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Essay on Radioactive Waste
Essay # 1. Introduction to Radioactive Waste:
The substances, which emit the radiations, are known as radioactive. The phenomenon of spontaneous emissions of radiations from radioactive substance is known as radioactivity.
The examples of radioactive substances are – uranium, polonium, radium, radon, ionium, thorium, actinium, etc. It is clearly known that all naturally occurring elements whose atomic numbers are greater than 82 are all radioactive and radioactivity is the property of atom of the element concerned in a compound because the radiation are unaffected by chemical and physical change.
α (alpha), β (beta) and γ (gamma) radiations are, at low levels, naturally part of our environment. Any or all of them may be present in any classification of wastes. All three kinds of radiations are a health hazard. They can cause leukemia, eye cataracts, various forms of cancer and, from a high dose, death. The hazard is greatest if the radionuclide enters the body through the intake of contaminated food, water and air.
Radioactivity enters the environment from natural and man-made sources. Radioactivity can exist as gaseous, liquid or solid materials. Radon is a well-known example of a radioactive gas. Water often contains dissolved amounts of radium and uranium. Solid radioactive waste is produced from many sources, including the uranium and rare earth mining industries, laboratory and medical facilities, and the nuclear power industry.
Radiation is a part of natural environment. The total radiation exposure, both external and internal, resulting from natural and man-made sources is important for assessing the effects of radiation on human beings. The external exposure comes out from extra-terrestrial sources in the form of cosmic rays and also from terrestrial radiation sources.
Radioactivity in the environment incites public reaction more rapidly than any other environmental incidence. The mere word radioactivity reminds fear in most people, even trained and skilled workers in the field. This fear has been imprinted in the public memory by such names as Hiroshima, Three Mile Island and Chernobyl.
Essay # 2. Types of Radioactivity:
Radiation comes from atoms, the basic building blocks of matter. Most atoms are stable; a carbon-12 atom for example remains a carbon-12 atom forever, and an oxygen-16 atom remains an oxygen-16 atom forever, but certain atoms eventually disintegrate into a totally new atom. These atoms are said to be ‘unstable’ or ‘radioactive’. Each element exists in the form of atoms with several different sized nuclei, called isotopes. Unstable isotopes (which are thus radioactive) are called radioisotopes. Some elements, e.g., uranium, have no stable isotopes. Some isotopes are radioactive, most are not.
When an atom of a radioisotope decays, it gives off some of its excess energy as radiation in the form of gamma rays or fast-moving sub-atomic particles. If it decays with emission of an alpha or beta particle, it becomes a new element. One can describe the emissions as gamma, beta and alpha radiation. All the time, the atom is progressing in one or more steps towards a stable state where it is no longer radioactive.
Another source of nuclear radioactivity is when one form of a radioisotope changes into another form, or isomer, releasing a gamma ray in the process. The excited form is signified with an “m” (meta) beside its atomic number, e.g., technetium-99 m (Tc-99 m) decays to Tc-99. Gamma rays are often emitted with alpha or beta radiation also, as the nucleus decays to a less excited state.
Apart from the normal measures of mass and volume, the amount of radioactive material is given in Becquerel (Bq), a measure that enables us to compare the typical radioactivity of some natural and other materials. A becquerel is one atomic decay per second (A former unit of radioactivity is the curie, 1 Bq = 27 x 10–12 curies).
Bacquerel discovered radioactive decay in 1896 when he found that a uranium salt blackened a photographic plate even in complete darkness. The work of Marie and Pierre Curie, Rutherford and Villard established three kinds of radiations called α (alpha)—α helium atom nucleus, β (beta)—ejected from the nucleus when a neutron changes spontaneously to a proton and γ (gamma)—this is a very energetic form of electromagnetic radiation with a very short wavelength (high frequency). A fourth kind, neutron radiation, generally only occurs inside a nuclear reactor (Fig. 13.1).
