Advancement of a Delayed Gamma Dosimeter for Spent Nuclear Fuel Assay

Abstract

An in-depth fuel assay is crucial for spent nuclear fuel management. Spent fuels with high radiation dose levels also require an appropriate dosimeter. A widely used detector for nuclear radiation dosimetry is the Geiger-Muller detector. Pulses from this detector are of the same amplitude and no information about particle energy is provided. Dead time is a distorting effect as a nonlinear response is observed at large counting rates. This requires correction methods to avoid nonlinearity. The special measuring tool must be consistent with the structures and constraints of spent nuclear fuels, spent fuel storage, and its construction design. Spent nuclear fuel assemblies are kept in 10-meter water in the open reactor pool for a specific cooling period before transportation to the spent fuel storage pool. Measurement of high dose rates requires specific equipment. In this work, a spent fuel active dosimeter is developed for the spent fuel assay in TRR. Due to high radiation exposure, equipment parts are specially designed to resist gamma radiation. To eliminate the pulse pile-up effect and noise cancellation, a bandpass filter is employed. As an advanced technique, time interval distribution (TID) is also developed using digital electronics. By utilizing a Co-60 standard gamma source in the Karaj Secondary Standard Dosimetry Laboratory (SSDL), the detector tests and calibration are also accomplished. Validation of the system is performed with a commercial measuring tool.

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