Comparison between measured and design dose rate equivalents on board of Nuclear Ship Mutsu

The power-up test of the Nuclear Ship Mutsu was restarted in March 1990 and completed successfully in February 1991. The experimental voyages were carried out for about one year and all experiments were completed in February 1992. A comparison between the measured and design dose rate equivalents on board is described with showing a modified method in the shielding design. The measured values were obtained extensively in the cavity between the primary and secondary shields, in the double bottom, outside the secondary shield, and on the surface of the main coolant loop. The shielding design calculations were made with the most conservative geometries and material compositions within the allowed tolerance. In addition, a conservative model was adopted in case of performing the approximation due to the geometrical restriction of calculation code. The computational accuracies were evaluated based on various experimental analyses. The evaluated value was used as the design value. The shield structures were determined with a judgement that the real value does not exceed the design value. The adequacy of the judgement was confirmed by measurements on board. The measured dose rate equivalents in all positions on board satisfied the design criteria. (author)