Radioactive waste: The problem and its management

Radioactive waste, arising from civilian nuclear activities as well as from defence-related nuclear-weapon activities, poses a formidable problem for handling and protecting the environment to be safe to the present and future generations. As nuclear power and arsenal grow, continuous monitoring and immobilization of the waste over several decades and centuries and deposition in safe repositories, assumes great relevance and importance.

Radioactive Waste

Two basic nuclear reactions, namely fission of nuclei like 235U, 239Pu and fusion of elements like hydrogen result in release of enormous energy and radioactive elements. Controlled vast releases of energy are possible in nuclear power plant reactors through the fission reaction. The dream of controlled vast releases of energy through fusion reaction is still to be realized. Uncontrolled vast releases of energy through both these reactions have been possible in ‘atom’ and ‘hydrogen’ (thermonuclear) bombs. As in many other industrial processes, in the nuclear industry also, one gets unusable and unwanted waste products; the residues turn out to be hazardous. Waste that emits nuclear radiation is radioactive waste.

Artificial Radioactivity:- Radioactivity was discovered about a hundred years ago. Following the Second World War and discovery of the fission process, human activity added radioactivity artificially to the natural one. Two main sources have been:

(a) the civilian nuclear programmes, including nuclear power production, medical and industrial applications of radioactive nuclides for peaceful purposes, and

(b) the military nuclear programme, including atmospheric and underground nuclear-weapon testing and weapon production .

The cause for Concern

A>Radiation effects On Humans

Radioactive waste, whether natural or artificial, is a potential harbinger of radioactive exposure to humans through many channels. The routes are direct exposure to materials that are radioactive, inhalation and ingestion of such materials through the air that one breathes or food that one consumes. The quantum of exposure (dose into duration of exposure) decides the deleterious effects that may result. Exposure may occur to particular organs locally or to the whole body. Sufficiently high exposure can lead to cancer.Radiation effects are also classified in two other ways, namely somatic and genetic effects. Somatic effects appear 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 subfertility 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.

B>Radiation effects On Environment

1>The recent emphasis arises because of concern to the effects on the environment over a very long period of time. High-level radioactive waste is potentially toxic for tens of thousands to millions of years; it is also the most difficult to be disposed safely because of its heat and radiation output. Thermal, chemical and radiological gradients operate on the environment over periods as long as 500,000 years.
2>nuclear power plants are managed subject to several radiation protection control practices. Secondly, one may also note that ‘a 1000 MW electric coal-fired power plant releases into the environment nearly 6 million tonnes of greenhouse gases, 500,000 tons of mixtures of sulphur and nitrogen oxides and about 320,000 tonnes of ashes’. These ashes containing NORMs are potentially capable of subjecting humanity to a collective dose of radiation higher than that attributable to wastes discharged into the environment by nuclear power plants generating the same amount of electricity. In spite of this ground reality, public perception about nuclear wastes is rather skewed against nuclear power in several countries.

Quantifying Nuclear Waste

It is estimated that the nuclear waste, as a result of nuclear power production around the world over the past 50 years, is of the order of 1000 EBq and is growing at the rate of approximately
100 EBq/year. Typically, a large nuclear power plant of generating capacity of 1000 MW electricity produces ‘around 27 tonnes of high-level radioactive waste, 310 tonnes of intermediate-level and 460 tonnes of lowlevel radioactive waste’.

Classification of Radioactive Waste

i)Low-level radioactive waste
ii)High-level radioactive waste

i)Low-level radioactive waste=Large amounts of waste contaminated with small amounts of radionuclides, such as contaminated equipment (glove boxes, air filters, shielding materials and laboratory equipment) protective clothing, cleaning rags, etc. constitute low-level radioactive waste.

ii)High-level radioactive waste=This waste includes uranium, plutonium and other highly radioactive elements created during fission, made up of fission fragments and transuranics. (Note that this definition does not specify the radioactivity that must be present to categorize as high-level radioactive waste.) These two components have different times to decay. The radioactive fission fragments decay to different stable elements via different nuclear reaction chains involving alpha, beta and gama emissions to innocuous levels of radioactivity, and this would take about 1000 years. On the other hand, transuranics take nearly 500,000 years to reach such levels. Heat output lasts over 200 years. Most of the radioactive isotopes in high-level waste emit large amounts of radiation and have extremely long half-lives (some longer than 100,000 years), creating long time-periods before the waste will settle to safe levels of radioactivity.

