The document discusses a study on radon migration through a single-layer cover on a uranium tailings pond. It summarizes the history of uranium mining in Hungary and characteristics of the tailings pond. A model is developed to calculate radon exhalation rates based on parameters like radium content, moisture content, density, and diffusion coefficients. Results show exhalation rates increase with higher radium content and moisture levels. Compacting the cover layer decreases exhalation rates. Based on average conditions, 1.5 meters of cover is needed to meet regulatory limits. Multilayer covers and revegetation can further reduce radon risks.

1. RADON MIGRATION STUDY ORADON MIGRATION STUDY ONN SINGLESINGLE--
LAYER COVERAGELAYER COVERAGE PROCESS OFPROCESS OF
URANIUM ENHANCINGURANIUM ENHANCING TAILINGTAILINGSS PONDPOND
Andras Varhegyi,Andras Varhegyi, Norbert KavasiNorbert Kavasi,, Tetsuo IshikawaTetsuo Ishikawa
October 19October 19, 2010, 2010
3535thth ARPS Conference Challenges for a New DecadeARPS Conference Challenges for a New Decade
AdelaideAdelaide,, AUSTRALIAAUSTRALIA

2. Born of TailingsBorn of Tailings
Crude uranium oreCrude uranium ore Physical digestionPhysical digestion Chemical digestion (HChemical digestion (H22SOSO44 ))
SolutionSolution SolidSolid
RaRa--226 ~99%226 ~99%
U isotopes ~10%U isotopes ~10%
Th isotopes ~70%Th isotopes ~70%
NeutralizationNeutralization
Tailings pondTailings pond
MultiphaseMultiphase
processprocess
PrecipitationPrecipitation
FiltrationFiltration
WashingWashing
DryingDrying
Yellow cakeYellow cake
Introduction

3. Uranium mining in HungaryUranium mining in Hungary
19531953-- Investiagtion of uranium ore in TheInvestiagtion of uranium ore in The
West Mecsek Mountain (Pecs)West Mecsek Mountain (Pecs)
19571957-- Exploitation of Uranium ore, transportExploitation of Uranium ore, transport
to Soviet union.to Soviet union. During the 40 yearsDuring the 40 years
operationoperation periodperiod
approximately 46approximately 46 million t ofmillion t of
rock has been minedrock has been mined outout resulted inresulted in
app. 19 million t barrenapp. 19 million t barren rocks.rocks.
19671967-- Set up chemical separation factorySet up chemical separation factory
Altogether 25.8 million t uranium oreAltogether 25.8 million t uranium ore
were chemically treatedwere chemically treated
19921992-- Commence the recultivation processCommence the recultivation process
19971997-- Shut down the uranium mining andShut down the uranium mining and
processingprocessing
20082008-- Recultivation was accomplishedRecultivation was accomplished

4. Characters of tailings pondCharacters of tailings pond
Facility piece: 2Facility piece: 2
Area: 163 haArea: 163 ha
Disposed material: 20.4 MtDisposed material: 20.4 Mt
Disposed tech. solution: 32 Mm3Disposed tech. solution: 32 Mm3
U: ~1 kBq kgU: ~1 kBq kg--11
RaRa--226 ~4.5 kBq kg226 ~4.5 kBq kg--11
PbPb--210 ~6.5 kBq kg210 ~6.5 kBq kg--11
γγ--dose rate: ~2.4dose rate: ~2.4 µµSv hSv h--11
Rn exhalationRn exhalation--44--10 Bq m2s10 Bq m2s
CRn: 200 BqmCRn: 200 Bqm--3 (1003 (100--400)400)

5. Cost of the remediation work at uraniumCost of the remediation work at uranium
mine and vicinitymine and vicinity
TotallyTotally cost incost in allall facility itefacility items wasms was 20.720.7 Billion HUF (Billion HUF (7474 Million EUMillion EURR))

