A refined analysis on the power reactivity loss measurement in Monju

The present paper describes an evaluation of power reactivity loss data obtained from the Japanese prototype fast breeder reactor Monju. The most recent analysis on the power reactivity loss measurement (Takano et al, 2008) is updated in consideration of the following findings: (a) in-core temperature distribution effect, (b) crystalline binding effect, (c) logarithmic averaging of the fuel temperature, (d) localized fuel thermal elongation effect, (e) updated Japanese Evaluated Nuclear Data Library, JENDL-4.0, and (f) refined corrections on the measured values. The influences of these updates are quantitatively identified and the most precise and probable calculation-to-experiment (C/E) C/E value is derived and a thorough uncertainty evaluation is conducted. These reveal that analysis overestimates measurement by 4.6% with a measurement uncertainty of 2.0%. This discrepancy is reduced to as small as 1.2% when the core bowing effect is taken into account, which implies the importance of this effect in the calculation of power reactivity loss.