Measurement of the Gamma Dose Rate Distribution in a Spent Fuel Assembly with a Thermoluminescent Detector

Thermoluminescent detectors (TLDs) were applied to measurements of gamma dose rates and their distributions in spent fuel assemblies irradiated in a boiling water reactor, the Japan Power Demonstration Reactor (JPDR). Materials used for the TLD were Mg₂SiO₄:Tb and LiF. Feasibility of the technique was confirmed by an on-site measurement in a spent fuel pond of the JPDR. The highest gamma dose rate calibrated to a ⁶⁰Co gamma field was 4 × 10³ R/h in the measured positions in a spent fuel assembly, with an average burnup of 5639 MWd/MTM and a cooling time of 8 yr. Reliability of the measurement by means of a TLD was tested via duplicate measurements on a fuel assembly. In the fields of nuclear safeguards and fuel management, application of TLDs will be effective in obtaining inside information of a spent fuel assembly nondestructively.