A very high-temperature gas-cooled reactor (VHTR) has been developed by Japan Atomic Energy Research Institute and its core consists of so-called fuel blocks, removable reflector blocks and so on. These graphite blocks are supported by thin cylindrical graphite bars called support posts. These posts are in contact with the blocks through hemispherical seats to absorb the relative displacement of blocks by small inclination or rotation of the posts. Stress distributions and stress concentration coefficients of the support post under the reactor core weight are analysed by means of photoelastic experiment and compared with two-dimensional calculation by using the finite element method. The following are the conclusions we have derived: 1. (1) Stress concentration coefficients of the post are expressed uniquely as a function of Ed( 1 rp- 1 rp) σg regardless of the shapes of model and material properties. 2. (2) Inclination of the post caused by small rotation has little effect on the stress concentration coefficients.
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