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Modernizing Liquid Waste Processing

The nuclear sector puts a new spin on a pharmaceutical tool.

We live in a world where we are continually driven to increase efficiency while lowering costs — to do more with less. The nuclear industry is no different. Developing innovative techniques or adapting creative ideas found in other industries can support that pursuit of cost reduction and, in this case, also waste reduction, while providing operational safety. Such actions build confidence in our industry and allow nuclear power to continue to be part of the narrative of our clean-energy future.

It goes without saying that the nuclear fuel cycle produces a variety of liquid wastes. The nature of each effluent determines if it will be stored on-site in an approved containment, or processed and then discharged. There are several well-established techniques to tackle such liquid wastes, one being the fixed-column ion-exchange system. The process of ion exchange employs beads of ion-exchange media (resins) that exchange harmful contaminant ions in the liquid with harmless ions. This is done with a bed of ion-exchange media enclosed in a fixed cartridge or column, similar to residential water purification cartridges. Deployment of this technology has had significant operational success, but it also has its challenges, including:

  1. ineffective use of ion-exchange media,
  2. inability to process different liquids with significantly different matrices
  3. channelling/wall effects, and
  4. footprint of equipment required to be installed.

Out-of-the-box thinking has taken a non-nuclear solution to decontaminate liquids and introduced it to the nuclear industry: A series of successful tests using rotating bed reactor (RBR) — a patented technique called Spinionic™ — took place in several nuclear industrial environments. The technology proved to remove radioactive or other undesired elements from wastewater or other fluids while increasing the efficiency of the clean-up process through the better use of media and a streamlined process.

The RBR was developed by the Swedish technology company SpinChem AB and was first successfully deployed as a research tool in the pharmaceutical industry, which sought to improve the chemical processing of liquids. For a similar need, the Canadian company AtkinsRéalis partnered with SpinChem to develop the RBR system for deployment in nuclear environments.

The RBR technology works differently from a traditional column system where the media is packed into a cylinder. In columns, the fluid is pumped through while the media gradually removes impurities and the treated fluid stream exits the column the other end. A variety of columns, implemented sequentially, might be needed to treat for different impurities. This owes to the circumstance, that most columns usually only hold one type of media, depending on particle size and mechanical stability.

In contrast, an RBR, with its multiple compartments, can hold media of different particle sizes and characteristics, thereby treating more than one type of impurity at a given time. Also, the RBR can be loaded with any media a column unit uses, in addition to media that cannot be used in columns due to mechanical stability. A common problem in column treatment is the inefficiency of the packed bed and the use of all the material in an imperfectly packed column. The pressurized flow takes the path of least resistance and creates a problem that is normally referred to as channeling (or, if the least resistant path is close to the wall, "wall effects"). Such limitations are avoided when using RBR because the principles applied to creating flow through the packed media are different.

 

Fig. 1. Working principle of the Spinionic™ rotating bed reactor.

Explanation of the Rotating Bed Reactor

The RBR is a cylinder packed with media that is restrained by a robust mesh. When used to treat liquid waste, it spins rapidly in the liquid to aspirate it through the bottom of the stirrer and percolates it through the media. In this way it allows the RBR to act as a pump and ensures that all liquid is treated. Because of its simplicity, the media held by the RBR can be deployed directly into the containment structure holding the liquid waste. With the addition of minimal external equipment, cleanup can occur in situ. In doing so, it offers the following key benefits:

  • Greatly simplified installation, reducing human interaction with ionizing radiation and enhancing safety by reducing worker exposure to radiation.
  • When mounted to the container/tank opening or suspended into open containments, the RBR can run in situ for hours to days or weeks, as required, without operator intervention.
  • No hoses, pumps, filters, ion-exchange columns, or associated shielding are required.
  • Limited equipment is required; installation and demobilization can be done in less than a day, saving plant support and associated costs.
  • More effective media utilization means less waste is generated.

The RBR makes it possible to minimize slow-reaction kinetics caused by poor mass transfer between the fluid and solid phase. The Spinionic™ design is flexible and can be used for numerous applications in situ to treat tanks of radioactive waste, or in-process to treat continuous waste streams.

The RBR design allows multiple ion-exchange materials, selectively targeting multiple isotopes, to be used in parallel within a single reaction process, giving it the ability to remove multiple radioactive ions from the waste stream. Species in equilibrium, such as iodide and iodate in an aqueous solution, can be removed simultaneously by using two different ion-exchange media in the RBR compartments.

Using the RBR typically results in faster processes, higher decontamination factors, and/or reduced generation of secondary waste, depending on the type of process used. In addition, the RBR extends the lifetime of the solid-phase particles by minimizing grinding and attrition, while at the same time simplifying the solid-phase collection and recycling or disposal.

Spinionic™ may be used as the sole process method or used as a pretreatment upstream of installed equipment to remove impurities that may cause harm and potentially result in larger volumes of waste generation and extended system downtime. It can also be used as a polisher downstream of existing equipment. Ultimately, it has the potential to replace or protect large mobile or in-plant column-based ion-exchange or membrane systems.

 

Applications include:

  • Scavenging of oil and grease using activated granular carbon.
  • Rremoval of a wide range of ions with standard anion and cation exchanger.
  • Isotope-specific removal with ion-specific media.
  • Removal of activity from chemically tainted solutions with elevated levels of acid or basic solutions.
  • Process-contained solutions or spills that do not have an existing pathway to process equipment.
  • Preconditioning solutions prior to plant equipment.

