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The disposal of nuclear waste is a pressing problem for society worldwide.

 

By

Dr. Nitish Priyadarshi

Geologist.

 

The nuclear disaster in Fukushima, Japan, caused many countries to rethink their appetite for nuclear power. It is also, in subtler ways, altering the fraught discussion of what to do with nuclear plants’ wastes.

 

Harnessing the power of the atom has propelled humanity forward at an astonishing rate since the dawn of the Nuclear Age. However, the proper disposal and storage of nuclear waste leaves an incomplete equation. Nuclear waste comes from nuclear power reactors and byproducts of military-grade bombs. This waste can come in the form of spent nuclear fuel rods or even toxic sludge. Perhaps the greatest danger of nuclear energy is the long-term investment in waste disposal that will be passed to future generations.

 

For more than 50 years, waste from nuclear power stations has been accumulating into what is now the most dangerous rubbish dump in the world. But we are still very far from coming up with a permanent, safe solution for the disposal of radioactive material.

 

Seven years ago, there were around 250,000 tonnes of highly radioactive waste worldwide. Towards the end of 2010, the International Atomic Energy Agency (IAEA) estimated it to be 345,000 tonnes, and in 2022, 450,000 tonnes. What  are we going to do with it all.

 

According to another report, a typical nuclear power plant in a year generates 20 metric tons of used nuclear fuel. The nuclear industry generates a total of about 2,000 - 2,300 metric tons of used fuel per year.

Over the past four decades, the entire industry has produced about 67,500 metric tons of used nuclear fuel. If used fuel assemblies were stacked end-to-end and side-by-side, this would cover a football field about seven yards deep. 

 

A recent study found that, on average, people in Britain live about 42km (26 miles) away from one of more than 30 radioactive waste sites, including power plants and military bases, in the UK.

 

Half-a-century after launching the nuclear programme, India has finally begun working on a “deep geological repository” to permanently store its nuclear waste.

Over the next five years, scientists are going to study a set of physical and geological parameters required for setting up the nuclear waste storage facility before zeroing in on its location. 

The options vary from underground storage in rocky central India to plains where the storage may be housed inside layers of clay.

 

India's existing nuclear waste site is located at Tarapur where high-level radioactive waste is first converted into inert and stable materials which are kept inside stainless steel canisters sealed with lead covers. 

 

Sixteen nuclear reactors produce about 3% of India’s electricity, and seven more are under construction. Spent fuel is processed at facilities in Trombay near Mumbai, at Tarapur on the west coast north of Mumbai, and at Kalpakkam on the southeast coast of India. Plutonium will be used in a fast breeder reactor (under construction) to produce more fuel, and other waste vitrified at Tarapur and Trombay. Interim storage for 30 years is expected, with eventual disposal in a deep geological repository in crystalline rock near Kalpakkam.

 

In 1997, IAEA members proposed certain criteria for nuclear waste disposal. It should be done, “wherever possible”, in those countries that have produced the waste. Further, it should avoid “imposing undue burden on future generations”.

 

But at present, “no country has a geological site for the interim and permanent storage of spent fuel rods,” complain experts of the IAEA.

 

Radioactive wastes come in many different forms including the following:

1. protective clothing of people in contact with radioactive materials

2. the remains of lab animals used in experiments with radionuclides

3. cooling water, used fuel rods, and old tools and parts from nuclear power plants

4. mill tailings from uranium-enrichment factories

5. old medical radiation equipment from hospitals and clinics

6. used smoke detectors which contain radioactive americium-241 sensors

 

 

How does nuclear waste get to you?

 

The planet's water cycle is the main way radiation gets spread about the environment. When radioactive waste mixes with water, it is ferried through this water cycle. Radionuclides in water are absorbed by surrounding vegetation and ingested by local marine and animal life. Radiation can also be in the air and can get deposited on people, plants, animals, and soil. People can inhale or ingest radionuclides in air, drinking water, or food. Depending on the half life of the radiation, it could stay in a person for much longer than a lifetime. The half life is the amount of time it takes for a radioactive material to decay to one half of its original amount. Some materials have half-lives of more than 1,000 years!

 

 

On 26th June 1954, 110 km from Moscow, the first civil nuclear reactor of the world supplied current in the grid. At the end of 2011, in 31 countries where nuclear power is produced, there were 435 reactors in use, 104 in the US alone. They meet 15 per cent of the world’s electricity demand, though the national ratios vary. While France  generates almost three-quarters of its own electricity through nuclear power and also exports the surplus, India’s figure is 3 per cent, and even USA’s only 20 per cent. But however small the total amount of nuclear energy may be, the consequences are colossal.

 

Nuclear fission and decay not only produces radiation but also heat. This heat is used in power plants to generate electricity. The core of the fuel rods in the reactors must heat  up to about 1,200 degree centigrade. When they are worn out, they are lifted with a remote-controlled crane into a cooling pond, where they are stored for many years.

 

If the heat dissipation fails and the rods heat to over 2,500 degree centigrade, there is a risk of nuclear meltdown, which is what happened in March 2011 in Fukushima in Japan.

