Development of reactivity feedback effect measurement techniques under sub-critical condition in fast reactor, 1-3; A Study on neutron detector response evaluation model

Nishi, Hiroshi; Kitano, Akihiro ; Suzuki, Takayuki ; Okajima, Shigeaki  

A simulation calculation study has been carried out on the relationship between the control rod insertion patterns and the neutron detector responses under sub-critical state, assuming a measurement of the core reactivity change by the modified source multiplication (MSM) method. Location-dependent characteristics of the neutron detectors were analyzed based on the results of the simulation calculations. A sensitivity analysis on the fuel composition burn-up change to the neutron detector responses was performed at the same time, and the major sensitive macroscopic cross-sections were identified. It is important to take into account the actual burn-up reactivity change of the actual reactor in order to reduce the effect of the uncertainty, induced by the fuel composition burn-up change, on the modification factor for MSM. It was concluded that the adjustment of these major macroscopic cross-sections will be effective and practical for this purpose.