The Use of Remotely Operated Vehicles (ROVs) in Nuclear Decommissioning
Initially, ROVs were developed to inspect torpedo tubes on nuclear submarines but were quickly adopted and developed for use in the offshore oil & gas industry to assist with exploration at deeper depths than those at which divers could operate safely. The original ROVs were purely observation vehicles, but over the years sophisticated manipulators, tooling packages, sonars and survey equipment have been developed to allow ROVs to carry out a multitude of underwater tasks.
Over 25 years ago, RSL started using ROVs in nuclear decommissioning projects and over that period the major changes have been in the usage of the vehicle, in that initially the ROV was used as an ‘eyeball’ to conduct visual surveys of many redundant and irradiated ponds and buildings within establishments built and used during the early 1950’s in the race for the atomic bomb.
Now site regulations and improved industry safety standards mean that both in-air and underwater ROVs are now regularly used in the nuclear industry to conduct visual and radiometric inspection surveys, take samples, demolish and size reduce contaminated structures, and remove equipment remotely to an area where it can be worked on or stored safely.
With the early ROVs, a problem specific to the nuclear industry became apparent in that the levels of radioactivity present in certain buildings and ponds affected the on-board electronics, thus making the vehicles unreliable. In order to rectify this, it was vitally important to keep to a minimum the amount of electronic components actually on board the vehicle, therefore most of the nuclear ROVs are controlled via a composite umbilical in which all of the controls and power supplies are hard wired directly to a surface control console.
On a swimmer ROV this umbilical presents its own set of problems with regard to snagging and entanglement on items on the pond floor. This problem was overcome by developing a floating umbilical which remains on the surface and enables the ROV pilot to navigate around structures without having to worry about the umbilical being trapped.
Perhaps the most important component of the ROV is the pilot. It takes hundreds of hours of flying experience to develop the spatial awareness necessary to fly the ROV within a confined area, as well as use sonar systems to aid navigation in bad visibility and help with obstacle avoidance, and then finally use the actual tooling/cameras at the work site that the ROV is the actual “taxi” for. It can therefore be seen that an ROV is a versatile tool, but they are only as good as the pilot operating them.
The range of equipment that is available as tooling packages include the following:
• High specification color zoom cameras;
• Obstacle avoidance scanning sonars;
• Multi-beam mapping sonars;
• USBL tracking systems, which give the GPS position of the ROV in the pond;
• Ultrasonic thickness measuring systems;
• 1,3,5 & 7 function hydraulic and electric manipulators;
• Cutters and shears;
• Coring & drilling equipment;
• Hydraulic power packs;
• Silt samplers;
• Silt removal systems; and
• Gamma Radiation probes.
Within the nuclear industry the gamma probe is an invaluable piece of equipment. The gamma probe is usually found in a fixed position within the pond, however attached to an ROV the Gamma Probe is able to monitor hot spots within a pond, which allows for constant, up-to-the-second response times from an operator. The added advantage for the gamma probe is that its payload is minimal.
Sonar Surveys are also being used more frequently. As the technology moves from being a simple 2D image to a sophisticated 3D image, the range of use has grown. Surveys can now visualize the whole of a pond and accurate estimates of amounts of silt, etc. can be estimated. Once a survey is complete, a full 3D, interactive model can be built and maneuvered through using any computer. Placing these two technologies side-by-side creates a highly detailed map from both a physical and a radiological point of view. This gives a real advantage to any operator/site licensee, as a map of work can be tailored to the exact needs.
One important aspect of in-water ROVs is the engineering design. When design engineers specify the equipment, they should have a thorough understanding of how the equipment will be used, and of the fact that it needs to be neutrally buoyant and powered via an umbilical. Size is a major consideration too, as ROVs will have limitations due to the environment in which they are used.
By designing for the specific task at hand, engineers can take the proper time to fully understand the problem being faced and the best strategy for accomplishing the job. This can be done with the use of 3D CAD software, which enables the engineer to theoretically prove the technology, confirm any prescribed restraints, and take a project forward with the full understanding of the client.
Perhaps the most important part of the program is testing the practical operation of the ROV and tooling package in simulated conditions to ensure that the pilot can do the actual task. Training and practice cannot be overemphasized.
The disadvantage of working within the nuclear decommissioning sector is that once a vehicle has been commissioned, designed and manufactured, it is then deployed into a radioactive environment from which it is never coming back (in most cases). The specifications of the contract need to be covered and the testing procedures detailed. Factory Acceptance Tests are mandatory as the client needs to witness all operations available on the vehicle. Once the vehicle is signed off on and deployed, both the client and the manufacturer must know that it will work.
One of the main problems found with using ROVs within the nuclear sector is the amount of personal protective equipment (PPE) that an operator must wear. If you are working within a restricted area, it may be that you have to wear three pairs of gloves, a full body suit and a respirator. This level of PPE makes small movement difficult as well as restricting the usable space on board an ROV. An engineer in a standard workshop can take the chance of placing his hands into small, confined and difficult-to-reach places and not worry about the possibility of a small cut. In the nuclear environment the possibility of contamination entering a small cut is a major problem.
With this in mind, any ROV being operated in the sector needs extra vigilance when it comes to items such as tie wraps or jubilee clips. Frequently maintained components must be free from any snags. Their position must be big enough for a hand with a tool to be inserted safely and with enough space for the operator to maintain the component; this can only be achieved during the design stage.
As previously mentioned, the advancement in remote technologies brings its own challenges. The client is now asking for more and more sophisticated tooling options, in smaller packages. ROVs are becoming multi-purpose vehicles with tooling being used on easily detachable and interchangeable skids. The tools must be designed and manufactured for use with an existing umbilical.
The advances in technology and sophistication of the electronics and hydraulics enable the operator to use the ROV as an extension of his/her own limb. With experience, the operator can achieve most results. There are many possibilities when it comes to tooling: manipulation of components, shearing of unwanted materials, wall cleaning, dredging, etc. Whatever the client can think of there is a possible solution which, with the right amount of skill sets, can be designed, manufactured and implemented.
With the use of computers and the general advancement in remote technology we will see many changes within the industry over the next few years. Tooling options will grow and various nuclear establishments must share information and technology on specific operations to save re-inventing the wheel, which often happens now.
However, two things will remain a constant: the need for ROV manufacturers to continue designing low-tech simple solutions, and the need for good ROV pilots.
Rovtech Systems Limited is a British manufacturing, operating and testing company with nearly 30 years of experience in both the offshore and nuclear markets. To learn more, visit www.rovtechsystems.co.uk/.Tags: demolition, Market, ROVs, site decommissioning