Dispersion in Water

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IAEAInternational Atomic Energy Agency

Regional Workshop on Site Selectionand Evaluation for NPPs, Vienna,

24 28 November 2008

Day 4, Unit 4: Dispersion in water

Leonello Serva (Italy), IAEA Consultant


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DISPERSION IN GROUNDWATER

Glossary

General considerations

Objectives of groundwater investigation

Data necessary for investigations of groundwater

A Case study: Montalto di Castro (Italy)

Modelling of dispersion and retention of radionucl ides in

groundwater

Groundwater remediation

Quality assurance programme


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Glossary

Aquifers: layers of rock sufficiently porous to store water and

permeable enough to allow water to f low through them.

Confined aquifers: aquifers that have the piezometric surface above

their upper physical boundary (an aquitard or aquiclude).

Aquitard: rocks that permit water to move through them at muchlower rates than through the adjacent aquifers.

Aquicludes: rocks that do not allow water to move through them

under typical hydraulic gradients.


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Glossary

Geological barriers: layers of higly impermeable rocks. These are:

unfractured crystalline rocks and, more occurently, shales, evaporites.

Hydraulic conductivity (K): describes the ease with which water can move

through pore spaces or fractures of rocks

Transmissivity (T): the transmissivity of an aquifer is a measure of howmuch water can be transmitted horizontally, such as to a pumping well. It

is directly proportional to the aquifer thickness (b) and hydraulic

conductivity (K): T=bK

Porosity: i t is a measure of the void spaces in a material, and is measured

as a fraction, between 01, or as a percentage between 0100%


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Glossary


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The hydrosphere is a major exposure pathway by which radioactive materials

that are routinely discharged under authorization or are accidentally released

from a nuclear power plant could be dispersed to the environment and

transported to locations where water is supplied for human consumption.

Radionuclides are transported rapidly in some surface waters such as rivers,

and very slowly in groundwater.

geological barrier

source

aquifer

surface waterThe rates of transport

depend on manyparameters


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Order of magnitude 10 E 10 8 6 4 2 0 - 2 - 4 - 6 - 8 - 10

Time scale of geological

processes

y

Released energy f romearthquake

MJ

Coseismic surfacefaulting

mm

Subsidence rate mm/y

Rate of gravitationalphenomena

m/s

Volume of landsl ides m

Density of landslides forintense rainfall

n/

km

Recurrence time for

activation of landslides

y

Daily rainfall mm

Daily snowfall mm

Rainfall rate mm/h

Scale of geological phenomena


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Daily rainwater in ~ 100

km basins

m

Recharge areas km

Flow rate at spr ings m/s

Depression of potentio-metric sur face (pump)

m

Hydraulic conductivity m/s

Hydraulic gradient inrivers m/km

Flow rate of rivers m/s

Recover rate of

potentiometric surface

m/h

Flooded areas km

Order of magnitude 10 E 10 8 6 4 2 0 - 2 - 4 - 6 - 8 - 10

Scale of hydrogeological parameters


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A discharge of radioactive material from a nuclear power plant maycontaminate the groundwater system in the region either directly orindirectly, via earth, atmosphere or surface water, in the followingthree ways:

Indirect discharge to the groundwater through seepage and infiltration ofsurface water that has been contaminated by radioactive material dischargedfrom the nuclear power plant;

Infi ltration into the groundwater of radioactive liquids from a storage tank orreservoir;

Direct release from a nuclear power plant; an accident at the plant might

induce such an event, and radioactive material could penetrate into thegroundwater system. The protection of aquifers from such events should beconsidered in the safety analysis for postulated accident conditions, and ageological barrier to provide protection should be considered.


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Objectives of groundwater investigation

the estimated concentration of radioactive material in groundwater at the

nearest point in the region where groundwater is drawn for human

consumption;

the transport paths and travel times for radioactive material to reach the

source of consumption from the point of release;

the transport capacity of the surface flow, interflow and groundwaterrecharge;

the susceptibility to contamination of the aquifers at different levels;

time and space distributions of the concentrations in the groundwater of

radioactive material resulting from accidental releases from the plant.


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Objectives of groundwater investigation (2)

The estimated concentration of radioactive material in groundwater at

the nearest point in the region where groundwater is drawn for human

consumption

?

Obj ti f d t i ti ti


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The transport paths and travel times for radioactive material to

reach the source of consumption from the point of release

The transport capacity of the surface flow, interflow and

groundwater recharge



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The susceptibil ity to contamination of the aquifers at dif ferent levels



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Time and space distributions of the concentrations in the

groundwater of radioactive material resulting from accidental

releases from the plant or tanks.


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Regional &localhydrogeological information

climatological data

init ial concentrationof radionuclide

major hydrogeological units

their parametersturnover times of GW

recharge and discharge

relationships

data on surfacehydrology


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Data necessary for investigations of groundwaterclimatological data

In regions where rainfall makes a substantial contribution to

groundwater, hydrometeorological data on seasonal and annualrainfall and on evapotranspiration that have been systematically

collected should be analysed for as long a period as they are

available. From meteorological (precipitation) data, groundwater

recharge should be calculated. Alternatively, tracers (chemical or

isotopic) of the water cycle could be introduced to calculate

groundwater recharge.

D t f i ti ti f d t


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Isothermes and isohyetes representing annual average temperatue (left)

and rainfall (right)

D t f i ti ti f d t


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Water balance of studied area

Water entering in the area= water leaving the area +/-any change in storage

P-ETR=I+RWhere:

P rainfall

ETR evapotranspirationI infiltration

R runoff



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Data necessary for investigations of groundwaterMajor hydrogeological units



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Data should be obtained on the types of the various geological formations in the

region and their stratigraphic distribution in order to characterize the regional

system and its relationship with the local hydrogeological units.

