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Use of Tank Waste Retrieval Remote Manipulator Systems in Nuclear Cleanup

Submitted by on November 20, 2011 – 12:45 pm

Retrieval and processing of legacy nuclear waste is a top priority of government agencies throughout the world. Millions of gallons of this legacy waste are contained in waste storage tanks. Reducing the environmental risks associated with these tanks requires either the removal of the contained waste for processing or transfer to other containments for secure interim storage.

As it stands today, the methods and processes used to remove bulk nuclear waste from waste tanks are well understood, and have been implemented at many nuclear facilities around the world. However, after the bulk volume of the waste is removed from accessible tanks, a significant amount of residual highly radioactive waste can remain leading to additional issues.

This dilemma presents a significant waste removal problem for numerous sites for a large variety of reasons, among which two issues have become prominent: (1) obstructions to tank access, and (2) waste forms which are varied and complex in constituents.

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BELOW: Operating the RDA waste retrieval manipulator from a remote control console TOP RIGHT & MIDDLE: Illustration of compact deployment sequence for manipulator used in restrictive plant rooms RIGHT: RDA performing vacuuming activities during factory acceptance testing

Challenges of Tank Waste Retrieval

Storage tanks with access obstructions encompass a myriad of installation or operation interferences including: plant equipment interferences, in-tank obstructions, overhead lifting limitations, access door sizes, floor loading, tank penetration size and location, and tank size and geometry. Complicating matters even further, the presence and project impact of each of these obstacles varies not only from site to site, but also from tank to tank. The space restrictions resulting from these tank access obstructions, and the lack of commonality between waste tanks, contributes greatly to the difficult deployment of equipment for final tank waste retrieval.

Another challenge for final waste removal is that much of the legacy waste currently remaining in nuclear material storage tanks is not homogeneous. Various fluid and solid waste forms are often present within a single tank, and the presence of varying waste forms requires a versatile and fit-for-purpose solution when dealing with tank waste. Differing waste forms require separate means of retrieval in the form of new tools or systems, each with added complexity and costs.

For those decommissioning sites with obstructions to waste tank access, the decision-making process must initially consider whether to perform site or tank modifications to allow installation of basic retrieval systems, or to procure and install a more advanced retrieval system to reduce or remove the requirement for site/tank modifications. This key decision must be made early on in the project lifecycle, as it can significantly alter the immediate focus of a project. Unfortunately, this decision is not always straightforward, and may not be the same for all tanks requiring final waste removal. Depending on the tank in question, modifying the existing structure of the tank or its surroundings can allow for ease of equipment access; however these modification activities are often time-consuming, costly or introduce additional hazards.

In many nuclear facilities poised for decommissioning, issues such as proper containment and structural concerns quickly increase the size and scope of modifying the existing civil structure. Additionally, in some instances, modification to the existing plant structures is not possible due to the operating equipment in the surroundings which must remain intact. These are just a few of the issues that can make tank waste retrieval and processing a difficult problem to be solved.

Examples of tools that  will be deployed with  the Rotary Deployment Arm System:  Vacuum Tool Petal Grab Jet Wash Scoops Scrapers Grubber Rake

Examples of tools that will be deployed with the Rotary Deployment Arm System: Vacuum Tool, Petal Grab, Jet Wash, Scoops, Scrapers, Grubber Rake

A Solution Emerges in Remote Manipulators

In recent years, advanced waste retrieval systems have been proven to be advantageous in that they can often be designed and built to work within the existing facility constraints. With these systems, modifications to the facility are often very minimal, if required at all. One type of advanced waste retrieval system that has seen increased visibility and usage for these types of waste problems is the use of remote manipulators. There are a number of off-the-shelf manipulators available in the marketplace, however the capabilities and versatility of a multidimensional tank retrieval manipulator system offer many advantages.

Advantages of Multidimensional Tank Retrieval Manipulator Systems

These advanced systems allow personnel to manipulate and utilize tools within a hazardous environment from a remote location via cameras and virtual feedback systems. Specifically, manipulator system technology combines the form factor and versatility required for successful deployment and operations for tank waste retrieval.

The latest waste retrieval manipulator systems have been designed to be easily moved from tank to tank, through existing plant rooms and doors, and to accommodate a multitude of plant room constraints including limited head room, access in and out of doorways, existing equipment, and penetration locations. The ability for these systems to be installed and operate in extremely tight quarters without impacting the infrastructure is very advantageous when considering the cost, scope and safety concerns associated with modifying existing tank structures.

Until recent years, most manipulator deployments have required heavy machinery and open areas to operate and install the equipment. With advances in composite structural materials and micro-hydraulic systems, similar systems can be pushed through small doorways and around obstructions that would otherwise prevent a remote manipulator installation or deployment.

