Nuclear optics4 September 2019
The nuclear sector is seeing increased requirements for radiation resistant cameras, says Mark Pontin, managing director of Resolve Optics Ltd.
NEI: Where is visual monitoring used in nuclear facilities and for what applications?
Mark Pontin: There are many applications that require visual monitoring, such as critical areas that could become radioactive in the event of a spillage, accident or natural disaster. Without radiation-resistant CCTV monitoring it would be extremely difficult to maintain visual access to key areas of the plant that are exposed to higher levels of radiation. Regular maintenance inspections can also be facilitated using radiation-resistant CCTV systems. An interesting example of a maintenance application we were involved with was a radiation-resistant camera system for monitoring cooling water pipework around reactors to look out for corrosion or cracks. In short, radiation-hard vision systems are used wherever the radiation is too high for a person to work safely or monitor directly.
NEI: What are the challenges of using optics in these areas?
MP: Radiation affects different optical materials in different ways. Standard optical glasses will turn brown or grey, quickly rendering them opaque, when exposed to radiation. Over the last 30 years we have developed several generations of radiation resistant lenses that use specialised non-browning lenses and ensure a clear bright image up to a total dose of 10,000,000 rads. As optical systems typically comprise a mixture of lens and mounting components we have to make sure, right down to careful selection of the greases used, that all materials used are radiation-resistant or known to be unaffected by radiation.
NEI: What optical solutions/technologies are available?
MP: We offer a comprehensive range of standard fixed focus and zoom non-browning lenses for use in radioactive environments. All our lenses are manufactured to the highest standards of quality and performance and are designed to withstand a total radiation dose of 10,000,000 rads. Due to the highly regulated nature of the nuclear industry nothing changes quickly. Our biggest challenge is to keep up with changing sensor formats, as CMOS sensors begin to replace the traditional tube cameras.
NEI: What factors must be considered when selecting optics and camera products?
MP: Higher radiation doses place considerable demands on optical components and cameras in terms of reliability, quality and operating lifetime. Vision systems once installed in a radioactive environment cannot be easily maintained, repaired or serviced for obvious safety reasons. The nuclear industry tries to keep contaminated waste to a minimum. Therefore, it is in everyone’s interest that visions systems used in areas of high radiation should have an operating life that exceeds five years. Even though specialist non- browning lenses are considerably more expensive than equivalent off the shelf optics, you will save on replacement costs and waste over the lifetime of a radiation-resistant vision system.
NEI: Resolve Optics recently supplied an infrared endoscope for a vitrification plant. How does this technology work?
MP: This endoscope was designed to work in conjunction with a bolometer-based infrared camera. Our customer at a nuclear reprocessing plant required a method of monitoring the temperature of their waste material, to ensure that there was not an excessive buildup of heat that could lead to fire. With the level of radiation around the vitrification process unsafe for operators — and likely to rapidly destroy the infrared camera — a remote measurement solution was sought. Operating at 7-14 microns, the prime function of the IR endoscope was to provide the desired field of view to monitor the vitrification cell and to transfer the image to the bolometer-based IR camera. For added safety the thermal camera was mounted after a 90° fold to ensure it was not in the shine path of the radiation. Due to the large aperture and sensitivity of the bolometer-based camera the endoscope required carefully positioned baffles to ensure there were no stray light reflection that could degrade the performance of the camera, leading to imprecise monitoring of the vitrification process.
NEI: Are there any trends you are seeing from the nuclear industry regarding optics?
MP: Many customers in the nuclear industry have sought a colour camera that can withstand the same levels of radiation as traditional tube cameras. We are seeing more use of CMOS sensors that can withstand higher levels of radiation, though still not quite to the levels of the tube cameras. However, what the CMOS sensors provide is higher resolution, colour images.
As traditional non-browning lenses use glasses that are very yellow in appearance the image produced has a yellow tint when viewed in colour. Last year we introduced our Model 357 non-browning zoom lens range, which utilises specially selected glasses that are radiation-resistant, but result in a clear high-resolution image that works well with the new CMOS colour sensors.
Author information: Mark Pontin, Managing director, Resolve Optics Ltd