Reeling in a prize catch28 February 1999
Improving outage efficiencies by making reactor maintenance and inspection easier is a high priority for the nuclear industry. RolaTube Technology, a small company in west London, has been working with BNFL Magnox Generation on a simple piece of equipment which has the potential to make remote inspection a far simpler process.
Bistable Reeled Composite, made and patented by Rolatube Technology, has two distinct states. A solid plastic built up around a glass fibre structure, it is stable either flat, or rolled around itself into a tube. When flat, it is possible to pressurise both sides until the material snaps sharply into the tubular position, a movement of such rapidity it can sting your fingers.
It is this bistable nature of the composite that offers great potential to the nuclear industry, particularly for remote inspection within a reactor. Currently during outages, cameras are lowered into a reactor using a rigid metal mast. Traditional metal masts weigh in excess of 300 kg and are bulky and awkward to move. Manipulating one above a reactor and inserting it through a standpipe into the reactor requires the use of the pile cap crane, which is often in great demand during an outage. Its large size and weight means a specialised long vehicle, typically 14 metres, is needed to transport it and it has to be supported by a metal structure known as a ‘strong back’. Specially trained staff are needed for transportation, manipulation and rigging.
Clearly the complexity of operation involved in the traditional technique has associated costs. In particular the necessity to use the pile cap crane means that the delivery of the mast during an outage has to be very carefully planned to ensure that everything is ready for the remote inspection so that time is most efficiently used. Particularly with the pressures on nuclear power stations to reduce outage times to improve performance, anything which simplifies the inspection process is of great interest.
At the Magnox Electric development facility at Littlebrook, models of the reactors at Bradwell, Sizewell A and Dungeness A are used to test new developments in outage technology. The engineers at Littlebrook work on a project from its conception, through its design, commissioning, construction, rehearsal to its eventual use on site. Roger Shead, a task engineer at BNFL Magnox Generation, has been involved with RolaTube developing the crane free delivery system from the project’s outset. The Rolatube system at the moment can only move vertically, and is therefore not suitable for replacing the traditional metal masts for complex operations involving sideways movement.
“Between the pile cap and the pressure vessel is reinforced concrete,” says Shead. “We work at the pile cap level, placing vertical masts with cameras into the reactor. We’re not at the moment looking to replace sideways movement systems with RolaTubes; for complex problems RolaTube is not yet applicable, but there is a lot of potential for development. We are working to develop a single lateral movement rather than multijointed systems.” The RolaTube composite in its ‘flat’ position can wrap around itself so that it forms a roll. The weight of a 17 metre length of the material is 27 kg. The crane-free delivery system that RolaTube Technology has developed and tested at Littlebrook consists of a drum around which the material rolls, a DC motor and a drive box. The drum is held within a frame 2.4 metres high and by a triangular base with sides of 1.7 metres. The total weight is less than 100 kg and it can fit inside a high-top van. The whole assembly can be moved on castors or on ball transfer units for precise positioning, by one person.
As the RolaTube rolls off the drum, it snaps into its tubular form. A special coupling has been designed to fit an inspection camera to the bottom of the RolaTube mast. All equipment entering a reactor requires an umbilical connection to provide electrical power and control signals to manipulate the camera once inside the reactor. As the RolaTube mast is extended into the reactor, the umbilical is enclosed within the tube, ensuring it is protected from contamination. The tensile strength of the tube is three tons; a safety margin of ten to one means loads of up to 300 kg can be easily delivered.
“It is a very nice way of working,” says Shead. “The pile cap crane is a critical path item. If we can get away from dependence on the crane there is the potential for greater flexibility and hopefully reduced costs.” “The key things it offers is portability, flexibility and serviceability,” says RolaTube Technology managing director Quentin Compton-Bishop. “It complements existing infrastructure, is easy to operate and requires fewer specialised people. It is designed to reduce the direct costs of an inspection and maintenance outage and therefore hits the bottom line of the station.
“We hope it will become a core piece of kit. At the moment it is very simple and can only move straight up and down. In the future we want to increase the inspection complexity by looking at sideways deployment.”
Developments past and future
The original developer of the bistable reeled composite was Rolatube’s technical director, Andrew Daton-Lovett. A client expressed the desire for a portable hand-held mechanism for extending sensors into ducts and other areas difficult to access. The idea for the structure came to Daton-Lovett from working with garden trellising. A materials expert, he worked with glass fibre and a basic polymer. The RolaTube composite is made from a polypropylene matrix and glass fibre, but carbon fibres and higher quality plastics can be used for work in harsher conditions.
In July 1998 the product was first used in a horizontal application at Hartlepool NPP for British Energy. The vertical rig, developed for BNFL Magnox Generation, was first put into action during an outage at the Bradwell power station in October 1998. It lowered a camera 12 metres into the reactor pressure vessel. According to Shead, the images from the camera were as good as would have been available using the traditional method and following the successful application at Bradwell at least three other nuclear power stations are considering using it during outages currently planned.
Compton-Bishop emphasises the potential for improved safety.
“Doing things faster and using fewer people provides an additional margin of safety,” he said.
Cleaning and decontaminating the composite after it has been inside a reactor is a relatively easy process. The smooth surface of the material prevents radioactive material from embedding itself within it and the nature of the material, made up largely from carbon, hydrogen, oxygen and nitrogen, means it is reactor compatible. The material does not contain neutron absorbers and does not contribute to corrosion.
Beyond remote inspection Compton-Bishop envisages a number of other applications for the composite. There is clearly potential for inspection of underwater pipelines and any other industrial situation in which access is limited, but Compton-Bishop is also considering its potential for remediation work.
“In the future we’re looking at waste handling,” he says. “For example in the States there are a number of sites where waste is stored in tanks and it needs to be removed. Currently a ‘ship-in-a-bottle’ technique is used to build removal equipment within a tank. Not only would this equipment be easier to construct, the plastic can be incinerated and it is therefore easier to dispose of once contaminated.”