nuclear waste managemnt

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Department of CE, GEC, Thrissur

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Nuclear waste management

1. INTRODUCTION

Nuclear waste, like other wastes, may be composed of materials varying inorigin, chemical composition, and physical state. However, what differentiates

nuclear waste from other waste forms is that it contains components that are

unstable due to radioactive decay. Managing nuclear waste requires different

approaches to ensure the protection of both humans and the environment from the

radiation.

In general, three options exist for managing nuclear waste: (1) concentrate and

contain (concentrate and isolate the wastes in an appropriate environment); (2)

dilute and disperse (dilute to regulatory-acceptable levels and then discharge to

the environment); and; (3) delay to decay (allow the radioactive constituents to

decay to an acceptable or background level). The first two options are common to

managing non- radioactive waste but the third is unique to nuclear waste.

Eventually all nuclear wastes become benign because they decay to stable

elements while non-radioactive, hazardous waste remains hazardous forever or

until their chemical speciation is changed.

By far the largest source of radioactive waste from the civilian sector results

from the generation of power in nuclear reactors. Much smaller quantities of

civilian radioactive waste result from use of radio nuclides for scientific research

as well as from industrial sources such as medical isotope production for

diagnostic and therapeutic use and from X-ray and neutron sources. The other

significant sources of radioactive waste are due to defence related activities that

support the production and manufacture of nuclear weapons.

2. SOURCES OF WASTE

Radioactive waste comes from a number of sources. The majority of waste

originates from the nuclear fuel cycle and nuclear weapons reprocessing.

However, other sources include medical and industrial wastes, as well as naturally

occurring radioactive materials (NORM) that can be concentrated as a result of the


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processing or consumption of coal, oil and gas, and some minerals, as discussed

below.

2.1 Nuclear fuel cycle

The major steps generating radioactive waste in the uranium fuel cycle are:

2.1.1 Mining and Milling

This waste results from the production of uranium. It contains low

concentrations of uranium and is contaminated principally by its daughter

products, e.g. thorium, radium and radon.

2.1.2 Fuel supply

This waste may result from purification, conversion and enrichment of uranium

and the fabrication of fuel elements. It includes contaminated trapping materials

from off-gas systems, lightly contaminated trash, and residues from recycle or

recovery operations. This radioactive waste generally contains uranium and, in the

case of mixed oxide fuel, also plutonium.

2.1.3 Reactor operations/power generation

This waste results from treatment of cooling water and storage ponds,

equipment decontamination, and routine facility maintenance. Reactor waste is

normally contaminated with fission products and activation products. Radioactive

waste generated from routine operations includes contaminated clothing, floor

sweepings, paper and concrete. Radioactive waste from treatment of the primary

coolant systems and off-gas system includes spent resins and filters as well as

some contaminated equipment. Radioactive waste may also be generated from

replacement of activated core components such as control rods or neutron sources.

2.1.4 Management of spent fuel

In addition to the radioactive waste described above, reactor operations

generate spent nuclear fuel. This material contains uranium, fission products and


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actinides. It generates significant heat when freshly removed from the reactor.

Spent fuel is either considered a waste or waste is generated from reprocessing

operations. Reprocessing operations generate solid and liquid radioactive waste

streams. Solid radioactive waste such as fuel element cladding hulls, hardware,

and other insoluble residues are generated during fuel dissolution. They may

contain activation products, as well as some undissolved fission products, uranium

and plutonium. The principal liquid radioactive waste stream, however, is the

nitric acid solution which contains both high activity fission products and

actinides in high concentrations.

2.2 Nuclear weapons decommissioning

Waste from nuclear weapons decommissioning is unlikely to contain much beta

or gamma activity other than tritium and americium. It is more likely to contain

alpha-emitting actinides such as Pu-239 which is a fissile material used in bombs,

plus some material with much higher specific activities, such as Pu-238 or Po.

Some designs might contain a radioisotope thermoelectric generatorusing Pu-

238 to provide a long lasting source of electrical power for the electronics in the

device.

2.3 Medical

Radioactive medical waste tends to contain beta particle and gamma

ray emitters. It can be divided into two main classes. In diagnostic nuclear

medicine a number of short-lived gamma emitters such as technetium-99m are

used. Many of these can be disposed of by leaving it to decay for a short time

before disposal as normal waste.

2.4 Industrial

Industrial source waste can contain alpha, beta, neutron or gamma emitters.

