Off-gas system

Off-Gas Treatment. Before the advent of the shear, the gases released from the spent fuel were mixed with the entire dissolver off-gas flow. Newer shear designs contain the fission gases and provide the opportunity for more efficient treatment. The gaseous fission products krypton and xenon are chemically inert and are released into the off-gas system as soon as the fuel cladding is breached. Efficient recovery of these isotopes requires capture at the point of release, before dilution with large quantities of air. Two processes have been developed, a cryogenic distillation and a Freon absorption. 

In the reprocessing environment there are many mthenium compounds, some of which are gaseous. Some reprocessing approaches, notably the REDOX process, require a mthenium removal step in the off-gas system. The PUREX process maintains mthenium in one of its nonvolatile states. 

According to the vendor, this project could provide a compact, low-cost reactor to treat aqueous mixed waste streams containing nitrates or nitrites, eliminate the need for chemical reagents, and minimize or eliminate secondary wastes such as nitrous oxide and secondary products such as ammonia, H2, and O2 that are prevalent with other nitrate destruction processes. By removing nitrates and nitrites from waste streams before they are sent to high-temperature thermal destruction and vitrification, production of NO can be decreased with the attendant decrease in off-gas system requirements. Biocatalytic nitrate destruction is applicable to a wide range of aqueous wastes with a highly variable composition. All information is from the vendor and has not been independently verified. 

The limiting factors for successful soil mixing treatment include the presence of boulders and subsurface utilities such as underground wires or piping. Depth to the water table may adversely impact the vapor extraction components effectiveness because vapor phase off-gas systems cannot process liquid streams. The vendor claims that depth to the water table may also influence lateral migration of processing gases. 

A limitation of this technology is that at least some additives are normally required before processing to control the properties of the final waste form. Since only a small part (approximately 30%, according to the vendor) of the waste is incorporated into the final glass product, most of the material is converted to gases and particulate that must be processed by the off-gas system. 

Mercury is not contained within the melt and must be trapped by the off-gas system. 

R-2 MAIN REACTION PRODUCT LIQUID-LIQUID SEPARATOR VP LOWER PHASE OFF-GAS SYSTEM VACUUM PUMP... 

In the off-gas system of radiochemical laboratories, filters are installed which retain aerosols and vapours. These filters have to be checked regularly for radio-... 

Radionuclide released Release fraction for a simple off-gas system Estimated range at releases from a 50 kg dissolution (Bq) of 1000 MWd/t fuel... 

Internal tank pressure is also measured and transmitted to the control panel. If the relief valve is activated, the pressure is released to a line that vents directly to the stack. The normal tank venting system is connected to the process vessel off-gas system in the main plant, which is a filtered system. 

Figure 4, Typical decontamination factors achieved in WCF off-gas system. The contamination factor for a component is the ratio of the quantity entering to the quantity exiting per unit of time.

Mound Facility Caustic Waste. About 6000 l of so-called caustic waste containing 0.5 to as much as 8 mg Pu/ are generated yearly at the Mound Facility. The bulk (90 vol ) of this particular waste stream consists of a k wt NaOH solution used as a scrubber in the corrosive off gas system. The remainder originates as filtrates from NH OH precipitation of Pu(0H)i ... 

Off-gas from the calcination process was passed through sintered-metal filters located in the upper section of the calcination vessel. The process off-gas was then cooled in the offgas condenser where most of the N09 released in the denitration process was recovered as nitric acid and collected in the condensate tank. Uncondensed vapors were passed successively through the de-entrainer, the off-gas preheater, the HEPA filter, and then vented to the off-gas system. 

The off-gas condenser was a shell-and-tube (water-cooled) heat exchanger a 260 liter capacity stainless steel tank was used to collect condensate and a stainless steel wire-mesh de-entrainer, a shell-and-tube (steam-heated) preheater and a HEPA filter were used in the off-gas system. 

But, while there are difference between this system and others described there are also many similarities.Thus the rice husks are added at the top of the convertor through, a quick disconnect inlet feed port and the charcoal removed at the bottom through a simple sliding grate. Process air is introduced near the bottom of the system and passes upward to exit through the off-gas system and then enters the condenser/demister which removes the oil-tar fraction. 

