Technology control

The release of radioiodine has generally been controlled by means of two methods (1) holdup for decay and (2) collection by scrubbing systems and solid sorbents. Both holdup and collection have been practiced. But the former is not suitable for I. When only small amounts of radioiodine are involved, as with reactor effluents, the holdup method may be adequate and charcoal filters or charcoal delay beds can be utilized. In fuel reprocessing plants, both holdup and collection have been used with more recent effort concentrating on collection and disposal. 

Several wet scrubbing systems have been used and proposed for use as primary systems. 

Caustic scrubbing is one of the earlier methods used for primary cleanup (CEC, 1982a). NaOH or KOH in solution is used in a packed column or bubble plate column. Decontamination factors (DF) of 10 or more have been achieved. I2 is effectively trapped but organic 

The lodox process employs high concentration (20 to 23 M) nitric acid to scrub iodine from the gas stream (Holladay, 1979). Iodine is removed as anhydroiodic acid (HIsOs). AH iodine species are converted to and, as a result, DF s greater than 10 are possible. However, the equipment is expected to be expensive because of corrosion problems with the concentrated nitric acid. The product of this process is very soluble in water and would have to be converted to a more insoluble form before final storage. 

The Mercurex process employs mercuric nitrate-nitric acid in a packed column (Holladay, 1979). While dilute nitric acid has been investigated, improved organic iodine remove is obtained with concentrated acid ( 10 M). Mercuric iodine complexes are formed. One treatment method involves oxidation to the iodate, followed by filtration of the iodate. The mercuric iodate can be filtered off. DF s for the mercurex process are affected by aromatic vapors and may be 100 or less. The toxicity and cost of mercury are disadvantages as well as the lack of demonstrated conversion technology for the mercurex solution. 

These transform the output signal of a measuring instrument into a standardized signal (e.g., 4-20 or 0-20 mA, 0.2-1 bar) [MeEumformer 1999]. 

This auxiliary controller is used where the load on drive and control element is high or when the quality of control is to be improved. It mechanically measures the true valve position in situ and compares the value with the controller output y provided by the 

Time behavior of control circuits (important controiier is in manuai mode) 

Time behavior of controller types (important without controi circuit) 

The following are measures of the controllability Tu/Tc 1/10 well controllable T j/Tc as 1/6 just controllable Tu/Tc 1/3 difficult to control 

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PEGULATORYAGENCIES - CHEMICALPROCESS INDUSTRY] (Vol21) Best practicable control technology ppCp... 

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