Different types of radiation require different forms of protection:
i. Alpha radiation cannot penetrate the skin and can be blocked out by a sheet of paper, but is dangerous in the lung.
ii. Beta radiation can penetrate into the body but can be blocked out by a sheet of aluminium foil.
iii. Gamma radiation can go right through the body and requires several centimetres of lead or concrete, or a metre or so of water, to block it.
All of these kinds of radiations are, at low levels, naturally part of our environment. Any or all of them may be present in any classification of wastes.
All three kinds of radiations (alpha, beta and gamma) are a health hazard. They can cause leukemia, eye cataracts, various forms of cancer and, from a high dose, death. The hazard is greatest if the radionuclide enters the body through the intake of contaminated food, water and air.
The effect of radionuclide depends on:
(i) The extent to which it is retained.
(ii) The energy level of its emitted radiation.
(iii) Its half-life.
(iv) The organ of the body where it is retained, α-particles are the most damaging to biological cells. Due to their poor penetrative power they cause damage mainly to lungs, e.g., if small α-particles are inhaled in the body.
Half-life and Decay of Radioisotopes:
The radioactive half-life for a given radioisotope is a measure of the tendency of the nucleus to ‘decay’ or ‘disintegrate’ and, as such, is based purely upon that probability. For example, carbon 14 decays to nitrogen 14. To put that another way, each radioactive nuclide emits radioactivity at its characteristic rate, different from that of other nuclides. The rate of radioactive decay is related to the energy change that accompanier, the transformation, but it is not a direct relationship.
The rate of radioactive emissions of a radioactive nuclide is directly proportional to the amount of radioactive material present. The various radioactive isotopes have half-lives ranging from fractions of a second to minutes, hours or days, through to billions of years. Radioactivity decreases with time as these isotopes decay into stable, non-radioactive ones. The rate of decay of an isotope is inversely proportional to its half-life; a short half-life means that it decays rapidly. Hence, for each kind of radiation, the higher the intensity of radioactivity in a given amount of material, the shorter the half-lives involved.
The half-life is independent of the physical state (solid, liquid, gas), temperature, pressure, the chemical compound in which the nucleus finds itself, and essentially any other outside influence. It is independent of the chemistry of the atomic surface, and independent of the ordinary physical factors of the outside world. The only thing which can alter the half-life is direct nuclear interaction with a particle from outside, e.g., a high energy collision in an accelerator.
An unstable atom has excess internal energy, with the result that the nucleus can undergo a spontaneous change towards a more stable form. This is called ‘radioactive decay’. A radioisotope has unstable nuclei that do not have enough binding energy to hold the nucleus together. Radioisotopes would like to be stable isotopes, so they are constantly changing to try and stabilize. In the process, they release energy and matter from their nucleus and often transform into a new element.
This process, called transmutation, is the change of one element into another as a result of changes within the nucleus. The radioactive decay and transmutation process continues until a new element is formed that has a stable nucleus and is not radioactive. Hence all decay process result from energy changes that eventually result in the formation of a stable nucleus. For example, thorium decays to radium, which decays to actinium, which eventually produces non-radioactive lead 208.
Radioactivity in the Natural Environment:
Radioactivity in the environment comes from natural and man-made sources. Although natural radioactivity is the most likely to be encountered in the environment due to its widespread dispersal, man-made radioactivity poses the greatest environmental risk. Natural radioactivity harnessed by man and not properly disposed of is also a potential threat to the environment.
Naturally—occurring radioactive materials are widespread throughout the environment, although concentrations are very low and they are not normally harmful. Soil naturally contains a variety of radioactive materials-uranium, thorium, radium and the radioactive gas radon, which is continually escaping to the atmosphere. Many parts of the earth’s crust are more radioactive than the low-level waste described above. Radiation is not something which arises just from using uranium to produce electricity, although the mining and milling of uranium and some other ores brings these radioactive materials into closer contact with people, and in the case of radon and its daughter products, speeds up their release to the atmosphere (Table 13.1).
