BASIC STUDY ON A PSEUDO TREND PHENOMENON OF THE FEYNMAN-α ANALYSIS WITH BUNCHING METHOD

Sin-Ya Hohara,Tomohiro Endo,Kazuki Takahashi,Kunihiro Nakajima,Tadafumi Sano,Atsushi Sakon,Kengo Hashimoto,M Margulis,P Blaise

doi:10.1051/epjconf/202124709008

Abstract

In these years, reactor noise analysis methods have been studied to apply for the Debris’ criticality management at the Fukushima Daiichi NPP, Japan. The Feynman-α analysis with bunching method is one of the candidate techniques, however the bunching method itself has never been validated in detail. This synthesis technique is useful to reduce a time required for the experiment, however it is known that a non-physical trend unrelated to the state of a nuclear reactor is generated by the multiple use of time series data, and this phenomenon (we call “pseudo trend phenomenon”) has never been systematically studied in detail. In this study, Poisson events, whose statistical characteristics were clarified, were employed to investigate the pseudo trend phenomenon of the bunching method. The time-sequence count data for various statistical parameters were generated by the Monte Carlo time series simulator. Comparing the two results obtained by applying the conventional bunching method and the moving-bunching method for the same Poisson event time series, and it was found that the same pseudo trend component appears in both results of the bunching method and the moving bunching method. In addition, it was also found that the fluctuation width of the pseudo trend component is smaller than the statistical fluctuation range.

Highlights

In recent years, in Japan, the development of criticality safety assessment methods for fuel debris at the TEPCO Fukushima Daiichi Nuclear Power Plant has become a topic
As those observed as the most typical influence by the bunching method, there is a trend component that occurs with respect to the time gate direction as described above, it has been confirmed that does not occur when not applying the bunching method.[4][5] This trend component is not present in Feynman's theory and has a dependency component of more than the fluctuation width for time gate, but shows a different tendency in each observation time series even under the same core conditions
We investigated the basic characteristics of pseudo trend phenomena occurring in Feynmanα/ bunching method, one of the reactor noise analysis method

Summary

Introduction

In Japan, the development of criticality safety assessment methods for fuel debris at the TEPCO Fukushima Daiichi Nuclear Power Plant (hereinafter referred to as "1F") has become a topic. When the bunching method is applied for the data analysis, the fluctuation of the Feynman-α plot becomes smaller than the theoretical statistics error range.[3][4] In addition, there are some unclear strange effects on the bunching method As those observed as the most typical influence by the bunching method, there is a trend component that occurs with respect to the time gate direction as described above, it has been confirmed that does not occur when not applying the bunching method.[4][5] This trend component (we call it a "pseudo trend") is not present in Feynman's theory and has a dependency component of more than the fluctuation width for time gate, but shows a different tendency in each observation time series even under the same core conditions.

Methods

Results

Conclusion