It is no secret that some products of nuclear fission are extremely radioactive. Treating this waste is therefore one of the biggest challenges in creating a sustainable nuclear industry. Radioactive products of fission include plutonium (the most common) and other minor actinides such as neptunium, americium and curium, which we find in quantities of around 800 grams per ton of spent fuel. Currently, waste products from nuclear fission must be securely stored for extremely long periods of time because of their protracted half-lives (the time for their radioactivity to drop by half). Plutonium-239, for example, has a half-life of around 24,000 years.
NuClear Decontamination
RADIOLOGICALLY PROVEN and efficient dry process
With our new PhotonClean, nuclear contaminations with rates of 99.6 % and more for α and particularly high factors for β and γ radiation can be removed. The homogenized blasting technology makes it possible to gently clean all common geometries and metal materials below the degradation threshold for reuse or recycling.
The process can thus be used economically and in an environmentally friendly manner for both decommissioning and maintenance work on running nuclear power plants. Cleaning using laser light as a dry process replaces the chemical wet and the mechanical blasting process.
ADVANTAGES
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- Decontamination rates of 99.6 % and more
- High decontamination area rates with > 15 m²/h for slightly adhering contaminations (rust, oxides) and > 8 m²/h for solid contamination (hot area, paint)
- Enormous reduction of hazardous and expensive secondary waste (further development of extraction systems)
- Flexible technology configurations in mobile or stationary control cabinets, hand-held and/or automated optics, up to 50 m fiber tube package
- Negligible influence on base material allows reuse of decontaminated devices/products (hardness, tensile and macro tests successful)
- Prevention of the spread of impurities (corrosion infiltration tests successful)
PhotonClean: Efficient decommissioning of nuclear power plants
Minimizing costs thanks to the latest generation of Lasermach Laser cleaning technology
The increasing scale of dismantling of nuclear power plants in Europe and worldwide, leads to massively rising costs. The conditioning and final storage of radioactive waste and secondary residues produced by conventional decontamination processes amount up to 13,000 tons per reactor. The final disposal site in particular poses an enormous problem for the companies in charge of dismantling as well as for the population.
Abrasive processes involving chemicals and blasting processes generate large amounts of secondary waste, are complex in their implementation and imply significant health risks for decontamination personnel.
Our most recent generation of our power laser cleaning systems has been specially designed for the efficient deconstruction. The high intensity of the laser beam enables decontamination of low to medium level of surface contamination of metals and concrete structures up to release level. The laser decomposes a high dose rate within seconds, removes oxides, paints, greases and other coatings down to bare, clean metal while producing a secondary waste of just a few grams per square meter.
Decontamination costs as low as only a few cents per kilogram
The process is media-free and thus free of recontamination, causes no mechanical stress to workers, is fast to implement, and requires no pre-treatment. It is a s sustainable and efficient alternative to previous processes.
Laser decontamination in the nuclear industry
Water cooled nuclear reactors that use the fission process for creating electricity need to be decommissioned after 30 to 40 years for safety purposes. During the decommissioning process, two targets have to be achieved. First the, recyclable metal that has been contaminated needs to be cleaned off from radioactive contamination so that it can be recycled for the next generation nuclear reactors. Secondly disposable material such as concrete needs to be cleaned off so it can be transferred to temporary repositories and later to be transferred to permanent geological repositories.
Although in nuclear industry, chemical cleaning methods are often used for decontamination and metal component cleaning, it would result in metal surface damage and decrease in corrosion resistance. Creation of a huge amount of secondary waste is another disadvantage of using chemical cleaning methods which makes use of alternative greener methods of cleaning a reasonable and an attractive option.
Corrosion products are released from the main structure, get radioactively contaminated and are deposited into oxide lasers of recirculation pipes; As years go by, the dosage of contamination increases and therefore during the decommissioning, the recirculation pipes which are the main source of contamination need to be dismantled and cleaned. The main cause of pollution is cobalt 60 which gets deposited in the oxide layer of recirculation pipes. We can describe the process of formation of the oxide layer in more detail as follows: Under the action of high temperature, high pressure and presence of water, the more soluble alloying element, i.e. iron (Fe) gets dissolved into primary coolant and forms an oxide layer which gets deposited on the outer surface of the pipes. This oxide layer is mostly made of hematite and magnetite and removing it using a method such as chemical cleaning would substantially reduce the contamination.
The same can be said about dry ice blasting as a decontamination technique with the difference that the ice pellets evaporate immediately and turn into CO2 gas which is a global warming gas and is therefore damaging to the environment.
In general, the current techniques and most common methods of decontamination of nuclear power plants are:
- Wiping, dusting and flushing with water
- Grit blasting
- Dry ice blasting
- Chemical cleaning
- Decontamination by gel and foam
The main drawback of these methods are secondary radioactive waste that is generated and needs to be dealt with. In particular grit blasting process where sand particles are ejected from a high pressure nozzle can create a lot of secondary pollution and can also damage the structure or reduce the corrosion resistance.
An alternative most efficient method of cleaning is laser cleaning. Fiber pulsed laser of few hundred watt power and nanosecond pulse width with repetition rates of few hundred kHz have been used to blast off the nuclear decontamination from pipes, metal tools and concrete blocks. The great advantages of laser cleaning are:
- It is a process that can be automatized, so it increases cleaning speed
- There is no secondary waste since all the debris are absorbed by a suction pump equipped with Hepa filter. So it is cleaner for the environment
- Remote handling is possible so there is less exposure to workers.
If one wants to mention a few disadvantage of laser cleaning, it would be the need to focus the beam and also the speed of operation which could be slower than sandblasting for example. However, the absence of secondary waste and possibility of automation and auto-focusing that makes the speed faster, outweighs these disadvantages and makes laser cleaning the method of choice for future cleaning.