Development of Multi-Section Multi-Division Reactor-In-Core Controlled Irradiation Capsule and Fundamental Processes of Neutron Radiation Damage

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Development of reactor in-core irradiation capsules to enable perfectly control of systematic irradiations is the major technical task of this research project, and the establishment of unified understanding of fundamental neutron radiation damages processes is the final aim. The first step was to develop multi-division controlled irradiation capsules and to perform irradiations and post-irradiation experiments. The second was the development of multi-division multi-section removable controlled irradiation capsule.Comparison of the defect structures introduced by the two modes of temperature control, conventional and improved, was strictly made for in-core irradiation with Japan Materials Testing Reactor, and the difference up to 100 % was confirmed to exist depending on the kind of materials and the type of defect structures, indicating the essential needs for the improved control. It became possible for the first time in the world to compare the irradiations with fission and fusion neutron irradiation, and the correlation factors were found to vary widely depending on materials and irradiation temperature.The final step of the development of irradiation capsule in the present project was to design and construct the multi-division multi-section controrable irradiation capsule. With this advanced capsule, parts of samples can be removed from the irradiation field at an arbitorary time during irradiation without disturbing the irradiation condition such as temperatures. Most important and difficult performance of this capsule was mechanical uncontact compatible with thermal contact between thermal-media and specimen container, and the design was established after several steps of model experiments. Final mock-up test with exactly the same dimension as that installed in the reactor was finished, and the first trial irradiation is scheduled to be performed in the year of 1993 with a suitable arrangement of operation cycle of JMTR.