Gamma emitters are used in radiography while neutron emitting sources are used

in a range of applications, such as oil well logging.
http://en.wikipedia.org/wiki/Tritiumhttp://en.wikipedia.org/wiki/Americiumhttp://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generatorhttp://en.wikipedia.org/wiki/Medical_wastehttp://en.wikipedia.org/wiki/Beta_particlehttp://en.wikipedia.org/wiki/Gamma_rayhttp://en.wikipedia.org/wiki/Gamma_rayhttp://en.wikipedia.org/wiki/Nuclear_medicinehttp://en.wikipedia.org/wiki/Nuclear_medicinehttp://en.wikipedia.org/wiki/Technetium-99mhttp://en.wikipedia.org/wiki/Industryhttp://en.wikipedia.org/wiki/Alpha_decayhttp://en.wikipedia.org/wiki/Beta_decayhttp://en.wikipedia.org/wiki/Neutron_emissionhttp://en.wikipedia.org/wiki/Radiographyhttp://en.wikipedia.org/wiki/Oil_wellhttp://en.wikipedia.org/wiki/Oil_wellhttp://en.wikipedia.org/wiki/Radiographyhttp://en.wikipedia.org/wiki/Neutron_emissionhttp://en.wikipedia.org/wiki/Beta_decayhttp://en.wikipedia.org/wiki/Alpha_decayhttp://en.wikipedia.org/wiki/Industryhttp://en.wikipedia.org/wiki/Technetium-99mhttp://en.wikipedia.org/wiki/Nuclear_medicinehttp://en.wikipedia.org/wiki/Nuclear_medicinehttp://en.wikipedia.org/wiki/Gamma_rayhttp://en.wikipedia.org/wiki/Gamma_rayhttp://en.wikipedia.org/wiki/Beta_particlehttp://en.wikipedia.org/wiki/Medical_wastehttp://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generatorhttp://en.wikipedia.org/wiki/Americiumhttp://en.wikipedia.org/wiki/Tritium


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2.5 Naturally occurring radioactive material (NORM)

Radioactive materials which occur naturally and where human activities

increase the exposure of people to ionising radiation are known by the acronym

'NORM'. NORM results from activities such as burning coal, making and usingfertilisers, oil and gas production.

2.6 Oil and gas

Residues from the oil and gas industry often contain radium and its daughters.

The sulfate scale from an oil well can be very radium rich, while the water, oil and

gas from a well often contain radon. The radon decays to form solid radioisotopes

which form coatings on the inside of pipework.

2.7 Coal

Coal contains a small amount of radioactive uranium, barium, thorium and

potassium, but, in the case of pure coal, this is significantly less than the average

concentration of those elements in the Earth's crust. The more active ash minerals

become concentrated in the fly ash precisely because they do not burn well. The

radioactivity of fly ash is about the same as black shale and is less than phosphate

rocks, but is more of a concern because a small amount of the fly ash ends up in

the atmosphere where it can be inhaled.

3. CLASSIFICATION OF NUCLEAR WASTE

The classification of radioactive wastes varies from country to country, the

following groupings are generally accepted internationally.

3.1 Exempt waste & very low level waste

Exempt waste and very low level waste (VLLW) contains radioactive materials

at a level which is not considered harmful to people or the surrounding

environment. It consists mainly of demolished material (such as concrete, plaster,

bricks, metal, valves, piping etc) produced during rehabilitation or dismantling

operations on nuclear industrial sites. Other industries, such as food processing,

chemical, steel etc also produce VLLW as a result of the concentration of natural


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radioactivity present in certain minerals used in their manufacturing processes.

The waste is therefore disposed of with domestic refuse, although countries such

as France are currently developing facilities to store VLLW in specifically

designed VLLW disposal facilities.

3.2 Low Level Waste (LLW)

All civilian and defense-related facilities that use or handle radioactive

materials generate some LLW. These include research laboratories, hospitals

using radionuclides for diagnostic and therapeutic procedures, as well as nuclear

power plants. LLW includes materials that become contaminated by exposure to

radiation or by contact with radioactive materials. Items such as paper, rags, tools,

protective clothing, filters and other lightly contaminated materials that contain

small amounts of short-lived nuclides are usually classified as LLW. By its nature,

LLW does not require shielding during normal handling and transportation and

both principles of "delay to decay" and "dilute and disperse" can be employed for

disposal depending on the exact nature of the waste. Often, it is advantageous to

reduce the volume of LLW by compaction or incineration before disposal.Worldwide it constitutes ~90% of the volume but only ~1% of the radioactivity

associated with all radioactive waste. However, wastes containing small amounts

of long-lived radionuclides can be included under the LLW classification. The

disposal options for this class of waste are near-surface burial or no restrictions

depending on level of radioactivity.

3.3 Intermediate-level Waste (ILW)

ILW contains lower amounts of radioactivity than HLW but still requires use of

special shielding to assure worker safety. Reactor components, contaminated

materials from reactor decommissioning, sludge from spent fuel cooling and

storage areas, and materials used to clean coolant systems such as resins and

filters are generally classified as ILW. The most common management option is

"delay to decay" for short-lived solid waste, but for the long-lived waste, the

"concentrate and contain" principle (solidification for deep geologic disposal) is


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required. ILW comprises about 7% of the volume and, roughly, 4% of the

radioactivity of all radioactive wastes. The disposal options for this class of waste

are burial in a deep geologic repository for the long-lived radionuclides and near-

surface burial for the short-lived ones. Intermediate-level waste (ILW) - requires

shielding. If it has more than 4000 Bq/g of long-lived (over 30 year half-life)

alpha emitters it is categorised as "long-lived" and requires moresophisticated

handling and disposal.

