Activation of Steel Components

Summary

Trace elements leading to long-lived induced gamma activity have been assessed in selected reactor steels. Concentrations of Mo, Ni, Nb, Co, Ag, Eu, Sm and Ho have been measured. Particular attention has been paid to the detection limits of various techniques. Three techniques have been applied to Nb determination and concentrations close to the detection limit of 5 ppm measured in a number of steels. Concentrations of Ag in the vicinity of 1 ppm were observed in all steels analysed. The second aspect of the work described concerns evaluation of gamma emitting nuclides in structural materials of the Garigliano BWR power plant. The trace element composition of samples of vessel steel have been measured. A series of detailed two-dimensional neutron transport calculations have been carried out and, with the aid of the operating history, the time dependent flux leading to activation of vessel, liner and thermal shield estimated. The dose rate at the centre of the reactor vessel has been calculated as a function of time following shutdown. The form of the contribution to dose rate from the vessel differs from that from the liner and thermal shield, due mainly to the need to make pessimistic assumptions of steel composition in the absence of trace element analysis for these latter two components.