Friday, January 23, 2015
Disposal of Nuclear Wastes in India
Management of radioactive waste in Indian context includes all types of radioactive wastes generated from the entire nuclear fuel cycle and also from installations using radionuclides in medicine, industry and research. In the choice of processes and technologies adopted utmost emphasis is given to waste minimisation and volume reduction. The comprehensive radioactive waste management operations are carried out fulfilling all prescribed regulatory requirements.
Nuclear waste is classified into high, intermediate and low levels depending on the level of radioactivity in it. The spent fuel which contains long lived radioisotopes are stored for a long period to reduce the level of radioactivity and subsequently reprocessed at reprocessing plants for collecting fissile elements. The generation of high level waste is at reprocessing plants. The quantity of this waste in our country is much smaller due to our adoption of the closed fuel cycle.
High level waste generated from the reprocessing plant is vitrified into a glassy form, contained in multiple barrier containers and stored for an interim period of three to four decades in engineered vaults with necessary surveillance facilities. After cooling down in these storage facilities, waste containers will be stored for long term in deep geological repositories.
Reprocessing and Waste Management plants are currently being operated by Bhabha Atomic Research Centre (BARC).
The low and intermediate level nuclear waste containing radioactive substances with short half life are generated at nuclear power plants and are processed at the site in the following manner:
§ The generated waste is solidified by fixing this in materials like cement, polymers, glass etc., to ensure that it does not move
§ The solidified waste is then stored in specially fabricated double walled high integrity stainless steel container
§ The containers containing the solidified waste are stored inside a high integrity concrete pit at each of the nuclear power plant site
As the waste is fixed in cement, glass, polymer; it is immobilized and its placement in high integrity containers inside a pit ensures that the radioactive wastes is completely insulated from the environment.
The radioactivity level of the stored wastes reduces with time and by the end of the plant life, including decommissioning falls to normal levels. Such facilities for handling low and intermediate level waste are located at all the nuclear power stations viz. Tarapur (Maharashtra), Rawatbhata (Rajasthan), Kalpakkam (Tamilnadu), Narora (Uttar Pradesh), Kakrapar (Gujarat) and Kaiga (Karnataka). The quantity of low and intermediate level waste to be stored at site during the life time including decommissioning is within 0.15 cubic meters/year/MW.
The Government is using latest technology for disposing the nuclear waste generated during operation of nuclear power plants. The details are as follows:
§ The low and intermediate level radioactive waste generated during operation and maintenance of nuclear power plants is segregated, its volume reduced using various technologies and solidified. This solid/solidified waste is packaged in suitable containers to facilitate handling, transport and disposal
§ Disposal of low and intermediate level waste is carried out in specially constructed structures such as stone lined trenches, reinforced concrete trenches and tile holes. These disposal structures are located both above and underground in access-controlled areas. Disposal system is designed based on multi barrier principle for ensuring effective containment of the radioactivity. The areas where the disposal structures are located are kept under constant surveillance with the help of bore-wells laid out in a planned manner. The underground soil and water samples from these bore wells are routinely monitored to confirm effective confinement of radioactivity present in the disposed waste.
§ Gaseous waste is treated at the source of generation. The techniques used are adsorption on activated charcoal and filtration by high efficiency particulate air filters. The treated gases are then diluted with exhaust air and discharged through a tall stack with monitoring.
§ Liquid waste streams are treated by various techniques, such as filtration, adsorption, chemical treatment, thermal and solar evaporation, ion exchange, reverse osmosis etc. The concentrate from treatment of liquid waste is immobilized in inert materials like cement, polymer etc.
The nuclear waste handling, treatment, storage and disposal is carried out as per the well laid down procedures and guidelines stipulated by the Atomic Energy Regulatory Board (AERB).