3.4 High Level Waste (HLW)

HLW generally refers to the radioactive nuclides at high levels from nuclear

power generation, (i.e. reprocessing waste streams or unprocessed spent fuel) or

from the isolation of fissile radio nuclides from irradiated materials associated

with nuclear weapons production. High-level waste (HLW) - sufficiently

radioactive to require both shielding and cooling, generates >2 kW/m3 of heat and

has a high level of long-lived alpha-emitting isotopes.HLW is highly radioactive,

generates a significant amount of heat, and contains long-lived radio nuclides.

Typically these aqueous waste streams are treated by the principle of "concentrate

and contain," as the HLW is normally further processed and solidified into either a

glass (vitrification) or a ceramic matrix waste form. Spent nuclear fuel not

reprocessed is also considered as HLW. Because of the highly radioactive fission

products contained within the spent fuel, it must be stored for "cooling" for many

years before final disposal by isolation from the environment. HWL constitutes

only a small fraction (a few percent). However, the vast majority of the

radioactivity (> 95%) resides in the HLW. The only disposal option for this class

of waste is burial in a deep geologic repository.

4. EFFECTS OF RADIATION

Every inhabitant on this planet is constantly exposed to naturally occurring

ionizing radiation called background radiation. Sources of background radiation

include cosmic rays from the Sun and stars, naturally occurring radioactive

materials in rocks and soil, radionuclides normally incorporated into our bodys


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tissues, and radon and its products, which we inhale. We are also exposed to

ionizing radiation from man-made sources, mostly through medical procedures

like X-ray diagnostics. Radiation therapy is usually targeted only to the affected

tissues.

Much information of the effects of large doses of radiation comes from

survivors of the atomic bombs dropped on Hiroshima and Nagasaki in 1945 and

from other people who received large doses of radiation, usually for treatment.

Only about 12% of all the cancers that have developed among those survivors are

estimated to be related to radiation. Ionizing radiation can cause important

changes in our cells by breaking the electron bonds that hold molecules together.

Radiation can damage our genetic material (DNA). But the cells also have several

mechanisms to repair the damage done to DNA by radiation. Potential biological

effects depend on how much and how fast a radiation dose is received. An acute

radiation dosage (a large dose delivered during a short period of time) may result

in effects which are observable within a period of hours to weeks. A chronic dose

is a relatively small amount of radiation received over a long period of time. The

body is better equipped to tolerate a chronic dose than an acute dose as the cells

need time to repair themselves.

Radiation effects are also classified in two others ways, namely somatic and

genetic effects. Somatic effects appears in the exposed person. The delayed

somatic effects have a potential for the development of cancer and cataracts.

Acute somatic effects of radiation include skin burns, vomiting, hair loss,

temporary sterility or sub-fertility in men, and blood changes. Chronic somatic

effects include the development of eye cataracts and cancers. The second class of

effects, namely genetic or heritable effects appears in the future generations of the

exposed person as a result of radiation damage to the reproductive cells, but risks

from genetic effects in humans are seen to be considerably smaller than the risks

for somatic effects.


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5. FUNDAMENTAL PRINCIPLES OF RADIOACTIVE WASTE

MANAGEMENT

Responsible radioactive waste management requires the implementation of

measures that will afford protection of human health and the environment since

improperly managed radioactive waste could result in adverse effects to human

health or the environment now and in the future.

The timely creation of an effective national legal framework and an associated

organizational infrastructure provides the basis for appropriate management of

radioactive waste. The individual steps in radioactive waste management may be

dependent on each other, and thus require co-ordination. Taking this

interdependence into account will help to ensure safety in all radioactive waste

management steps.

Observance of the principles of radioactive waste management will ensure that

the above considerations are addressed, and thus contribute to achieving the

objective of radioactive waste management. The principles and their supporting

text should be considered as an entity and are presented in the following text.

i. Protection of human healthRadioactive waste shall be managed in such a way as to secure an acceptable level

of protection for human health.

ii. Protection of the environmentRadioactive waste shall be managed in such a way as to provide an acceptable

level of protection of the environment.

iii. Protection beyond national borders


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Radioactive waste shall be managed in such a way as to assure that possible

effects on human health and the environment beyond national borders will be

taken into account.

iv. Protection of future generationsRadioactive waste shall be managed in such a way that predicted impacts on the

health of future generations will not be greater than relevant levels of impact that

are acceptable today.

v. Burdens on future generationsRadioactive waste shall be managed in such a way that will not impose undue

burdens on future generations.

vi. National legal frameworkRadioactive waste shall be managed within an appropriate national legal

framework including clear allocation of responsibilities and provision for

independent regulatory functions.

vii. Radioactive waste generation and management interdependenciesInterdependencies among all steps in radioactive waste generation and

management shall be appropriately taken into account.

viii. Safety of facilitiesThe safety of facilities for radioactive waste management shall be appropriately

assured during their lifetime.

