Measurement of eigenvalue separation by using position sensitive proportional counter

Eigenvalue separation is an important index of power reactor stability in the view of neutronics. In recent years, a long, slender Position Sensitive Proportional Counter has been developed. By using this proportional counter, the spatial neutron flux distribution of a nuclear reactor can be measured rapidly. Using these characteristics, we intend to develop the experimental method evaluating eigenvalue separation as an index for reactor stability. A method based on spatial integrals of neutron flux measured at a subcritical system with an external source is proposed. To verify this method, experiments were carried out at Kyoto University Critical Assembly. It was confirmed that eigenvalue separation can be evaluated within a relative error of 10%.