From pharmaceutical industry to nuclear industry

The RBR technology originated as a protection aid for a solid-phase catalyst in pharmaceutical applications. The catalyst was made of palladium-soaked ion-exchange beads. Problems, however, arose with conventional stirring techniques in batch reactors in which the beads were damaged. This led to the exploration of a solution to mechanically protect the beads, with the first result involving the use of plastic tubing and magnets, ultimately culminating in the use of more sophisticated tools. The desire to create flow through packed media beds was the driving force throughout the development. First applications were small-volume screenings for catalysts, adsorbents, and ion-exchangers, eventually expanding to larger volume applications in the thousands of liters.

RBR technology was then used in research and development applications in the pharmaceutical, cosmetics, and food industries to either modify an active ingredient molecule to add new functionalities or to change its properties. Immobilized enzymes, so-called biocatalysts, have been the most commonly used solid-phase material in the RBR, as it allows to effectively use proteins to modify functional groups of complex molecules in fewer steps compared to classical synthetic chemistry. Using immobilized enzymes saves time and money while new synthetic routes are made possible.

Other applications evolved to remove unwanted by-products or metal residues that are prohibited in final products. Especially in the downstream processing and treatment of industrial wastewater it was that the RBR showed its strength in processing large liquid volumes compared with conventional technologies. Such applications were in line with the removal of radioactive isotopes in the nuclear industry, leading to nuclear waste management applications.

Over the years, AtkinsRéalis has developed and deployed a number of approaches to the application of ion-exchange processes to radioactive liquid wastes. These included submersible ion-exchange columns, magnetic ion-exchange particles, and seeding with powdered ion exchange for subsequent removal by cross-flow filtration. The company worked to nuclearize the SpinChem RBR and, working closely with SpinChem, initial prototypes were readily realized and demonstrated.

Preparation and deployment

Liquid waste is sampled to determine the best media for the desired removal. Testing and computational fluid dynamics (CFD) computer modeling help determine the RBR size to deploy and operational parameters to use. The selected media are loaded into the RBR compartments either separated or mixed. The RBR assembly is submerged into the fluid, and the drive motor is engaged at the desired speed. As the RBR spins, a continuously circulating flow develops inside the tank or vessel.

The fluid inside the RBR is thrown out through the outer wall retention screen by centrifugal force, and new fluid is pulled into the top and bottom openings (Fig. 1). The fluid is then efficiently passed through the media-loaded annulus. There is continuous circulation through the RBR while it mixes the tank. There are several different ways of deploying the Spinionic™ technique — in batch or continuous mode — depending on the specific requirements.

Real-life applications in 2020

Historically, in terms of schedule and cost, introducing a new technology into the nuclear fuel cycle has been challenging due to the highly regulated environment. But as the industry recognizes these challenges, the door is now open to new ideas that could offer unseen efficiencies and cost reductions while still meeting stringent nuclear regulations. In 2020, Spinionic™ was implemented in nuclear environments on three different continents for three different nuclear applications.

 

North America

At an operational nuclear station contaminated water was stored in a purpose-built vessel. Due to the chemical composition of the water, it could not be processed via the plant’s on-site treatment facility. A number of lab trials showed that Spinionic™ could be deployed to remove the impurities. As the configuration and location of the tank access were restrictive, the Spinionic™ deployment was customized in such a way that it can could be operated through the existing opening in the vessel. The deployment rig was designed in a modular fashion to minimize the working time of operators. The Spinionic™ technology allows to use media that targets the specific contaminants and processes the wastewater in-situ. Full deployment scheduled for first quarter of 2020.

 

Europe

A fuel pond at a research facility entered the decommissioning phase of its life cycle. Due to the nature of the work in the facility, there are significant levels of radioactivity in the area, which hamper operations required to decommission the facility. One of the radioactive sources within the facility is the fuel pond water. Spinionic™ is to be deployed in the pond through existing penetrations in the concrete structure, allowing the operator to manage the radiation levels within the facility and accelerate decommissioning activities. While laboratory-scale trials identified the best treatment media, full-scale deployment is scheduled for 2020.

 

Asia

Here, a nuclear power station is undergoing decommissioning and has been processing a significant amount of contaminated water. The on-site treatment facility has successfully removed many impurities, but in some cases, trace quantities of residual radionuclides remain. This has left a large quantity of water stored on-site for either further processing or another strategy for safe disposition. Spinionic™ technology has demonstrated a high degree of efficiency in removing trace quantities of radionuclide contaminants and is therefore well suited for this task. To facilitate Spinionic™ deployment, a modular system that can be deployed directly into the storage tanks has been developed. Currently, full-scale efficacy evaluations of Spinionic™ are underway.

 

Volumes and Sizes

The RBR can range in size from less than one liter to over 100 liters of media capacity depending on the application (drums, totes, large tanks (>2,000 m3) ponds, fuel pools, sumps, or large-area basins). The system’s equipment, frame, and drive motor are designed to fit container openings or tank manways (Fig. 2). Larger deployments, such as open basins, sumps, and pools, may require more than one RBR to adequately circulate the solution. The only service required for operational support is electrical power, depending on solution/tank size, deployment equipment and motor size.

To accelerate the deployment of RBR technology, AtkinsRéalis and SpinChem have fully funded a five-year plan with the aim of further maturing Spinionic™ to develop a range of products to address the various challenges of treating liquid waste. Cost-effective management of nuclear waste continues to be important in ensuring that nuclear power remains a viable choice and a key contributor to the energy mix for future generations.

 

Fig. 2. A detailed design showing the in-tank RBR deployment.