The terrestrial natural radiation comes from constituent elements of soil, rocks and mineral and is mainly 40k, 232Th and 238U and their decay products. The other important nuclides are 87Rb and 235U.
Elster and Geital in 1899 and Wilson in 1900 first detected the cosmic rays. These rays produce a range of radionuclides in the atmosphere, biosphere by a variety of nuclear reactions. These rays are highly penetrating radiations consisting of high-energy penetrating atomic nuclei which are continuously coming from outer space. About 1018 of them reach the earth each second. They have a wide range of energy from 109 to 1018 electron-volts.
The areas marked as high dose rate areas around the world are associated with thorium-bearing and uranium-bearing materials. Mineral sands containing monazite are prime examples of the former. Absorbed dose rates from gamma rays near separated monazite may reach upto 105 nGy depending upon the geometry.
Essay # 3. Types of Radioactive Waste:
Radioactive wastes are generated in the nuclear fuel cycle as well as in nuclear applications (the use of radionuclides in medicine, research and industry). The radiological and safety risk from radioactive wastes varies from very low in short-lived, low-level wastes up to very large for high-level wastes. Annually about 2,00,000 m3 of low-level and intermediate-level waste and 10,000 m3 of high-level waste (as well as spent nuclear fuel destined for final disposal) is generated worldwide from nuclear power production.
These volumes are increasing as more nuclear power units are taken into operation, nuclear facilities are decommissioned and the use of radionuclides increases. Important factor in managing wastes is the time that they are likely to remain hazardous. This depends on the kinds of radioactive isotopes in them, and particularly the half-lives characteristic of each of those isotopes. After four half-lives, the level of radioactivity is 1/16th of the original and after eight half-lives 1/256th.
Three general principles are employed in the management of radioactive wastes:
The first two are also used in the management of non-radioactive wastes. The waste is both concentrated and then isolated, or it is diluted to acceptable levels and then discharged to the environment. Delay-and-decay, however, is unique to radioactive waste management; it means that the waste is stored and its radioactivity is allowed to decrease naturally through decay of the radioisotopes in it.
Radioactive wastes are normally classified as low-level, medium-level or high-level wastes, according to the amount and types of radioactivity in them as given below:
Low-level Radioactive Waste (LLRW) is a general term for a wide range of materials contaminated with radioisotopes. It is generated from hospitals, medical, educational and research institutions, laboratories 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 is not dangerous to handle, but must be disposed of more carefully than normal garbage. Usually it is buried in shallow landfill sites. To reduce its volume, it is often compacted or incinerated (in a closed container) before disposal. Worldwide, it comprises 90% of the volume but only 1% of the radioactivity of all radioactive wastes. These wastes are generated in many physical and chemical forms, and at many levels of contamination.
Intermediate-level Radioactive Waste (ILRW) contains higher amounts of radioactivity and may require special shielding. It typically comprises resins, chemical sledges and reactor components, as well as contaminated materials from reactor decommissioning. Worldwide it makes up 7% of the volume and has 4% of the radioactivity of all radioactive waste. It may be solidified in concrete or bitumen for disposal. Generally short-lived waste (mainly from reactors) is buried, but long-lived waste (from reprocessing nuclear fuel) will be disposed of deep underground.
High-level Radioactive Waste (HLW) consists of spent fuel elements from nuclear reactors, waste produced from reprocessing, and waste generated from the manufacture of nuclear weapons. HLW may be the spent fuel itself, or the principal waste from reprocessing this. While only 3% of the volume of all radioactive waste, it holds 95% of the radioactivity. It contains the highly-radioactive fission products and some heavy elements with long-lived radioactivity. It generates a considerable amount of heat and requires cooling, as well as special shielding during handling and transport.
The history of the various unfortunate experiences with x-rays and radioactive materials is a familiar one – repeated severe skin burns suffered by the early physicists and physicians using x-rays, skin cancers occurring in some of these same individuals at the sites of the repeated burns, bone sarcomas occurring among those who used radium-containing luminescent paints on watch and clock dials, and more recently, various neoplasms occurring in some patients receiving x-ray exposures in clinical procedures.
