17 Radioactive wastes: Definition, sources, classification, collection, segregation, Treatment and disposal

Rajeev Pratap Singh

Objectives:

1. To have a basic understanding of radioactive wastes

2. To gain knowledge on the sources of radioactive waste generation

3. To understand the management practices followed for radioactive waste

4. To familiarize the treatment and disposal options available for radioactive waste

1. Introduction:

To understand radioactive waste management it is necessary to understand what are radiations and their sources. X-rays were discovered by Wilhelm Roentgen in the year 1895. Thereafter, instantly Henri Becquerel detected radiation originating from certain uranium salts similarly to X-rays. Marie and his husband Pierre Curie studied radiation from two uranium ores i. e. pitchblende and chalcolite in year 1898, and isolated two supplementary elements that exhibited radiation similar to that of uranium, but substantially stronger. These two elements were named radium and polonium. Atomic age started with the discovery and isolation of radioactive elements i. e. radium and polonium. Curie classified the radiation according to the direction of deflection in a magnetic field into three types namely alpha (α), beta (β), and gamma (γ) radiation. Antoine Henri Becquerel, a physicist was the first person to discover evidence of radioactivity in 1896. The SI unit for radioactivity the becquerel (Bq), is named after him.

In 1905, Ernest Rutherford identified alpha particles emanating from uranium as ionized helium atoms, and in 1932, Sir James Chadwick characterized as neutrons the highly penetrating radiation that results when beryllium is bombarded with alpha particles. Some other subatomic particles were subsequently identified by modern physics. Management of radioactive waste requires understanding of the sources and effects of alpha, beta, gamma, and neutron emissions.

Table 1: Properties of Ionizing Radiation

A radioactive atom has an unstable nucleus and they moves towards a more stable condition by emitting an alpha or beta particle or neutron; this emission is frequently accompanied by emission of additional energy in the form of gamma radiation. On account of these emissions, the radioactive atom is transformed into either an isotope of the same element (neutron or gamma only emission) or into an isotope of a different element (alpha or beta emission). This transformation is known as radioactive decay, and the emissions are known as ionizing radiation.

The rate of radioactive decay can be expressed by a first-order rate equation:

Where

N = the number of radioactive nuclei and

Kb = a factor called the disintegration constant; Kb has the units of time-1

Integrating over time, we get the classical equation for radioactive decay:

The data points in Figure. 1 corresponds to this equation. After a specific time period t = t1/2, the value of N is equal to one-half of N0. That is, one-half of the radioactive atoms have decayed (or disintegrated) during each time period t1/2. This time period t1/2 is called the radiological half-life, or sometimes simply the half-life. Looking at Fig. 16-1, we see that at t = 2t1/2, N becomes 1/4No; at t = 3t1/2, N becomes 1/8 No; and so on. Equation (16.2) is so constructed that N never becomes zero in any finite time period; for every half-life that passes, the number of atoms is halved. If the decay constant Kb is known, the half-life may be determined from equation

Figure 1 Decay of Radioactive atom with time

Table 3: Some Important Radionuclides

Radionuclide	Type of Radiation	Half-life
Krypton-85	Beta and gamma	10 years
Strontium-90	Beta	29 years
Iodine-131	Beta and gamma	8.3 days
Cesium-137	Beta and gamma	30 years
Tritium (Hydrogen-3)	Beta	12 years
Cobalt-60	Beta and gamma	5 years
Carbon-14	Beta	5770 years
Uranium-235	Alpha	7.1×108 years
Uranium-238	Alpha	4.9×109 years
Plutonium-239	Alpha	24,600 years

2. Effects of radioactive pollution:

The effect of radioactive pollution depends upon:

a. Half –life i. e. time of exposure

b. Energy releasing capacity i. e. intensity of radiation

c. Rate of diffusion: This is also referred to as the movement of a substance down a concentration gradient. Diffusion rates increase with temperature, and decrease with increasing pressure, molecular weight, and molecular size.

d. Type of ionizing radiation (i.e. its penetration power)

e. Various atmospheric and climatic conditions such as wind, temperature, rainfall also

determine their effects.

