Experimental condition for the ROSA-II cold-leg break test was selected to test the break configuration predicted by RELAP-3 code in that extremely severe core cooling during blowdown is resulted. Adequacy of the prediction was confirmed by parametric tests on the conditions.
The major conclusions are as follows:
(1) Effective core cooling during blowdown process can be guaranteed by only small amount of core flow regardless of the flow direction. However core coo1ing becomes very poor when core flow becomes stagnant. Detailed analysis on fluid behavior in primary system is, therefore, needed to well predict fuel surface temperature in such flow condition.
(2) Driving force of circulation pump strongly affects blowdown core cooling either by promoting or by degrading the core cooling.

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In the conceptional design study of the large JAERI tokamak device JT-60 and the preliminary design study major problem areas in the toroidal field coils (TF-coil) design were identified. They included; (1) Fabrication procedures of large bore coils which are wedge-shaped at the center support side, (2) High stresses in the conductors produced by large electromagnetic forces, (3) Comparatively high temperatures in the conductors reached during the long current pulse.
The research and development (R & D) of TF-coils was planned to establish design and fabrication procedure of these coils. The R & D program was initiated in October 1975 and was satisfactorily completed in February 1977.
This report describes the R & D of the TF-coils. The R & D program was first made on the selection of the conductor and insulation materials. Further the key techniques for manufacture were made. Finally a full scale mock-up coil was manufactured to establish fabrication technique and to demonstrate the performance of the TF-coils through mechanical and electrical tests.
In order to verify the results of the design, three types of tests were performed using scaled model coils and conductors fabricated as a trial; the cooling test, destruction test and fatigue test.

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The present peport describes the research and development (R & D) of poloidal field coils in the JAERI large tokamak JT-60. The R & D is classified into two development stages of basic techniques and of fabrication procedures. The first stage includes the development of the demountable mechanical joint, the turn-to-turn connection, the welding process of copper conductors, the insulation system and the cooling system. The most suitable mechanical joint is selected from about 30 types of joint structures. The turn-to-turn connection chosen is a pin-jointed one using FRP insulation. A welding process without preheating is chosen for the connection of conductors. A resinrich mica-epoxy insulation system is adopted for the most part of the conductor, while the mechanical joint is insulated with a unique insulation system using FRP covers and resin-rich mica tapes. The contact resistance of the mechanical loint and its temperature distribution when a current is driven through it are measured before and after the application of cyclically loaded mechanical forces simulating the electromagnetic forces. In the second development stage, a full scale two-turn ohmic heating coil and a full scale 90° magnetic limiter coil sector are fabricated using the basic fabrication techniques mentioned above and tested to examine their mechanical, electrical and thermal properties. It is found that the developed techniques and procedures are applicable to the construction of JT-60 poloidal field coils.

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