Effective delayed neutron fraction measurements in FCA-XIX cores by using modified Bennett method

As the part of the international benchmark experiment of the effective delayed neutron fraction held in the Fast Critical Assembly of the Japan Atomic Energy Research Institute, we measured the effective beta for the FCA XIX-1 (Uranium) core, XIX-2 (Plutonium/Natural Uranium) core, and XIX-3(Plutonium) core by using a modified Bennett method. This method was proposed by these authors to suppress scatter of covariance data. Final results of effective beta were 782 ± 16 pcm for the U-core, 368 ± 6 pcm for the Pu/NU-core, and 256 ± 4 pcm for the Pu-core. The ratio of calculated to measured effective beta values were 0.990, 1.022, and 0.980 for U, Pu/NU, and Pu cores, respectively.