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Characteristics of acceleration frequency spectra for an impact signal were studied and loose part mass was estimated, using variation in the frequency spectral patterns. T h e frequency spectral pattern for the acceleration induced by impact depends on the loose part mass and not on the impact energy and the loose part shape. It was found that the frequency spectral pattern for an impact which occurred at the lower plenum vessel wall is not influenced by the impact point. On the other hand, the maximum acceleration amplitude depends not only on the loose part mass but also on the impact energy, the loose part shape and the distance from the impact point. It was also found that the foremost portion of the accelerometer output signal is influenced by the impact force between a loose part and the vessel. However, a second portion is influeuced by the sensor resonance and structural resonances. Loose part mass estimation, using "FR" values (ratio between low frequency component and high frequency component), is useful. The uncertainty range for the estimated loose part mass is about 0.7 decade.

In order to measure reactivity from instant to instant during reactor operation, real time computation based on reactor kinetic equations must be made.The authors developed some reactivity meters capable of such computation based on the analog computer technique. After their characteristics were checked by an analog computer and a kinetic simulator, they were applied to reactor experiments and operation. It was found that the reactivity meter method for measurement of reactivity worth (especially for control rod calibration) is better than other current methods, and the reactivity meter can also serve as a tool in nuclear instrumentation of reactors for its ability to indicate reactivity even in reactor start up conditions.

In order to measure reactivity from instant to instant during reactor operation, real time computation based on reactor kinetic equations must be made.The authors developed some reactivity meters capable of such computation based on the analog computer technique. After their characteristics were checked by an analog computer and a kinetic simulator, they were applied to reactor experiments and operation. It was found that the reactivity meter method for measurement of reactivity worth (especially for control rod calibration) is better than other current methods, and the reactivity meter can also serve as a tool in nuclear instrumentation of reactors for its ability to indicate reactivity even in reactor start up conditions.

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