[en] The nuclear powered ship 'Otto Hahn' was commissioned in 1968, and ended its mission in 1979. The decommissioning was approved in December, 1980, and after the dismantling and removal of the reactor plant were completed, the decommissioning was recognized in September, 1982. The features of the method of decommissioning Otto Hahn were the carrying-out of the reactor pressure vessel together with the primary shielding tank as one body, and after the machinery, equipment and structures in the controlled area were removed or decontaminated, the ship was reconstructed to a diesel freighter. It is considered that the method of decommissioning of Otto Hahn and the data obtained by this work furnish much information for the decommissioning of nuclear power stations and nuclear powered ships hereafter. In this report, the course of decommissioning of Otto Hahn and its experience are synthetically summarized. The propulsion plant of Otto Hahn, the radiological condition, the conceptual design of decommissioning, the dismantling works, the procedures of permission and approval, the procedure for removing the control, the execution of decommissioning, and the removal of the controlled area are reported. (K.I.)

[en] Procedures of shielding analysis are described which were used for the shielding modification design of the Nuclear Ship 'MUTSU'. The calculations of the radiation distribution on board were made using Sn codes ANISN and TWOTRAN, a point kernel code QAD and a Monte Carlo code MORSE. The accuracies of these calculations were investigated through the analysis of various shielding experiments: the shield tank experiment of the Nuclear Ship ''Otto Hahn'', the shielding mock-up experiment for 'MUTSU' performed in JRR-4, the shielding benchmark experiment using the ¹⁶N radiation facility of AERE Harwell and the shielding effect experiment of the ship structure performed in the training ship 'Shintoku-Maru'. The values calculated by the ANISN agree with the data measured at 'Otto Hahn' within a factor of 2 for fast neutrons and within a factor of 3 for epithermal and thermal neutrons. The γ-ray dose rates calculated by the QAD agree with the measured values within 30% for the analysis of the experiment in JRR-4. The design values for 'MUTSU' were determined in consequence of these experimental analyses. (author)