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“ Effect of Cover Layer on Radiological Impact of Landfill for TENORM Waste from Tin Industry in Bangka Island ”

Nazhira Shadrina, Zeni Anggraini, Budi Setiawan, Dadong Iskandar Center for Radioactive Waste Technology – BATAN

InfoPublik - BATAN Kini Punya Aplikasi Layanan Pengelolaan Limbah Radioaktif

The  4 th  International Conference  on Nuclear Energy Technology and Science  2021 8 th   September  2021

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Tin Mining Low-grade Tin Ores Enrichment of Tin Ore High-grade Tin Ore  (>72% Sn) Mine Tailings Tin Tailings Tin Smelting Tin Metal Tin Slag Separation element among zircon, monazite, ilminite using magnetic separator,  high-voltage separator, etc Monazite, Zircon, Ilminite, etc Waste from  by-product industry Low concentration of  NORM High dose rates for the worker and elevated  NORM  concentration

Uranium
Protactinium
Thorium
Actinium
Radium
Radon gas
Lead
ISh
5.15 v
3_63
gas
Rn.m
55.6S
Bi.212
055 m
Pb.212
stable
1064 h
Tl-208
3053m
s«ies
Rn-222
.824
Pb-214
268 m
Bi-214
13.9m
Pb.210
222 Y
Low solubiüty
Low solubility
Bi-210
5.012 d
Pb-206
stable
Uranium series

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Large volume  →   ±   43,851,618 kg of tin slag from several smelters in Bangka Island Can cause radiological dose to worker  >20 mSv Need to stored properly and safely TENORM   → Very Low Level Waste →  can be disposed in Landfill The crucial part is Cover layer  to prevent rainwater infiltration and radionuclide migration  Degradation the geomembrane leads to  optimization on clay layer  “thickness” By evaluating effect of various thickness on radiological consequences using RESRAD-ONSITE

Obtain optimum thickness of clay layer which its radiological consequences can comply with regulations

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The Bangka Regency The  Tanjung   Genting  Formation  is  composed of  clay soil   which  has a  low  permeability  . Climatological  data  A verage  rainfall  :   2.0733 m/y  A verage  wind speed  :   1.44  m/s Landfill  area  is 4200 m 2   with 4 m  depth Distance  between highest groundwater level and landfill base is  4 m

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METHODOLOGY “Landfill design & Inventory”

Density of tin slag    : 2.65 g/cm 3 Concentration  Activity 232 Th   10,14 Bq/g  226 Ra   6 Bq/g  40 K   0.66 Bq/g  Clay density  in  cover  system  :  1.3  g/cm 3

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Occupancy   	 Work duration  :  2,000 hours per year ,  spending   6 hours/day  ( indoor)   and 2 hours/day  ( out door) I nhalation  rate  for  a  worker is 1.3 m 3 /h A verage   soil ingestion  is 36.5 g/year. The exposure duration  of  the  worker is 30 years.

Sou r ce
Environm ental
Direct Exposure
Exposur e
External
Radi ation
Inhalation
Ingestion
Dose
On-site
Air
Radon
Direct Ingestion

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Dose j,p ( t )    :  the effective dose DCF j,p ( t )    :  dose conversion factor ETF j,p ( t )   :  the environmental transport factor, SF i,j ( t )    :  the source factor S i ( O )    : t he soil concentration of the radionuclide.  BRF   :  braching  factor (dimensionless);  RC   :  coefficient of external radiation risk ED  : d uration  of exposure Index label for environmental pathway  ( p ) , line component  ( q ), initially  existance  radionuclide  ( i ) , and radionuclide in decay chain of radionuclide  i   ( j ) ,

CANCER RISK E xternal  exposure I nhalation  and  S oil ingestion

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I ncreasing   the  thickness  of clay layer  by 1 m can reduce the accepted dose by 64 %  at first year The thickness of 5 m and 6 m give   dose acceptance below  dose limit for public  ( 1  mSv /year )

TABLE   1.   Maximum   total   dose   at   variation on   cover   thickness Cover   Thickness   (m) Maximum   Total   Dose   ( mSv /y) At year 1 53.8 1 2 19.1 1 3 6.84 1 4 2.46 1 5 1.12 598 ± 1 6 0.92 60 03

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Only calculate excess cancer risk by radiation exposure from activated pathways It is influenced by accepted dose The excess cancer risk  still higher than risk limit for disposal facility  ( 10 - 5 )

(s.reaA) aul!l
00001
0001
001
01
DII!liiiidiiiiiiiidiiiiiiii6

TABLE   2.   Accepted   dose   and   cancer   risk   after   applying   6-meters clay   layer t   (years) 0 1 30 100 300 1000 3000 10000 TDOSE   ( mSv /y ) 3.17 ×10 -1 3.16 ×10 -1 3.09 ×10 -1 3.64 ×10 -1 6.00 ×10 -1 4.29 ×10 -1 3.75 ×10 - 2 8.68 ×10 -9 Excess  Cancer   Risk 7.54×10 -4 7.5 4 ×10 -4 7.3 7 ×10 -4 9.8 1 ×10 -4 1.4 8 ×10 -3 1.01×10 -3 8. 90 ×10 - 5 2.00×10 -11

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The  radionuclides  that most influenced dose acceptance are Ra dium  and its progeny  Critical Pathways → Radon (  both  water independent and dependent) Exposure from T h-232  and its progeny  affect in increase of radiological impact after 5000  year ( water-independent pathways)

Pathways
Radionuclide
Radon (Water Independent) — — -Soil Ingest
— Til-232
— Ra-226
— - Radon (Water Dependent) — — - External
K-40
— — -Inhalation
1.0
0.8
0.6
0.2
0.0
10000
1
10
100
1 ooo
Time (Years)

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I n the worker scenario, the most critical radionuclide is  Radium and its decay products  Inhalation of Radon  is the major contributor toward radiological impact.  The  thickness of  clay layer should be more than 4 meters.  From the simulation results,  total accepted dose and cancer risk  reached the minimum value when the thickness of  clay layer  becomes  6 meters, with the value of  0.92  mSv /y  and  2.14  ×10 -3 , respectively.  Therefore, we propose that  the cover thickness  for  the  landfill facility is  6 meters  to ensure safety for worker s until thousands of years after closure.

"Effect of Cover Layer on Radiological Impact of Landfill for TENORM Waste from Tin Industry in Bangka Island"

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