Gas-cooled systems

Plastic packing of very low pressure drop (just greater than wood slats), transfer Coefficients about same as 2-inch Raschig rings. Most useful applications in gas cooling systems or biological trickling filters. 

Losses Residual air Combustion gases Cooling water system Gas cooling system Others... 

Comparison of Temperature-control Characteristics of Various Types of Reactors. Several methods of heat removal are used in the various reactors. Heat removal for the most part may be considered to take place either directly, as in the oil- or gas-cooled systems where the catalyst surface is in contact with the cooling medium, or indirectly, as in the fixed or fluid beds where heat must be transferred through the bed to a cooling surface. Admittedly this is an oversimplification, especially in the case of the fixed and fluid beds where some direct heat transfer occurs. 

The situation for the AHTR, shown in Fig. 4.2, has the potential to be more favorable. The molten salt coolant offers additional fission product containment features and may reduce some licensing barriers. Key features are the low-pressure coolant and gas-trapping system and the retention of the most important radiotoxic fission products in the salt. With a low-pressure coolant, a true containment building is a more practical option than for a high-pressure, gas-cooled system. 

Zenith is designed for the study of the physics of high-temperature gas-cooled systems. Circulation of nitrogen gas over a 250 kW heater at the base of the core allows the core and side reflector regions to be heated to 800°C and 400°C respectively. 

The excellent heat transfer properties of molten fluoride salts, compared with those of helium, reduce the temperature drops between (1) the fuel and molten salt and (2) the molten salt and any secondary system. Comparable calculations for a typical prismatic geometry were made of the temperature drop between the centerline prismatic fuel temperatures and coolant for helium and molten-salt coolants. The temperature drops for helium and molten-salt coolants were 415 and 280 C, respectively. The better heat transfer capabilities of molten salts (a liquid) compared with those of helium allow reactor designs with higher coolant exit temperatures and power densities than in gas-cooled systems for the same maximum temperature limit in the fuel. 

Primary sodium is circulated in the reactor by four electromagnetic (EM) pumps. These pumps are self-cooled by the pumped sodium. This results in higher temperature for the electrical insulation material than for an arrangement with an external gas cooling system. However, suitable ceramic and mica-based materials have been developed and qualified for a life expectancy in excess of 30 years. The self-cooled EM pump simplifies the head... 

The ratios of the various capture and fission rates, relative to the Pu fission rate, are obtained by the standard methods, such as foil activation (see Section 1.8). Measurements of this kind are among those which have ted to the abandonment of the concept of the steam-cooled fast reactor, which was at one time considered as a competitor for the liquid-metal- and gas-cooled systems. Measurements of (Xg showed that the degradation of the neutron spectrum had increased the capture-to-fission ratio to such an extent that the breeding ratio was no longer economic. 

The thermal capacity of the bucket Is sufficient to maintain fuel cladding at less than the on-power operating temperature during the time taken for normal transfer between the reactor vessel and the CCS. To cater for the risk that a hold up occurs while the fuel Is out of the sodium pools, the bucket will be finished with a profile which enables the heat to be transferred to the ramp tubes by radiation. A steady state heat removal capacity of about 35 KW can be achieved within a temperature limit which will not jeopardise the fuel pin Integrity. By switching on a gas cooling system the heat removal capacity can be enhanced. 

In high temperature systems, there are also temperature induced mechanisms for corrosion that are dependent upon large temperature differences in the heat transport system. The classic example is the transport of carbon in the form of various oxides in gas cooled systems, resulting in depletion of carbon in one part of the system and the deposition of carbon in another part. Parallel mechanisms have been seen in liquid salt test loops. In this system, the primary concern has been the selective chemical transport of chromium (an alloy constituent of many alloys) from hot to cold locations in the reactor system by uranium, where the equilibrium is temperature dependent ... 

There are two well-known commercial processes for partial oxidation, the Shell process and the Texaco process. These processes are broadly similar, but differ in areas such as the carbon recovery system and the reactor gas cooling system. 

In an Oak Ridge study [61] various types of fluidized-bed reactors were compared. Systems investigated were (a) a sodium-cooled fast reactor, (b) a gas-cooled system, (c) an organic-moderated reactor, (d) a heavy-water-moderated reactor, and (e) a light-water system. A detailed study of this latter system was carried out to compare its characteristics and performance with solid-fuel heterogeneous pressurized-water reactors. The results indicated that both the light-water-moderated and organicmoderated fluidized reactors showed promise, while the gas-cooled, the D20-cooled, and the fast (unmoderated) reactors were found to be less satisfactory for application of the fluidized-bed technique. 

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