By Bob Timberlake
Risk at a nuclear power plant can take many forms. Operators are concerned about factors that impact consistent, efficient energy production. Engineers are concerned about component reliability, compatibility and quality. All are focused on safety on the job. As a result, plant managers seek methods of mitigating risk. Any technique that is able to transform an “unknown” into a “known” factor is considered highly beneficial.
Metrology, the science of measurement, offers an easy method of mitigating risk. In fact, the smart application of modernized metrology techniques can have substantial benefits for plant managers.
Now, the word “metrology” probably makes most plant managers think about as-built plans. Indeed, metrology techniques such as laser scanning are most commonly used to complete as-builts after a construction project. However, metrology goes far beyond this simple use.
There are many “tools in the toolbox” when it comes to metrology. Measurement technologies are ever evolving, getting more precise and accurate. Modern metrology equipment can make measurements so precise, they are accurate down to the atomic level. By recognizing all of the unique tools available and taking a holistic look at each project, it’s easier to match up the perfect tool for the project to ensure the most effective use of metrology each time.
|Photogrammetry uses high-resolution photography to measure discrete features using adhesive targets strategically placed on points of interest to capture as-built dimensions. Photo courtesy: AREVA NP|
Turning “I Think” Into “I Know”
Metrology’s greatest benefit for nuclear plants is the mitigation of risk. Metrology can be used on a wide range of projects to help reduce risk, dose, and maintain or improve schedule, safety, financial success and project predictability. When applied early, as projects are set up, these techniques can turn a set of unknowns into a set of knowns. This prevents stopping and starting due to mid-project delays. Ultimately, removing the unknowns helps turn “I think I can” into “I know I can” and mitigates any issues up front.
How? One example is where metrology provides the necessary information to allow a virtual reality simulation of components. The simulation tells you if you can remove and re-install components based on supplied plans versus real-world conditions. It also captures accurate as-built dimensions for the entire plant, reducing uncertainty and inaccuracy of plant components, locations and dimensions. This can help with retrofitting and reverse engineering of components in plants because it increases the ability to put the “knowns” down on paper, rather than taking the paper and trying to build it to fit the unknowns.
Ideally, metrology should be introduced in a project during the initial project planning phase in order to optimize and take full advantage of the benefits for the project. Metrology can also be applied at the design, fabrication and implementation stages of a project timeline. Depending on the complexity and needs of the project, application times can be measured from minutes to weeks as a project progresses. However, even if the project is measured in weeks, the typical industrial application survey duration tends to average a few hours.
Some project examples include:
- Component replacements – Component replacement projects come with many challenges such as load path interference identification, rigging and new versus old component dimensions, as well as installation challenges. Using metrology during all stages of a project, from planning through installation, takes the guess work out of project decisions.
- Plant modifications – Using metrology techniques during the design phase of a project to capture the as-built configuration of the project area versus relying solely on original design drawings is a means to remove project risk while increasing confidence and predictability. The project team utilizes the plant’s as-built configurations for design purposes, reducing rework caused by original design versus as-built differences. Follow-on work includes the pre-fabrication of piping, hangers, etc., as well as layout for pumps, foundations and more.
- Flow-accelerated corrosion (FAC) piping – As plants age, FAC continues to be an issue that all plants must monitor. Using metrology allows project teams to better prepare and install more retrofitted piping in a shorter time with first time fit-up quality.
- 3-D modeling and animations – Laser scan data has many uses to enhance a project’s predictability. Generating 3-D models of the plant’s as-built configurations using laser scan data gathered through metrology enables engineers to design and plan in the real-world environment. Additionally, rigging and component moves are created in the virtual database, enabling the team to prove out rigging scenarios and identify interferences along the prescribed load path.
|This technology takes photogrammetry underwater and without the need for adhesive targeting. Photo courtesy: AREVA NP|
The “Tools in the Toolbox”
Despite the advances of metrology tools and the myriad of uses it can have, adoptions of metrology techniques in the nuclear industry have been slow. Meanwhile, other industries such as civil engineering and heavy construction have eagerly adopted these technologies. Certain metrology techniques have even been used for accident reconstruction and crime scene investigations, proving the portability and versatility of these technologies.
There are a wide range of modern metrology tools to support projects within the nuclear industry. These include:
- Laser scanning – This technology is used to capture 3-D coordinate values for everything in sight between 18 inches and 500 feet. This is a commonly used metrology technique, as it collects large amounts of incredibly detailed data. Different levels of scanners can be used to ensure the best data collection for each project. For example, AREVA NP maintains three levels of scanners – a large volume scanner (± 0.125″ accuracy, used to measure a whole building), a medium volume scanner (± 0.015″ accuracy at 20 to 30 feet from an object) and small volume scanners (± 0.001″ accuracy at 1 to 2 feet from an object).
- 3-D CADD modeling – Data collected through laser scanning creates 3-D models, animation, load-path type interferences and plans, with ± 0.125″ accuracy.
- Portable coordinate measuring machine arm – This single-point portable measurement device can measure applications on its own with ± 0.0015″ accuracy.
- Photogrammetry – Photogrammetry uses high-resolution photography to measure discrete features using adhesive targets strategically placed on points of interest to capture as-built dimensions at ± 0.005″ accuracy. For context, most of today’s maps are made using this type of technology. In fact, industrial photogrammetry was developed from the aerial photogrammetry technique. This development drove the accuracy possibilities down to a few thousandths of an inch, making the application a versatile, easy to use measurement tool.
- Underwater photogrammetry – This technology, uniquely offered through a partnership between AREVA NP and the DimEye Corp., takes photogrammetry underwater and without the need for adhesive targeting. For use in areas previously thought to be inaccessible such as spent fuel pools, jet pumps, core spray, etc., the housing and cabling for the camera has been designed specifically for these environments. This technique is accurate to ± 0.015″.
- Laser tracking – Laser tracking uses servo motors and encoders to accurately “track” a mirrored prism. The system has the ability to collect measurement data on the “tracked” prism thousands of times a second, rendering the statistical data to be accurate to ± 0.001″. It can have many applications, including placing a part or component in its final location or supporting machining operations.
- Total station – This device captures measurements of anything within its line of sight, similar to a land surveying instrument. This single tool actually incorporates all those used for land surveying, including an electronic distance meter (EDM) that aims at a point and shows distance from scope center, and computes slope and angle to provide 3-D coordinates at that point. It is typically accurate down to ± 0.024″.
For nuclear plants, where plant managers most frequently need to ensure accurate measurements on as-built plans prior to planning plant upgrades or replacements, laser- and photography-based tools are frequently the most effective. But, the exact technology used often depends on what one is trying to measure. For example, when measuring large areas for projects that require load path interference analysis or to capture plant as-builts in the case of planning and designing a plant modification, laser scanning technology is typically applied. This technique produces accuracies in the .065″ to .125″ range. However, when installing a new component or retrofitting piping, a higher degree of accuracy requires technologies such as photogrammetry and laser tracking.
Why Use Metrology
Metrology offers a practical, easy way for plant managers, engineers and project managers to make more informed decisions. Smart application of a growing number of tools can increase detailed control of all project elements. In turn, this can help prevent mistakes, saving time and budget
Bob Timberlake is the product line manager for AREVA NP’s Metrology Services. He has more than 30 years of applied practice in the metrology field.