RADON MIGRATION STUDY ORADON MIGRATION STUDY ONN

SINGLESINGLE-- LAYER COVERAGE LAYER COVERAGE PROCESS OF PROCESS OF

URANIUM ENHANCING URANIUM 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 DecadeAdelaideAdelaide, , AUSTRALIAAUSTRALIA

Born of TailingsBorn of TailingsCrude uranium oreCrude uranium ore Physical digestionPhysical digestion Chemical digestion (HChemical digestion (H22

SOSO44

))

SolutionSolution SolidSolid

RaRa--226 ~99%226 ~99%U isotopes ~10%U isotopes ~10%Th isotopes ~70%Th isotopes ~70%

NeutralizationNeutralization

Tailings pondTailings pond

Multiphase Multiphase processprocess

PrecipitationPrecipitationFiltrationFiltrationWashingWashingDryingDrying

Yellow cakeYellow cake

Introduction

Uranium mining in HungaryUranium mining in Hungary

19531953--

Investiagtion of uranium ore in The Investiagtion of uranium ore in The West Mecsek Mountain (Pecs)West Mecsek Mountain (Pecs)

19571957--

Exploitation of Uranium ore, transport Exploitation of Uranium ore, transport to Soviet union. to Soviet union. During the 40 years During the 40 years operation operation period period approximately 46 approximately 46 million t of million t of

rock has been mined rock has been mined out out resulted in resulted in app. 19 million t barren app. 19 million t barren rocks. rocks.

19671967--

Set up chemical separation factorySet up chemical separation factoryAltogether 25.8 million t uranium ore Altogether 25.8 million t uranium ore were chemically treatedwere chemically treated

19921992--

Commence the recultivation processCommence the recultivation process19971997--

Shut down the uranium mining and Shut down the uranium mining and

processingprocessing20082008--

Recultivation was accomplishedRecultivation was accomplished

Characters of tailings pondCharacters of tailings pond

Facility piece: 2Facility piece: 2Area: 163 haArea: 163 ha

Disposed material: 20.4 MtDisposed material: 20.4 MtDisposed tech. solution: 32 Mm3Disposed tech. solution: 32 Mm3

U: ~1 kBq kgU: ~1 kBq kg--11RaRa--226 ~4.5 kBq kg226 ~4.5 kBq kg--11PbPb--210 ~6.5 kBq kg210 ~6.5 kBq kg--11

γγ--dose rate: ~2.4 dose rate: ~2.4 µµSv hSv h--11Rn exhalationRn exhalation--44--10 Bq m2s10 Bq m2sCRn: 200 BqmCRn: 200 Bqm--3 (1003 (100--400)400)

Cost of the remediation work at uranium Cost of the remediation work at uranium mine and vicinitymine and vicinity

Totally Totally cost in cost in allall

facility itefacility items wasms was

20.720.7

Billion HUF (Billion HUF (7474

Million EUMillion EURR))

(D(Dff

··

))1/21/2

JJz=0z=0

= = ––––––––––––––––

··

cc00

+ c+ cf f ··[ch(h/d[ch(h/dff

) ) ––

1]1]sh(h/dsh(h/dff

))

where where

JJc=0c=0

––

surface exhalation rate (Bqsurface exhalation rate (Bq

mm--22

ss--11))--limit: 0.74 limit: 0.74 BqBq

mm--22

ss--11

DDc/tc/t

––

Diffusion coeffitient mDiffusion coeffitient m22ss--1 1

((influencedinfluenced

by by 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 distance diffusion distance (D/(D/

))1/1/

22

(m(m22))

cc00

––

boundary surface Rn concentration (Bqboundary surface Rn concentration (Bq

mm--33) )

((influencedinfluenced

by by 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

by by ccRaRa

, , EE--emanation coefficient emanation coefficient , , ρρ, , pp, , ww))

Developed Model CalculationDeveloped Model Calculation

Characters Tailings Covering ClayRa-conc Bq/kg 4500 (3000-6800) 43 (27-61)

E -

emanation coeff. % 16 12ρ

– density kg/m3 2.0 1.9

P -

Porosity Vol% 50 38w –

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/m2s s exhalation rate limit:exhalation rate limit:

most optimistic circumstances:most optimistic circumstances:

0.8 m0.8 maverage circumstances:average circumstances:

1.1 m1.1 m

most wrong circumstances:most wrong circumstances:

1.5 m1.5 m

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

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.

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.

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

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

ConclusionsConclusionsAccording to the model calculation, observable that the incremenAccording to the model calculation, observable that the increment of the Ra t 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 is vering layer is significantly while the exsiccation of tailings and covering laysignificantly while the exsiccation of tailings and covering layer is extremely er 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 expected as 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--10 10 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 (dose 4 Bq/m2s (dose limit 1 mSv/year).limit 1 mSv/year).

Using multilayer covering landscape recultivation, water reserUsing multilayer covering landscape recultivation, water reservoir voir protection, erosion and dust spreading protection are also resoprotection, erosion and dust spreading protection are also resolvable.lvable.

Some Pictures about the remediation workSome Pictures about the remediation work

Covering processCovering process

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 mChemical fertilizer:

- N 120 kg / ha- P2 O5 100 kg / ha- K2 O 170 kg / ha

Biological Biological remediationremediation

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

Thank you very much for your kind attention!