Transfer function measurements in JOYO by pile oscillator method

Using the pile oscillator technique, the reactor transfer functions of the experimental fast reactor ''JOYO'' were examined to ascertain reactor stability and to elucidate the reactor feedback mechanism. Measurements were made in the frequency range of 0.001 to 3Hz at various reactor power levels. Major results were as follows: (1) Satisfactory agreement obtained between the zero-power transfer function measurements and calculations made by one point reactor model with six delayed neutron groups. (2) Reactor stability confirmed from measurements of at-power frequency responses; large negative feedback effect (-0.85 $/Δphi/phi at 50 MWt) observed. (3) Feedback transfer function and transfer function between neutron flux and outlet temperature at the central fuel subassembly found expressible in approximation by first-order lag model with a time constant of about 3.5s. (author)