The possible general effects of radioactive wastes are categorized into:

1) Somatic Effect

2) Genetic Effect

3) Biomagnification

Somatic effect: Affects somatic cells. It appears within individual and disappears with the death of the individual.

Immediate effects: Anaemia, Reduced immune response, Hemorrhage, skin burn, mouth ulcers, CNS Damage

Delayed effects: Eye cataract, Leukemia, Cardiovascular disease, Premature ageing, Reduced life span, reduction of fertility

Genetic Effects: The radiation affects the genes of the gamete cells. The changes are not apparent in the individual. The effects are exhibited by offspring and in the subsequent generations. They affect the DNA, RNA replication and chromosome. It causes-

• Mutation

• Chromosomal aberration

• Chromosomal fragmentation

• Inhibition of RNA, DNA synthesis (Levy et al. 2011)

Table 4: Effects of radioactive radiation on living beings

3. Radioactive waste Definition

Waste, by definition, is any material materials solid, liquid or gas that has been or will be discarded as being of no further use (Garvin 1995). Radioactive waste is any material that is either radioactive itself or is contaminated by radioactivity, for which no further use is expected. According to Atomic Energy Regulatory Board (AERB) India, radioactive waste is material, whatever its physical form, left over from practices or interventions for which no further use is foreseen: (a) that contains or is contaminated with radioactive substances and has an activity or activity concentration higher than the level for clearance from regulatory requirements, and (b) exposure to which is not excluded from regulatory control. Waste from one process can also be served as resource material of other (IAEA 1996). Department of Atomic Energy (DAE) which was established in 1954 is the administrative agency for all activities related to atomic energy. Keeping in mind the safety parameters the sites for nuclear installations are selected. Numerous physical barriers are designed which make sure any significant escape of radiation from the reactor. On a monthly basis the radiation dosage received by workers are monitored. The dose limit (i.e) 30 millisievert (mSv) has been fixed by the Atomic Energy Regulatory Board (AERB) for workers.

This is in agreement with the limit set up by International Commission on Radiological Protection (ICRP), an independent international non-governmental organization, which provides recommendations and guidance on radiation protection. The Atomic Energy Regulatory Board, an autonomous body of Atomic Energy Commission constituted on November 15, 1983 by the President of India, carries out all regulatory and safety functions as assigned under the Atomic Energy Act, 1962 covering all establishments of Department of Atomic Energy. The headquarters is located in Mumbai. It is also empowered to take decision with regard to site selection, design, construction and commissioning, operation, etc. of all nuclear installations.

4. Sources of Radioactive waste:

Radioactive waste is generated from a variety of industries. Any waste that contains or contaminated with radioactive materials are called as radioactive waste. They can be generated from operation and decommissioning of nuclear facilities, radionuclides using industry, radionuclides containg raw material, medicine and research (IEAE 2000). Radioactive waste is also generated during the cleanup of sites affected by radioactive residues from various operations or accidents. At certain times, the materials generated as waste may be reused or recycled.

Radioactive waste arises from many different activities:

Operation and decommissioning of nuclear facilities (e.g. nuclear power plants) Application of radionuclides in industry, medicine, and research

Cleanup of contaminated sites

Processing of raw materials containing naturally occurring radionuclides

a. Radioactive waste from the nuclear fuel cycle consists of materials with varied range of radioactivity levels. The spent nuclear fuel contains radionuclides like uranium, plutonium, their decay products and many fission products. In many countries, the spent fuel is reprocessed to separate U and Pu. Handling of spent fuel should be done with great care through sophisticated remote handling techniques. Proper shielding should be provided while handling these wastes.

b. Operational waste includes a variety of lower-level wastes, either in the form of filtering residues (e.g. ion exchange resins) or as contaminated supplies (e.g. clothing) containing fission and activation products.

