Introduction:-

A multi barrier approach is followed in the disposal of radioactive solid wastes. The overall safety against migration of radionuclide is achieved by proper selection of waste form, suitable engineered barriers, backfill materials and the characteristics of the geoenvironment of the repository site. Based on the nature and type of the radionuclide present in the solid waste and its concentration the repository could be  near-surface or in deep geological formations. Operation of various Near Surface Disposal Facilities (NSDF) has led to considerable expertise in this field. Our programme on site selection & host rock characterization is under evaluation for deep geological disposal.

DISPOSAL OF RADIOACTIVE WASTES

Disposal as a final step in the management of radioactive waste involves confinement or isolation of these wastes from biosphere in the repositories. Based on the longevity and concentration of the radionuclide present in the waste, the repository could be either near-surface or in deep geological formation. India has extensive & varied experience in the operation of near surface disposal facilities (NSDFs) in widely different geohydrological and climatological conditions. Over the years,  considerable expertise has gone in refining and improving the design and construction of these NSDFs. A system of multiple barriers employed in these NSDFs ensures isolation and release of radionuclides below permissible limits to the environment. This is ensured by regular monitoring and periodic performance assessment of these NSDFs. Disposal of long-lived and high level waste in deep underground geological formation is one option which has received world-wide attention.  In India, the most promising formation is granitic rocks. In this context, our programme of site selection and host rock characterization for an Underground Research Laboratory is under evaluation.

NEAR SURFACE DISPOSAL

As a national policy, each nuclear facility in India has its own Near Surface Disposal Facility (NSDF). There are seven NSDFs currently operational within the country. These NSDFs in India have to address widely varied geological and climatological conditions. The performance of these NSDFs is continuously evaluated to enhance the understanding of migration, if any and to adopt measures for upgrading the predictability over a long period of time.

Performance assessment and service life prediction of Reinforced Concrete Trenches:

Performance assessment of Reinforced Concrete Trench (RCT) is systematically undertaken through field investigations and predictive modeling. NDT investigations on operating RCTs and laboratory studies on NSDF materials have demonstrated that RCTs are in sound condition even after an operational period of three to four decades. Mathematical models have been developed to predict the probability of failure as a function of target lives for various safety indices such as concrete cover thicknesses, climatic factors, maintenance period for the structure, water to cement ratio, water proofing etc. Modeling studies for a typical RC trench under limiting conditions have predicted a minimum service life of nearly 240 years. This study was completed in collaboration with CBRI, Roorkee.