6. STEPS IN NUCLEAR WASTE MANAGEMENT

Once created, radioactive waste will undergo some of the following stages

depending on the type of waste and the strategy for its management

6.1 Treatment and Conditioning of Nuclear Wastes


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Treatment and conditioning processes are used to convert radioactive waste

materials into a form that is suitable for its subsequent management, such as

transportation, storage and final disposal. The principal aims are to:

i. Minimise the volume of waste requiring managementvia treatment processes.

ii. Reduce the potential hazard of the waste by conditioning it into a stablesolid form that immobilises it and provides containment to ensure that the

waste can be safely handled during transportation, storage and final

disposal.

6.1.1 Incineration

Incineration of combustible wastes can be applied to both radioactive and other

wastes. In the case of radioactive waste, it has been used for the treatment of low-

level waste from nuclear power plants, fuel production facilities, research centres

(such as biomedical research), medical sector and waste treatment facilities.

Following the segregation of combustible waste from non-combustible

constituents, the waste is incinerated in a specially engineered kiln up to around

1000oC. Any gases produced during incineration are treated and filtered prior to

emission into the atmosphere and must conform to international standards and

national emissions regulations. Following incineration, the resulting ash, which

contains the radionuclides, may require further conditioning prior to disposal such

as cementation or bituminisation. Compaction technology may also be used to

further reduce the volume, if this is cost-effective.

6.1.2 Compaction

Compaction is a mature, well-developed and reliable volume reduction

technology that is used for processing mainly solid man-made low-level waste

(LLW). Some countries (Germany, UK and USA) also use the technology for the

volume reduction of man-made intermediate-level/transuranic waste. Compactors

can range from low-force compaction systems (~5 tonnes or more) through to


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presses with a compaction force over 1000 tonnes, referred to as supercompactors.

Volume reduction factors are typically between 3 and 10, depending on the waste

material being treated.

Figure 6.1.2 Compaction apparatus

Low-force compaction utilises a hydraulic or pneumatic press to compress

waste into a suitable container, such as a 200-litre drum. In the case of a

supercompactor, a large hydraulic press crushes the drum itself or other receptacle

containing various forms of solid low- or intermediate-level waste (LLW or ILW).

The drum or container is held in a mold during the compaction stroke of the

supercompactor, which minimises the drum or container outer dimensions.. Two

or more crushed drums, also referred to as pellets, are then sealed inside an

overpack container for interim storage and/or final disposal.

6.1.3 Cementation


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Figure 6.1.3 Cementation of nuclear wastes

Cementation through the use of specially formulated grouts provides the means

to immobilise radioactive material that is on solids and in various forms of sludges

and precipitates/gels (flocks) or activated materials.

In general the solid wastes are placed into containers. The grout is then added into

this container and allowed to set. The container with the monolithic block of

concrete/waste is then suitable for storage and disposal.

.

6.1.4 Vitrification

Figure 6.1.4 Vitrification experiment for the study of nuclear waste disposal

The immobilisation of high-level waste (HLW) requires the formation of an

insoluble, solid waste form that will remain stable for many thousands of years. In


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general borosilicate glass has been chosen as the medium for dealing with HLW.

The stability of ancient glass for thousands of years highlights the suitability of

borosilicate glass as a matrix material.

This type of process, referred to as vitrification, has also been extended for

lower level wastes where the type of waste or the economics have been

appropriate.

Most high-level wastes other than spent fuel itself arise in a liquid form from

the reprocessing of spent fuel. To allow incorporation into the glass matrix this

waste is initially calcined (dried) which turns it into a solid form. This product is

then incorporated into molten glass in a stainless container and allowed to cool,giving a solid matrix. The containers are then welded closed and are ready for

storage and final disposal.

6.2 Transport of Nuclear Waste

The nuclear waste should be properly transported to the sites where it is treated

for future disposal or to the respective sites for disposal.

6.2.1 Transport of LLW and ILW

Low-level and intermediate-level wastes (LLW and ILW) are generated

throughout the nuclear fuel cycle and from the production of radioisotopes used in

medicine, industry and other areas. The transport of these wastes is commonplace

and they are safely transported to waste treatment facilities and storage sites.

Low-level radioactive wastes are a variety of materials that emit low levels ofradiation, slightly above normal background levels. They often consist of solid

materials, such as clothing, tools, or contaminated soil. Low-level waste is

transported from its origin to waste treatment sites, or to an intermediate or final

storage facility.

