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Nuclear

Nuclear MarketsThe nuclear power industry demands leak-free joints and as such has adopted a ‘right first time' philosophy.

Hydratight's range of specialist bolt tensioning equipment, is proud to partner these utilities, helping them to meet their ALARA objectives. As a new addition to the Hydratight range, the remarkable Self Contained Tensioner (SCT) (formerly known as Biach Self Contained Tensioner) tensioner brings greater safety, reduced manpower and shorter downtime to a critical task.

Hydratight has also been a critical supplier of on-site machining equipment and nuclear qualified technicians for a variety of nuclear machining projects.

Our application solutions include:

Steam Generators

Maintenance associated with steam generators is critical during outages. No other service provider in the world has Hydratight's experience when it comes to bolting applications for nuclear steam generators used in power plants.

Hydratight has developed Multi-Stud Tensioning systems (MSTs) to fit the majority of primary, secondary, hand-holes and inspection ports for almost every style of steam generator, and has supplied numerous MSTs for manways and flanges to various nuclear plants throughout the world, and major global operators including Exelon, EDF and British Energy.

The MST is capable of tensioning all of the studs on any one cover simultaneously. Common MSTs for the primary and secondary applications contain four-five segments, while the smaller hand-holes and inspection ports typically have two.

In some cases, space restrictions are so severe that conventional circular ram designs cannot solve the problem. To combat this Hydratight has developed a uniquely designed asymmetrical ram which enables the tool to fit almost all applications. Speed and accuracy are the two driving factors for determining tooling for this application.

Reactor Coolant Pumps

Using our expertise in identifying high-risk joints and designing fasteners and stud tensioning equipment, Hydratight engineers have designed a tensioning system which significantly reduces planned outage time and prevents leakage on reactor coolant pumps. Based on this new stud and nut design, Hydratight has developed a tensioning system that not only precisely loads each fastener, but can also operate in the restricted space of the pump motor stand.

Client testimonial:
"By identifying high risk joints and then designing fasteners and stud tensioning equipment to fit, the engineers from Hydratight and multiple power utilities have significantly reduced planned outage time and prevented leakage of the Westinghouse Reactor Coolant Pumps."

Case study:
For one of our customer's applications, the previous method of tightening their flange joints was with large bolt heaters or large hydraulic torque wrenches. Both methods are time consuming and do not achieve the precise pre-load accuracy necessary for leak-free joints, especially in borated reactor coolant systems.

The biggest challenge involved tensioning 24 x 4½" bolts for the reactor coolant pump main flange. Each bolt was in a restricted area with minimal side clearance and had to be pre-loaded to 500,000lb (.046" stretch) to prevent reactor coolant leakage from the system.

As mentioned previously, the special small-headed bolts were tightened using bolt heaters and hydraulic torque wrenches which meant eight mechanics working for 36 hours (three x 12 hour shifts) in a highly radioactive environment. Another issue facing the engineers was the joint, on similar pumps throughout the industry; it has a history of leakage, resulting in boric acid degradation of the bolting and subsequent unplanned re-work.

Hydratight modified the design for the 4½" fasteners from a bolt to a stud and nut fastening, utilising a hardened washer. The new fasteners were designed to be tensioned with hydraulic tensioners instead of the old method of heating and cooling and/or torque wrenching.

Hydratight managed and delivered the entire project including engineering, designing and supplying the new fastener and the hydraulic equipment, and product training. And by applying Hydratight's technology, the time associated with this specific maintenance activity was more than cut in half.

HP Turbines

There are only a few high pressure steam turbines which are designed with horizontal bolting tensioning, one in particular is the Westinghouse BB296.

Hydratight supply tensioners for this joint to both the OEM and service companies. Here are a few of the plants we supply who utilise this tooling:

• Westinghouse BB296 Frame
• First Energy - Beaver Valley Power Station
• Dominion - North Anna
• TVA - Sequoyah
• HL&P - STP
• Exelon - Braidwood
• FP&L - St. Lucie
• Progress Energy - Shearon Harris

Specialised Applications

Hydratight has provided cutting-edge field machining expertise within several areas of nuclear power plants, and although there is an abundance of general machining requirements, a few specialised applications are worth highlighting:

Boiling Water Reactors

  • Reactor nozzles - the main nozzles coming off the reactor are susceptible to inter-granular stress corrosion cracking (IGSCC). Typically this is found on the N1 through to N19 nozzles and include the jet pump nozzle. Typically cracking is identified during outage inspection and the repair for this is weld overlay of Inconel 52. Once the overlay process is completed, Hydratight can then mechanically cut or grind the weld to profile the weld for UT inspection.
  • Main steam isolation valve - the replacement of wedge-gate valve seats along with standard valves and piping replacements, require field machining. Hydratight provides both qualified technicians and state-of-the-art equipment to perform this service.

Pressurised Water Reactors

  • Steam generator replacement - Hydratight has designed and manufactured a variety of cutting equipment to assist in the extraction of old steam generators and the insertion of replacements.
  • Reactor to steam generator - the hot and cold leg nozzles between these two components are susceptible to cracking, caused by service water stress corrosion cracking (SWSCC). A plant typically can identify this cracking during in-service inspection. This cracking requires a weld overlay of Inconel 52. Once the overlay is completed, Hydratight can mechanically cut or grind the weld to profile the weld for UT inspection.
  • Pressuriser - there are many lines running between the pressuriser and safety relief valves. There are typically one or two nozzles which require overlay repair during normal maintenance activities and Hydratight is able to supply both the equipment and manpower to perform this machining.
  • Feed-water heaters - Hydratight has developed a process where we can perform a partial shell replacement, due to erosion of the steam inlet baffle plate. This is a process where we remove the steam inlet nozzle along with a segment of the feed- water heater shell. After the internals are repaired, a new fabricated shell section is used to replace the old.

Nuclear

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