PK Narayan, RR Rakesh, RK Bajpai & RN Nair BARC- … A case study BARC- IAEA Regional Training Course on Development of Near Surface Disposal Facility Mumbai, India February 15-19,

BARC- IAEA Regional Training Course

on

Development of Near Surface Disposal Facility

Mumbai, India

February 15-19, 2010

Post-Closure Safety Assessment of a

NSDF: A case study

PK Narayan, RR Rakesh, RK Bajpai & RN Nair


NSDF: A case study

Operating NSDF In India 1. Seven NSDF operational

2. Built in remarkably different geological, hydrogeological and

climatologically varying domains

Coastal Facilities

Three NSDF located in weathered basalts, high rainfall, low recharge, gentle

slopes, highly sorptive soil

One in lateritic soil profile developed over crystalline rock, coastal humid

climate,high rainfall, poor sorption

One more located along the east coast in weathered profile over charnockite

rocks ,moderate rain fall, moderate sorption

Inland Facilities One located in flat bedded sandstones, thin soil cover,semi arid climate

One located in Alluviums of Northern Plains, high groundwater potential


NSDF: A case study

Safety Assessment Case

Study of a coastal site

Site specific charecterization &

Safety Assessment


NSDF: A case study

About the Facility

Location In Basaltic Terrain along the West Coast

Disposal Modules : Stone Lined Trench, RCT and Tile Holes

Waste Source : Operation of research reactors,

Various radiological laboratories and the reprocessing

plant .

Industrial and medical application of radiation sources

Waste volume disposed ( Till Dec. 1997) Approximately 20,500 m3

13925 m3 in Earth Trenches (ET)/Stone Lined

Trenches (SLT), 6525 m3 in RC Trenches (RCT)

and remaining 50 m3 in Tile Holes (TH)


NSDF: A case study

Site characterization

Regional Geological framework

Topography

Dominantly flat topography with a few high relief (110m elevation) hills

with steep step like slopes, occupied by layers of basaltic flows. The

succession consists of almost 40 flows with a total thickness of ~2km.

Regional Tectonics

Forms a part of Western Ghat Escarpment running along the West

Coast of India, Located to the west of a group of N-S trending stable

faults,Mild density of lineaments, high heat flow,

Seismicity

Lies in seismic zone II with max horizontal acceleration of 0.10g (IS

Code) , Maximum magnitude earthquake < 4


NSDF: A case study

Tsunamis

No reported Tsunamis so far, except mild inland sea water intrusions during 1615

Absence of high potential collision tectonics in Arabian sea

Presence of protective Western Ghat high relief geomorphic feature along the west coast

Geology

Mostly dominated by alternate amygdaloidal and basaltic flow ranging in thickness from a

few meter to tens of meter and separated by sedimentary interbeds. Top soil cover is about 2-

10m thick. Flows are undeformed and homogeneous.

Hydrogeology

Generally two aquifers represented by amagdaloidal basalt and vesicular basalt separated

by sedimentary interbeds.

Transmissivity of weathered basalts, vesicular basalts and fractured basalts of the Deccan

trap area range from 90 to 200 m2/day, 50 to 100 m2/day and 20 to 40 m2/day respectively.


NSDF: A case study

A typical cross section of the site showing subsurface geology and dip of the flows

Local Geology

Located on the southern slope of

a EW trending hill with max

elevation of 110m ,

Rocks are dominantly shallow

dipping basalt flows overlain by

thick soil cover, Three dominant

fracture trends N-S. NE-SW and

E-W

N


NSDF: A case study

Local Hydrogeology

1. Weathered zone (top 10m) constitutes the most productive water

bearing horizon Fractured basalts at deeper level are water

bearing ,Contacts of flows are also water conducting pathways

2. Absence of sea water intrusion in coastal aquifer as indicated by

ground water chemistry

3. Transmissivity of basalts 0.1-500m2/day

4. Aquifer thickness 2-8m

5. Water table fluctuates from 0.5 to 10 m bgl.

6. Water flows towards south with a velocity of 0.1 to 0.5m/day

7. Infiltration rates are of the order of 10cm/year

8. The annual average precipitation from 1959 to 2001 is 2376 mm


NSDF: A case study

Host rock/soil characteristics

Porosity: Weathered basalt ~ 34%

Vesicular basalt ~ 50%

Fractured Basalt ~ 15%

Massive basalt <2%

Hydraulic conductivity: 0.01-1 m/d

Mineralogy: Important mineral constituents are as under

Basalt: Plagioclase, biotite, augite, magnetite, sphene

with secondary zeolite, palagonite, aragonite

Weathered basalt Sericite, smectite, chlorite, leucoxene,

Soil Clays, organic matter,

Distribution coefficient for key radionuclides (ml/g)

