CONDENSATE POLISHING SYSTEM

The condensate polishing system must be in excellent working order and typically operating in the ammonia cycle. 

Two types of condensate-polishing systems are available, both capable of removing suspended material, such as corrosion products, as well as ionized solids. 

Recommended limits should be low because all solids in the feedwater will either deposit in the boiler or be earned over with the steam to the turbine. Consequently, water-treatment chemicals must be volatile. All cycles should have condensate-polishing systems to meet the limits show ll in Table 3. A schematic diagram is shown in Fig. 11. Laboratory tests as well as field studies show that high-flow-rate condensate-polishing systems 25 to 50 gal per min per sq ft (1015-2030 liters/minute/square meter) of cross-sectional bed area] perform as filters of suspended material and ionized particles. Ammonia is added to control the pH in die system. Fig. 12 indicates the amount of ammonia required, in terms of ppm or solution conductivity, to give a certain pH in the system. Hydrazine is added to the cycle for oxygen scavenging. 

Fig. 11. Schematic diagram of condensate-polishing system with high quality makeup treatment (four-bed ion exchange or equivalent)...

Ion exchange desalination - DESAL , SIROTHERM Membrane desalination - Reverse Osmosis, Electrodialysis Continuing fixed bed counterflow development Condensate polishing systems Ion Chromatography analysis, and Pellicular resins Polymeric adsorbents... 

Principal Component POWER CONVERSION GROUP (Continued) Condensate Polishing System Demineralizer Modules Regeneration System Valves... 

The steam produced in the reactor pressure vessel is directed to the high-pressure part of the turbine downstream, the condensate formed on the high-pressure turbine is separated and directed to the heater drains. The residual steam powers the low-pressure part of the turbine and, finally, is completely condensed in the main condenser. The main condensate is purified in the condensate demineralizers where corrosion products and ionic impurities are retained. The feedwater then is recycled via preheaters to the reactor pressure vessel. In older BWR plants, all the condensates are purified in the condensate polishing system in the newer, forward-pumped plants only the main condensate is purified there, while the heater drains are directly pumped to the feedwater tank. In some of the BWR plants the feed-water tank is equipped with an electromagnetic filter for removal of suspended corrosion products (mainly iron oxides). 

In RBMK reactors, oxygen (up to 0.2mg/kg) is injected into the feedwater circuit downstream from the condensate polishing system in order to prevent corrosive attack on the perlitic steels, and then removed from the water in the deaerator (Dragunov et al., 1992). Attempts have also been made to inject hydrogen as a remedy for intergranular corrosion attack on stainless steels. 

In those BWR plants in which all condensates from the turbine cycle are directed to the condensate polishing system, the equations mentioned above can be used with the modification that allowance must be made for the carry-over constant, which describes the loss of some iodine and other non-gaseous fission products from the coolant to the steam phase. The carry-over constant A is added to the term (X + 8), making it (X -I- 8 + A) A is calculated according to... 

In BWR plants with forward-pumped heater drains, however, a large fraction of the iodine and other non-gaseous fission products carried by the primary steam is directly returned to the reactor water without passing the condensate polishing system. When calculating source strengths from the activity concentrations in the reactor water, the fission product input with the feedwater has to be taken into account as an additional source for the reactor water (Lin, 1983). 

In the water—steam circuit, the fission product iodine which is carried by the main steam is distributed between different water and steam flows. A substantial fraction of it is plated out in the cyclone downstream of the high-pressure part of the turbine, and is transported back with the separated condensate to the feedwater storage tank. Similar washdown of iodine occurs at the other locations where condensates are separated from the remaining steam, so that only a small fraction reaches the main condenser. Here as well the major part is plated out to the main condensate water phase and is retained in the ion exchangers of the condensate polishing system the fraction of iodine which passes over to the condenser off-gas represents only a few percent of the amount originally carried by the main steam. 

Lin (1983) also reported on a detailed investigation of the distribution of iodine volatilized from the reactor water in BWR water—steam circuits with forward-pumped heater drains. In this plant design, only the main condensate is directed to the condensate polishing system, whereas the different drains from the turbine are fed directly back to the feedwater tank. Under such plant conditions, about 75% of the iodine carried by the main steam flow is precipitated together with the condensate in the moisture separator downstream from the high-pressure part of... 

As was pointed out at the beginning of this section, the second possible mechanism of radionuclide production and of contamination buildup is neutron activation of corrosion products which are temporarily deposited inside the neutron field, in particular on the claddings of the fuel rods. These corrosion products mainly stem from the turbine cycle of the plant and are introduced into the reactor pressure vessel with the feedwater. In most of the BWR plants, where all the arising condensates are purified in the condensate polishing system (mainly using precoat... 

The condensate polishing system chemically cleans up the condensate by passing it through ion exchange resins to remove corrosion products and ionic impurities. It is required during start-up, imtil the desired water quality is attained, but during power operation would be used only when abnormal secondary conditions exist, such as a continuous condenser tube leak. 

No design requirements associated with maintaining safety functions are placed on the condensate polishing system. 

The purification of condensate can be achieved by various condensate polishing systems. The resin beds in the purification systems remove both dissolved and suspended solids. These ion exchange beds are regenerated periodically. 

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