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Hydratight demonstrates benefits of nuclear maintenance with new technology

5 December 2017

​Hydratight has introduced its new Self Contained Tensioner (SCT) into nuclear maintenance schedules across the USA, to bring safety and speed to the removal of reactor pressure vessel heads for refueling and forced outages.

The role of the SCT is to replace traditional central pumping unit and hose operated RPV stud tensioner systems with a modern equivalent. It has already been deployed in power plants during scheduled refueling outages, demonstrating measurable efficiencies.

During retrofitting of the SCT, set-up time, tensioning time and manpower hours were all reduced, resulting in lower potential rad exposure and reactor downtime. The SCT can replace old thread on, QD (quick disconnect) and QD-H (quick disconnect helical thread version) designs.

Reliable and compatible

Hydratight combined the use of the new SCT with its Electronic Stud Drive Tools (ESDTs), which were employed to remove and re-install the studs holding the head in place.

It was one of the first times the new SCTs and ESDTs had been used in combination during an outage and the work was carried out under the supervision and guidance of a highly skilled and trained team.

The ESDTs were used to remove studs which have a 6-7” diameter and weigh around 900lbs. The tools have significant safety benefits because their use avoids the need for the operator to be in close proximity during stud removal, reducing As Low As Reasonably Achievable (ALARA) exposure. The tool also has built-in reaction arms to prevent potential injury if a stud becomes stuck.

The SCT control system is a widely accepted industry design for increased reliability and familiarity, ensuring safety and accuracy.

Successful campaign

On one recent project, work was carried out in two phases. The de-tensioning took place while the old head was still in place with the tensioning being carried out a few weeks later after installation of the new head. Replacing the head within certain plants has allowed sites to obtain 20-year license extensions from the US Nuclear Regulatory Commission (NRC).

Wayne Rymer, Hydratight Nuclear Field Service Engineer, said: “We anticipated that using the new equipment, coupled with Hydratight technical support, would reduce de-tensioning and tensioning times. The result was a process lasting only around 90 minutes for detensioning/tensioning, with completion in under two hours for stud turnout.”

SCT specifications

Power requirements: 460-480VAC at 10 amps (high speed industrial network communication protocol via category five ethernet cable bundled with power distribution cable

Pressurization time: Less than 20-30 seconds

Accuracy: +/- 15 psi at 10,000 psi maximum pressure

Weight: 3000 to 4600 lbs. (depending on single or two stage cylinders)

Height: comparable to existing QD or QD-H style stud tensioners

Stud Engagement Interface: Quick connect / disconnect design for fast performance based on over 30 years of field proven use. Can engage annular groove design or helical thread form RPV studs.

A total of 12 sites are using the SCT across the USA.

About Hydratight:

Hydratight provides world-class bolted joint solutions and machining services, plus innovative mechanical weldless connectors, to power generation, oil and gas, nuclear, wind and aerospace industries. Over the last 20 years Hydratight has pioneered systems for complete joint integrity assurance that are now incorporated in industry-wide safe-working guidelines around the world.

Hydratight is wholly owned by Actuant Corporation, a diversified industrial company serving customers from operations in more than 30 countries and headquartered in Menomonee Falls, Wisconsin. Actuant trades on the NYSE under the symbol ATU. For further information on Actuant and its businesses, visit the Company’s website at