90Sr 140-300

137Cs 600-1000


NSDF: A case study

Important techniques and tools used

1.Geological mapping on hill slope, pits, trenches and outcrops

2.Ground Penetrating Radar Surveys

3.Borehole and auger hole drilling

4.Pump and Slug test for aquifer parameter determination

5.Field Tracer Test for RN transport and infiltration studies

6.Laboratory based testing of rock and soil samples


NSDF: A case study

Details of emplaced waste ET/SLT : mainly metallic scrap, PVC, rubber, processed cake, HEPA

filters, glass wares, concrete chippings, soil, and other assorted

materials.

RC Trench mainly of solidified mucks/flocs sludges.

Tile holes depleted and defective sources, high radiation solid wastes

(Beta-Gamma) and suitable for disposal in NSDF within

permissible limits.

Estimated inventory for 35 years


NSDF: A case study

Sl.No. Properties Cemented waste form

1. Waste loading (%) 66.66

2. Compatibility With alkaline waste

3. Specific activity(Bq/g) 1.48-2.22x104

4. Density(g/cc) 1.8-2.0

5. Compressive strength(MPa) 10-15

6. Leach Rate(g/cm2/day) 10-4-10-5

7. Radiation stability No damage up to 108 Rads

8. Homogeneity Very good

9. Thermal stability Very good upto 100○C

Characteristics of the cement waste forms

The radioactive sludge cakes are immobilized in cement matrix.

Waste pack with cement matrix has a diameter of 600 mm and height of 900

mm. The spent resin is stored in 200 litre steel drum and is not immobilised


NSDF: A case study

Safety Assessment

an exercise undertaken to evaluate the performance of a disposal system

under a given set of conditions to make an assessment of its impact on human

health and environment. In the following discussions various components of a

typical safety assessment case as applied to the above site discussed.

Assessment Context

The purpose :

understand the behaviour of site with respect to groundwater flow and

migration of radionuclides.

suggest further data acquisition programme in order to improve the overall

safety wherever required.


NSDF: A case study

Phenomena FEP Number Features, Events, Processes

1. Natural

Phenomena 1.1 Geological 1.1.1 Soil heterogeneity

1.2 Climatological 1.2.1 Precipitation, temperature and soil water

balance 1.3

Geomorphological 1.3.1 1.3.2

Denudation, eolian fluvial Chemical denudation

1.4 Hydrological 1.4.1 Recharge to ground water

1.4.2 Ground water discharge, exploitation GW well

1.4.3 Ground water condition

1.4.4 Saline or sea water intrusion

1.4.5 Effects at saline - fresh water interface

FEP’S

OF

COASTAL

SITE


NSDF: A case study

1.5 Transport and Geochemical

1.5.1 Advection and dispersion

1.5.2 Diffusion

1.5.3 Matrix diffusion

1.5.4 Solubility limit

1.5.5 Sorption

1.5.6 Dissolution, precipitation and crystallization

1.5.7 Colloid formation, dissolution and transport

1.5.8 Complexing agents

1.5.9 Accumulation on soils and organic debris

1.5.10 Mass, isotopic and species dilution

1.5.11 Chemical gradient (electrochemical effects,

osmosis)

Contd...


NSDF: A case study

Contd...

