Post-irradiation investigations of boron steel

Boron steel from an irradiated control rod was investigated in order to determine the residual lifetime of the control rods of the reactor WWER-2 of the Rheinsberg nuclear power plant. No critical property changes could be observed by metallographic and density tests after an average 10B burnup of about 20%. The bend-fracture tests showed the expected reduction of the already generally low plasticity of this material. Special care was taken of effects visible after annealing at 800 0C of the irradiated material followed by hardness tests. The results confirm that, due to the residual 10B reserve in the control rods, the materials state of the boron steel allows further operation of the existing control rod inventory of the WWER-2 reactor. (author)