two waste evaporators, each having a capacity of approximately 1.7m³/h, are employed. Two types of evaporators are usually used for this purpose, i.e. an immersion heater type and a circulation heating type. The former uses a heating unit to heat and evaporate water in the evaporator drum. The latter uses a heater outside the evaporator drum and a circulating pump; this type evaporator has merits of getting higher concentration and decontamination factors than the immersion type evaporator. Moreover, local precipitation of highly concentrated chemicals, as often seen in the immersion heater type evaporator, is prevented from occurring by using this type evaporator. Boron recycle evaporators are usually the immersion heater type, since they are used to process high quality, low chloride concentration liquid mainly composed of the reactor coolant which flows down via the letdown line in the CVCS. Waste liquid evaporators to process low quality liquid wastes are usually the circulation heating type. These two types of evaporators are illustrated in Figures 3.9.4 and 3.9.5.

Figure 3.9.4 Boron recycle system evaporator (immersion heater type)

Figure 3.9.5 Waste evaporator (circulation heating type)

Laundry and hot shower processing units to treat liquid wastes accumulated in laundry and hot shower tanks are usually either an evaporator, or a reverse osmosis or micro-filter type unit

Reverse osmosis or micro-filter type units remove radioactive materials and particulates in the wastes by reverse osmosis membranes or micro-filters. The processed clean water is released to the environment, while the concentrates are pumped to the drumming station. The numbers and the total capacity of the units are determined based on the requirement that the total capacity of the unit, or units, should be at least two times greater than estimated system loads. Usually one reverse osmosis unit with a capacity of approximately 2m³/h is employed.

When laundry and hot shower evaporators are employed, they perform the same functions as the waste evaporators outlined above.

In the design of recent plants, BOD (biochemical oxygen demand) or COD (chemical oxygen demand) levels in processed laundry and hot shower wastes released to the environment must be sufficiently reduced to allow the nuclear power plants to be accepted as eco-friendly. Figure 3.9.6 shows a schematic flow diagram of a laundry and hot shower waste processing unit, using an activated sludge membrane separation method to bio-degrade organic substances in sludge by activating them microbiologically. A micro-filter unit in the clarification drum removes radioactive materials and particulates in the discharged water, and effectively clarifies the processed water, preventing activated sludge from leaking. Since bacteria in the activated sludge grow by ingesting organic substances, excess sludge is periodically drawn out of the clarification drum and burned in an incinerator.

2. Demineralizers

Three types of demineralizers are used in the liquid waste processing systems, i.e. the boron recycle demineralizer, the boron recycle condensate demineralizer and the liquid waste condensate demineralizer. Both the boron recycle demineralizer and the boron recycle condensate demineralizer are employed in the boron recycle system, upstream and the downstream from

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NSRA, Japan