1.6 Ecological 1.6.1 Plant uptake, (aquatic plant)

1.6.2 Animal uptake, (biota)

1.6.3 Uptake by rooting species, burrowing animal

1.6.4 Soil and sediment biturbation

1.6.5 Weathering, erosion and deposition

2. Human Activities

2.1 Design and construction

2.1.1 Common cause failure

2.1.2 Poor quality construction

2.1.3 Chemical effect (oxidation of soil)

2.2 Operations and

Closure 2.2.1 Heterogeneity of waste form (chemical,

physical)


NSDF: A case study

2.3 Post Closure 2.3.1 Ground water abstraction 2.4 Post Closure Surface Activity

2.4.1 Altered soil or surface water chemistry

2.4.2 Land use change

2.4.3 Agriculture and fisheries practice changes

2.4.4 Demography change, urban development

3. Waste and Repository Effects 3.1 Chemical 3.1.1 Interaction of waste and repository materials

with host material 3.1.2 Metallic corrosion

3.1.3 Interaction of host materials and

groundwater with repository material, 3.1.4 Microbiological effects

3.3 Radiological 3.3.1 Material property change

Contd....


NSDF: A case study

System Description Near-field

waste

the disposal area,

the engineered barriers (waste packages, disposal modules, disposal facility

cover, etc.)

the disturbed zone of the natural barriers that surround the disposal facility

Geosphere

soil,

unsaturated zone and the saturated zone

hydrogeology, geochemistry

tectonic and seismic conditions

Biosphere

climate and atmosphere,

Human population residing nearby and its activity,

sea


NSDF: A case study

Near Field FEPs Features Waste Inventory, engineering Barriers (Waste forms, Disposal Modules such as Earth Trench

(ET)/Stone Line Trench (SLT), Reinforced Concrete Trench (RCT) and Tile Holes (TH)).

Events •Precipitation;

•Human intrusion

oExcavation-inhalation

oDwelling-inhalation

Processes

Erosion of disposal modules

Degradation of engineered barriers

Near Field Flow and Transport (infiltration of groundwater, diffusion, dissolution and

transport in unsaturated zone):


NSDF: A case study

Features aquifer, sea, dug well

Events flooding,

earthquake,

landslide,

tsunami.

All the above are having a very small probability of occurrence and their impact on

transport process will be negligible for this site.

Processes: Flow and radionuclide transport through aquifer

Sorption and desorption during transport through aquifer

Discharge into sea through geologic media:

Dilution and dispersion of the radionuclides in the sea

Far Field FEPs


NSDF: A case study

Features Human inhabitants (critical group)

Atmosphere (air, groundwater) and

Marine foods (fish, invertebrate, salt etc.)

Events

Human intrusion at the site(construction activities at the site)

Processes

Internal Exposure

Ingestion: Consumption of drinking water, marine food such as fish,

invertebrate, salt etc.

External Exposure: Swimming activity on beach

Biospheric FEPs


NSDF: A case study

Scenario Development

Near field scenario:

a) Failure of top cover of RC trench and direct inflow of rainwater

b) Failure of bottom cover of RC trench/tile holes

c) Failure of top and bottom cover

d) Failure of complete RC trench/tile holes

e) Degradation of waste form

Far field scenario: A human habitation and a well are postulated in south-east

direction at a distance of about 800 meters from the fence of the facility and outside

the boundary of the centre. The groundwater flows towards the bay in the southward

direction. The modification of the groundwater direction in future is a low probability

event. However, in the altered evolution scenario of groundwater flowing towards the

postulated habitation, the drinking water pathway has also been considered.


NSDF: A case study

Waste forms in Near Surface Disposal Facilities

Radioactivity release in local aquifer

Drinking underground

water from a well

Flux into the sea

Internal exposure External exposure

Swimming

Ingestion

Inhalation

Beach activity

Intrusion after institutional

control (300 years)

Dose to individual

Complete failure of disposal modules

Radioactivity release in near field by

diffusion and dissolution mechanism

Fish

Invertebrate

Salt

Excavation

Inhalation

Dwelling

Inhalation

Pathways and Scenarios


NSDF: A case study

Conceptual modeling of the site & the far

field scenario


NSDF: A case study

Mathematical model

Source Term Modeling: Leaching from cylindrical waste form has

been calculated by diffusion and dissolution mechanism. The

diffusion coefficient considered for this analysis is retarded diffusion

coefficient The release mechanism of radionuclides from spent resin

and spent source is governed by solubility-limited release.

Radionuclides Half life

(years)

Diffusion coefficients (cm2/sec.)