6. (D(Dff ·· ))1/21/2
JJz=0z=0 == –––––––––––––––– ·· cc00 + c+ cff ··[ch(h/d[ch(h/dff)) –– 1]1]
sh(h/dsh(h/dff))
wherewhere
JJc=0c=0 –– surface exhalation rate (Bqsurface exhalation rate (Bq mm--22 ss--11))--limit: 0.74limit: 0.74 BqBq mm--22 ss--11
DDc/tc/t –– Diffusion coeffitient mDiffusion coeffitient m22ss--11
((influencedinfluenced byby ρρ--density,density, pp--porosityporosity,, ww--moisture content)moisture content)
(D(Dairair = 10= 10--55 mm22ss--11, D, Dwaterwater = 10= 10--99 mm22ss--11))
 –– decay constant of Rn (2.1decay constant of Rn (2.1··1010--66 ss--11))
hh –– thickness of covering layer (m)thickness of covering layer (m)
ddcc –– diffusion distancediffusion distance (D/(D/ ))1/1/ 22 (m(m22))
cc00 –– boundary surface Rn concentration (Bqboundary surface Rn concentration (Bq mm--33))
((influencedinfluenced byby cct/ct/c , D, Dt/ct/c , k, k--RnRn solubility coefficientsolubility coefficient,, hh))
cct/ct/c –– tailing/covering pore Rn concentration (Bqtailing/covering pore Rn concentration (Bq mm--33))
((influencedinfluenced byby ccRaRa,, EE--emanation coefficientemanation coefficient ,, ρρ,, pp,, ww))
Developed Model CalculationDeveloped Model Calculation

7. Characters Tailings Covering Clay
Ra-conc Bq/kg 4500 (3000-6800) 43 (27-61)
E - emanation coeff. % 16 12
ρ – density kg/m3 2.0 1.9
P - Porosity Vol% 50 38
w – moisture cont.
Vol%
32 (29-33) 26 (23-27)
D – diffusion coeff.
m2/s
1.5E-7 (8E-8-2E-7) 2E-7 (6E-8-5E-7)
The calculated thickness of single layer covering for 0.74 Bq/m2The calculated thickness of single layer covering for 0.74 Bq/m2ss
exhalation rate limit:exhalation rate limit:
most optimistic circumstances:most optimistic circumstances: 0.8 m0.8 m
average circumstances:average circumstances: 1.1 m1.1 m
most wrong circumstances:most wrong circumstances: 1.5 m1.5 m

8. Some Results of the Calculation I.Some Results of the Calculation I.
Influence of Ra content of tailing s on the exhalation rateInfluence of Ra content of tailing s on the exhalation rate

9. Influence of Moisture content on the exhalation rateInfluence of Moisture content on the exhalation rate
Some Results of the Calculation II.Some Results of the Calculation II.

10. Influence of compaction on the exhalation rateInfluence of compaction on the exhalation rate
Some Results of the Calculation II.Some Results of the Calculation II.

11. Results after the covering process I.Results after the covering process I.
Rn concentration in pore after the covering processRn concentration in pore after the covering process

12. Results after the covering process II.
Exhalation rate after the covering processExhalation rate after the covering process

13. ConclusionsConclusions
According to the model calculation, observable that the incremenAccording to the model calculation, observable that the increment of the Rat of the Ra
concentration in the tailings is less, the exsiccation of the coconcentration in the tailings is less, the exsiccation of the covering layer isvering layer is
significantly while the exsiccation of tailings and covering laysignificantly while the exsiccation of tailings and covering layer is extremelyer is extremely
significantly could increase the exhalation rate of radon concensignificantly could increase the exhalation rate of radon concentration.tration.
Compacting the covering layer as decreasing the porosity as it wCompacting the covering layer as decreasing the porosity as it was expectedas expected
decreased the exhalation rate is mark able.decreased the exhalation rate is mark able.
Tailings with average Ra content 4.5 kBq/kg and exhalation ratTailings with average Ra content 4.5 kBq/kg and exhalation rate 4e 4--1010
Bq/m2s requires 1.5 m single layer coverage to fulfill the 0.7Bq/m2s requires 1.5 m single layer coverage to fulfill the 0.74 Bq/m2s (dose4 Bq/m2s (dose
limit 1 mSv/year).limit 1 mSv/year).
Using multilayer covering landscape recultivation, water reserUsing multilayer covering landscape recultivation, water reservoirvoir
protection, erosion and dust spreading protection are also resoprotection, erosion and dust spreading protection are also resolvable.lvable.

14. Some Pictures about the remediation workSome Pictures about the remediation work
Covering processCovering process

15. Grass:
- 200 kg mixed grass seeds / ha
Bushes or trees:
- 21 species
- 8 000 pieces / ha (1-2 years old)
- distance between the rows: 2,5 m
- distance in the rows: 0,5 m
Chemical fertilizer:
- N 120 kg / ha
- P2O5 100 kg / ha
- K2O 170 kg / ha
BiologicalBiological
remediationremediation

16. 2001 2003 2006
Tailings pond No. I. and II.Tailings pond No. I. and II. ––landscape from the airlandscape from the air
Autumn, 2003 Spring, 2004

17. Thank you very much for your kind
attention!