As a thumb-rule one may note that ‘volumes of lowlevel radioactive waste and intermediate-level waste greatly exceed those of spent fuel or high-level radioactive waste’. In spite of this ground reality, the public concerns regarding disposal of high-level radioactive waste is worldwide and quite controversial.

Radioactive Waste Management

The International Atomic Energy Agency (IAEA) is promoting acceptance of some basic tenets by all countries for radioactive waste management. These include:
(i) securing acceptable level of protection of human health;
(ii) provision of an acceptable level of protection of environment;
(iii) while envisaging (i) and (ii), assurance of negligible effects beyond national boundaries;
(iv) acceptable impact on future generations; and
(v) no undue burden on future generations.

Approaches to Radioactive Waste Disposal

The following options have been aired sometime or the other. Each one of the options demands serious studies and technical assessments:
•Deep geological repositories
•Ocean dumping
Seabed burial
•Sub-seabed disposal
•Subductive waste disposal method
•Transforming radioactive waste to non-radioactive stable waste
•Dispatching to the Sun.

Major problems due to legal, social, political and financial reasons have arisen in execution due to
•Environmental perceptions
•Lack of awareness and education
•‘Not-in-my-backyard’ syndrome
•‘Not-in-the-ocean’ syndrome
•Lack of proven technology.

Geologic Disposal

The deep geological sites provide a natural isolation system that is stable over hundreds of thousands of years to contain long-lived radioactive waste. In practice it is noted that low-level radioactive waste is generally disposed in near-surface facilities or old mines. High-level radioactive waste is disposed in host rocks that are crystalline (granitic, gneiss) or argillaceous (clays) or salty or tuff. Since, in most of the countries, there is not a big backlog of high-level radioactive waste urgently awaiting disposal, interim storage facilities, which allow cooling of the wastes over a few decades, are in place.

Ocean-Dumping

Though this practice has been banned by most of the countries with nuclear programmes, the problem still persists. Russia, which currently 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 alternative method. 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.

Sub-seabed Disposal

Seabed disposal is different from sea-dumping which does not involve isolation of low-level radioactive waste within a geological strata. The floor of deep oceans is a part of a large tectonic plate situated some 5 km below the sea surface, covered by hundreds of metres of thick sedimentary soft clay. These regions are desert-like, supporting virtually no life. The Seabed
Burial Proposal envisages drilling these ‘mud-flats’ to depths of the order of hundreds of metres, such boreholes being spaced apart several hundreds of metres. The high-level radioactive waste contained in canisters, to which we have referred to earlier, would be lowered into these holes and stacked vertically one above the other interspersed by 20 m or more of mud pumped in.

However there are questions that remain to be answered:
•Whether migration of radioactive elements through the ocean floor is at the same rate as that already 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 happens to insoluble species like plutonium?
•What is the likelihood 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?

Added to these technical problems are others:
•International agreement to consider seabed-burial as distinct from ‘ocean-dumping’.
•This method would be expensive to implement, but its cost would be an impediment to any future plutonium- mining endeavour.

Subductive Waste Disposal Method

Subduction is a process whereby one tectonic plate slides beneath another and is eventually reabsorbed into the mantle. The subductive waste disposal method forms a high-level radioactive waste repository in a subducting plate, so that the waste will be carried beneath the Earth’s crust where it will be diluted and dispersed through the mantle.

Transmutation of High-level Radioactive Waste

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.

Solar Option

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’.

Concluding Remarks

The problems associated with radioactive waste management on a long-term are major ones that humanity has not been able to come to terms with so far. It is nearly 45 years since the IAEA was founded. Over these years the Agency has deliberated on various issues that confront radioactive waste management and has been providing guidelines and forums for technical and non-technical debates and discussions. As time passes by, new issues crop up, which need to be discussed. One example is how does one ‘plan for retirement of nuclear facilities’, sometimes referred to as ‘decommissioning of facilities’. Similarly changes in concepts of long-term issues on health and safety need to be addressed – ‘dose and risk for a remote time in the future are not believable, since habits of human populations are impossible to be predicted’.

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