Cs137 30.2 5.60x10-06

Sr90 28.8 1.15x10-08

Co60 5.3


NSDF: A case study

Dissolution and Diffusion Phenomenon considered in

the model

Dissolution of

cement waste

from due to

interaction

with

groundwater Diffusion

of RN

Through

matrix

Groundwater

Radionuc

lides

Spent resin Spent source Sludge cakes 137Cs 90Sr 60Co 192Ir 137Cs 90Sr

Inventory

(Bq)

9.32×1

013

1.04×1

013

4.67×1

013

- 1.64×1

013

1.82×

1013

Total

inventory

1.04×1014 4.67×1013 1.82×1013

Inventory of radionulcides considered in the

safety assessment

For governing

equation of

these processes

pl refer to

training notes

Sl. No. Properties Cemented waste form

1. Waste loading (%) 66.66

2. Compatibility With alkaline waste

3. Specific activity(Bq/g) 1.48-2.22x104

4. Density(g/cc) 1.8-2.0

5. Compressive strength(MPa) 10-15

6. Leach Rate(g/cm2/day) 10-4-10-5

7. Radiation stability No damage up to 108 Rads

8. Homogeneity Very good

9. Thermal stability Very good up to 100○C


NSDF: A case study

Estimation of dose to critical group

through groundwater pathway

Code used : PLAFLX

Assumption : Isotropic K, Kd

Parameters Values

Groundwater Velocity (m/day) 0.5

Porosity (%) 30

Bulk density (g/ml) 1.7

Kd (137Cs, ml/g) 600

Kd (90Sr, ml/g) 140

Retardation factor for 137Cs 3400

Retardation factor for 90Sr 793

Aquifer thickness (m) 6.0

Length of the area source (m) 200.0

Width of the area source (m) 30.0

NW Parameters of the geo-

spherical transport model


NSDF: A case study

Radionuclide

concentration in

groundwater at

different

distances

Radionuclide

Concentration (Bq/m3)

200 m

distance 800 m distance

Maximum

permissible for

drinking

purpose

90Sr 7.36 x 10-1 8.04 x 10-21 3.7 x 103

137Cs negligible negligible 4. x 105

ciRii DCCD

Conversion of radionuclide concentration in

groundwater into radiological dose using

the equation Radionuclide Ingestion Inhalation

137Cs 1.3x10-8 3.9x10-8

90Sr 3.1x10-8 1.6x10-7

Dose conversion factors (Sv/Bq)

where,

Di = dose due to ith radionuclide (Sv/y)

Ci = concentration of ith radionuclide in groundwater (Bq/m3)

CR= annual consumption rate of groundwater for drinking purpose (m3/y)

Dci = dose conversion factors of ith radionuclide (Sv/Bq.)


NSDF: A case study

where,

Q = maximum flux (Bq.m-2.y-1)

(40.269 for Sr90 at 200 m distance)

W = width of the facility (m) 600

H = thickness of the aquifer (m) 2

V = bay volume (m3) 4.5x107

r/V = fractional renewal rate in the sea (18.25 y-1)

= radioactive decay constant.

The radioactive flux entering into sea is

translated into radionuclide concentration

in the sea, CW (Bq/m3), using the equation

V

rV

HWQCW

.

Marine exposure pathway

Cw for Sr90 = 5.876 x 10-5 Bq/m3


NSDF: A case study

Dfish=Cw x Dci x Tf x Crf

Where,

Cw= Concentration of radionuclides in sea water=5.876x10-5Bq/m3

Dci=Dose conversion factor due to ingestion=3.1x10-8Sv/Bq for Sr90

Tf =Transfer factor for fish(ranges between 82x10-3to 14000x10-3 m3/kg)

For gold fish Tf = 9.33x10-3 m3/kg

Crf = consumption rate of fish=36.5 kg/y

Which gives

Dfish = 6.20x10-13Sv/y

A simple illustrative example of

dose due to the fish intake from

marine pathway

Estimation of dose to critical group through

Marine pathway


NSDF: A case study

Marine exposure pathway


NSDF: A case study

Parameters used in the marine exposure pathway

Consumption rates

Fish (g/y) 3.65x104

Invertebrate (g/y) 1.83x104

Salt (g/y) 5.48x103

Inhalation (m3/y) 7.3 x103

Occupancy

Swimming (hr/y) 500

Beach activity (hr/y) 1750

Other parameters

Contaminated food fractions 0.5

Fraction of activity in air 0.05

Suspended sediment in air (g/m3) 1x10-4

Salt particles in air (g/m3) 1x10-5

Ingestion dose coefficient (Sv/Bq)

