Sludge lank

Figure 3.9.6 Laundry/Hot shower waste processing unit (activated sludge membrane separation type)

Discharge

to Incinerator

the boron recycle evaporator, respectively. The former removes ionic impurities other than boric acid in the liquid prior to treatment, while the latter removes trace boric acid contained in the evaporator condensate. The liquid waste condensate demineralizers further clean up the waste evaporator condensate.

Numbers and capacities of these three types of demineralizers are determined based on such parameters as their decontamination factors, amounts of impurities in processed liquids and estimated system loads. In the case of the liquid waste condensate demineralizer, one demineralizer charged with 0.34m³ of resin is usually employed.

3. Solid Waste Disposal System

(1) System composition and functions

The solid waste treatment system treats solid wastes from various sources, according to their properties and forms. The main components of the solid waste treatment system were shown previously in Figure 3.9.3. The system flow diagram is shown in Figure 3.9.7. The solid wastes consist of the following.

• Concentrated wastes from liquid waste evaporator packages and laundry and hot shower processing units and strong acid drain from the chemical laboratory.

• Spent resin from demineralizers.

• Miscellaneous solid wastes, such as clothing, paper, rags, and so on.

• Spent liquid filter elements.

• Spent ventilation filter elements.

Each type of solid wastes is treated as described below.

1. Concentrated wastes including strong acid drain

Concentrated wastes, including strong acid drain, from liquid waste evaporator packages and laundry and hot shower processing units are sent to an asphalt solidification unit, where the wastes are mixed with heated asphalt, and solidified in drums after the water in the mixture of the wastes and the asphalt is evaporated. Strong acid drains are pumped to a cement solidification unit, where they are solidified, after being mixed with cement in drums.

In some recent plants, there are new systems to concentrate wastes through drying-up by heating before being granulated with drier­granulator units. Or further concentration of the concentrated wastes is done by generating borated calcium of low solubility, using Ca in a high reduction rate cement solidification unit.

2. Spent resin

Spent resins from demineralizers are transferred to the spent resin storage tank and stored in the tank for a long time to allow sufficient decay of their radioactivities. A drumming facility is employed for drum packaging of the spent resins.

In some plants, spent resins are divided into two categories, low radioactivity resins and high radioactivity resins. Low radioactivity resins are burned in an incinerator together with miscellaneous combustible solid wastes, while high radioactivity resins are processed by a spent resin processing unit using a sulfur-dissociation method as shown in Figure 3.9.8. Radionuclides adsorbed onto resins are sulfur-dissociated from resins in a dissociating unit. Spent resins, from which radionuclides have been dissociated,

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Figure 3.9.7 Solid waste disposal system

Figure 3.9.8 Spent resin processing unit (sulfuric acid dissociation type)

are burned in an incinerator and changed to inorganic materials. The sulfur acid containing radio nuclides is sent to a sulfuric acid recovery unit. Ninety percent of the sulfuric acid in the waste liquid are recovered in the recovery unit, by putting the waste liquid in contact with pure water across anion exchange membranes having positive charge fixing groups. The remaining liquid is condensed in a condenser, and the

condensed radionuclides are stored in a tank,

3. Miscellaneous solid wastes

Hie combustible miscellaneous solid wastes are incinerated in a waste incinerator, and the non­combustible wastes are compacted by a baler. Both kinds of combustible and non-combustible wastes are then packaged in drums after the respective reductions in their volumes.

In some recent plants, high-frequency induction

.r- m

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the drumming of spent resins. Hie capacity of the spent resin storage tank is determined based on an estimated amount of spent resins generated in the demineralizers, and their required storage period. Normally, the tank is sized to have a storage capacity for a five year operation of the plant.

2. Drumming facility

Two types of drumming facilities are used, i.e. as asphalt solidification type and a cement solidification type. The asphalt solidification unit concentrates wastes, mixes them with heated asphalt and solidifies the mixture in drums after water in the mixture is evaporated. The asphalt solidification unit has an advantage of less solidified waste volume, approximately, one fourth of that of a cement solidification unit.

The cement solidification unit is mainly used for the solidification of strong acids. A vacuum injection method is employed to inject waste liquids into drums where they are mixed with cement

3. Incineration facility

The incineration facility incinerates combustible solid wastes. The facility consists of an incinerator, an waste gas treatment system and an incinerated ash treatment system. Three types of incinerators are employed in nuclear power plants, a fixed-bed type, a two-stage type, and a fluidized-bed type. Among them, the fixed-bed type incinerator is widely used in domestic PWR plants at present.

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3-112

Figure 3.9.9 Technical requirements for low-level radioactive waste drums

Figure 3.9.10 Waste drum shipment Inspection unit

3~ 113

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