Nuclear W aste Disposal

Nuclear Waste Disposal

Geological ConstraintsAnd Indian Overview

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Preface

Since the development and utilization of nuclear energy during World War II, countries have struggled with the issue of disposing of high-level nuclear waste .

Nuclear waste is one of the biggest downsides to nuclear power, and can remain dangerous for hundreds of thousands of years.

Geological disposal is often stated as the most preferable way of dealing with it, but what does it entail?

In this report we will discuss problems that need to be overcome , ongoing research and try to choose a suitable location in India for disposal.

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Index

Production and typesMethods of disposal

Geological constraints

Indian context

Bibliography




Classification of waste on basis of radioactivity:

1.low level (90%)2.intermediate level (7%)3.high level(3%)

90

73

volume of waste

low level waste intermediate level waste high level waste




Low-level waste Generated from hospitals and industry, as well as the nuclear

fuel cycle. Low-level wastes include paper, rags, tools, clothing, filters. Some high-activity LLW requires shielding during handling and

transport but most LLW is suitable for shallow land burial




Intermediate-level waste Intermediate-level waste (ILW) contains higher

amounts of radioactivity and in some cases requires shielding

Includes resins, chemical sludge and metal reactor nuclear fuel cladding

It may be solidified in concrete or bitumen for disposal Short-lived waste (mainly non-fuel materials from

reactors) is buried in shallow repositories Long-lived waste (from fuel and fuel reprocessing) is

deposited in geological repository




High-level waste

It contains fission products and transuranic elements generated in the reactor core.

Though it is only 3% of total volume but it is responsible for 95% of total radioactivity.

It is highly radioactive and often hot. HLW is the most dangerous and the main candidate for geological

disposal Certain radioactive elements (such as plutonium 239) in “spent”

fuel will remain thousands of years Tc-99 (half-life 220,000 years) I-129 (half-life 15.7 million years)




Management of High-level wastes

Immobilization of high level liquid waste into vitrified borosilicate glasses.

Engineered interim storage of vitrified waste for passive cooling in pools near power-plant and surveillance over a period of time qualifying it for ultimate disposal.

Ultimate storage disposal of vitrified waste a deep geological depository

Vitrified waste




Disposal of Waste

Depending on level of waste following methods are used

Above ground disposal

Geological disposal

Deep borehole disposal

Disposal at subduction zones

Ocean disposal

Disposal in outer space




Impractical methods

Methods Main Reasons

Disposal in outer space Very costlyHigh risk of space vehicle failure

Ocean Disposal Declared illegal by international treaty

Disposal at subduction zones High risk of earthquakes since located on plate boundariesRate of subduction is very slow




Above ground disposal

Generally used for intermediate and high level waste Waste from a spent fuel pool is sealed (along with an inert gas) in a steel

cylinder, which is placed in a concrete cylinder which acts as a radiation shield.

Cheap , relatively easy to construct and monitor.

Dry cask storage area




Deep borehole disposal

Disposing of high-level radioactive waste from nuclear reactors in extremely deep boreholes

Placing the waste as much as five kilometers beneath the surface of the Earth

Waste is sealed in strong steel containers and lowered down the borehole, filling the bottom one or two kilometers of the hole

Borehole is then sealed with materials, including perhaps clay, cement, crushed rock backfill, and asphalt, to ensure a low-permeability




Advantages of Deep borehole disposal A high-temperature scenario involves very young hot waste in the

containers which releases enough heat to create a melt zone around the borehole.

As the waste decays and cools, the melt zone re-solidifies, forming a solid granite sarcophagus around the containers, entombing the waste forever.

Environmental impact is small. Can be carried out near nuclear power-plant eliminating

transportation risks.




Geological Repository

A deep geological repository is a nuclear waste repository excavated deep within a stable geologic environment (typically below 300 m).

Repositories include the radioactive waste, the containers enclosing the waste, other engineered barriers or seals around the containers, the tunnels housing the containers, and the geologic makeup of the surrounding area

Geological disposal can be safe, technologically feasible and environmentally sound




Schematics of geological repository

C : high level

B :intermediate level

CU : spent fuel(high level




Ongoing research

Nuclear waste disposal is currently a matter of study. Study is undergoing in many countries related to geological disposal.

European Countries like Finland , Sweden ,Germany ,Belgium have done considerable amount of research and constructing their repositories.