 

New ideas for repositories have kept cropping up, some as absurd as the one patented in 1956 by a physicist from Munich, who proposed that waste containers be airdropped  over Antarctica, which would then melt into the depths of the ice on their own. This proposal was discussed in trade conferences for many years.

 

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 could be technically considered for all types of radioactive wastes, it has only been seriously investigated for high-level waste (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.

 

 

American scientists even considered shooting the waste into the Sun. the proposal was rejected as too unsafe and too expensive. To send a load of just half a kilo into the earth’s orbit would cost 10,000 dollars. And in USA, more than 70,000 tonnes of highly radioactive material is already in storage.

 

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.

The high cost means that such a method of waste disposal could only be appropriate for separated high-level waste (HLW) or spent fuel (i.e. long-lived highly radioactive material that is relatively small in volume). The question was investigated in the United States by NASA in the late 1970s and early 1980s. Because of the high cost of this option and the safety aspects associated with the risk of launch failure, this option was abandoned.

 

 

No doubt that’s why a final burial inside the earth is considered the safest option. Natural and technical barriers should ensure that no radiation leaks out. The waste can be sequestered in steel containers, embedded in a concrete sarcophagus, which is further surrounded by heat-resistant stone, and buried under hundreds of metres of rock.

 

Deep borehole concepts have been developed (but not implemented) in several countries, including Denmark, Sweden, Switzerland and USA for HLW and spent fuel. Compared with deep geological disposal in a mined underground repository, placement in deep boreholes is considered to be more expensive for large volumes of waste. This option was abandoned in countries such as Finland and USA. The feasibility of disposal of spent fuel in deep boreholes has been studied in Sweden, in order to check whether deep geological disposal remains the preferred option. The borehole concept remains an attractive proposition under investigation for the disposal of sealed radioactive sources from medical and industrial applications.

 

Although burial and long-term storage remain the best solutions for nuclear waste disposal, geologic processes pose a significant danger to these repositories. In reality, our limited ability to accurately predict moving fault lines, earthquakes, and volcanic eruptions is the true danger. The likelihood and possible location of future earthquakes is the initial concern when selecting a disposal site. On the other hand, flooding and groundwater pose their own geologic threat to underground disposal sites. Rising groundwater can erode away containment zones and spread radioactive waste into the water table.

 

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 both by 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.

Researchers have short listed four kinds of rock for the construction of such a repository.

 

  1. In Germany, rock salt is preferred at present. Salt is very dry. As long as there’s no water nearby, it can tolerate heat well, which is important for storing radioactive substances. And its protective coating ensures that cracks are quickly closed. Its mobility, however, is a disadvantage because whatever’s inside the salt moves within it.
  2. Finland and Sweden have settled on granite, which is hard and immovable.
  3. In the US, tuff rock found in the Nevada desert was being used till now.
  4. In Switzerland and France, clay is being tested. 

A New Solution

The newest solution, sending the waste to the center of the earth, is the one solution combining safety, economy and permanence to nuclear waste disposal. At first glance, this seems impossible. There has never been a hole drilled in the earth's crust, so how can one be drilled to the center of the earth? The answer? Let the earth itself do the work through known subduction faults.

What is a subduction fault? This is an earthquake fault at the edge of a continental crust that is in collision with the adjoining oceanic crust. Since the continental crust is lighter than the oceanic crust, the latter deflects below the former when the two plates are colliding.

Permanent RadWaste Solutions has developed a process that utilizes a subduction fault for sending the waste to the center of the earth. This has the benefits of being permanent, no maintenance, much less expensive than other proposals, terrorist-proof, and no threat to people, fish, crabs or the environment.

To do this requires burying a specially designed pressure-and-temperature-compensating submersible transport vehicle (STV). It is to be buried in the sediments at a subduction fault.

 

Other countries are also looking at waste in new ways in the post-Fukushima world. Right now, worldwide, most spent fuel waste is stored on the site of the facility that produced it, in spent-fuel pools and, after it eventually cools, dry casks. Experts say dispersed storage is expensive and that central storage would be more secure.

Few countries , apart from Sweden and Finland, have moved forward on centralized disposal sites, deep in the earth, designed to hold the waste permanently.

France is evaluating a permanent disposal site for spent fuel , near the remote northeastern village of Bure. Japan also hopes to choose a site and build a geological disposal facility in the coming decades.

 

The disposal of nuclear waste is a pressing problem for society worldwide. Potential health and safety concerns require that nuclear waste be stored in a controlled and secure manner. The issue is further complicated by the extremely long half life of radioactive materials, some of which retain half of their dangerous properties 100,000 years after production. The disposal and storage of nuclear waste is one of the major factors limiting society's use of nuclear power as a widespread energy source.

Till today there is no safe way of disposing of nuclear waste and one of the most important lessons is not to create any more, which means until and unless safe disposal method is identified we should not go for new nuclear power plants.

 

Views: 30

Tags: Fukushima, Kalpakkam, Radioactive, Rock, Tarapur, nuclear, salt, subductionfault., waste

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