Guidelines established for the structural design of the experimental fast reactor JOYO

Compared with light-water reactors, sodium-cooled fast reactors operate at higher temperature and lower pressure. Thus, high thermal stresses are induced in the structural components at steady as well as transient operation, while mechanical stresses due to internal pressure are comparatively low. The materials used for the structural components exposed to sodium are liable to creep under the stress, while the mechanical properties are further impaired by mass transfer in hot sodium circuits. Sodium-cooled fast reactors also differ radically in the principles that govern safety considerations and the composition of the coolant system the design critaria of the components of such reactors are largely governed by these safety considerations and by the particularities of the coolant system. The guidelines established for the structural design of JOYO have involved these new problems which applied to all the sodium coolant system pressure boundaries including the core support structure. An outline is give of the guidelines established for the design. (author)