Low-level wastes are transported in drums, often after being compacted in order

to reduce the total volume of waste. The drums commonly used contain up to 200


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litres of material. Typically, 36 standard, 200 litre drums go into a 6-metre

transport container. Low-level wastes are moved by road, rail, and

internationally, by sea. However, most low-level waste is only transported within

the country where it is produced.

The composition of intermediate-level wastes is broad, but they require

shielding. Much ILW comes from nuclear power plants and reprocessing facilities

Intermediate-level wastes are taken from their source to an interim storage site,

a final storage site or a waste treatment facility. They are transported by road, rail

and sea.

The radioactivity level of intermediate-level waste is higher than low-level

wastes. The classification of radioactive wastes is decided for disposal purposes,

not on transport grounds. The transport of intermediate-level wastes take into

account any specific properties of the material, and requires shielding.

6.2.2 Transport of used nuclear fuel

When used fuel is unloaded from a nuclear power reactor, it contains: 96%

uranium, 1% plutonium and 3% of fission products (from the nuclear reaction)

and transuranics.

Used fuel will emit high levels of both radiation and heat and so is stored in

water pools adjacent to the reactor to allow the initial heat and radiation levels to

decrease. Typically, used fuel is stored on site for at least five months before it

can be transported, although it may be stored there long-term.

From the reactor site, used fuel is transported by road, rail or sea to either an

interim storage site or a reprocessing plant where it will be reprocessed.

Used fuel assemblies are shipped in casks which are shielded with steel, or a

combination of steel and lead, and can weigh up to 110 tonnes when empty. A

typical transport cask holds up to 6 tonnes of used fuel..


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6.2.3 Transport of plutonium

Plutonium is separated during the reprocessing of used fuel. It is normally then

made into mixed oxide (MOX) fuel.

Plutonium is transported, following reprocessing, as an oxide powder since this

is its most stable form. It is insoluble in water and only harmful to humans if it

enters the lungs.

Plutonium oxide is transported in several different types of sealed packages and

each can contain several kilograms of material. Criticality is prevented by the

design of the package, limitations on the amount of material contained within the

package, and on the number of packages carried on a transport vessel. Special

physical protection measures apply to plutonium consignments.

6.2.4Transport of vitrified waste

The highly radioactive wastes (especially fission products) created in the

nuclear reactor are segregated and recovered during the reprocessing operation.

These wastes are incorporated in a glass matrix by a process known as

'vitrification', which stabilises the radioactive material.

The molten glass is then poured into a stainless steel canister where it cools and

solidifies. A lid is welded into place to seal the canister. The canisters are then

placed inside a cask, similar to those used for the transport of used fuel.

The quantity per shipment depends upon the capacity of the transport cask.

Typically a vitrified waste transport cask contains up to 28 canisters of glass.

6.3Storage and Disposal Options

Most low-level radioactive waste (LLW) is typically sent to land-based disposal

immediately following its packaging for long-term management. This means that

for the majority (~90% by volume) of all of the waste types, a satisfactory

disposal means has been developed and is being implemented around the world.


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Concentrating on intermediate-level waste (ILW) and high-level waste (HLW),

many long-term waste management options have been investigated worldwide

which seek to provide publicly acceptable, safe and environmentally sound

solutions to the management of radioactive waste.

6.3.1 Near-surface disposal

The International Atomic Energy Agency (IAEA) definition of this option is the

disposal of waste, with or without engineered barriers, in:

i. Near-surface disposal facilities at ground level. These facilities are on orbelow the surface where the protective covering is of the order of a few

metres thick. Waste containers are placed in constructed vaults and when

full the vaults are backfilled. Eventually they will be covered and capped

with an impermeable membrane and topsoil. These facilities may

incorporate some form of drainage and possibly a gas venting system.

ii. Near-surface disposal facilities in caverns below ground level. Unlikenear-surface disposal at ground level where the excavations are conducted

from the surface, shallow disposal requires underground excavation of

caverns but the facility is at a depth of several tens of metres below the

Earth's surface and accessed through a drift.

These facilities will be affected by long-term climate changes (such as

glaciation) and this effect must be taken into account when considering safety as

such changes could cause disruption of these facilities. This type of facility is

therefore typically used for LLW and ILW with a radionuclide content of short

half-life (up to about 30 years).

6.3.2 Deep geological disposal

The long timescales over which some of the waste remains radioactive led to

the idea of deep geological disposal in underground repositories in stable

geological formations. Isolation is provided by a combination of engineered and

natural barriers (rock, salt, clay) and no obligation to actively maintain the facility

is passed on to future generations. This is often termed a multi-barrier concept ,


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with the waste packaging, the engineered repository and the geology all providing

barriers to prevent the radionuclides from reaching humans and the environment.

A repository is comprised of mined tunnels or caverns into which packaged

waste would be placed. In some cases (e.g. wet rock) the waste containers are then

surrounded by a material such as cement or clay (usually bentonite) to provide

another barrier (called buffer and/or backfill). The choice of waste container

materials and design and buffer/backfill material varies depending on the type of

waste to be contained and the nature of the host rock-type available.

