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NORM VIII
Natural radionuclides in sediments from
Poços de Caldas Plateau
– Brazil
N. C da Silva, H. L. C. Alberti, E. T. Z. Guerrero, M. R. L. Nascimento, R. L.
Bonifácio, H. A. Franco do Nascimento, R. A. S. Villegas
Brazilian Commission for Nuclear Energy - CNEN
Laboratory of Poços de Caldas - LAPOC
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NORM VIII
Outline
1. Area location
2. Why Poços de Caldas Plateau?
3. Acid Mine Drainage at Caldas site (former
uranium mine)
4. Sampling strategy
5. Analytical procedures
6. Results
7. Conclusions
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NORM VIII
Brazilian Commission for Nuclear Energy- CNEN
DIFOR, Fortaleza
CRCN-NE, Recife
CDTN, Belo HorizonteLAPOC, Poços de Caldas
IPEN, São Paulo
CNEN CEO, IRD; IEN, DIANG (Angra dos Reis) , Rio de Janeiro
DICAE, Caetité
DIPLAN, BrasiliaCRCN-CO, Goiânia
Nuclear regulatory authority and research & development
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NORM VIII
• Located at the border of States
of Minas Gerais and São Paulo
(230 km far from São Paulo),
Southeast Brazil;
• Volcanic caldera: ~35 km
~250.000 inhabitants
Area Location (Poços de Caldas Plateau)
Average altitude 1200 – 1600 m
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NORM VIII
Why Poços de Caldas Plateau?
• Elevated altitude compared to the surrounding area
• Some radioactive anomalies (e.g. Morro do Ferro)
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NORM VIII
Why Poços de Caldas Plateau?
Industrialarea
Mine
pit
wrp#8
wrp#4
Tailing
dam
* area 1800 ha
• First Brazilian uranium mining and milling
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NORM VIII
Acid Mine Drainage
Source: https://www.dwa.gov.za/projects/amdfslts/default.aspx
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NORM VIII
Acid water treatment and sludge management
Annual acid water treated ~ 2.5 million m3
(~ 1.4 lime kg/m3 treated
water)
Annual lime consumption ~ 3500 tons
Thickener overflow high pH >11
• Flow rate to mine pit 45 m3/h• Sludge density ~1.04 g/cm3
• Dried mass 16 g /L
* Operating since 1982
Energy consumption 3.5 – 4.3 TW-h/year
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NORM VIII
Settlement pond #D3 and #D4
Thickener overflow ~300 m3/h
Settlement pond D3
Settlement pond D4
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NORM VIII
Environmental impact on Águas Claras Reservoir
Sludge settlement
U concentration ?
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NORM VIII
Experimental - Sampling strategy
Bottom sediments were collected in 4 campaigns (held
on January- 2015, March-2015, October-2015 and
January- 2016) in 8 sampling stations located in
reservoirs of Antas river (creek) or in its affluents.
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NORM VIII
Experimental - Sampling strategy
• P1- Pitagueiras Creek, uranium mine upstream (background)
• P2- Águas Claras Reservoir, uranium mine upstream
• P3- Discharge point of uranium mine water treatment plant
• P4- Águas Claras Reservoir, downstream P3
• P5- Águas Claras Reservoir (near to its mouth), uranium mine downstream
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NORM VIII
Experimental – Sampling strategy
• P6- Cipó
Reservoir
• P7- Bortolan
Reservoir
• P8- Rolador
Reservoir
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NORM VIII
Experimental – Sampling procedure
• A dredger drag, operated using a boat, was used to collect
bottom sediment in all reservoirs.
• Samples were stored in plastic bags (20 kg maximum
capacity) before being transported to laboratory.
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NORM VIII
Experimental – Sample treatment
• Samples were dried at 110°C until reaching constant weight,
milled in a jar mill (of stainless steel balls, diameter of 1
inch, at 30 rpm) and sieved at 1,70 mm (10 mesh)
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NORM VIII
Experimental – Ra-226, Ra-228 and Pb-210
determination
High Resolution gamma-ray spectroscopy (Canberra HPGe of 20%
relative efficiency)
• Dried samples were kept in sealed metal boxes for 30 days (to
ensure secular radioactive equilibrium between Ra-226 and its
daughters Pb-214 and Bi-214)
• The photopeak 186.1 keV of Ra-226 was not considered due to high
U content (and interference from photopeak 185.7 keV of U-235)
• For Ra-226 determination, the photopeaks used were 609 keV and
1020 keV of Bi-214
• The photopeak 911 keV of Ac-228 (6.12h half-life) was used for Ra-
228 determination
• For determination of Pb-210, the photopeak 46.5 keV was used
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NORM VIII
Experimental – U and Th determination
Inductively coupled plasma mass spectrometry, ICP-MS
• Samples were previously solubilized using nitric digestion
in closed vessel on a microwave-assisted digestion device
following a procedure similar to USEPA Standard 3050B
These assays (ICP-MS, HPGe) are currently under process of
accreditation by the Brazilian Accreditation Authority –
CGCRE/INMETRO
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NORM VIII
Results- Background
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NORM VIII
Results- Águas Claras Reservoir
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NORM VIII
Results- reservoirs downstream
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NORM VIII
• Sampling Stations #4 and #5 (Águas Claras reservoir)
present significantly high concentrations of uranium in
sediments, confirming anthropogenic contribution.
• A strong dilution trend of this element is observed when
comparing sampling stations #3 and #4 to the others
downstream.
• A situation of environmental liability is observed and
represented by these high concentrations, which come
from the Acid Water Treatment System and should be
environmentally remediated.
Conclusions
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NORM VIII
• The high sulfate concentration in the acid water, which led
to the precipitation of Ra-226 and Pb-210, explains the low
concentration of these two radionuclides in the sediment
• The low thorium content in rocks located in the uranium
mining site explains the low concentration level of this
radionuclide and its daughter Ra-228 in the sediment
Conclusions
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NORM VIII
Acknowledgements