VARIANCE-TO-MEAN METHOD GENERALIZED BY LINEAR DIFFERENCE FILTER TECHNIQUE

The conventional variance-to-mean method (Feynman-alpha method) seriou sly suffers the divergency of the variance under such a transient cond ition as a reactor power drift. Strictly speaking, then, the use of th e Feynman-alpha is restricted to a steady state. To apply the method t o more practical uses, it is desirable to overcome this kind of diffic ulty. For this purpose, we propose an usage of higher-order difference filter technique to reduce the effect of the reactor power drift, and derive several new formulae taking account of the filtering. The capa bility of the formulae proposed was demonstrated through experiments i n the Kyoto University Critical Assembly. The experimental results ind icate that the divergency of the variance can be effectively suppresse d by the filtering technique, and that the higher-order filter becomes necessary with increasing variation rate in power. (C) 1998 Elsevier Science Ltd. All rights reserved.