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This paper describes two separate visual-based inspection procedures used at CANDU nuclear power generating
stations. The techniques are quantitative in nature and are delivered and operated in highly radioactive environments
with access that is restrictive, and in one case is submerged. Visual-based inspections at stations are typically qualitative
in nature. For example a video system will be used to search for a missing component, inspect for a broken fixture, or
locate areas of excessive corrosion in a pipe. In contrast, the methods described here are used to measure characteristic
component dimensions that in one case ensure ongoing safe operation of the reactor and in the other support reactor
refurbishment.
CANDU reactors are Pressurized Heavy Water Reactors (PHWR). The reactor vessel is a horizontal cylindrical low-pressure
calandria tank approximately 6 m in diameter and length, containing heavy water as a neutron moderator. Inside
the calandria, 380 horizontal fuel channels (FC) are supported at each end by integral end-shields. Each FC holds 12 fuel
bundles. The heavy water primary heat transport water flows through the FC pressure tube, removing the heat from the
fuel bundles and delivering it to the steam generator. The general design of the reactor governs both the type of
measurements that are required and the methods to perform the measurements.
The first inspection procedure is a method to remotely measure the gap between FC and other in-core horizontal
components. The technique involves delivering vertically a module with a high-radiation-resistant camera and lighting
into the core of a shutdown but fuelled reactor. The measurement is done using a line-of-sight technique between the
components. Compensation for image perspective and viewing elevation to the measurement is required.
The second inspection procedure measures flaws within the reactor's end shield FC calandria tube rolled joint area. The
FC calandria tube (the outer shell of the FC) is sealed by rolling its ends into the rolled joint area. During reactor
refurbishment, the original FC calandria tubes are removed, potentially scratching the rolled joint area and, thereby,
compromising the seal with the new FC calandria tube. The procedure involves delivering an inspection module having a
radiation-resistant camera, standard lighting, and a structured lighting projector. The surface is inspected by rotating the
module within the rolled joint area. If a flaw is detected, its depth and width are gauged from the profile variation of the
structured lighting in a captured image. As well, the diameter profile of the area is measured from the analysis of a series
of captured circumferential images of the structured lighting profiles on the surface.
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