Operating characteristics and some phenomena of thermal hydraulics in JOYO

The JOYO is a sodium cooled, loop type, experimental fast reactor with a thermal output of 100 MW. The reactor has been operated without any serious troubles since its initial criticality, attained in April 1977; the cumulative thermal output reached about 1,500 GWH in March 1985. In this paper, the following operating experiences and studies in JOYO are introduced from the standpoint of reactor thermal hydraulics: (1) Design evaluation of steady state heat transfer of the reactor cooling system; (2) Thermal transient behavior of the cooling system during the reactor trips, related to the peculiar sequence controlling method; (3) Measurement results of in-vessel flow distribution and time dependent change of the core pressure drop due to irradiation; (4) Disturbance of the temperature field above the core subassemblies due to unequal flow distribution; and (5) Flow-induced vibration of the control rods, causing reactor power fluctuation. (author)