Thus, it became quickly known that large doses of radiation could cause severe acute symptoms ranging from localized skin burns to generalized severe damage to vital tissues, such as bone marrow, and at high enough doses, death. Soon it began to be noted that some of those who recovered from the acute symptoms of over-exposure went on, later, to develop serious consequences such as various kinds of neoplasms including, particularly, leukemia.
The estimates of risks associated with exposure to radiation are often expressed in the number of cases of whatever is being considered per rad of radiation exposure per million people exposed. A rad is one of the units used to measure the quantity of radiation exposure.
It has been shown, for example, that the average exposure to humans from naturally occurring sources of ionizing radiation is near 0.1 rad, or 100 milliards, per year. This natural exposure comes from cosmic rays, radioactive isotopes in the ground and building materials, and radioactive materials in our food and water. The 0.1 rad per year exposure is that which existed prior to the advent of weapons testing with its resultant fallout and does not include medical use of ionizing radiation.
It has been known for many years that large doses of ionizing radiation, very much larger than background levels, can cause a measurable increase in cancers and leukemia (‘cancer of the blood’) after some years delay. It must also be assumed, because of experiments on plants and animals, that ionizing radiation can also cause genetic mutations that affect future generations, although there has been no evidence of radiation-induced mutation in humans. At very high levels, radiation can cause sickness and death within weeks of exposure.
The degree of damage caused by radiation depends on many factors – dose, dose rate, type of radiation, the part of the body exposed, age and health, for example. Embryos, including the human fetus, are particularly sensitive to radiation damage.
But what are the chances of developing cancer from low doses of radiation? The prevailing assumption is that any dose of radiation, no matter how small, involves a possibility of risk to human health. However, there is no scientific evidence of risk at doses below about 50 millisieverts in a short time or about 100 millisieverts per year. At lower doses and dose rates, up to at least 10 millisieverts per year, the evidence suggests that beneficial effects are as likely as adverse ones.
Higher accumulated doses of radiation might produce a cancer, which would only be observed several up to twenty years after the radiation exposure. This delay makes it impossible to say with any certainty, which of many possible agents were the cause of a particular cancer. In western countries, about a quarter of people die from cancers, with smoking, dietary factors, genetic factors and strong sunlight being among the main causes. Radiation is a weak carcinogen, but undue exposure could certainly increase health risks.
The body has defense mechanisms against damage induced by radiation as well as by chemical and other carcinogens. These can be stimulated by low levels of exposure, or overwhelmed by very high levels. Given below is the impact of various sources of radioactive wastes.
The invisible radioactive radon gas lurks in the mines to sign death warrants by lung cancer for the mining workers. This is in addition to the irreparable damage to the environment. In the end, around the abandoned mines, generations are doomed to lead lives of pain and misery. The story has been the same in several parts of the world. Navajo Indians in the midst of Navajo reservations that stretch from New Mexico into Arizona and the aboriginal Canadians in Canada’s north-western areas of Saskatchewan and Ontario and in other continents, all have been at the receiving end.
Now it commences for a second time in India in the Nalgonda district of Andhra Pradesh in south India, while the first instance in India is more or less complete in and around the uranium fields of Jadugoda in Jharkhand in the north. Children in the 15 villages surrounding the uranium mines showed signs of genetic mutation and over 60 per cent of the workers manning the tailing ponds were afflicted with serious ailments like bone, blood and kidney disorders, brain damage, cancer, paralysis, tuberculosis and nausea.
The most serious of leftover piles of radioactive sand or uranium tailings are thorium-230, radium-226, radon-222 (radon gas) and the radon progeny including polonium-210. If this radioactive sand is left on the surface and is allowed to dry out, it can blow in the wind and be deposited on vegetation far away, entering the food chain. Or it can wash into rivers and lakes and contaminate them.
