Calculated Response Contributions of gamma Rays Emitted from Fuel Pins in an Irradiated PWR Fuel Assembly

摘要

The relative contributions of gamma rays originating in specific fuel pins to the total gamma-ray source strength were calculated as a function of initial gamma-ray energy for a pressurized-water-reactor fuel assembly. Gamma-ray energies used in the calculations ranged from 511 to 2186 keV, the energy range in which most long-lived fission and activation products emit gamma rays. Nondestructive gamma-ray measurement techniques use specific signatures of exp 137 Cs or exp 134 Cs/ exp 137 Cs and exp 154 Eu/ exp 137 Cs isotopic ratios to determine the exposures of irradiated fuel assemblies. Nearly 92% of the measured exp 137 Cs signature (661.6 keV) originates in the three outer rows of fuel pins. However, because only 78% of the exp 154 Eu signature (1275 keV) originates in these three outer rows, a ratio of exp 154 Eu/ exp 137 Cs does not sample exactly the same volume segment of the fuel assembly. Other examples are presented that evaluate the effect of using a collimator at different angular orientations on quantifying the contributions from specific fuel pins to the total source strength. (ERA citation 08:048999)