Tank type FBR type reactor

The present invention prevents wavings at the surface of liquid metal coolants formed in a reactor container. That is, in a tank type FBR reactor comprising incore structures, a ring for moderating thermal stress and a ring for suppressing waves are disposed coaxially in a region near the outer circumferential surface of the incore structures where the liquid surface of coolants are vertically fluctuated. With such a constitution, coolants, heated in the reactor core and flown out, reach the liquid surface, and are brought into contact with each of structures, and are waved in a complicated manner to form a complicate flow. However, the waving is moderated by the waving suppression ring, and temperature distribution in the vicinity of the liquid surface of each of the structures is made uniform by the thermal stress moderating ring. Accordingly, thermal stress or repeating thermal fatigue applied to the structures in the reactor container can be prevented. As a result, integrity is improved. (I.S.)