IBT’s Industrial Maintenance Technologies Inside at Nuke Power Plant Outage

IBT’s Industrial Maintenance Technologies Inside at Nuke Power Plant Outage

Nuclear power plants are extremely complicated to maintain, especially because of the safety and security factors.

Although much of the work that is needed to keep a plant up and running can be done during normal operations, each plant schedules a major outage at eighteen month intervals to allow for refueling and other major repair, refitting and reconstruction.

Cooper Nuclear Station in Brownsville, Nebraska, owned by Nebraska Public Power District, have just completed a major outage, and IBT’s IMT was involved in the process.

The major work undertaken during the outage went way beyond refueling, assessing the plant’s electrical systems or testing and maintaining valves. It also included the installation of two new huge turbine rotors, imported from Germany.

The turbines had quite a journey. They left their manufacturing plant in Europe, traveled by ship to Texas, and then were transported to the station via heavy-haul trucks. They arrived in December of 2004.

They’re big! Almost 16 feet in diameter. One rotor is 28 feet long and weighs 147 tons. The second rotor is 31 feet long and tips the scales at 152 tons. The plant’s turbine bay crane wrestled the massive pieces of equipment into place.

During the outage, IMT was on the job with a critical task, one made more complicated by the nature of the site. They balanced two of four cooling fans located inside the reactor area.

Normally, there is a high degree of skill and experience involved with a balancing task. The job called for vibration analysis, using portable electronic balancers to measure reference angles and phase changes. After the level of unbalance is determined, weight is added strategically to prevent “vibration.”

The two fans that IMT balanced use 75 hp motors to turn four foot blower wheels at approximately 1700 rpm. The wheels weigh approximately 400 pounds each. At the beginning of the process, they were out of balance by as much as 5 mils. When balanced, that had been shaved to less than 1 mil. The addition of approximately 50 grams- at just the right places – made all the difference.

Further adding to the challenge of the job was the venue. The fans are located inside an area known as the dry well, which is accessible only during outages. When the plant is active, the drywell area is radioactive and uninhabitable. In fact, it is surrounded by a radiation-retarding wall that is made up of eighteen layers of 3.5 inch concrete blocks

The fans IMT balanced play a critical role. They are used to keep the drywell cool. If the temperature is not controlled, the reactor must cut load, resulting in loss of production. They must be fixed right, the first time, because access to the space is not possible without shutting down the whole plant.

Working in the dry well is also challenging. Special protective gear and clothing is required. Access is limited. As a result, IMT’s Bill Cooper found that he needed to work fast – and also stay on it. They spent as long as seven hours at the task, without the benefit of breaks.

Approximately 1,000 contractor personnel worked during the outage, which took 34 days, 22 hours and 33 minutes to complete. It was the fourth shortest refueling outage duration in the plant’s history and the shortest since 1979 when the plant was in near new condition and refurbishment requirements were more limited.

“I’m proud of the work IMT did,” reports manager Chris Treat. “We worked under harsh and demanding circumstances and performed with efficiency and professionalism. It is also a tribute to our growing reputation that we were able to be seriously considered for – and then awarded – the job by Nebraska Public Power District. We look forward to working with them again in the near future.”

For more information about vibration analysis and the entire range of services available form IMT,
ask your IMT representative
 for more information.

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