Some radioactive waste will be generated from NPP operation in the form of liquid effluents, solid waste and gaseous effluents. The liquid effluents with low levels of radioactivity are treated using appropriate processes and recycled as far as possible, but some liquid effluents will have to be dis­charged to the environment. Such discharges are generally done using the dilute and disperse principle. The effluents are diluted, for example by the large quantities of condenser cooling water outlet from the NPP, and then dispersed in large water bodies like a lake, river or sea near the NPP site. Solid radioactive waste is generated from plant operation in the form of replaced components or their parts, piping sections, used filters, exhausted ion exchange resins, radioactively contaminated personnel protective wear like coveralls, gloves and caps and materials like mops used for decontami­nation of floors and other surfaces. The solid radioactive waste is stored in near-surface disposal facilities after volume reduction and packaging where feasible. Such facilities may be co-located with the NPP or they could be centralized facilities located elsewhere and may store radioactive waste from several installations. Some solid wastes such as ion exchange resins may require special treatment before disposal, such as fixation of radioac­tivity in the resin in cement or polymer matrix to prevent its leach-out during extended storage. Facilities for such special treatment have to be built as part of the NPP complex. Radioactive gaseous effluents are generated by neutron activation of air and suspended particulates and by pick-up of radioactivity by reactor ventilation air during its passage through radioactively contaminated areas. The ventilation exhaust air from the reactor building and other plant buildings having a potential for giving rise to airborne radioactivity is filtered through high-efficiency particulate filters for removal of particulate activity and, if necessary, through special filters like those made of activated charcoal for trapping radioactive iodine. It is then released through a tall stack into the atmosphere for dilution and dispersal.

It can be seen that radioactive waste management at NPP sites is an ongoing activity that requires special expertise. This function is important as it is to be ensured that radioactive waste disposal to the environment must be within the prescribed limits. Further, even within the specification limits, it should be kept as low as reasonably achievable to minimize adverse impact on the environment in the long term. This objective can be achieved only through having a dedicated radioactive waste management team with high technical competence. Ongoing research and development at the tech­nical support organizations is also necessary towards developing improved processes for recycling of liquid waste and reducing waste volumes to the maximum extent possible.

7.7.6 Spent fuel management

Spent fuel removed from the reactor core has to be properly and safely stored for several years before it can be shipped out for reprocessing, final disposal or further storage at a different site. Spent fuel is stored under water in the spent fuel storage pool in fuel storage racks that have inbuilt high neutron-absorbing materials to ensure sufficient subcriticality. The pool water has to be circulated, cooled and purified to remove the decay heat transferred from the stored fuel to pool water and to maintain its chemistry parameters to minimize corrosion of the fuel cladding. For trans­portation of spent fuel from the NPP site, specially designed shielded casks are used and transportation is done after the decay heat in the fuel has come down to a level when natural convection cooling by surrounding air is sufficient to keep the fuel and fuel cladding temperature within specified limits.

If the storage capacity in the pool becomes insufficient due to inability to ship out the fuel for any reason, timely action is necessary for construc­tion of away-from-reactor storage pools to augment the storage capacity. The away-from-reactor pools have to be built and operated in the same way as the storage pool at the reactor site. It is also possible to store spent fuel in dry storage casks or dry storage facilities after it has been cooled for a sufficiently long period. Such casks and facilities may have to store spent fuel for a fairly long time till the final disposition of the fuel is decided. Accordingly they have to be kept under proper surveillance by periodic checks on fuel clad integrity and structural integrity of the casks and the facilities. Expertise in spent fuel management over extended periods of time that can run into several decades has to be acquired by the operating organization. The technical support organizations and the regulatory body also need to develop adequate technical competence in this field.