c. Decommissioning of nuclear power stations gives rise to large volumes of contaminated material, including some highly-activated reactor components as well as structural materials that may be slightly contaminated by activation products and/or fission products.

d. Wastes generated from other units of the nuclear fuel cycle include milling wastes containing decay products of natural uranium, such as radium and radon and radon daughters etc. Long lifetimes of these materials pose a great problem. Sometimes, the radioactivity is increased when few daughter products are combined. Facilities where the ore is refined, enriched and processed into fuel also result in radioactive waste (Hubbard 2013). In the case of depleted uranium tails, in addition to direct toxicity of the uranium, daughter products (radium and radon) buildup on long time scales also increase the toxicity.

e. Radionuclides are used extensively in industrial research, agricultural research, geological exploration, constructions for measuring thickness, density or volume of materials. They are also used in smoke detectors; tracers; sealed sources for irradiation, heat/power source

5. Classification of Radioactive waste:

In the International Atomic Energy Agency (IAEA) general safety guide 2009, the classification scheme of radioactive waste has been modified with the intention to address the shortcomings identified with the previous scheme and to reflect experience gained in developing, operating and assessing the safety of disposal facilities. The classification scheme developed previously is not completely comprehensive in that it does not cover all types of radioactive waste, nor does it provide a direct linkage with disposal options for all types of radioactive waste. These aspects of the former classification scheme have been deemed limitations on its use and application

A comprehensive range of waste classes has been defined and general boundary conditions between the classes are provided. More detailed quantitative boundaries that take into account a broader range of parameters may be developed in accordance with national programs and requirements. In cases when there is more than one disposal facility in a State, the quantitative boundaries between the classes for different disposal facilities may differ in accordance with scenarios, geological and technical parameters and other parameters that are relevant to the site specific safety assessment.

A number of elements of the previously set out classification scheme (International Atomic Energy Agency, Categorizing Operational Radioactive Wastes, IAEA–TECDOC-1538, IAEA, Vienna 2007) have been retained. A complete range of waste classes has been defined and general boundary conditions between the classes are provided to reflect the experience gained in developing, operating and assessing the safety of disposal facilities. More detailed quantitative boundaries will be prepared according to the national programmes and requirements. In cases when there is more than one disposal facility in a State, the quantitative boundaries between the classes for different disposal facilities may differ in accordance with scenarios, geological and technical parameters and other parameters that are relevant to the site specific safety assessment. Six classes of waste have been derived and used as the basis for the classification scheme:

(1) Exempt waste (EW): Waste that meets the criteria for clearance, exemption or exclusion from regulatory control for radiation protection purposes.

(2) Very short lived waste (VSLW): Waste that can be stored for decay over a limited period of up to a few years and subsequently cleared from regulatory control according to arrangements approved by the regulatory body, for uncontrolled disposal, use or discharge. Eg. Waste containing primarily radionuclides with very short half-lives often used for research and medical purposes.

(3) Very low level waste (VLLW): Waste that does not necessarily meet the criteria of EW, but that does not need a high level of containment and isolation and, therefore, is suitable for disposal in near surface landfill type facilities with limited regulatory control. Such landfill type facilities may also contain other hazardous waste. Typical waste in this class includes soil and rubble with low levels of activity concentration. Concentrations of longer lived radionuclides in VLLW are generally very limited.

(4) Low level waste (LLW): Waste that is above clearance levels, but with limited amounts of long lived radionuclides are categorized as LLW. Such waste requires robust isolation and containment for periods of up to a few hundred years and is suitable for disposal in engineered near surface facilities.