6.3.3 Multinational repositories

Not all countries are adequately equipped to store or dispose of their own

radioactive waste. Some countries are limited in area, or have unfavourable

geology and therefore siting a repository and demonstrating its safety could be

challenging. Some smaller countries may not have the resources to take the proper

measures on their own to assure adequate safety and security, or they may not

have enough radioactive waste to make construction and operation of their own

repositories economically feasible.

It has been suggested that there could be multinational or regional repositories

located in a willing host country that would accept waste from several countries.

They could include, for example use by others of a national repository operating

within a host country, or a fully international facility owned by a private company

operated by a consortium of nations or even an international organisation.

However, for the time being, many countries would not accept nuclear waste from

other countries under their national laws.

6.3.4 Interim waste storage

Specially designed interim surface or sub surface storage waste facilities are

currently used in many countries to ensure the safe storage of radioactive waste

pending the availability of a long-term management/disposal option. It must be

noted that interim storage, whether short-term or long-term, is not a final solution

- something will still remain to be done with the waste. Interim storage facilities


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are generally used for intermediate-level waste (ILW) and high-level waste

(HLW), although some countries, namely Finland, Sweden and the USA, now

have disposal facilities for ILW in operation. Similar arrangements exist for the

storage of used nuclear fuel from reactors.

The multi-layer approach to containment is designed to ensure that the most

penetrating forms of radiation cannot enter the outer environment. Recognising

that long-term management options, specifically for ILW and HLW, may require

significant time to be achieved, interim storage arrangements may need to be

extended beyond the time periods originally envisaged.

6.3.5 Long-term above ground storage

Figure 6.3.5 Steel Canisters for Radioactive Waste Storage

Above ground storage is normally considered an interim measure for the

management of radioactive waste. Long-term above ground storage involves

specially constructed facilities at the earth's surface that would be neither

backfilled nor permanently sealed. Hence, this option would allow monitoring and

retrieval at any time without excessive expenditure.


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Suggestions for long-term above ground storage broadly fall into two categories:

i. Conventional stores of the type currently used for interim storage, whichwould require replacement and repackaging of waste every 200 years or

so.

ii. Permanent stores that would be expected to remain intact for tens ofthousands of years. These structures are often referred to as 'Monolith'

stores or 'Mausoleums'.

The latter category of store is derived from the principle of 'guardianship',

where future generations continue to monitor and supervise the waste.

Both suggestions would require information to be passed on to future

generations, leading to the question of whether the stability of future societies

could be ensured to the extent necessary to continue the required monitoring and

supervision.

6.3.6 Deep boreholes

For the deep borehole option, solid packaged wastes would be placed in deep

boreholes drilled from the surface to depths of several kilometres with diameters

of typically less than 1 metre. The waste containers would be separated from each

other by a layer of bentonite or cement. The borehole would not be completely

filled with wastes. The top two kilometres would be sealed with materials such as

bentonite, asphalt or concrete.

Boreholes can be readily drilled offshore as well as onshore in host rocks both

crystalline and sedimentary. This capability significantly expands the range of

locations that can be considered for the disposal of radioactive waste.

6.3.7 Rock melting

The deep rock melting option involves the melting of wastes in the adjacent

rock. The idea is to either produce a stable, solid mass that incorporates the waste

or encases the waste in a diluted form (i.e. dispersed throughout a large volume of


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rock) that cannot easily be leached and transported back to the surface. This

technique has been mainly suggested for heat generating wastes such as vitrified

HLW and host rocks with suitable characteristics to reduce heat loss.

The HLW in liquid or solid form could be placed in an excavated cavity or a

deep borehole. The heat generated by the wastes would then accumulate resulting

in temperatures great enough to melt the surrounding rock and dissolve the

radionuclides in a growing sphere of molten material. As the rock cools it would

crystallise and incorporate the radionuclides in the rock matrix, thus dispersing the

waste throughout a larger volume of rock. There are some variations of this option

in which the heat-generating waste would be placed in containers and the rock

around the container melted. Alternatively, if insufficient heat is generated the

waste would be immobilised in the rock matrix by conventional or nuclear

explosion.

6.3.8 Disposal at a subduction zone

Subduction zones are areas where one denser section of the Earth's crust is

moving towards and underneath another lighter section. The movement of one

section of the Earth's crust below another is marked by an offshore trench, and

earthquakes occur adjacent to the inclined contact between the two plates. The

edge of the overriding plate is crumpled and uplifted to form a mountain chain

parallel to the trench. Deep sea sediments may be scraped off the descending slab

and incorporated into the adjacent. As the oceanic plate descends into the hot

mantle, parts of it may begin to melt. The magma thus formed migrates upwards,

some of it reaching the surface as lava erupting from volcanic vents. The idea for

this option would be to dispose of wastes in the trench region such that they would

be drawn deep into the Earth.

