Exposure control, radiation shielding

Shield Door Hydraulic System Controls Protection of HCF personnel from potentially lethal radiation exposures. HCF operators must ensure that shield door 1 is not lowered while shield door 2A is down and that shield door 3A is not lowered with workers In Zone 2A, the Zone 2A airlock, or the north end of Room 112. Administrative controls are in place to ensure adequate control of shield door operating keys. 

There are several types of engineering controls to limit dangerous exposures to radiation. Controls include limiting radiation emissions at the source, limiting time of exposure, extending the distance from a source, and shielding. Certain other controls will also help prevent dangerous exposures. 

One feature of reprocessing plants which poses potential risks of a different nature from those ia a power plant is the need to handle highly radioactive and fissionable material ia Hquid form. This is necessary to carry out the chemical separations process. The Hquid materials and the equipment with which it comes ia contact need to be surrounded by 1.5—1.8-m thick high density concrete shielding and enclosures to protect the workers both from direct radiation exposure and from inhalation of airborne radioisotopes. Rigid controls must also be provided to assure that an iaadvertent criticahty does not occur. 

Typical irradiation facilities consist of a process chamber containing the radiation source, some sort of conveyor systems to transport products inside and outside the shielding walls, and sophisticated control and safety systems. Irradiation facilities are built with several layers of redundant protection to detect equipment malfunctions and protect employees from accidental exposure. Technical details depend on the type of irradiation. Typical processing parameters are compared in Table 2 [7]. 

Three basic principles are recommended for keeping radiation exposure to a minimum shielding, control, and distance. If a radiochemical laboratory is designed properly and the work performed in such a manner that the g eral background contamination is suffici tly low to do valid low level tracer experiments, then the health aspects of radiation control are satisfied. We indicate the main principles for work with radioactive substances, but in each notion, special rules may apply. 

An insufficiently shielded external radiation source can influence background measurements from some distance. Airborne radionuclides typically are gaseous radon and its particulate progeny, but after nuclear tests or major nuclear accidents may include fission and activation products. Efforts should be made to control such exposures for long-term radiation background stability. 

Suitable provisions shall be made in the design and layout of the plant to minimise exposure and contamination from all sources of radioactivity. Such provisions shall include adequate design of systems and components with respect to low radiation exposure during maintenance and inspection, shielding from direct radiation, reduction of corrosion-product activation by specification of appropriate materials, means of monitoring, control of access to the plant, minimisation of the time to be spent in contaminated areas, and suitable decontamination facilities. 

Protection of HCF personnel from potentially lethal radiation exposures Zone 2A canyon physical structures (concrete walls, shield steel, shielding windows) Worker safety Provide radiation protection such that worker exposures in continuously occupied areas under normal and abnormal conditions are in accordance with 10 CFR 835 Shield design (Design Feature) Radioactive material control (Administrative Control)... 

Target Entrance System Mechanical Interlock Protection of HCF personnel from potentially lethal radiation exposures. The TES mechanical interlock must prevent a STB operator from removing the TES shield cover when the lid has been removed from a shield cask inside the TES. Administrative controls are in place to ensure periodic testing of the TES mechanical interlock that prevents removal of the TES shield cover when the shield cask lid has been removed. 

Shield Cask Protection of HCF personnel from potentially lethal radiation exposures. Workers must ensure shield cask integrity prior to and during movement of the cask from the ACRR highbay to the HCF with an irradiated target. Administrative controls are in place to ensure that the cask lid is securely bolted in place prior to cask movement and to minimize the potential for accidents during cask transport. 

The key to risk control is to prevent exposnre of those who could be at risk. In the workplace it is not possible to have no exposnre if anything is going to get done. It is important to limit the potential exposnre or amount of exposure. The basic principles of protection from radiation exposnre provide the fonndation for risk control. The three elements of exposnre control are distance, time, and shielding. Distance provides the best mechanism to prevent exposure. Distance can be physical distance or remote distance where robotics can provide the distance and limit the... 

As was discussed in the preceding sections, in many operating nuclear power plants the buildup of contamination results in radiation levels at the systems and components which lead to considerable radiation exposure of workers, in particular during the course of inspection and repair work. In order to meet this situation, permanent or temporary shieldings are frequently installed and, as far as necessary, remote-controlled and automatically operating equipment is employed to reduce, as far as possible, the stay time of people in the radiation field. Nevertheless, there are often operations to be carried out whose preparation and execution make the removal or at least a radical reduction in the radiation sources, i. e. a decontamination of the respective regions, necessary. 

White, D.1994. Shielding to RF/microwave radiation exposure, emf-emi control Journal. 

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