Induced radioactivity and waste classification of reactor zone components of the Chernobyl Nuclear Power Plant unit 1 after final shutdown

The dismantlement of the reactor core materials and surrounding structural components is a major technical concern for those planning closure and deco ntamination and decommissioning of the Chernobyl Nuclear Power Plant (NPP). Specific issues include when and how dismantlement should be accomplished and what the radwaste classification of the dismantled system would be at t he time it is disassembled. Whereas radiation levels and residual radiologi cal characteristics of the majority of the plant systems are directly measu red using standard radiation survey and radiochemical analysis techniques. actual measurements of reactor zone materials are not practical due to high radiation levels and inaccessibility. For these reasons, neutron transport analysis was used to estimate induced radioactivity, and radiation levels in the Chernobyl NPP Unit I reactor core materials and structures. Analysis results suggest that the optimum period of safe storage is 90 to 1 00 yr for the Unit I reactor. For all of the reactor components except the fuel channel pipes (or pressure tubes), this will provide sufficient decay time to allow unlimited worker access during dismantlement, minimize the ne ed for expensive remote dismantlement, and allow, for the dismantled reacto r components to be classified as low- or medium-level radioactive waste. Th e fuel channel pipes will remain classified as high-activity, waste requiri ng remote dismantlement for hundreds of years due to the high concentration of induced Ni-63 in the Zircaloy pipes.