Simulation by Monte Carlo Method of Power Varying with Time Detected by Fission Chamber in TRACY Water-Reflected System

概要

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Numerical simulation of power varying with time detected by fission chamber was performed using the continuous-energy Monte Carlo code MCNP4B to comprehend time delay of neutron detection in power burst experiments arranged for systems incorporating water reflector as well as devoid of reflector in the Transient Experiment Critical Facility (TRACY). The simulation indicated that power generation in core during an initial power burst was detected by fission chamber earlier in a water-reflected than in a non-reflected system. The difference is ascribed to the water reflector surrounding the core tank functioning as shield against neutrons traveling toward the concrete walls and floor of the building structure, to lower the probability of detection by fission chamber of the neutrons proceeding from walls and floor, to result in earlier termination of neutron detection, and hence shorter lapse of time between neutron emission from core and detection. The difference between water-reflected and non-reflected systems in the delay time, however, is quite small—within about 1 ms. The difference is even smaller when expressed in terms of inverse period, and can be considered to affect little the evaluation of feedback reactivity based on the inverse period.
社団法人日本原子力学会の論文
2002-01-25