Thorium-230 is the uranium decay product with the longest lifetime. It lasts for hundreds of thousands of years—in human terms, forever. Thorium is especially toxic to the liver and the spleen. It has been known to cause leukaemia and other blood diseases. It decays to produce radium-226, which in turn produces radon gas (radon-222). So the amount of radium in the waste and the quantities of radon gas produced by it will not diminish for a long time, because they are constantly being replenished by the decay of the very long-lived thorium-230.
Radium-226 is one of the more dangerous uranium decay products. It is a radioactive heavy metal and a potent alpha emitter. As it decays, it produces radon gas as a by-product. Radium is chemically similar to calcium, and, when ingested, it migrates to the bones, the teeth and the milk. It is readily taken up by vegetation. In aquatic plants, it can be concentrated by factors of hundreds or even thousands.
Radon-222 is a toxic gas created by the decay of radium-226. Most of the radon is normally trapped in the ore-bearing rock deep within the earth. But when the rock is excavated and crushed, a lot of radon gas is released into the air. The uranium miners breathe this radioactive gas into their lungs. Radon (the gas and its progeny) is a very powerful cancer-causing agent. Even small doses inhaled repeatedly over a long time can cause lung cancer.
The production of plutonium and highly enriched uranium (HEU) for nuclear weapons over the past fifty years caused enormous environmental damage and posed risks to the health of workers and communities.
The dangers posed by plutonium and HEU are three-fold – they can be used to make nuclear weapons, they are radioactive and toxic, and their production processes involve other hazardous substances.
Outside the body, plutonium and uranium pose minimal risks to human health unless exposure is on a sustained basis. This is because the main type of radiation from both materials, i.e., alpha radiation, is very short-range and is stopped by the outer dead layer of skin. However, if plutonium or uranium enter the body, the high-energy alpha radiation can damage cells and cause cell mutations that can lead to cancer. The main health concern for plutonium is inhalation of small particles or absorption through cuts or wounds. While the amount of data is limited, animal studies suggest that as little as one millionth of an ounce of plutonium lodged in the lung is very likely to cause cancer.
Like plutonium, uranium is a health hazard when small particles are inhaled or absorbed through wounds. But uranium is also more easily absorbed than plutonium through the gastrointestinal tract. Animal studies suggest that uranium may damage reproductive organs, may harm a developing fetus, and may increase the risk of leukemia and soft tissue cancers. Uranium is far less radioactive than plutonium, and uranium can cause acute damage to the kidneys by heavy metal poisoning well before radiation effects are manifest.
When in the form of small pieces of metal, plutonium and HEU can ignite upon exposure to air. Under certain conditions, the accumulation of plutonium or HEU (such as in ventilation ducts or in solutions) can lead to a criticality, a chain reaction of fissioning atoms. The energy release from a criticality can be high enough to cause threats to worker safety and damage the container holding the materials.
One of the most serious health hazards associated with producing HEU is uranium mining. The cancer risk from uranium mining is mainly due to exposure to the decay products of radon, which is itself a decay product of uranium-238.
In human terms, nuclear weapons are enormously destructive. A weapon with a ten-megaton yield can destroy most of the buildings of a modern city, while a weapon with a hundred-megaton yield (although the deployment of such a weapon would be considered impractical) would set wooden structures and forests alight up to 60-100 miles (100-160 km) from ground zero.
A nuclear weapon detonated in the upper atmosphere will also generate an electromagnetic pulse which can disrupt or disable electronic communications and instruments over a wide area, causing more difficulties for those who survive the effects of a detonation. Concerns over the health and environmental effects of nuclear testing led to the passing of the Partial Test Ban Treaty in 1963 which prohibited atmospheric (above-ground), underwater, or outer space nuclear tests (underground testing continued, however).
Since most of the effects of nuclear weapons are blast, thermal, or fallout, well-known civil defense efforts could greatly reduce the total loss of life in a nuclear war.
