentrations in the PG piles

Doses estimated through this route: RADIOACTIVITY IN “TOTAL SUSPENDED PARTICLES” IN PG PILES Doses estimated through this route: < 10 µSv/y Sample

ACKNOWLEDGEMENTS MAIN CONCLUSIONS The distribution and fluxes of several natural radionuclides from the U-series have been analysed along the industrial process. It has served as a basis for the design of dosimetric campaigns. An external gamma dose rate map has been performed inside one of the factories. Taking in consideration the occupational factors, doses lower than 1mSv/year are received by the workers trough this route. The effective doses received by the workers involved in the construction and maintenance of the piles is also lower than 1 mSv/year, taking into consideration external radiation, inhalation of 222Rn and inhalation of suspended particles. ACKNOWLEDGEMENTS Financial support from Spanish National Security Council (CSN) through its I+D programme 2004-2007 is deeply acknowledged. - We are indebted to FERTIBERIA staff (especially Mr. Garralda) for the collaboration in the performance of this work.

DANKE SCHON thank you MUCHAS GRACIAS 9th European ALARA Network Workshop. Augsburg, 18 – 21 October 2005

Odiel Channel PR discharge point PR stores P2O5 factory (AF1) PG pumping to the piles

EXTERNAL GAMMA DOSE RATES Milling 0.35 - 3.2 Attack ~ 0 Filtration 4 - 12 Worker rooms ~ 0 Concentration step 1.6 - 2.8 Estores PR ~ 0.30 Acid Tanks 0.7 - 4.4 Entrance factory (Background) Δexternal doses (mGy/yr) Background = 0.60 mGy/yr

Activity concentrations in PG from active piles (Bq/kg) Average concentrations (Bq/kg) 238U 230Th 226Ra 210Pb 200 550 650 500 Average concentrations (Bq/kg) 228Ra 40K 137Cs 20 < 20 < 0.7 Tables 7 Activity concentrations in WATERS from PG piles (Bq/L) Sample 238U 230Th 226Ra 210Po 232Th 228Th 235U 40K E 200 2.5 0.8 5 1 9 8 P 180 2.3 3 0.4 {E} = Water from regulator pool (Bq/L) {P} = Water from the leachated recovered in permitral channel (Bq/L) Table 8

222Rn in the piles Monthly average values Activity concentration 222Rn (Bq m-3) Monthly average values

“TOTAL SUSPENDED PARTICLES” IN PG PILES DOSIMETRIC IMPLICATIONS Radionuclide Average increment (Bq m-3) Dose Conversion Factor (Sv/Bq) Dose increment (Sv/m3) 238U 1.34·10-5 8.0·10-6 1.07 10-10 234mPa 4.0·10-10 5.36 10-15 234Th 7.7·10-9 1.03 10-13 234U 9.4·10-5 1.26 10-10 230Th 7.42·10-6 1.4·10-5 1.04 10-10 226Ra 1.10·10-5 9.5·10-6 1.05 10-10 210Pb Not detected 5.6·10-6 background 210Po 4.3·10-6 Dose increment 4.4·10-9 Sv m-3 Inhalated volume 8760 m3 Occupational factor 0.20 0.77 µSv·y-1