Nuclear entombment (also referred to as "safe enclosure") is a method of nuclear decommissioning in which radioactive contaminants are encased in a structurally long-lived material, such as concrete. This prevents radioactive material and other contaminated substances from being exposed to human activity and the environment. Entombment is usually applied to nuclear reactors, but also some nuclear test sites. Nuclear entombment is the least used of three methods for decommissioning nuclear power plants, the others being dismantling and deferred dismantling (also known as "safe storage"). The use of nuclear entombment is more practical for larger nuclear power plants that are in need of both long and short term burials, as well as for power plants which seek to terminate their facility licenses. Entombment is used on a case by case basis because of its major commitment with years of surveillance and complexity until the radioactivity is no longer a major concern, permitting decommissioning and ultimate unrestricted release of the property. Considerations such as financial backing and the availability of technical know-how are also major factors.
Preparation
The first step is to cease operations and stow any spent fuel or waste. Nuclear reactors produce high-level waste in the form of spent nuclear fuel, which continues to release decay heat due to its powerful radioactivity. Storing this waste underwater in a spent fuel pool prevents damage and safely absorbs the radiation. Over a period of years the radioactivity and heat generation declines, until the spent fuel can be removed from the water and stored in casks for burial. When a reactor is decommissioned, partially spent fuel can be treated the same way. The reactor is sealed in order to allow no escape of radioactive particles or gases. Lastly the heating water is then pumped out and put in containers to await proper decontamination. Decontamination is the process of removal of radioactive contaminants on the remaining surface. Washing and mechanical cleaning are processed during the decontamination process by using the chemical reactors, and the global objective is to protect public safety and the environment. The coolant is also removed and stored for proper disposal. This procedure is often performed by the company that owns the plant, and if the company is unable to then properly qualified contractors are brought in. After this procedure comes the next one which deals with the radioactivity and radioactive waste.
The second procedure is the dismantling of the site. The decommissioning project is for removing the radioactive materials. Thermal cutting and mechanical cutting are two technical ways to dismantle and demolish. Thermal cutting is used for the metals by burning with high energy in one concentration area. The mechanical cutting takes place in the workshop with mechanical force and cuts reactive materials into two parts or in small pieces. The most dangerous waste is placed inside radioactive-resistant containers, after which the containers are transported to storage facilities. The rest of the site can then be decontaminated. The site is then checked thoroughly for any signs of radiation. Most of the remaining waste onsite can be disposed of normally as it is either not contaminated or radioactivity levels have dropped to within safe limits. This process is often completed using robots, which are able to access the difficult to reach areas deemed too radioactive for human workers. The robot was made by WWER-440-type-NNR and is mostly in central and Eastern of Europe, Russia. The main idea of using robots in decontamination is to reduce the radioactive to a level, therefore workers can be exposed. The robot’s energy was provided from the robot control system and was placed in the manipulator. The manipulator can be controlled by the remote. The “Decomler” robot works in decontamination by using the wheel system and track system. Also, the robot needs to be strictly licensed by national regulating authorities, because the materials processed by the robot need to ensure they are not discharged to outside. Otherwise, it will cause nuclear pollution to both the environment and humans.