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Nuclear Waste Storage

In our periodic table, heavier elements which are placed at the bottom of the table with high atomic number are very unstable due to high n/p ratio. They have tendency to decompose to stable nuclei with lose of excess mass in the form of radiations. Such elements are called as radioactive elements. These radioactive materials show nuclear reactions and convert into stable nuclei.

The radioactive elements are unstable and tend to decay with the emission of some radiations like alpha, beta, gamma etc. These radiations are called as radioactive radiations. The radioactive decay or nuclear reactions results the formation of some stable and small nuclei as final products with emission of radiations. These reactions involve a large amount of heat therefore cannot furnish under normal conditions of temperature and pressure but require certain arrangements that can control the energy released during the process.

The nuclear energy can be used in the production of electricity and one of the best energy providers. Nuclear reactors are devices in which nuclear reactions occur under control conditions of temperature and pressure. The nuclear reactors are specially designed reactors in which nuclear reactive materials are introduced in the reactor with some particles for bombardment in the radioactive materials. The resultant products may or may not be radioactive in nature. The main disadvantage of nuclear reactors is the nuclear waste which is very hazardous in nature and difficult to dispose.

 

How is Nuclear Waste Stored?

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The remaining nuclear materials that already used in nuclear reactors is called as nuclear waste. It includes the nuclear fuel that was loaded into the reactor with metal rods, ceramic pellets etc. The nuclear fuel like Uranium or Thorium, oxygen and steel are mainly introduced in the nuclear reactor which after nuclear reactions converts into various isotopes of different transition metals. The nuclear waste is also called as spent fuel.

It is dangerously radioactive in nature and takes long time to decompose. Due to its toxic behaviour, spent fuel is lethal and cannot be unshielded. There are many ways to store the nuclear fuel and waste like keeping it in underwater as water is an excellent shield. Other options are deep geologic storage and recycling. On the basis of exposure of radiations, nuclear waste can be classified as low level, intermediate and high level waste. The low level wastes are mainly used to handle the nuclear materials and equipments of nuclear reactors. These kinds of wastes can be stored for 15 years in secure storage and later can pack and dispose like other normal waste materials. The intermediate levels of nuclear waste materials are bulky and have low heat emission.

They are metal fuel, chemical sludges and other radioactive wastes. These kinds of waste materials are encased in concrete and sealed in steel drums. These drums then dispose in concrete trenches (around 18 m deep). The completely filled tranches are then covered with concrete slabs and clay. The high level nuclear wastes like extremely radioactive materials are mainly stored by the use of glass vitrification.

Radioactive Waste Storage

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The main nuclear fuel is Uranium Oxide fuel, $UO_{2}$ which is loaded in nuclear reactor with neutrons. Many of neutrons are absorbed by uranium atoms and causes fission to form fission products. Some of the uranium atoms absorb neutron but does not fission and transforms to a heavier isotope like U-239 which further shows beta-decay to form Np-239 and Pu-239.

The absorption of neurons by heavier nuclide forms even heavier element, known as transuranics. Nuclear waste is this nuclides only which left over after a reactor. The nuclear waste which is less hazardous can be stored for long time that make them least harmful and can dispose easily. Most uranium disposes off in place or near the mill after constructing a barrier of clay that prevents radon from escaping into the atmosphere.

Interim waste storage involves storage of nuclear waste in specially designed interim surface or sub-surface storage waste facilities that ensure the safe storage of nuclear waste. The interim storage facilities are mainly used for intermediate-level and high-level waste (HLW).

Storage of Nuclear Waste

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Above ground storage can be considered as effectively a disposal option. The controlled surface storage over longer time periods is a long-term waste management option. It involves specially designed facilities at the earth's surface. It allows us to monitor and retrieval at any time without excessive expenditure.

The long-term above ground storage can be in the form of conventional stores requires the replacement and repackaging of waste. The nuclear waste is also stored in storage ponds at reactors which have racked fuel assemblies are made of metal with neutron absorbers. Water is used to shield and cool the nuclear fuel.  Other storage assemblies have been cooling in ponds for long time is in dry casks with air circulation.

Underground Nuclear Waste Storage

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Initially UK plans to dispose of spent nuclear fuel and other radioactive hazardous materials in relatively shallow repositories which are 300 to 800 metres underground. But scientists were not convinced as this method was not safe and there can be many alternate methods of disposal and storage of nuclear wastes.

Major disadvantages of underground storage is leakage of radiations in the groundwater from the repository it could be disastrous. So we can say that radioactive materials are harmful for living organisms and also for our environment. We cannot stop their uses but can avoid their harmful effects by using safety tips and can make it one of the most powerful sources of energy for future. 
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