In addition to advantages in installation and deployment, waste retrieval manipulator systems are extremely versatile in operation. These systems are capable of deploying a multitude of tools to remove tank waste. The flexibility of tool deployment in a tank retrieval manipulator system is invaluable for removing non-homogeneous waste, and is much more efficient and cost effective than the use of a number of separate systems to complete various operations. Waste retrieval manipulator control and visualization options are also widely customizable, and can be suited to the needs of a specific tank or group of tanks. For example, manipulator control systems can include a full three-dimensional visual model of the deployed system on the interface screen to allow operators to instantly understand the configuration of the manipulator relative to the surrounding environment. This is extremely advantageous in applications with reduced visibility such as waste tanks flooded with water. In these applications the water is normally very opaque due to the entrained waste particles. All of these capabilities turn a seemingly impossible and expensive project into one that can be feasible and affordable.

RIGHT:  Inside the plant room during installation of the RDA at Magnox’s Trawsfynydd nuclear site in North Wales.

RIGHT: Inside the plant room during installation of the RDA at Magnox’s Trawsfynydd nuclear site in North Wales.

Design and Build of the Rotary Deployment Arm

An example of successfully deploying this technology can be seen at the Trawsfynydd nuclear power station in North Wales, UK. Over the past two years, S.A. Technology has been working in partnership with EnergySolutions-owned Magnox Ltd and ACTUS to design and build two long reach manipulators for retrieval of waste from three separate storage tanks.

The ‘Rotary Deployment Arm’ (RDA1 and RDA2) is a highly capable and versatile solution for the site’s tank cleaning dilemma. The RDA is designed to complete a variety of cleanup tasks within four main areas on site including the Resin Vaults (RV2 and RV3), Main Sludge Vault (MSV), and Pond North Void (PNV). These tanks have different size and technical constraints making it difficult to design a single solution that could meet each of the tank’s requirements.

The RDA is capable of being deployed through penetrations of 10 inches and larger in diameter; has a vertical reach of 32 feet; and a horizontal reach of 15 feet when fully extended. The RDA consists of mast and forearm assemblies, which are constructed from carbon fiber and stainless steel components, as well as electromechanical and hydraulic components to provide actuation. These mast and forearm assemblies reside inside the tanks during operations.

At the plant room floor level, the RDA is mounted inside a stationary support frame, which allows the RDA to be deployed into and retrieved from the various tanks, and provides cable management for the variety of required services. The RDA support frame also provides containment for operation, wash down capability for contamination control, and wheeled transportation. The frame itself is mounted to each of the plant room floors during operations. In its retrieved state, the RDA fits completely within the support frame, which is about the size of a large refrigerator. The RDA system includes a hydraulic power unit, electrical enclosure and integrated control system to provide motive power and control. Tooling for the system is designed to meet a variety of operational requirements for each tank and void.

Simplifying the Process and Maintaining Safety

The nuclear environment presents many risks and thus a safe working environment is always paramount. In an attempt to mitigate risk and maintain safety, new and custom equipment is cautiously used in nuclear decommissioning activities. The nuclear industry has begun to embrace remote manipulators as a viable solution to previously difficult decommissioning projects. While nuclear site decommissioning remains challenging, new technologies and methods continue to simplify the decommissioning process, and worker safety continues to be improved by the use of remotely operated systems.

Examples like the RDA offer many benefits by providing a highly capable and versatile solution for very difficult tank retrieval problems throughout the nuclear industry. Using remote manipulator technologies will help make the future of decommissioning facilities safer, more reliable, quicker and economical.

 

About the Authors:

Scott Martin has been employed as a design/project engineer at S.A. Technology in Loveland, Colorado, U.S. for almost 10 years. During this time, he has been involved with the design, manufacture and deployment of numerous bespoke manipulator designs for hazardous environment applications throughout the world. In his current position as a Senior Project Engineer, Martin is in charge of engineering direction for various projects in the U.S. and Great Britain. Prior to his employment at S.A. Technology, Scott received a bachelor’s degree in Mechanical Engineering from Colorado State University.

 

Marc Rood is Vice President Business Development manager at S.A. Technology. He has successfully managed some of S.A. Technology’s most technically intensive robotics projects including but not limited to the Powered Remote Manipulator (PRM) and Rotary Deployment Arm (RDA). Rood has also helped pursue several opportunities in the U.S., UK and China markets as a business development manager for the company. Rood has a BS in Civil Engineering from the Colorado School of Mines, recently completed his MBA in marketing from Regis University, and is an accredited Project Management Professional.