Although subduction zones are present at a number of locations across the

Earth's surface they are geographically very restricted. Not every waste-producing

country would be able to consider disposal to deep-sea trenches, unless

international solutions were sought. However, this option has not been


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implemented anywhere and, as it is a form of sea disposal, it is therefore not

permitted by international agreements.

6.3.9 Disposal at sea

Disposal at sea involves radioactive waste being shipped out to sea and dropped

into the sea in packaging designed to either: implode at depth, resulting in direct

release and dispersion of radioactive material into the sea; or sink to the seabed

intact. Over time the physical containment of containers would fail, and

radionuclides would be dispersed and diluted in the sea. Further dilution would

occur as the radionuclides migrated from the disposal site, carried by currents. The

amount of radionuclides remaining in the sea water would be further reduced bothby natural radioactive decay, and by the removal of radionuclides to seabed

sediments by the process of sorption. This method is not permitted by a number of

international agreements. This option has not been implemented for HLW.

6.3.10 Sub seabed disposal

For the sub seabed disposal option radioactive waste containers would be buried

in a suitable geological setting beneath the deep ocean floor. This option has been

suggested for LLW, ILW and HLW. Variations of this option include:

i. A repository located beneath the seabed. The repository would be accessedfrom land, a small uninhabited island or from an offshore structure.

ii. Burial of radioactive waste in deep ocean sediments.

Sub seabed disposal has not been implemented anywhere and is not permitted

by international agreements.

6.3.11 Disposal in ice sheets

For this option containers of heat-generating waste would be placed in stable ice

sheets such as those found in Greenland and Antarctica. The containers would

melt the surrounding ice and be drawn deep into the ice sheet, where the ice would

refreeze above the wastes creating a thick barrier. Although disposal in ice sheets


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could be technically considered for all types of radioactive wastes, it has only

been seriously investigated for HLW, where the heat generated by the wastes

could be used to advantage to self-bury the wastes within the ice by melting.

The option of disposal in ice sheets has not been implemented anywhere. It has

been rejected by countries that have signed the 1959 Antarctic Treaty or have

committed to providing a solution to their radioactive waste management within

their national boundaries. Since 1980 there has been no significant consideration

of this option.

6.3.12 Direct injection

This approach involves the injection of liquid radioactive waste directly into a

layer of rock deep underground that has been chosen because of its suitable

characteristics to trap the waste (i.e. minimise any further movement following

injection).

In order to achieve this there are two geological prerequisites. There must be a

layer of rock (injection layer) with sufficient porosity to accommodate the waste

and with sufficient permeability to allow easy injection (i.e. act like a sponge).

Above and below the injection layer there must be impermeable layers that act as

a natural seal. Additional benefits could be provided from geological features that

limit horizontal or vertical migration. For example, injection into layers of rock

containing natural brine groundwater. This is because the high density of brine

(salt water) would reduce the potential for upward movement.

Direct injection could in principle be used on any type of radioactive waste

provided that it could be transformed into a solution or slurry (very fine particles

in water). Slurries containing a cement grout that would set as a solid when

underground could also be used to help minimise movement of radioactive waste.

Direct injection has been implemented in Russia and the USA.

6.3.13 Transmutation of high-level radioactive waste


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This route of high-level radioactive waste envisages that one may use

transmutational devices, consisting of a hybrid of a subcritical nuclear reactor and

an accelerator of charged particles to 'destroy' radioactivity by neutrons. 'Destroy'

may not be the proper word; what is effected is that the fission fragments can be

transmuted by neutron capture and beta decay, to produce stable nuclides.

Transmutation of actinides involves several competing processes, namely neutron-

induced fission, neutron capture and radioactive decay. The large number of

neutrons produced in the spallation reaction by the accelerator are used for

'destroying' the radioactive material kept in the subcritical reactor. The scheme has

not yet been demonstrated to be practical and cost- effective.

6.3.14 Disposal in outer space

The objective of this option is to remove the radioactive waste from the Earth,

for all time, by ejecting it into outer space. The waste would be packaged so that it

would be likely to remain intact under most conceivable accident scenarios. A

rocket or space shuttle would be used to launch the packaged waste into space.

There are several ultimate destinations for the waste which have been considered,

including directing it into the Sun. It is proposed that 'surplus weapons' plutonium

and other highly concentrated waste might be placed in the Earth orbit and then

accelerated so that waste would drop into the Sun. Although theoretically

possible, it involves vast technical development and extremely high cost

compared to other means of waste disposal. Robust containment would be

required to ensure that no waste would be released in the event of failure of the

'space transport system'.