This class covers a very broad range of waste. LLW may include short lived radionuclides at higher levels of activity concentration, and also long lived radionuclides with relatively low levels of activity concentration. Low level Waste (LLW) is generated from hospitals and industry, as well as the nuclear fuel cycle. It comprises paper, rags, tools, clothing, filters etc which contain small amounts of mostly short-lived radioactivity. It does not require shielding during handling and transport and is suitable for shallow land burial. To reduce its volume, it is often compacted or incinerated before disposal

LLW includes everything not included in one of the other categories. LLW is not necessarily less radioactive than HLW and may have higher specific activity in becquerel per gram. The distinguishing feature of LLW is that it contains virtually no alpha emitters. To ensure appropriate disposal, the NRC has designated several classes of LLW:

Class A contains only short-lived radionuclides or extremely low concentrations of longer-lived radionuclides, and must be chemically stable. It is disposed of in designated LLW landfills as long as it is not mixed with hazardous or flammable waste.
Class B contains higher levels of radioactivity and must be physically stabilized before transportation or disposal. It must not contain free liquid.
Class C is waste that will not decay to acceptable levels in 100 years and must be isolated for 300 years or more. Power plant LLW is in this category.

Greater than Class C (GTCC) will not decay to acceptable levels in 300 years. A small fraction of power plant Class C waste is in this category. Some nations like Sweden treat GTCC waste like HLW, and the United States may do the same.

Mixed Low-Level Waste (MLLW) is LLW that contains hazardous waste as defined under the Resource Conservation and Recovery Act (RCRA).

(5) Intermediate level waste (ILW): Waste that, because of its content, particularly of long lived radionuclides, requires a greater degree of containment and isolation than that provided by near surface disposal. However, ILW needs no provision, or only limited provision, for heat dissipation during its storage and disposal. Intermediate level Waste (ILW) contains higher amounts of radioactivity and some requires shielding. It typically comprises resins, chemical sludges and metal fuel cladding, as well as contaminated materials from reactor decommissioning. It may be solidified in concrete or bitumen for disposal. ILW may contain long lived radionuclides, in particular, alpha emitting radionuclides that will not decay to a level of activity concentration acceptable for near surface disposal during the time for which institutional controls can be relied upon. Therefore, waste in this class requires disposal at greater depths, of the order of tens of meters to a few hundred meters.

(6) High level waste (HLW): Waste with levels of activity high enough to generate significant quantities of heat by the radioactive decay process or waste with large amounts of long lived radionuclides that need to be considered in the design of a disposal facility for such waste. A limit of 400 Bq/g on average (and up to 4000 Bq/g for individual packages) for long lived alpha emitting radionuclides has been adopted in some States. For long lived beta and/or gamma emitting radionuclides, such as 14C, 36Cl, 63Ni, 93Zr, 94Nb, 99Tc and 129I, the allowable average activity concentrations may be considerably higher (up to tens of kilo becquerel per gram) and may be specific to the site and disposal facility. Disposal in deep, stable geological formations usually several hundred meters or more below the surface is the generally recognized option for disposal of HLW. High level Waste (HLW) arises from the use of uranium fuel in a nuclear reactor and nuclear weapons processing. It contains the fission products and transuranic elements generated in the reactor core. It is highly radioactive and hot. HLW accounts for over 95% of the total radioactivity produced in the process of nuclear electricity generation.

Table 5: Common Categories of Radioactive Waste

http://www.pollutionissues.com/Pl-Re/Radioactive-Waste.html

Table 6: Typical characteristics of different waste classes

6. Management of Radioactive wastes:

Radioactive wastes contaminate air, water, soil and consequently vegetation that eventually affect public health and environment adversely. Since radioactivity is a long term phenomenon, proper and planned disposal of radioactive wastes should be ensured to prevent any negative impact on health and safety of living beings as well as on environmental quality (Ojovan and Lee 2014). According to IAEA (1995), the principles of radioactive waste management are: (1) protection of human health, (2) protection of the environment, (3) protection beyond national borders, (4) protection of future generations and avoid burden over them (6) national legal framework, (7) control of radioactive waste generation, (8) management interdependencies, and (9) safety of facilities.