Research was done in USA in Yucca mountains but constructing final repository there was cancelled.

It was stated that cancellation took place due to political reasons ,not technical or safety reasons.

Similarly in India research was done in kolar gold mines in mysore.




Geological constraints

Circulation of water Properties of Host Rock Depending on type. Erosion. Hazards like earthquake / volcanic eruption.




Water circulation

Water circulation, as well as providing a path for soluble waste to escape to the surface, will increase the speed at which engineered barriers such as metal casing will degrade.

Groundwater circulates in two distinct places within the bedrock, within the pores and within fractures.

Crystalline rocks like granite ,basalt /tuff have very low permeability but are often highly fractured.

In clays, such as those investigated in French and Belgian underground laboratories, the permeability is higher but fractures are much rarer.




Geo-hydrological study of area:

Potential groundwater pathways defined by top soil, weathered rock, fracture networks, interflow porous layers should be identified.




Host rocks

Each rock type has different geomechanical property. Moreover these property vary from site to site. So in following slides we will look upon research done in different

types of host rock.




Research in granitic rocks

In Finland research was done at onkalo . While in Sweden research was done at underground Äspö Hard Rock

Laboratory. Tunnels and other excavations in hard granitic rocks are stable over

long period of time. But excavation results in stress release and opening of fractures. Permeability is very low unless water conducting joints or open

fractures are present.




Research in Tuff

Volcanic tuffs are also candidates for nuclear waste depositories, such as the Yucca Mountain site in the U.S.A.

Welded tuffs can have low permeabilities, but the most attractive property of tuffs is their ability to trap some radionuclides through sorption.

Yucca mountain range




Research in clay based rocks In France Andra (French National Radioactive Waste Management

Agency) is the public body responsible for the long-term management of all radioactive waste.

Research was done at Meuse/Haute-Marne underground research laboratory which is in clay formation.

Meuse/Haute-Marne is underground laboratory, located at a depth of 490 meters in the heart of a very stiff (indurated) clay formation (argillite).

Over 10 years of research was done using: > 1,300 km of seismic profiles studied > 27 deep boreholes > 4.2 km of cored boreholes > 2.3 km of argillite cores




Meuse/Haute-Marne underground research laboratory




Properties of the rock formation the geological environment is stable; very low seismic risk. the clay layer is regular and homogeneous over a large surface

area.It does not present any fault Argillite has excellent properties. It is a stiff (indurated) sedimentary

rock with very low permeability Radioactive or nonradioactive elements dissolved in water move very

slowly through this rock the rock can withstand mining excavation work.




Bentonite clay

These layers are placed between host rock and waste to restrict groundwater flow and retard migration of radionuclides.

Their swelling properties helps in sealing the fractures in host rock. Bentonite clay being used in sealing waste overpack




Indian context

India has extensive & varied experience in the operation of near surface disposal facilities (NSDFs) in widely different geo-hydrological and climatological conditions by BARC.

There are seven NSDFs currently operational within the country.

In India, the most promising formation is granitic rocks. A program for development of a geological repository for

vitrified high level long lived wastes is being pursued actively, involving In-situ experiments, site selection, characterization and laboratory investigations




In-situ underground experiments For assessment of the rock mass response to thermal load from

disposed waste , an experiment of 8-years duration was carried out. At a depth of 1000 m in an abandoned section of Kolar Gold mine.




Choosing a location

absence of seismic risks in the long term. absence of significant water circulation inside the repository, rock suitable to underground installations excavation. confinement property for radioactive substances. sufficient depth to keep the waste safe from potential aggressions. absence of nearby rare exploitable resources.




Choosing low risk seismic zone.And avoiding high population density areas.




Overlap of seismic and population level.

1.2.3.4.

Western RajasthanLower ChhattisgarhWestern Andhra PradeshEastern Karnataka




Choosing arid areas i.e. low rainfall.

Lower Chhattisgarh ruled out because of high rainfall




Conclusion

Based on above study these three regions in India can be used for disposal Western Rajasthan, Western Andhra Pradesh, Eastern Karnataka.

Since this is very preliminary study , further research in these narrowed down regions can be carried out.

Further research required on: This sub-surface information by drilling and lithological studies. Geophysical surveys using Ground Penetration Radar (GPR). Water circulation study. Absence of exploitable natural resource.




Bibliography

Wikipedia Andra.fr barc.gov.in




Nuclear W aste Disposal

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