Measurement of Coupling Coefficient by Variance-to-Mean Ratio Method, and Investigation of Its Space-Dependence

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In the management of criticality safety, an important problem is to evaluate the effect of neutron interference between nuclear fuel units. As a measure of this effect, I have proposed to use the coupling coefficient representing the strength of coupling between cores in a coupled-core reactor.In this study, the variance-to-mean ratio method was employed, and its availability was investigated with the use of the Argonout-type coupled-core reactor at Kinki University Atomic Energy Research Institute.The following results were obtained through this study.1. The dead-time of a measuring system plays an important role in data processing. Then, the new formula taking account of the effect of dead-time was derived, and its validity was confirmed.2. The data acquisition technique with a data-recoder was employed. Then, it was found that the sampling points more than 40,000 were required in order to get good statistics. But, in spite of this technique, it was difficult to obtain the sufficient sampling points within practical acquisition time at large gate width.3. The coupling coefficient measured was 1.99+0.53 dollars, and it agreed with the calculational value of 2.33 dollars within the experimental error, which was evaluated by two-dimensional, two-energy group diffusion theory.