Since the combination of direct introduction of process air through the convertor walls and the flush mounted off-gas system is... 

Another safety feature that is required is a pressurized air system that can be used to keep the concentration of radiolytic hydrogen below a given safety level as well as to prevent solids from settling. The air stream may also be useful to regulate in>tank evaporation and radiolytic stripping of HNO3. The air has to be released via an elaborate off-gas system. 

An off-gas system ensures that no excessive radioactivity is released together with the sparge air. Condensate from the off-gas can be transferred either back to the HLW tank or to the intermediate-level waste tank. 

A spray calciner designed for a 5 MT/day reprocessing plant has an incoming waste flow rate of 118 liters/h with 75 g/liter solids to be combined with an off-gas system recycle of 8 liter/h to a total calciner feed of 126 liter/h with 70 g/liter solids. The product stream is 15.6 kg/h calcined solids. The demand on atomizing air is 0.85 m /min. 

The off-gas system ensures that the bulk of active material escaping from the furnace is trapped in a coimtercurrent water-scrubbing column and recirculated directly to the calciner. Further off-gas treatment includes a condenser, an absorption colunm, and a washit colunm. The low-activity liquid from this section of the plant is recycled to the adjoining reprocessing plant. 

Process gases vented from the rotary MPT, batch MPT, ERD, and various process tanks are sent to the MPT quench tower, from which they are passed in series through a flame arrestor, a preheater, a CATOX unit, and a water-cooled heat exchanger. The cooled gases are then sent to the MDB ventilation system, which contains activated carbon adsorbers. The CST off-gas treatment system has the same design and capacity as the MPT off-gas system. 

The silver chloride 5X treatment unit was an electrically heated oven with forced-air circulation to prevent cold spots. The temperature of the silver chloride was measured with a thermocouple mounted in the unit. The vent air from the unit containing nitric acid vapors was passed through a condenser prior to flowing into the main plant off-gas system. 

To identify the main factors of safe work of the advanced melters EP-500/3,4, six years of experience using the melter EP-500/lp are summarized efficiency, technological deviations, and equipment failures, as well as violations of water-cooled system, off-gas system, control and measuring instruments that resulted in the temporary shut down of the vitrification process are studied. 

Vitrification Cells. Liquor is fed from the HAL cell to one of the two duplicate vitrification cells in the WVP. These house the main chemical process equipment, namely the calciner, melter, and primary off-gas vessels. The Vitrification Cell equipment evaporates the HAL liquor to dryness, mixes it with pre-formed glass (inactive) and other additives, and melts the mixture to form the glass product at a temperature of around 1100 C. The primary off-gas system removes dust, water vapor, and a proportion of the radioactive species that are entrained in the off-gas stream. HAL liquor is fed continuously into the Vitrification Cell and the glass product is poured in batches, approximately every 8 hours. Process conditions within the cells are generally manually controlled. All vitrification instrumentation is logged to a central control room an interlock system is provided to trip the vitrification process if pre-set conditions are exceeded. 

ESP Cell. There are two electrostatic precipitators (ESPs), each in its own ESP cell. The electrostatic precipitator is the first stage of the secondary off-gas cleanup in which entrained particles of liquid droplets are removed from the off-gas stream. Only one ESP is on line at any one time the other is isolated from the off-gas system by the ESP Seal Pots. 

Abnormal Discharges. Failure in dissolver off-gas systems, contamination of effluents streams, misrouting of effluent streams. 

Zincor is limited in roaster concentrate feed rate by the off-gas system capacity. Dust handling systems cannot handle the quantity of calcine dust if the dust elutriation rate exceeds 85% of the feed at 10% over design feedrates. 

Each roaster off gas system contains two cyclones in parallel. No established changes have occurred to cyclone availability since the introduction of oxygen emichment. 

Cleanup recirculation pump coolers Off-gas system glycol coolers Control rod drive supply pumps Radwaste concentrator condensers Radwaste concentrated waste tank Control rod drive supply pumps... 

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