Development of reactivity feedback effect measurement techniques under sub-critical condition in fast reactor, 1-6; A Feasibility study on sub-critical reactivity measurement system application to power reactors

Kitano, Akihiro ; Nishi, Hiroshi; Suzuki, Takayuki ; Okajima, Shigeaki  ; Kanemoto, Shigeru*

A study on the basic algorithm and application to actual reactors of the synthesis method, which combines the reactor noise analysis and modified source multiplication (MSM) method, has been conducted based on numerical simulation calculations, in order to establish a concept of the sub-critical reactivity measurement system. Required performances of the sub-criticality measurement algorithm for the reactor noise analysis was studied, assuming the reference sub-criticality measurement by noise analysis for MSM. As a result it was found out that the accuracy of the measurement will be dominated by the neutron detector efficiency and the improvement of the accuracy will be expected by using lower frequency amplitude data for the break (corner) frequency method. A numerical simulation was performed for actual reactors based on these results, and the dual-detector method was identified to be effective, which can avoid the influence of higher-order effect.