The major aim of the environmentalist is to abate the introduction of radioactive materials into the biosphere and environment. Control of the possible direct impact on the human environment is essential but not enough, since radionuclides can be transmitted through water, air, and land pathways for several years and even for generations. Some radioactive waste may be recovered and recycled by future reprocessing, but reprocessing process creates its own radioactive waste stream. The majority of radioactive waste can be treated only by isolating it from the available environment until its radioactivity no longer poses a threat. Isolation requirements vary for different classes of radioactive waste (Table 1).

Table 1: Different kind of radioactive waste and its handling

A few radionuclides, mainly those that make up HLW, contain half-lives of tens of thousands of years, or even hundreds of thousands of years. It is difficult to find the technology that solves the problem of ultimate disposal of radioactive waste so long term storage is the only solution till date.

7. Segregation of Radioactive Waste

The secure, environmentally acceptable and economic management of radioactive waste arising from the nuclear power is an essential component of nuclear power programmes. Noteworthy technical advancement has been achieved and substantial experience of all stages of waste management has been accumulated in many countries. Waste processing, conditioning, storage and transportation have become regular and demonstrably safe activities (Salvato et al. 2003).

Radioactive wastes should be separated according to their isotopes and placed in separate containers. Tritium (3H) and Carbon-14 (14C) can occupy the same container. Radioactive waste besides segregation based on isotopes, are also separated by physical form (Streffer et al., 2011). Ten (10) basic physical forms of radioactive waste include:

a) Solid

b) Glass

c) Sharps

d) Liquid

e) Liquid Scintillation Vials

f) Biological

g) Animal Remains

h) Source Vials

i)Lead Pigs

j) Sealed Sources

a. Radioactive Solids:

It consists of disposable items, radioactive material contaminated lab items such as plastic/rubber gloves, tubing, and syringes; unbroken glassware such as pipettes, beakers, flasks, columns, etc. Specific type of containers is used for collection and storage of solid radioactive waste. Plastic bags are commonly used to collect the solid radioactive waste materials. Yellow radioactive material bags should be avoided for this type of waste expect when they are placed in closeable waste receptacle (for e.g. plastic foot operated trashcan) which remains closed always. The prerequisites for safe handling and disposal of solid radioactive waste include

Extreme care while handling radioactive wastes
Proper labeling of all bags with the date, month, year, isotope, total activity and department’s name.
Before placing waste into the bags, remove all radioactive and labware labels.
All the bags should be checked for leaks prior to waste collection. Sometimes, second yellow bag can be used to contain the waste if necessary.
Take care to segregate sharps to avoid tearing of bags
Avoid placing of bags with solid radioactive waste in such places where there are chances of the
waste be picked up by housekeeping personnel and disposed off along with municipal waste. Waste containers must always remain closed.

b.Radioactive Glass:

It included radioactive material contaminated glassware/ other unbroken glass which should be packaged separately from other solid radioactive waste. A strong cardboard box properly labeled and sealed is used for storing the radioactive glass.

c. Radioactive Sharps:

Sharps are defined as anything that could tear the yellow radioactive material bag. Examples: Needles, broken glass, glass pipettes, razor blades, capillary tubes, etc. The container used for collecting such waste must be puncture resistant plastic tubes. These containers once full must be securely capped with orange/red top with complete labelling. The requirements for safe handling and disposal of this type of radioactive waste include

Care must be taken to avoid injury during packing of sharps in containers. Avoid overfilling of container.

Ensure that all sharps are dry before placing into container. When full, securely cap tube with orange/red top.

d. Radioactive Liquid

The radioactive liquid waste can be further divided into:

(a) Aqueous: Aquous liquids are those water based based liquids with a pH between 5.0-9.0, such as saline and buffer solutions that arise from contaminated laboratory glassware washings; weak acids or bases free of biological, pathogenic, or infectious materials

(b) Organic: laboratory solvents such as alcohols, aldehydes, ketones, and organic acids used for various purpose. This category does not include scintillation fluids and

Specially designated containers termed as carboys are used for disposing radioactive liquids. These carboys should be filled upto 80% of its volume. The prerequisites for safe handling and disposal of this type of radioactive waste include

In the laboratory the carboys should be provided with double containment as a precautionary measure against leakage. This will control carboy failure, necessary because pouring is usually accompanied by drips, dribbles, and seeping. Carboys should be placed in a tray or pan that will contain the liquid in the event of a spill of the carboy. At a minimum, plastic backed absorbent paper shall be placed under all liquid waste carboys.

