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Ahot cell is a name given to acontainment chamber that isshielded againstnuclear radiation. The wordhot refers toradioactivity.
Hot cells are used in both the nuclear-energy and the nuclear-medicines industries.They are required to protect individuals from radioactive isotopes by providing a safe containment box in which they can control and manipulate the equipment required.
Hot cells are used to inspectspent nuclear fuel rods and to work with other items which are high-energygamma ray emitters. For instance, the processing of medical isotopes, having been irradiated in a nuclear reactor or particle accelerator, would be carried out in a hot cell. Hot cells are of nuclear proliferation concern, as they can be used to carry out the chemical steps used to extract plutonium (whetherweapons grade ornot) from reactor fuel.[citation needed] The cutting of the used fuel, the dissolving of the fuel in hot nitric acid and the first extraction cycle of a nuclear reprocessingPUREX process (highly active cycle) would need to be done in a hot cell. The second cycle of the PUREX process (medium active cycle) can be done ingloveboxes.
Hot cells are commonly used in thenuclear medicines industry:
The user must never be subject toshine paths that are emitted from the radioactive isotopes and therefore there generally is heavy shielding around the containment boxes, which can be made out of316 stainless steel or other materials such asPVC orCorian.[citation needed] This shielding can be ensured by the use of lead (common) or materials such as concrete (very large walls are therefore required) or even tungsten. The amount of radioactivity present in the hot cell, the energy of the gamma photons emitted by the radioisotopes, and the number ofneutrons that are formed by the material will prescribe how thick the shielding must be. For instance a 1 kilocurie (37 TBq) source ofcobalt-60 will require thicker shielding than a 1 kilocurie (37 TBq) source ofiridium-192 to give the same dose rate at the outer surface of the hot cell. Also if some actinide materials such ascalifornium or spent nuclear fuel are used within the hot cell then a layer of water orpolyethylene may be needed to lower the neutron dose rate.
In order to view what is in the hot cell, cameras can be used (but these require replacing on a regular basis) or most commonly,lead glass is used.[1]There are several densities for lead glass, but the most common is 5.2 g/cm3. A rough calculation for lead equivalence would be to multiply the requiredPb thickness by 2.5 (e.g. 10 mm Pb would require a 25 mm thick lead glass window). Older hot cells used aZnBr2 solution in a glass tank to shield against high-energy gamma rays. This shielded the radiation without darkening the glass (as happens to leaded glass with exposure). This solution also "self-repairs" any damage caused by radiation interaction, but leads to optical distortion due to the difference in optical indices of the solution and glass.
Telemanipulators or tongs are used for the remote handling of equipment inside hot cells, thereby avoiding heavy finger/hand doses.
Lead loaded gloves are often used in conjunction with tongs as they offer better dexterity and can be used in low radiation environments (such as hot cells used in hospital nuclear medicine labs). Some companies have developed tungsten loaded gloves which offer greater dexterity than lead loaded gloves, with better shielding than their counterparts. Gloves must be regularly replaced as the chemicals used for the cleaning/sterilisation process of the containments cause considerable wear and tear.
Hot cells can be placed inclean rooms with an air classification ranging from D to B (C is the most common).
These cells are often used to test new chemistry units or processes. They are generally fairly large as they require flexibility for the use of varying chemistry units which can greatly vary in size (e.g. synthera andtracerlab). Some cells require remote manipulation.
This type of hot cell is used purely for production of radiopharmaceuticals. A chemistry unit is placed in each cell, the production process is initiated (receiving the radioactive18F from the cyclotron) and once finished, the cells are left closed for a minimum of 6 hours allowing the radiation to decrease to a safe level. No manipulation is necessary here.
Cells used to dispense products. For example, onceFludeoxyglucose (18F) (FDG) has been produced from18
F mixing with glucose, a bulk vial is put into in a dispense cell and its contents carefully dispensed into a number of syringes or vials. Remote manipulation is crucial at this stage.
