The Location of Spent Fuel Pins in Heavy Water Research Reactor in the Spent Fuel Pool

Abstract

Heavy Water Research Reactor was the first reactor in China. It adopted metallic uranium as fuel and aluminum alloy as cladding in the beginning. During the refueling procedure many years ago, several fuel pins dropped at the bottom of the spent fuel pool. The amount and the location of the fuel pins were not recorded. Before decommissioning, it is important to locate and take back the fuel pins. The fuel pin is φ40 mm × 100 mm and the pool is 17.8 m × 5.6 m. It is like dredging for a needle in the sea. What’s worse, it is not clear to find the fuel pins even with a waterproof camera for the bad water quality. Besides, radiation tubes, neutron detectors, and broken control rod were also stored in the pool.After reviewing on the localization method of radioactive source at home and abroad, it is determined to use γ dose rate meter and γ spectrometer in this case. Shields in different width and thickness were calculated with MNCP code. The optimization was 5cm in thickness and 5 cm width lead shield with a hole in the center. The waterproof camera was tied with Gama detector and finally 14 fuel pins were located and taken back safely.