Do not use glass containers for storage of radioactive liquid waste. If plastic-incompatible contaminated organic solvents are required to be kept in glass containers, the bottle must be doubled contained.

The first three rinses of the emptied containers must also be placed in the radioactive liquid waste container. No radioactive liquid is to be poured down the sink.

Avoid mixing of liquid waste types in the carboys (e.g. organic with aqueous). Pipettes and other such items should not be placed in the carboys.

All biological material in the carboys must be properly deactivated. Carboys should be kept free of contamination as far as possible.

e. Radioactive Liquid Scintillation Vials

Glass or plastic vials containing organic or aqueous based liquid scintillation fluid are included under this category. This type of waste is disposed of in the cardboard trays and placed in a yellow radioactive material bag. At certain cases, these wastes are double bagged in a yellow radioactive material bag for disposal Eg. glass vials are double bagged in yellow radioactive material bags and placed in a cardboard box. Absorbent material must be placed in the cardboard box to absorb any leakage from the vials. Empty vials are to be disposed of as dry and semi-solid radioactive waste. The requirements for safe handling and disposal of this type of radioactive waste are:

Assure that all tops are fixed tightly on the vials.

Avoid empting used vials into plastic bags. Leaking or seeping scintillation fluid will dissolve plastic.

Label each box of vials containing aqueous scintillation cocktail and segregate them from organic cocktail vials.

If the vials require reusability then pour the liquid waste into a carboy along with the first rinse of the vial. Because most scintillation cocktail solutions are volatile and will contain radioactive substances. The procedures of pouring out the solution should be conducted in a ventilated fume hood.

f. Radioactive Biological Waste

Radioactive waste containing biological, pathogenic, or infectious material and the equipment used to handle such material are categorized under radioactive biological waste. Examples: By-product animal waste (i.e. serum, blood, excreta), contaminated capillary tubes and other equipment contaminated with animal fluids, radioactive material labeled culture media. Yellow radioactive materials bags labeled with biological waste stickers or red biological bags labeled with radioactive material stickers are the container used for disposal. The prerequisites for safe handling and disposal of this type of radioactive waste include

Liquids must be absorbed into another material such as paper towels, sponges, gauze, etc. prior to placing into bags.

Pathogenic and infectious waste must be sterilized by autoclaving or chemical treatment. If autoclaved, the autoclave must be checked for radioactive contamination after use.

g.Radioactive Animal Remains

Examples: Radioactive animal carcasses, animal bedding, and by-product animal waste with the carcasses (i.e. viscera, serum, blood, excreta, tissue, etc.) and other animal tissue containing radioactive materials. Yellow Radioactive Materials bags are used as containers for disposing these wastes. The requirements for safe handling and disposal of this type of radioactive waste are:

Animal remains containing radioactive material in any quantity are subject to handling according to the guidelines. Avoid dumping of these wastes along with municipal wastes

A tag showing: the date, radioisotope, total activity, and the laboratory shall be tied to the bag. Bags not labeled cannot legally be disposed of, so an investigation will be performed to identify the generator of the unlabeled waste. If the bag is placed in the freezer by personnel from your lab, the same information must appear on the tag.

