Determination of Burnup from Measurements inside the Spent Fuel Assembly

Burnup of the spent fuel assembly can be determined from measurements of neutron, total gamma-ray, and gamma-ray spectroscopy. In most of the previous works, the neutron and gamma- ray were measured outside the spent fuel assembly. We have studied the determination of the burnup from measurements inside and outside the spent fuel assembly. A detector setup to measure the burnup was installed at Post Irradiation Examination Facility (PIEF) of KAERI. An ion chamber to measure the total gamma-ray dose distribution, and a fission chamber to measure the total neutron were inserted into the guide tube of the assembly, and the detectors were moved automatically along the fuel axis to measure the gamma-ray dose and neutron at each position of the assembly axis. The neutron and total gamma-ray distribution were also measured outside the fuel assembly with an ion chamber and a fission chamber. By inserting the detector into the guide tube of the assembly, the reproducibility of the data could be improved. With the help of MCNPX simulation of the assembly, the total gamma-ray distribution was converted into the burnup distribution, and it was compared with the burnup distribution from fuel rod scan. Our detector system was improved to shorten the measurement time.