Cs 137 1.3x10-8

Sr 90 2.8x10-8

Inhalation dose coefficient (Sv/Bq)

Cs 137 3.9x10-8

Sr 90 1.6x10-7


NSDF: A case study

Where,

Sp. act = Radionuclide sp. Activity (Bq/g)

dustout door = Out-door dust concentration (g/m3)

Oout door = Out-door occupancy (fraction)

Aair = Activity in air (fraction)

Ir = Inhalation rate (m3/y)

Dc = Dose conversion factor (Sv/Bq)

Dustcon = Dust Concentration in air (g/m3)

Occupancy = Occupancy at the site (hr/y)

Radiological dose to Critical Group is calculated for human intrusion scenario after

300 years of closure of radioactive waste disposal facility. Dose is calculated for (a)

dwelling inhalation in both out-door and in-door conditions, and (b)

excavation/construction scenarios using following expression.

Human intrusion pathway


NSDF: A case study

Dwelling - Inhalation

Inhalation Rate (m3/hr) = 1.2

Indoor dust concentration (g/m3) = 50

Outdoor dust concentration (g/m3) = 100

Indoor occupancy fraction = 0.80

Outdoor occupancy fraction = 0.20

Fraction of activity in air = 0.05

Excavation - Inhalation

Occupancy (hr/y) = 100

Dust concentration in air (mg/m3) = 1.0

Fraction of activity in air = 0.33


NSDF: A case study

Radiological dose (Sv/y) to critical group by drinking

water pathway, marine exposure pathway and human

intrusion pathway

Radionuclides

Pathways

Groundwater

drinking

pathway

Marine exposure pathway Human intrusion pathway

Ingestion Ingestion Inhalation External Dwelling

inhalation

Excavation

inhalation

Cs137 --- 2.60 x 10-20 2.66 x 10-26 7.50 x 10-20 1.26 x 10-10 1.88 x 10-10

Sr90 1.82 x 10-28 2.55 x 10-7 4.17 x 10-12 8.25 x 10-12 4.82 x 10-11 7.27 x 10-11

Co60 --- --- --- --- --- ---


NSDF: A case study

Confidence building

Radionuclide concentrations in groundwater and corresponding

radiological doses to the critical group as a function of different

geo-environmental parameters such as distribution co-efficient,

aquifer thickness (d) and groundwater velocity (U).

Sensitivity Analysis

Parameter Range

Groundwater velocity (m/d) 0.1-1.5

Distribution coefficient

(ml/g)

Sr90 140-300

Cs137 600-1000

Aquifer thickness (m) 2-8


NSDF: A case study

Variation of 90Sr peak concentration and corresponding peak concentration

arrival time as a function of groundwater velocity and distribution co-efficient

at a distance of 200m from boundary of the facility


NSDF: A case study

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.61E-24

1E-20

1E-16

1E-12

1E-8

1E-4

Kd (ml/g)

140

150

160

200

250

300

Pe

ak d

ose

arr

iva

l tim

e (

y)

90S

r P

ea

k d

ose

ra

te (

Sv/y

)

Groundwater velocity (m/d)

200

400

600

800

1000

1200

1400

1600

Peak dose arrival time

Peak dose rate

Variation of Sr90 peak dose rate and corresponding peak dose arrival time as

a function of groundwater velocity and distribution coefficient at a distance of

200m from boundary of the facility


NSDF: A case study

Bird's eye view of the great

Deccan Basalt Terrain of India

Thanks

Simple geology, hydrogeology and good

sorption characteristic of host rock/soil does

ensure confinement and isolation to such

waste……….

Documents

PK Narayan, RR Rakesh, RK Bajpai & RN Nair BARC- … A case study BARC- IAEA Regional Training Course on Development of Near Surface Disposal Facility Mumbai, India February 15-19,