A nuclear power company applies 3-D tools to save time—and cut risk—in the maintenance of its reactors.
This article was prepared by the Mechanical Engineering staff with outside contributors.

We all know time is money, even if we don’t bill by the hour. An operator of nuclear power plants is trying to save big money by reducing the time it takes for maintenance projects. It hopes to save time by carefully planning in vivid detail all the operations it takes to complete a job, and then making sure everyone involved knows what to do and when.

The company is Entergy Nuclear, a unit of Entergy Corp. of Jackson, Miss. It operates 12 commercial nuclear power reactors with a total nameplate capacity of about 11,000 megawatts. For each day that one of those reactors is shut down, the company estimates it has to purchase about $1 million in replacement power to deliver to its customers.

A 3-D model gives Entergy Nuclear a view into the Waterford 3 containment structure with its roof removed, and illustrates the challenge of replacing the reactor coolant pump motor.

Entergy Nuclear is adopting digital technology to do a more thorough and cost-effective job of engineering and planning maintenance tasks. It plans to model its plants and is even scanning components in its reactor containment buildings to get the models right. Then it will simulate maintenance operations to find the most efficient way to carry them out. The animations of the simulated results can be used to demonstrate to maintenance crews the most effective way to perform each task.

Potential savings are huge. As John M. Mahoney, innovations leader for Entergy Corp., sums it up: “Another day, another million dollars.”

Large-scale modeling and simulation projects can cost between $50,000 and $300,000. If a simulation can shorten an outage by a single day, the company comes out ahead.

The electric utility did three simulations in late 2008 and early 2009 for its Waterford 3 plant near New Orleans:

• The impact of a potential fire on equipment located in a key area of the plant.

• The replacement of a reactor coolant pump (RCP) motor. The pump circulates the water that cools the reactor and drives the plant’s generators. The motor is rated at 9,700 horsepower, considerably more power than a new railroad freight locomotive. It weighs 115,000 pounds, or more than 57 tons.

• The replacement of “thimbles” and in-core instrumentation (ICI) sensors that monitor reactor fuel. Replacing the sensors requires working underwater close to irradiated reactor components, to cut out old and install new units. This simulation is heavy on ergonomics and radiation-exposure monitoring.

Some of the simulations are being put to the test as this article goes to press. Waterford 3 was scheduled to be shut down for refueling some time in October. The outage will also be used for other maintenance tasks—replacing the reactor coolant pump motor and the in-core instrumentation thimbles, and inspecting steam generator tubes and the reactor head. The work is expected to take at least 30 days.  Work on the RCP motor will extend through most of the outage, a projected 25 days.  The simulation covers the two days when the old motor is moved out and its replacement moved into place.

Simulations have been done with 3-D software from Delmia and modeling was done with Catia. Both are brands of Dassault Systèmes. Some simulations were done by the Dassault Systèmes Industry Services project office in Montréal.

Nearly all U.S. nuclear power plants are 20 to 40 years old, so shutdowns for maintenance are nothing new. Traditionally, utility companies have planned outage work in containments with conferences, hundreds of paper drawings, project timelines, physical mockups, and similar training aids.

Previewing a task at Waterford 3: (From top)
Tight clearances for removing the reactor
coolant pump motor show up in 3-D. An
interference is discovered in simulating
a move of the pump motor (shown in brown and pink).
A side view of the pump motor lift shows
a second potential clearance problem in
the containment building. The pump motor
is lowered to the floor of the containment building.

The challenge lies in the complexity of the work that must be accomplished in a two- or three-week outage. For example, refueling a power plant has over 2,000 discrete tasks. This involves many different contractors and hundreds of what the industry calls “craftspeople”—pipe fitters, riggers, nuclear-certified welders, and so on. Few of them have ever been inside Waterford 3’s containment.

According to Mahoney, custom-built, full-size mockups can cost hundreds of thousands of dollars apiece, and they do not readily accommodate engineering changes or plant modifications, nor are they easily modified for reuse with other facilities. Digital simulations are much easier to adapt.

Gerald Butts was the Waterford 3 project manager when the reactor coolant pump project started. “A sheet metal mockup of the motor was made and moved in and out of containment,” he said. “But the necessary comfort level of really being able to move the motor was not reached. The 3-D modeling and simulation gave us an extra factor we had to have to start the project.”

According to Mahoney, the company is developing operational and engineering databases with 3-D software to track and manage all changes at a plant, starting with Waterford 3. Modifications of the plant as it was designed, as it was built, and as it has been maintained are being documented with a plant lifecycle management application. File-based data management systems are being phased out as Dassault Systèmes’ lifecycle management system, Enovia, is implemented.

The payoff is risk mitigation—focusing on ways to make sure all nuclear plant operations stay on schedule and within budget.

Short-term risk mitigation at Entergy Nuclear focuses on Waterford 3. Mahoney said the company expects bottom-line benefits such as optimized engineering designs, more efficient planning, tighter inventories, reduced supply chain requirements, and a reduction in unforeseen needs to bring in vendors and contractors.

“Industrial safety and radiological safety are also enhanced by laser scanning data, and using 3-D PLM allows for predetermination of hazards in workspaces,” he said. “These simulations help us identify any constraints that might hinder worker performance.”

A reactor coolant pump motor similar to the one in the Waterford 3 project is taken out of a utility company warehouse (top) and loaded on a flatbed truck for transport to a shop for refurbishing. In the photo above, a reactor containment building is visible in the background.

For longer-term risk mitigation, Mahoney said, “it is not far-fetched to link the use of this 3-D technology to a plant’s asset management program and long-range planning.”

According to Mahoney, “Scanning and simulation give the engineers an intelligent model with detailed specifications. Digital data accuracy is within plus or minus a quarter of an inch measured over dozens of feet, and in some cases an eighth of an inch.”

The accuracy is the direct result of scanning and photogrammetry. At Waterford 3, this work was done by Areva NP, a Lynchburg, Va., engineering-services unit of the French nuclear-power giant, Areva.

According to Mahoney, the value of modeling and simulation extends to the ability to communicate a proposed modification to a plant visually to the people who will carry out the job. “These technologies add new and unique opportunities to review options and ‘see’ the effects of the change virtually,” he said.

This can be done, he added, “while we are planning construction activities and conducting pre-job briefings.”

Simulations as 3-D videos can augment verbal instructions and paper drawings to reduce misunderstanding and human errors. As a result, plant employees and craftspeople can be trained better and sooner.

What’s more, seeing an animation of the job being carried out beforehand improves coordination among all the craftspeople and contractors on site. Animated virtual tours analyze task sequences, work practices, and tool selections in 3-D before anyone enters the containment building.

A digital simulation also makes it possible to evaluate new engineering ideas and alternative solutions faster and at far less cost than by older methods of trial and error.

Presenting results in animated visual form helps knowledge retention, and just as important, knowledge transfer, which is a major consideration today, when companies face the challenge of an aging workforce in which veteran employees retire in increasing numbers and companies lose the benefit of their experience.