A nuclear fuel verification system using digital imaging of Cherenkov light

Abstract

An UV-sensitive scientific CCD camera has been tested at a power reactor facility to image the faint Cherenkov light from irradiated nuclear fuel. The instrument mates custom optical components (lens, UV-pass filter) to a commercial scientific camera (Astrocam 4100) with a coated frame-transfer CCD chip (EEV 37-10) to produce 12-bit images of 512 × 512 pixels at several frames per second. A 250-mm f 2.6 catadioptric lens has been designed with transmissive optics optimized for this application, incorporating colour correction for viewing through 10 m of water. The filter has an average transmission of 80% from 280 to 320 nm, with visible-light transmission of less than 0.03% from 365 to 780 nm to block artificial lighting in the fuel bay. Measurements were made with this instrument at the Ringhals Nuclear Power Plant, and the CLAB fuel storage facility in Sweden. Both fuel and non-fuel assemblies of boiling-water reactor (BWR) type were studied. Performance is superior to that of the earlier Cherenkov viewing devices (CVDs) based on image intensifier tubes. Increased sensitivity extends the range of the Cherenkov verification technique to fuel with older discharge dates. Increased resolution allows fine details of the fuel to be examined for higher-confidence safeguards verification. Sample digital images are presented, and the advantages to irradiated-fuel verification of image quantitation, storage, transmission, and processing are discussed.