Optical Gas Imaging (OGI) is a proven technology for locating hydrogen leaks in nuclear and conventional power plants. OGI can improve plant safety during routine operations and reduce revenue lost to downtime during major overhauls.
A recent study by Bruce Power found that OGI cameras could be effective in reducing plant downtime that costs over $1 Million USD per day.
Most modern nuclear power plants use hydrogen (H2) cooled generators, with over 30,000 in operation worldwide. Hydrogen is used because it is an effective cooling medium, and because it increases generator efficiency.
However, H2 gas can self-ignite as an invisible flame, meaning that any leaks that develop in the hydrogen circuitry during normal operation must be quickly detected and fixed to avoid potentially catastrophic situations. Hydrogen leaks can occur from seals, fittings, and other components.
Until recently, fixing these leaks often required a full plant shutdown to locate the leaking component, costing time and resources. While many traditional methods such as catalytic bead sniffers, soap bubbles, and acoustics exist for hydrogen leak detection, none are ideal. In a study done by Amec Foster Wheeler and Bruce Power  none of these methods provided real time detection and localization, while also permitting measurement from outside of the range of a potentially explosive gas cloud.
Following a scheduled shutdown, there is a significant opportunity for optimization. During major overhauls, the entire turbine is opened for repair. Before the plant can be returned to service, the generators must be certified leak free. Historically, hydrogen sniffers have been used to detect any leaks prior to recommissioning, a very time-consuming process. This can extend the overhaul timeline, during which time the plant is not generating revenue. Validating hydrogen circuit integrity is therefore costly in terms of manpower and plant downtime.
SELECTING OGI CAMERAS FOR GAS DETECTION
A new hydrogen leak detection method using Optical Gas Imaging (OGI) is gaining favor in the power generation market. This technique uses a small amount of CO2 (4% to 6% in hydrogen) as a tracer gas. The CO2 tracer can be visualized by an OGI camera operating in the 4.2μm to 4.4μm range, such as the EyeCGas CO2, manufactured by Opgal Optronic Industries. This solution has major financial implications for plants using hydrogen cooled generators.
Most plants have ready supplies of CO2 for use as a purge gas, so there are no additional gas costs. During plant operation, up to approximately a 5% concentration of CO2 can be introduced into the hydrogen stream without compromising generator efficiency. In addition, the Opgal EyeCGas CO2 is classified as non-incendive as per CSA 22.2-M1987 for Class 1 Div. 2 environments and ANSI/ISA-12.12.01 – for use in Class I and II, Div. 2 and ATEX II 3G Ex nL IIC T6. This provides added safety, by greatly reducing the likelihood of the camera causing ignition if used near flammable materials, i.e. during H2 filled operational status.
In regard to this, Amec Foster Wheeler and Bruce Power  discussed the following key results from using OGI for power plant hydrogen leak detection:
1) OGI leak detection campaigns are more accurate and faster than current practices. “Outage Critical Path” can be reduced by hours or days and save utilities $1M/day per unit.
2) OGI leak searches can be performed offline in air and online in H2, allowing for preventative maintenance to be implemented.
3) Use of CO2 as a tracer gas with OGI cameras is a field tested, inexpensive, and commercially available option.
4) OGI cameras can remotely identify leaks, improving safety for personnel beyond current practices.
5) OGI cameras can detect leaks from inaccessible access points or complex angles, mitigating the risk of mischaracterizing the leak.
While a crucial part of the maintenance process, downtime in power plants can be extremely costly. Optimizing this process has become part of the logistical overhaul of many operational plants. When selecting tools for gas leak detection in sensitive environments, safety during use, fast results, and Instant ROI are the main considerations. With an average savings of $1 Million USD per day, the EyeCGas CO2 OGI camera for tracer gas leak detection is an ideal solution for this application.