Emission from reactors

It is convenient to consider reactor accidents alongside weapon explosions so that the release of fission products can be compared, but the mode of dispersion is quite different. The configuration and thermal capacity of power reactors are such that bomb-like explosions are not possible. In the Chernobyl accident, nuclear overheating, a steam explosion and steam/zirconium reactions all contributed to the disruption of the reactor (U.S.S.R. State Committee, 1986), but the longdistance environmental effects were due to the subsequent releases of fission products from the damaged reactor. 

Reactor fuel elements are contained in cans. In early British reactors, these were made of aluminium or aluminium/magnesium alloy to minimise capture of neutrons in the canning material. Nowadays, uranium fuel is enriched with respect to the 235U content, and the extra reactivity enables steel or zirconium cans to be used. In the original 

Windscale reactors, and some US reactors of the 1950 period, the fuel was cooled by air blown straight to atmosphere, and no use was made of the heat to produce power. In all power reactors now operating, the coolant is contained in a closed-circuit pressure vessel. Outer containment buildings, which can also withstand some pressure in the event of failure or leakage from the pressure circuit, enclose the US pattern pressurised water and boiling water reactors, but no such provision was made for the Russian boiling water reactor at Chernobyl. All defences (cans, pressure vessel, containment building if provided) must be breached before fission products can be released to atmosphere. 

Can failures occur from time to time. The release of fission products from them depends on the temperature and type of fuel. If the fuel is uranium metal, as in the Windscale and Magnox reactors, and the can fails, the uranium will oxidise in air or C02. In laboratory experiments, the mass median aerodynamic equivalent diameter (MMAD) of the particles produced by oxidation of uranium increased from about 40 ptm when the temperature of oxidation was 600°C to 500 jum at 1000°C (Megaw et al., 1961). At high temperature, a coherent sintered oxide layer formed on the uranium and this hindered the formation of particles. 

In Advanced Gas Cooled (AGR), Pressurised Water (PWR) and Boiling Water (BWR) reactors, and in the Russian RMBK, the fuel is U02. Experiments in the UK and USA, reviewed by Farmer Beattie (1976), showed less than 1% release of fission product iodine and caesium from punctured U02 fuel cans at about 1000°C in air or steam, rising to 10-50% release at 1800°C. At 2800°C, the U02 melted and there was nearly complete release of volatile nuclides (I, Te, Cs, Ru) but only small release of refractory alkaline earth and rare earth nuclides. 

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When the mercury present in the atmosphere is primarily in the form of an organic mercury compound, it may be preferable to utilise an aqueous scmbber. This method is particularly useful for control of emissions from reactors and from dryers. For efficient and economical operation, an aqueous solution of caustic soda, sodium hypochlorite, or sodium sulfide is reckculated through the scmbber until the solution is saturated with the mercury compound. 

A major potential source of discontinuous emissions in the polymer production processes is the reactor system. Discontinuous emissions from reactor systems occur during plant start ups (for instance purging), shut downs and emergency stops. 

Flaring of discontinuous emissions from reactors is considered BAT if these emissions cannot be recycled back into the process or used as fuel (see BAT 7 above). 

BAT is to reduce residual VCM emissions from reactors (see Section 12.4.3)... 

Increasing the nitrogen content in the reactor feed generally increases NO emissions in the regenerator. Increasing feed nitrogen content from 200—300 ppm to >100 ppm has been reported to increase NO emissions from 50 ppm to >450 ppm (46). 

Maurice, L.Q.W., and Blust, J.W., Emission from Combustion of Hydrocarbons in a Well Stirred Reactor, AIAA 1999. 

VOC) emissions from stationary sources, in Structured Catalysts and Reactors, 2nd edn, Chapter 5 (eds A. Cybulski and J. A. Moulijn), CRC Taylor, Francis, Boca Raton, p. 147. 

This technique is invasive however, the particle can be designed to be neutrally buoyant so that it well represents the flow of the phase of interest. An array of detectors is positioned around the reactor vessel. Calibration must be performed by positioning the particle in the vessel at a number of known locations and recording each of the detector counts. During actual measurements, the y-ray emissions from the particle are monitored over many hours as it moves freely in the system maintained at steady state. Least-squares regression methods can be applied to evaluate the temporal position of the particle and thus velocity field [13, 14]. This technique offers modest spatial resolutions of 2-5 mm and sampling frequencies up to 25 Hz. 

Despite environmental concerns (Chapter 3), since 1980 MTBE has made a significant contribution to the lowering of VOC emissions from car exhausts. This is due to its clean bum properties, (producing fewer hydrocarbon by-products). MTBE is commonly produced in a fixed-bed reactor by passing a mixture of 2-methylpropene and excess methanol over... 

Discharge water and emission from facilities that make americium smoke detectors or gauges or produce plutonium for nuclear weapons may contain americium. These operations are strictly regulated, but you can check local health advisories before consuming fish or other seafood from these waters. Nuclear reactors are not expected to discharge measurable amounts of americium. 

Emissions from SOCMI—reactor processes (tetra (methyl-ethyl) lead, tetramethyl lead)... 

Yasui et al. [29] have used solution of wave equation based on finite element method for characterization of the acoustic field distribution. A unique feature of the work is that it also considers contribution of the vibrations occurring due to the reactor wall and have evaluated the effect of different types of the reactor walls or in other words the effect of material of construction of the sonochemical reactor. The work has also contributed to the understanding of the dependence of the attenuation coefficient due to the liquid medium on the contribution of the vibrations from the wall. It has been shown that as the attenuation coefficient increases, the influence of the acoustic emission from the vibrating wall becomes smaller and for very low values of the attenuation coefficient, the acoustic field in the reactor is very complex due to the strong acoustic emission from the wall. 

Experiment 3 In general, sonoluminescence emission is not discemable with the naked eye. The luminosity of the secondary emission from luminol (oxidised by sonochemically produced OH radicals) however, is several orders of magnitude brighter and is easily seen in a dark room. Prepare a 0.1 mM aqueous luminol solution in 0.1 M NaOH. Sonicate this solution and observe the emission pattern. This will appear as bands of light and dark if a standing wave reactor is used or in more elaborate forms in different reactors. If a 20 kHz horn is used, a cone shaped zone of luminescence will be observed. Explain the emission pattern. 

In a continuous reformer, some particulate and dust matter can be generated as the catalyst moves from reactor to reactor and is subject to attrition. However, due to catalyst design little attrition occurs, and the only outlet to the atmosphere is the regeneration vent, which is most often scrubbed with a caustic to prevent emission of hydrochloric acid (this also removes particulate matter). Emissions of carbon monoxide and hydrogen sulfide may occur during regeneration of catalyst. 

When in 1984 the Environmental Protection Agency (EPA) proposed the lead phaseout from gasoline, the emphasis on FCC research shifted toward the generation of octane-selective catalysts. Environmental concerns have also proposed limits on sulfur emissions from FCC units, thus initiating research on on catalysts capable of sorbing S-impurities in the regenerator and releasing them as H S in the reactor side from where they can be easily adsorbed. 

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