Liquids surrounding carcasses must be absorbed onto another material (e.g. paper towels, sponges, gauze, etc.) prior to placing into yellow bags.

h.Source Vials Examples: The original vials with radioactive materials shipped from the supplier are categorized under this waste. This includes full, partially full, and empty vials. Source vials must be separated from the dry and semi-solid waste stream and placed in cardboard box for disposal

i. Lead Pigs

Examples: Original lead and lead impregnated shielding containers surrounding source vials are included in this category. Lead is a hazardous waste and must be disposed of accordingly. Avoid placing of these items in municipal waste. Cardboard shipping box for used disposal.

j. All Sealed Sources

Examples: Calibration sources, check sources, quenched standard sets, electron capture gas chromatograph detectors, etc. Sealed sources must be separated from the solid waste and placed in cardboard box for disposal. During disposal, check for broken or crushed sources and handle these damaged sources with extreme care. All sources must be disposed of properly by a private contractor, even if decayed. A final survey or leak test on all sources should be done prior disposal.

8.0 Disposal of Radioactive Waste

Nuclear waste from commercial reactors, medical applications, defense industry, radioactive research poses a great threat to the scientific community as well as the public (Nguyen, 1994). The solutions to high-level nuclear waste are still debatable, both technically and ethically. There are numerous proposals for disposing high-level nuclear wastes. However, the most favored solution for the discarding of radioactive wastes is segregating out radioactive waste from man and biosphere for a long period of time such that any prospective release of radionuclides from the waste repository will not occur thereby resulting in unwarranted radiation exposure. The primary idea behind this solution is to use stable geological environments that can held the radioactive material for millions of years to provide an appropriate isolation capacity for the duration required.

The main reason for relying on such geological environments is based on the following chief consideration: ‘Geological media is an entirely passive disposal system with no requirement for continuing human involvement for its safety. It can be abandoned after closure with no need for continuous surveillance or monitoring. The safety of the system is based on multiple barriers, both engineered and natural. The main one being the geological barrier (Rao 2001).

Numerous alternatives for the disposal of long-lasting wastes have been examined over the years. Studies have been performed on concepts such as disposal in oceanic sub-seabed sediments and ultra-deep boreholes, besides on more exotic proposals such as disposal into geologic subduction zones, in polar icecaps and launching into space (OECD Nuclear Energy Agency 2000). All of these concepts have been found inadequate in terms of costs or risks, or unfeasible owing to political or legal restrictions.

The following options have been aired sometime or the other. Each one of the options requires serious studies and technical assessments:

8.1 Deep geological repositories

8.2 Under water disposal i.e. Ocean dumping mainly

8.2.1 Seabed burial

8.2.2 Sub-seabed disposal

8.3 Subductive waste disposal method

8.4 Transforming radioactive waste to non-radioactive stable waste

8.5 Dispatching to the Sun.

Most important problems due to legal, social, political and financial reasons have arisen in implementation due to

• Environmental perceptions

• Lack of proper awareness and education

• ‘Not-in-my-backyard’ syndrome

• ‘Not-in-the-ocean’ syndrome

• Lack of proven technology.

8.1 Geologic disposal

For handling long-lived radioactive waste, disposal in deep geological formations: under continental crust or under seabed has been recognized since 1957. Deep geological disposal involves introducing waste packages in underground structures dug in an impermeable geological medium having favourable properties in terms of its geological stability, hydrogeology, geochemistry and response to mechanical and thermal stress. The chosen medium must avoid areas of exceptional interest in terms of exploitable underground resources. The structures must be located at least 200 m below the ground surface to avoid the effects of erosion and human intrusion. Depositing the waste in deep geological sites will favor isolation of waste and keep them stable over thousands of years. Long-lived radioactive wastes are buried in deep sites unlike low-level radioactive waste which is normally disposed in near-surface facilities or abandoned mines.

Mostly, crystalline (granitic, gneiss) or argillaceous (clays) or salty or tuff are preferred for disposal of high-level radioactive waste. Provisional storage facilities, which permit cooling of the wastes over a few decades also do exist in most of the countries. The majority of countries now believe deep geological disposal as the standard solution for final management of high-level and intermediate-level long lived waste. Granite; sedimentary formations, more especially clay beds; and salt are three types of geological formations on which most of the in progress research and studies are mainly focusing.

