Outline of reactor physics tests conducted during the power-up tests in the nuclear ship MUTSU

The present report describes the outline of a series of reactor physics tests conducted during the power-up tests in the nuclear ship MUTSU, which started on March 29, 1990. The basic physics design parameters have been confirmed from these test results. In spite of a 16 year reactor stop and refabrications of fuel assemblies and control rods in 1989, no change in reactor physics performance through the long period has been also demonstrated by comparing the present measured results with the data received in 1974. The digital reactivity meter used in the physics tests enabled us to perform more efficient and accurate measurements of reactivity than the conventional period method. Most of the physics test results show the three-dimensional (3-D) core characteristics peculiar to ship reactors which are caused by partial insertion of control rods even under full power conditions. A 3-D reactor physics code developed for the MUTSU reactor has given excellent calculation results which agree quite well with these measured characteristics. (author)