After decommissioning of the nuclear power plant Gundremmingen-A (KRB-A) several trepans have been taken from the pressure vessel for a validation program of sur-veillance test practice. To define neutron exposure after more than ten years' operation a complete analysis of the reactor power time history and of the three-dimensional burnup distributions at the beginning and end of each reactor cycle had to be performed. Neutron exposure parameters such as fast fluence (E > 1.0 and E > 0.1 MeV) and dpa have been calculated using the DOT 4.2 code. The attenuation of neutron exposure within the KRB-A vessel wall is discussed in context with the formulae proposed in Regulaton Guide 1.99, Revisions 1 and 2. To confirm the results of the transport calculations, calculated and measured Mn-54 activities of the trepans have been compared. Additionally dosimetry results from surveillance capsules have been analyzed.