Nuclear Decontamination
In nuclear facilities, laser cleaning helps decontaminate surfaces and remove radioactive contaminants safely.
One of the biggest challenges when working in the nuclear industry, is getting rid of nuclear waste. Nuclear waste is very dangerous and expensive. It's obvious that reducing nuclear waste can reduce the costs radically, and laser cleaning can be the solution in this case. When a nuclear system has to be disassembled, radioactivity can be found everywhere: in the walls, the steel structures, devices, etc. Laser cleaning can reduce the radioactivity in for example steel structers to up to 70%, because almost all of the radioactivity is located in the top layer of the structure. Same story goes for concrete walls or lead beams, laser cleaning reduces the radioactive values drastically. Another huge advantage is the lack of waste that is introduced during the cleaning operation. Traditional methods create a lot of 'cleaning waste', while laser cleaning only creates a radioactive dust, that can be captured and isolated very easily.
Removal of uranium compound particles such as uranyl nitrate (UO2(NO3)2 6H2O) and uranium dioxide (UO2) on surfaces in the nuclear industry is of utmost importance. Metal canisters in hot cell complexes and instrumentation in nuclear fuel production need to be cleaned off from these particles. Potential applications exists in Pebble Bed Modular Reactors (PBMR). Uranyl nitrate is the basic feed material for PBMR fuel production and uranium dioxide is the fissionable material of the fuel element kernels.
The issue of cleaning uranium particles metal canisters remains a common issue for all types of nuclear reactors.
Loose uranium compounds are much easier to remove as a form of contamination as compared to the contamination that has penetrated into the oxide layers of metal surfaces in a nuclear reactor. However, loose contamination is dangerous because firstly, it can be inhaled by a person and secondly it can be carried by footwear or clothing to another location outside of the restricted areas. Once these particles are inside the body, they pose a radiation hazard and as well as they are considered toxic.
There are many different methods of cleaning these loose particles such as chemical cleaning or water jetting. However, the addition of chemicals or water implies dealing with the secondary waste that is generated. The secondary waste is radioactive and needs to be properly disposed of. This adds to cost of using these cleaning methods and improper disposal of secondary waste could create health hazards or contaminate water supplies.
An alternative method is laser cleaning where a pulsed laser ablates the surface and removed the particles. This method is a dry process and removes all the contamination without the use of a secondary medium (such as water or chemicals). The particles are removed using an extraction system which contains a disposable dry filter such as HEPA filter (Reference 1).
As far as the choice of the laser is concerned, both the surface layer removal and Dry Laser Cleaning (DLC) are more efficient at shorter wavelengths such as in the visible region which could reduce the substrate damage. However, the choice of the laser is dictated by the over all efficiency of cleaning large areas which dictates the use of either a Q-switched Nd:YAG laser at the fundamental wavelength of 1064 nm, or an industry grade pulsed fiber laser.