Indeed, since the dawn of the atomic age, millions of people in other parts of the world have been affected by bomb production and testing. Children in several nuclear weapon testing sites have seen the risk of cancers rise from drinking milk contaminated with fallout from atmospheric nuclear tests.
Moving tests underground did not end the problem, even though it did greatly mitigate the problem of radiation doses from short-lived radionuclides such as Iodine-131. Large amounts of plutonium, iodine-129, cesium-135, and other long-lived radionuclides remain underground at the test sites. They possess the potential for migration into water bodies in the long term.
There are considerable uncertainties in the risk of cancer death from exposure to low levels of radiation, but all careful scientific evaluations, including the most recent ones, have concluded that every increment of exposure to radiation produces an incremental risk of cancer. The range of estimates of cancer deaths as a result of testing fallout, is between about 200,000 to more than half a million. The number of cancer cases, including thyroid cancer, which has a low fatality rate (about 5 per cent), would be considerably greater.
People who have been drinking water contaminated with tritium, which is radioactive hydrogen (released from a nuclear weapons materials plant). This contamination level is at about 5 per cent of the present-day drinking water standard. However, these standards are set for a grown male, called ‘standard man,’ and they do not consider the effects of radioactive water on developing fetuses. They do not consider miscarriages and other non-cancer effects.
It is a remarkable fact of nuclear weapons history and radiation risk that every nuclear-weapon state has, first of all, harmed its own people in the name of national security. For the most part, they have done so without informed consent. Nor is the damage confined to nuclear-weapon possessors. Uranium for nuclear weapons was mined in many non-nuclear-weapon states.
Effects of Thermal Pollution:
The biological and other effects associated with thermal pollution are listed below:
a. Thermal death—the sudden death of aquatic life due directly to increased temperature.
b. An increased predation rate, due, for example, to changes in avoidance reactions induced by temperature changes, decrease in swimming speed and stamina, etc.
d. Increased susceptibility of aquatic organisms to chemical or physical toxins.
e. Disruption of normal biological rhythms.
f. Disruption of migration patterns.
g. Decreased oxygen concentrations in heated waters at the same time as the organisms’ oxygen requirements are increased because of the increase in temperature.
h. Increase in anaerobic organisms with putrefaction of sludge, etc.
i. Increase in rooted plant growth leading, for example, to decrease flow rates, increased siltation, and a total disruption of the bio-system.
j. Increased susceptibility to pathogenic organisms.
k. Decreased spawning success and decrease in survival of young fish.
l. Death from thermal shock caused by rapid changes in water temperature.
m. Increased growth of taste-producing and odour-producing organisms such as blue-green algae.
n. Changes in efficiency of water purification and treatment methods.
o. Effects on various industrial processes which are temperature-dependent.
p. Replacement of cold-water species by other species. Effects on swimming and other recreational uses; increased decomposition of sludge, increase in sludge gas, increase in saprophytic bacteria and fungi, increase in algae formation.
q. Increase in incorporation of radioactive wastes into organic material and, hence, into the food chains when radioactive wastes are discharged along with thermal wastes (for example in association with a nuclear power plant).
The lethal exposure (following an accident) could range from none to a calculated maximum of 3,400 (deaths). This maximum could only occur under the adverse combination of several conditions which would exist for not more than 10 per cent of the time and probably much less.
Low-level wastes are almost uncountable, but a 1989 study projects an annual low-level radioactive waste volume of 1,300,000 cubic feet. This waste remains dangerous for hundreds to thousands of years. Aside from the long-term hazards of the waste produced by nuclear power plants, their everyday releases of radioactivity have been found to cause premature births, congenital defects, infant mortality, mental-retardation, heart ailments, arthritis, diabetes, allergies, asthma, rampant cancer, leukemia, genetic damage, environmental illness, chronic fatigue syndrome, which effects 4 to 6 million people, as well as previously unknown infectious diseases.