7. NUCLEAR WASTE MANAGEMENT IN INDIA

Sixteen nuclear reactors produce about 3% of Indias electricity, and seven

more are under construction. Radioactive waste management has been an integral

part of the entire nuclear fuel cycle in India. Low-level radioactive waste and

intermediate-level waste arise from operations of reactors and fuel reprocessing

facilities. The low-level radioactive waste liquid is retained as sludge after

chemical treatment, resulting in decontamination factors ranging from 10 to 1000.


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Solid radioactive waste is compacted, bailed or incinerated depending upon the

nature of the waste. Solar evaporation of liquid waste, reverse osmosis and

immobilization using cement matrix are adopted depending on the form of waste.

Underground engineered trenches in near-surface disposal facilities are utilized

for disposal of solid waste; these disposal sites are under continuous surveillance

and monitoring. High efficiency particulate air (HEPA) filters are used to

minimize air-borne radioactivity. Over the past four decades radioactive waste

management facilities have been set up at Trombay, Tarapore, Rawatbhata,

Kalpakkam, Narora, Kakrapara, Hyderabad and Jaduguda, along with the growth

of nuclear power and fuel-reprocessing plants. Multiple- barrier approach is

followed in handling solid waste.

After the commissioning of the fast breeder test reactor at Kalpakkam, one is

required to reprocess the burnt carbide fuel from this reactor. As the burn-up of

this fuel is likely to be of the order of 100 MWD/kg, nearly an order of magnitude

more than that of thermal reactors and due to short cooling-time before

reprocessing, specific activity to be handled will be greatly enhanced. The use of

carbide fuel would result in new forms of chemicals in the reprocessing cycle.

These provide new challenges for fast-reactor fuel reprocessing.

As a national policy, each nuclear facility in India has its own Near Surface

Disposal Facility (NSDF). There are seven NSDFs currently operational within

the country. These NSDFs in India have to address widely varied geological and

climatological conditions. The performance of these NSDFs is continuously

evaluated to enhance the understanding of migration, if any and to adopt measures

for upgrading the predictability over a long period of time. Performance

assessment and service life prediction of Reinforced Concrete Trenches:

Performance assessment of Reinforced Concrete Trench (RCT) is systematically

undertaken through field investigations and predictive modeling. NDT

investigations on operating RCTs and laboratory studies on NSDF materials have

demonstrated that RCTs are in sound condition even after an operational period of

three to four decades. Mathematical models have been developed to predict the

probability of failure as a function of target lives for various safety indices such as


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concrete cover thicknesses, climatic factors, maintenance period for the structure,

water to cement ratio, water proofing etc. Modeling studies for a typical RC

trench under limiting conditions have predicted a minimum service life of nearly

240 years.

8. CONCLUSION

Many people quite reasonably feel that the nuclear industry shouldn't continue

operation without having a solution for the disposal of its radioactive waste.

However, the industry has in fact developed the necessary technologies and

implemented most of them - the remaining issue is to ensure that the proposed

solutions are acceptable to the public.

Today, safe management practices are implemented or planned for all

categories of radioactive waste. Low-level waste (LLW) and most intermediate-

level waste (ILW), which make up most of the volume of waste produced (97%),

are being disposed of securely in near-surface repositories in many countries so as

to cause no harm or risk in the long-term. This practice has been carried out for

many years in many countries as a matter of routine.

High-level waste (HLW) is currently safely contained and managed in interim

storage facilities. The amount of HLW produced is in fact small in relation to

other industry sectors. The use of interim storage facilities currently provides an

appropriate environment in which to contain and manage this amount of waste. In

the long-term however, appropriate disposal arrangements are required for HLW,

due to its prolonged radioactivity. Disposal solutions are currently being

developed for HLW that are safe, environmentally sound and publicly acceptable.

The solution that is widely accepted as feasible is deep geological disposal, and

repository projects are well advanced in some countries, such as Finland, Sweden

and the USA.

With the availability of technologies and the continued progress being made to

develop publicly acceptable sites, it is logical that construction of new nuclear

facilities can continue. Nuclear energy has distinct environmental advantages over


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fossil fuels. As well as containing and managing virtually all its wastes, nuclear

power stations do not cause any pollution. The fuel for nuclear power is virtually

unlimited, considering both geological and technological aspects. There is plenty

of uranium in the Earth's crust and furthermore, well-proven (but not yet fully

economic) technology means that we can extract about 60 times as much energy

from it as we do today. The safety record of nuclear energy is better than for any

major industrial technology. All these benefits should be taken into account when

considering the construction of new facilities.

REFERENCES

1. Current Science, 1534 Vol. 81, No. 12, 25 December 2001

2. The Principles of Radioactive Waste Management, Safety Series No. 111-F, a

publication within the RADWASS programme, IAEA (1995).

3. Radiochemistry and Nuclear chemistry Nuclear Waste Management and the

Nuclear Fuel Cycle- Patricia. A. Baisden, Gregory R. Choppin.

4. The principles of radioactive waste management. Vienna : International

Atomic Energy Agency, 1995.


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