Studsvik has replaced a 40-year-old periscope for visual inspection of spent nuclear fuel with a fast and flexible camera-based inspection system that not only secures continued operation, but also significantly increases the company’s measurement capacity, since many of its features are automated
Studsvik Nuclear aims to improve nuclear reactor performance and reduce risks and costs related to nuclear and radioactive materials. One of Studsvik’s main areas of focus is fuel and materials testing. DVel is one of Studsvik’s partners, delivering custom equipment for the material testing and inspection.
Niklas Snis, head of fuel testing at Studsvik Nuclear, says that his experience in the nuclear industry is that new equipment is often developed within the company to meet its highly specific needs. However, this is changing, and he sees new value in going outside the company or even the industry, to get access to new knowledge and technologies. Companies like DVel, with experience from many different industries, can bring a valuable outside perspective to technical challenges within the nuclear industry. They can suggest innovative ideas and contribute to on-going discussions at Studsvik with a distinctive business perspective.
Importance of continuous improvement
Being the only fully commercial lab performing analysis of highly radioactive materials, Studsvik Nuclear has to increase the quality of its services continuously to remain at a highly rated international position. It must develop new measurement methods and analysis techniques and strive to become more efficient. There is also a strategic importance to continuously update older equipment to reduce the risk of down time due to malfunctioning systems.
In 2020, Studsvik decided to upgrade and replace parts of the periscope equipment used for visual inspection of nuclear fuel rods and other highly radioactive materials. The equipment is one of its most utilised and is a central piece of equipment in its laboratory. Results from the inspections are vital in documenting the investigated component’s status and they are used to identify what features need to be studied in more detail, using other techniques. The aim of the upgrade was to increase the capacity and flexibility of the visual inspection system.
Dealing with changing project requirements
The inspections are done inside a so-called hot cell, a highly shielded area with thick concrete and lead glass walls. Objects inside the cell are manoeuvred from the outside, using manipulators.
With the previous periscope equipment, the inspection of a single fuel rod could take several hours, since the operator had to manually move and inspect the samples. The manual operation also made the inspection results operator-dependent, whereas a modern system could support a highly automated image collection — including improved colour and contrast calibration.
The project was initially intended as an upgrade of the old inspection system, but when a mechanical mechanism in the old periscope started to malfunction the project developed to become a complete replacement. To make the measurement system even more flexible, it was also decided that the translation stage should be replaced, enabling a fully automatic inspection of fuel rods.
As the precise functionality evolved throughout the project, with several advanced features added at a late stage, the close cooperation between Studsvik and DVel was of great importance.
Hardware and software features
The periscope equipment was replaced by a less complicated optical setup. A camera and a zoom objective are placed inside the wall of the hot cell. A mirror, at a 45-degree angle, enables a view of the rod from above.
The fuel rod can be rotated and translated along three perpendicular axes, so that every part of the rod can be inspected and photographed. The operator can either manually move and take pictures of the rod or choose to perform an automatic inspection.
Camera and light settings can be adjusted to achieve the best possible image quality, something that is often a challenge in the hot-cell environment due to the strong yellow light of its sodium lamps.
The images are calibrated to provide the real-life position of each pixel and this calibration information is stored, together with the images, so it can be used during future inspections. The associated analysis software can be used to measure distances and sizes of defects on the fuel from the captured images.
The software also enables the user to change the colour balance of the images and look at two successive images together. There are also features to re-save an image and to easily save information about the position of a defect together with a related comment. The bulk of the visual inspection can thus be performed outside the hot cell, greatly reducing the bottleneck effect of the in-cell inspection.
Improving the measurement system
The new inspection system secures continued operation, but it also significantly increases Studsvik’s measurement capacity, since many of the new system features are automated.
One key aspect is that inspecting a fuel segment is substantially faster than before, so the hot cell is better utilised. The time required to image a one-metre fuel segment has been reduced from several hours to about 30 minutes. The inspection system can also be operated remotely which improved the ergonomics for the operator.
Finally, both the inspection system and the translation stage can now be serviced without entering the hot cell. This is a great improvement, since the hot cells are not required to be shut down during system maintenance.
The new system allows:
-Fast, automatic inspection of the whole rod.
-Automatic measurements of the diameter along the fuel rod.
-Automatic stitching of images along a rod.
-Manual inspection of defects.
-Remote supervision and control.
-Data storage of image information, such as resolution, position, and diameter profile.
-Offline inspection of stored images.
When updating systems in the nuclear industry Niklas Snis, head of fuel testing at Studsvik Nuclear recommends careful consideration of the need to modify quality and safety-related documentation. This can result in a significant amount of work. The smart approach is therefore to update a system in a way that keeps this documentation valid even after the new system is implemented. With proper preparation and assessment of the equipment it is often possible to improve the performance and usability of a system without too much change to safety and quality documentation.
An environment such as Studsvik’s hot cell laboratory also often requires reuse of parts and concepts. Having a partner like DVel that has the flexibility and skills to integrate new equipment or software with older hardware is critical for a successful system upgrade.
The close collaboration between Studsvik and DVel will continue to help Studsvik keep evolving its solutions. The general knowledge DVel has of Studsvik’s many customised hot cell systems facilitates a proactive approach, with smart new features developed as ideas emerge. This way Studsvik can develop its methods and techniques in an innovative way and keep on providing its services to the nuclear industry.
This article first appeared in Nuclear Engineering International magazine.