Development of Engenvalue Separation Monitor for Nuclear Reactor by Using Position Sensitive Proportional Counter

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The eigenvalue separation is important as an index for evaluating the degree of stability of nuclear reactors. We intend to develop an eigenvalue separation monitor by using spatial integral of neutron flux measured by the position sensitive proportional counter (PSPC). Through this study, the following results were obtained.(1) It was confirmed from experiments at Kyoto University Critical Assembly that the engenvalue separation can be estimated from the neutron flux measured with a PSPC.The effect of higher modes along the directions not measured must be corrected by numerical calculations.(2) It was confirmed also from experiments that the eigenvalue separation can be estimated without numerical corrections by solving the coupled equations of neutron flux distributions measured by multiple PSPCs. But, to estimate the engenvalue separations excluding an effect of initial flux distortion, multiple experiments depending on subcriticalities are necessary.(3) We prepared the system registering simultaneously both a position signal of the PSPC and its arrival time, and investigated ability of time-space correlation measurement.(4) By adding the nodal method to the previous numerical code on higher modes, we can estimate degenerate eigenvalues with high accuracy.(5) We confirmed that the spatial dependence of detector efficiency is caused by the variety about manufacturing of anode wire supports.It was concluded that the eigenvalue separation monitor based on the flux measured with the PSPC can be developed. But more investigations on the applicability to actual nuclear reactors are needed in future. The time-space correlation measurement is expected to be a new method for measuring parameters of reactor dynamics.