8.2. Underwater disposal

8.2.1 Ocean-dumping

Generally, two associated methods of underwater disposal of Spent Nuclear Fuel (SNF) exist: dumping containers of radioactive waste into the ocean, and sub-seabed disposal. The main reason of underwater disposal of SNF is the same as any other type of SNF disposal, which is to isolate radioactive waste from human contact and the environment long enough for any release of radiation to become harmless.

USA, France, Great Britain, and many more industrialized countries have opted dumping into the oceans as the least expensive method for disposal of the radioactive wastes. Before the U.S. government banned or stopped sea dumping of spent nuclear fuel (SNF) around the 1980s, the United States reportedly dumped about 112,000 containers of nuclear waste at thirty locations in the Atlantic and Pacific oceans.

Although this practice has been prohibited by nearly all of the countries with nuclear programmes, the problem still persists. Russia, which presently controls sixty per cent of the world’s nuclear reactors, continues to dispose of its nuclear wastes into the oceans. According to Russia’s Minister of Ecology, it will continue to dump its wastes into the oceans because it has no other alternative method (Rao, 2001). It will continue to do so until it receives enough international aid to create proper storage facilities. In response, the United States has pledged money to help Russia, but the problem continues. Although radioactive waste has known negative effects on humans and other animals, no substantial scientific proof of bad effects on the ocean and marine life has been found. Therefore, some nations have requested that ocean-dumping should be carried on. Others argue that the practice should be banned until further proof of no harm is available.

8.2.2. Sub-seabed disposal

Seabed disposal involves disposal of waste in deep oceans floor situated 5 km below the sea surface. These large tectonic plates are desert-like and are covered with hundreds of meters of thick sedimentary soft clay. Sub-seabed disposal is complexed and involves two associated methods: creating a repository with a possibility for retrieval of SNF, and everlasting burial (Krivit et al. 2010).

Sweden and the United Kingdom consider creating a repository method, which permits for retrieval of SNF and might, contains admittance to the repository from land. A benefit of such a sub-seabed repository would be an increased capability to supervise SNF, in contrast to the dumping method. Another advantage could be a potential for access from land, which could let the repository method to avoid violating international bans against oceanic dumping, but accessing certain underwater locations by land might be impossible.

In Seabed Burial method, the mud flats at the bottom of the ocean is drilled to depths of the order of hundreds of meters. Inside these bore holes the radioactive material that are enclosed in containers are stacked vertically one over the other. Inconsistency of the rock and high local permeability limits the use of rocks in ocean as basement. Moreover, oceanic water has a mixing time of the order of a few thousand years which does not serve as a good barrier for long-lived radionuclides.

Experimental works have already established that clays have the property of holding on to several radioactive elements, including plutonium; hence, seepage of these elements into saline water is negligible. Rates of migration of these elements over hundreds of thousands of years would be of the order of a few meters. Hence, during such long times, radioactivity will lessen to levels below the natural radioactivity in sea water as a result of natural radioactive decay. The clays also contain plastic-like behaviour to form natural sealing agents. Lastly, the mud-flats have rather low permeability to water; hence, leaching probability is rather low. It may be noted that the method depends on standard deep-sea drilling techniques routinely practiced and sealing of the bore-holes. Core samples from about half a dozen vastly separated sites in the Pacific and Atlantic oceans have ‘showed a continuous history of geological stillness over the past 50–100 million years’. However, there are several questions that still remain to be answered:

Whether migration of radioactive elements through the ocean floor is at the same rate as that measured in the laboratories?
What is the effect of nuclear heat on the deep oceanic-clays?
What is the import on the deep oceanic fauna and waters above?
In case the waste reaches the seabed-surface, will the soluble species (for example, Cs, Tc, etc.) be diluted to natural background levels? If so, at what rate?
What occurs to insoluble species like plutonium?
What is the possibility of radioactivity reaching all the way to the sea surface?
In problems of accidents in the process of seabed burial leading to, say, sinking ships, to loss of canisters, etc. how does one recover the waste-load under such scenarios?
What is the likelihood that the waste is hijacked from its buried location?