Significance of residual activity due to long-lived beta emitting radionuclides in reflectors and biological shield of research reactor, CIRUS - for decommissioning

Reactor system and structural components (SSCs) develop residual activity due to neutron irradiation during the operation of the reactor. The neutron activated components, are of significance in any planning of decommissioning of the reactors. Within the wide spectrum of radionuclides representing the radioactive inventory of a shut down nuclear facility, there are several radionuclides, mainly long lived, low energy beta emitters which pose a concern in long term waste management program. Even though in terms of radiation level, 60Co will be most predominant after few years of shutdown, long lived activation products like 59Ni, 63Ni, 55Fe, 14C and 3H etc. contribute to major activity on the irradiated structural components and would be of concern in the long term waste management. Quantification of such nuclides are essential for release of materials for reuse and recycling as per the clearance levels prescribed by the regulatory body. An attempt is made in this work to evaluate the significance of such radionuclides in the Graphite reflector and concrete bio-shield of CIRUS. (author)