Laser ablation systems designed for cleaning, stripping and decontamination can save the nuclear industry time and minimize costs. By Timothee Niemeier
High-powered laser ablation systems designed for industrial decontamination applications have proven effective at nuclear sites around the world. The Chernobyl and Fukushima disaster sites have successfully evaluated this technology to improve worker safety and effectively eliminate radiation.
The systems have come a long way since 2006, when the Electric Power Research Institute (EPRI) documented the successful testing of laser ablation to remove radioactive coatings, surface contaminants and oxides in power plant applications. . Today, these industrial laser systems are commercially available, powerful and ready to use to support the global nuclear industry, in power generation as well as military and medical applications. They have features designed to maximize the benefits of a unique method that uses only focused light to rapidly remove the fixed low level contamination of 80% of metallic nuclear waste that only has surface contamination.
Why process improvements are needed
Common processes used to remove low level contamination include sand blasting, wet blasting, CO2 granular blasting, chemical cleaning and power tool grinding. Although these methods can be effective, they generally produce a large volume of mixed hazardous waste which is difficult and time-consuming to collect, with a high disposal cost.
Operator safety is another important concern with traditional methods. Concerns are excessive dose rates, repetitive stress, risk of serious injury, excessive noise, and inhalation of hazardous airborne contaminants.
Abrasive blasting and CO2 blasting are generally not suitable for use near other operations. During installation, operation, and cleanup, plant operations personnel have limited access to work areas.
Abrasive blasting may damage adjacent surfaces and may remove excess base metal. Often, expensive custom tooling becomes unusable due to the lack of safe and damage-free decontamination technologies. These processes based on abrasive media are time consuming and expensive due to the large amounts of hazardous waste that must be contained, collected and disposed of.
While traditional decontamination methods can be helpful, commercially available laser light-based processes have been tested and proven to be a cost-effective solution for a growing number of nuclear sites and industrial service providers worldwide. .
What is Advanced Laser Ablation?
Laser ablation is a non-abrasive cleaning method that uses no consumables, chemicals or gases. It can be used near other activities, near sensitive controls, and on or near operating equipment.
Typical systems consist of a handheld laser source with a fiber optic bundle transmitted to a handheld or robot-mounted laser effector. The ablated materials are collected at the target surface by a laser smoke extractor, with multi-stage filtering, thus preventing release.
The capabilities and benefits of laser ablation include:
- Removal of contaminated coatings, oxides and rust and hydrocarbons
- Significant minimization of the volume of radioactive waste
- Radwaste reduced to less expensive waste disposal classification
- Reduced dose risk from potential sources of contamination
- Recovery of expensive tools
- Recycling precious metals that would otherwise be expensive radioactive waste
- Painting of critical weld beads for CND
Case Study: Using Lasers to Decontaminate Dump Trucks
In Oak Ridge, Tennessee, laser ablation has proven to be effective in reducing downtime, worker stress, and radioactive waste. The request involved the decontamination of carbon steel from large dump trucks used to transport contaminated materials from sites around the K-25 decommissioning at Oak Ridge. The contamination included various isotopes, primarily U-238. The contaminants were largely beta emitters, found in conjunction with low alpha contamination.
The tests were carried out by Adapt Laser and Philotechnics Ltd, which processes and transports radioactive waste. The latter provides radioactive and mixed waste management solutions, including decontamination and decommissioning services, augmentation of health radiation physics personnel, development of health and safety plans and qualification training radiological. Adapt and Philotechnics worked together to prove that laser ablation is a viable source for removing radiological contamination with potential time savings.
The current decontamination method involved manual grinding of the contaminated metal using large, heavy hand-held power tools. This process took 200 man hours and two technicians to complete a unique dump truck bed. The laser ablation process took just 7% of that time – one technician for four hours – to achieve similar results.
Other materials have also been laser ablated. These were contaminated lead objects from various locations around the country, all contaminated with Alpha (specifically radium). Lead sheets, lead bricks, lead “pigs” and even lead-lined gloves were decontaminated 100% effectively in seconds with only one or two passes under the laser beam.
During these tests, continuous air found no detectable airborne radiological contaminants or migration of contaminants to personnel or laser equipment.
Pre-testing and post-testing of contaminated surfaces revealed 100% effectiveness in removing alpha contamination and a significant reduction in beta particles. Areas with denser beta particles embedded deep in the base metal were not as easily removed by the laser, which does not damage the surface.
Ultimately, the greatest success of the laser came from its overall efficiency and a 93% time saving compared to the manual grinding method. It’s no surprise that technicians loved using the laser process over the stressful hours of grinding.
Study: decontamination of equipment by laser ablation
In a recent study conducted by Hi Tech Solutions and Reactor Services Inc, radiation decontamination by laser ablation was thoroughly tested over several weeks. The applications consisted of an aluminum intermodal container cover, a painted and raw steel intermodal container and a flexible steam turbine housing section, all with fixed contamination.
The surface of each component was probed and delineated to identify contaminated areas to measure contamination levels before and after laser ablation.
The aluminum lid of the intermodal container had already been chemically decontaminated. After that, and two days of power tool grinding, he retained fixed contamination that could not be removed.
After scanning the laser beam, the concentration of beta particles was reduced by an average of 79%. Fixed alpha contamination at up to 119 counts per minute was cleared from each contaminated area in less than a minute, allowing free release.
Contamination that could not be removed with conventional cleaning and grinding was removed from the lid by laser ablation in less than an hour.
The reduction of alpha and beta particles was measured after each pass of the scanned laser beam. Alpha particle measurements taken from the bare, painted steel intermodal container were on average 91% lower after a laser beam scan. In each case, a secondary beam pass eliminated nearly all detectable levels of contamination.
Decontamination by laser ablation
Adapt Laser has worked with partners including CleanLASER to develop its laser systems. The cleanDECONT CL1000 and CL2000 portable laser ablation systems use a high power Nd:YAG laser source. During operation, the laser source is protected by placing it in a clean location outside the radiologically controlled area.
In the process, handheld or robot-mounted laser optics are used to move an intense, focused, pulsed laser beam across the target surface. The end effector and fiber optic umbilical, up to 100m away, are packaged to keep clean and prevent contamination.
The laser vaporizes organic coatings, rust or oxides and hydrocarbons – which normally contain fixed, non-fouling radiological contaminants. Vaporized residue is collected immediately after ablation by a powerful point vacuum system that captures process residue. They go through multi-stage filtration to get rid of particulates and fumes, preventing dangerous airborne contaminants and minimizing cleanup.
Laser surface preparation by a mobile robot is another option.
Recent system enhancements and new features include:
- Laser ablation integrated with laser-induced pattern spectroscopy, a process control to analyze target surfaces before and immediately after laser cleaning to verify the absence of unwanted residues
- A simple way for end users to decouple and swap fiber optic cables
- Nuclear-grade glove box to safely decontaminate small parts
- Gantry-based robotic work cells for processing large parts inside a class 1 laser safety enclosure
Laser ablation decontamination will become more efficient in the future through automation, robotics and AI.
About the Author
Timothy Niemeier is Vice President of Adapt Laser Systems