Neutron multiplication factor evaluation method and critical proximity method of fuel assembly housing system

摘要

PPROBLEM TO BE SOLVED: To evaluate a multiplication factor (kSBj/SB) at each step of fuel assembly, in a neutron multiplication factor evaluation method for a fuel assembly housing system. PSOLUTION: Let a neutron multiplication factor in a containing step (j) of fuel assemblies be kSBj/SB, and let a primary neutron emission rate of the fuel assembly and the response sensitivity factor to neutron detector be SSBij/SBand wSBij/SB, respectively. Neutron flux SBij/SBat a neutron detector position on a fuel assembly (i) is expressed as, SBij/SB=wSBij/SBSSBij/SB/(1-kSBj/SB), neutron flux SBj/SBat a neutron detector, based on the whole number (y) of irradiation fuel assemblies at a containing step (j), is expressed as SBj/SB=(i=1,y)(SBij/SB)=(i=1,y)[(wSBij/SBSSBij/SB)/(1-kSBj/SB)], and a proportional coefficient that means detector sensitivity is expressed as dj. Here, a neutron count rate nSBj/SBobtained by neutron flux measurement is expressed as, nSBj/SB=dSBj/SB, SBj/SB=(i=1,y)[dSBj/SB(wSBij/SBSSBij/SB)/(1-kSBj/SB)], and the response sensitivity factor to neutron detector wSBij/SBis calculated. By independently calculating dSBj/SBand SSBij/SBand measuring the neutron flux SBj/SBor the neutron count rate nSBj/SB, the neutron multiplication factor kSBj/SBat the housing step of irradiation fuel assembly is obtained. PCOPYRIGHT: (C)2006,JPO&NCIPI