The geology and surface hydrology of the site area should be studied in

sufficient detail to indicate potential pathways of contamination to surface

water or groundwater.

D t f i ti ti f d t


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Any surface drainage system or

standing water body accessible from a

potential release point in an accident

should be identified. Areas from which

contaminated surface water can

directly enter an aquifer should be

determined. The relevant

hydrogeological information for

surface or near surface discharges

includes information on soil moisture

properties, infiltration rates,

configuration of unsaturated zones

and chemical retention properties

under unsaturated conditions.


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For consideration of the transport potential of seepage and groundwater in

the region of the site (a few tens of kilometres in radius), data on types of

aquifers, aquitards and aquicludes, their interconnections and the flow

velocities and mean turnover times should be investigated. Such data will

permit the regional flow pattern and its relation to the local flow pattern of

seepage and groundwater to be characterized. This investigation should

include the following data:

Data necessary for


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Data necessary for

investigations of groundwater

Geological data: lithology,

thickness, extent, degree of

homogeneity and degree of

surface weathering of thegeological units;

D t f i ti ti f d t


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D t f i ti ti f d t


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Hydrogeological data: hydraulic

functions of the unsaturated zone,

and hydraulic conductivities and

transmissivities, specific yield and

storage coefficients, dispersion

parameters, and hydraulic gradients

of the saturated zone for each

geological unit;



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Depth related water ages and mean turnover t imes;

Interconnections between aquifers and aquitards without and withgroundwater usage;



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The chemical composition of groundwater from the

respective aquifers and aquitards in comparison with their

lithology;

Physical properties of the groundwater, especially

temperatures, gas contents and density;

Variations of water levels in wells and mining shafts and in

the discharges of springs and rivers;

Locations of active and potential sink holes in the region.



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Data necessary for investigations of groundwaterWater bearing characteristics of the hydrogeological units



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y g gWater bearing characteristics of the hydrogeological units



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y g gMajor hydrogeological units

On June 15, 1994 " a 15-story-deep sinkhole opened up in an 80 million-ton pile ofphosphogypsum waste in a New Wales plant. The hole could be as big as 2 mill ion cubic feet,enough to swallow 400 railroad boxcars. Local wags call it Disney World's newest attraction --"Journey to the Center of the Earth" -- but there's nothing amusing about it. The cave-indumped 4 million to 6 million cubic feet of toxic and radioactive gypsum and waste water intothe Floridan aquifer, which provides 90 percent of the state's drinking water. The company has

voluntarily spent $ 6.8 million to plug the sinkhole and control the spread of contaminants inthe ground water.



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GUATEMALA CITY, Guatemala - A 330-foot-deep sinkhole

The pit emitted foul odors, loud noises and tremors, shaking thesurrounding ground. A rush of water could be heard from its depths



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Major hydrogeological units

Interrelationship between groundwater and surface

t


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water

The extent and degree of hydraulic connections between bodies of surface

water and groundwater should be identified. Topographic and geological

maps should be studied in order to identify lines or areas where such

hydraulic connections between surface water and groundwater are present.

The amounts of the exchanges should be estimated and their corresponding

exchange regimes should be determined.


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A Case study


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the nuclear plant of Montalto di Castro, Italy

Ubication

A Case studyth l l t f M t lt di C t It l


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Geological framework



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The dewatering project

plant

areapond

area

diaphragm walls

structural diaphragm wal



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The dewatering projectdiaphragm walls

Modelling of dispersion and retention ofradionuclides in groundwater


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radionuclides in groundwater

Models have been developed to calculate the dispersion and retention of

radionuclides released into groundwater. Standard calculational models are

generally satisfactory and should be used in most cases. The complexity of the

model chosen should reflect the complexity of the hydrogeological system at a

particular site.

Simplified evaluations should be performed with conservative assumptionsand data to evaluate the effects of postulated accidental releases of radioactive

material to the groundwater. Further, more refined analysis with more realist ic

assumptions and models should be performed if necessary.

Modelling of dispersion and retention of


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The direction of groundwater movement and of radionuclide transport

is in general orthogonal to the contours at groundwater level. Where

this is the case, the standard calculational models should be applied. If

aquifers are strongly anisotropic, and water and transported effluents

can move over a limited domain through fractures, most calculationalmodels are not valid. Field studies including tracer studies may be

necessary and should be considered.

Modelling of dispersion and retention ofradionuclides in groundwater


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The analytical models for radionuclide transport in groundwater

have several sources of uncertainty. The model used should bevalidated for each specific application. Validated hydrogeological

models that would apply for characteristics similar to those of the

site should be considered as a reference for purposes of

comparison.



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Path to groundwater remediation



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Permeable reactive barrier


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QUALITY ASSURANCE PROGRAMME


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The documentation generated in a monitoring programme forsurface water and groundwater should follow the recommendations

made in Section 7.



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A quality assurance (QA) programme should be established to cover

all the activities recommended in this Safety Guide. The process of site

evaluation includes the conduct of scientific and engineering analysesand the exercise of judgement. The data used in the analyses and in

making judgements should be as complete and as reliable as possible.

Data should be collected in a systematic manner and should be

evaluated by technically qualif ied and experienced personnel.

The QA programme for site evaluation is part of the overall QA

programme for a nuclear power plant (see Ref. [12], Code and Safety

Guide QA1).



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All the investigatory programmes and other studies recommended

in this Safety Guide, together with the necessary data and

information, should be documented for the purposes of site

evaluation.

In order for data to be collected, recorded and retained throughout

the lifetime of the plant, the media for recording and storing data

should be checked periodically to verify their compatibility with

the technology in use (both hardware and software).

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Dispersion in Water

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