radioactivity is measured. Radioactivity at the discharge pipe outlet should not exceed the limits in water in the monitored area, which are defined by METI in the "Notification defining the dose limits according to the rules for the installation, operation, etc. of commercial nuclear power reactors." In addition, target values for liquid waste release control should be established according to the NSC Regulatory Guide L-RE-I.O "Annual Dose Target for the Public in the Vicinity of light Water Power Reactor Facilities" and radioactivity should meet these target values. Example target values for a 1,350 MWe class BWR power plant are 3.7 x IO¹⁰ Bq/y excluding tritium and 3.7 x 10¹² Bq/y for tritium.

3. Solid Waste Treatment System

Solid wastes from a BWR plant are categorized as follows:

1. concentrated liquid wastes from the evaporator where regeneration liquid wastes and floor drains (high conductivity liquid wastes) are processed;

2. filter sludge and spent ion exchange resins (referred to as spent resins hereafter) generated from the condensate demineralizer system;

3. filter sludge and spent resins generated from the reactor water clean-up system and the fuel pool cooling and filtering system;

4. filter sludge and spent resins from the liquid waste treatment system;

5. miscellaneous solid wastes contaminated with radioactive materials, such as air filters used in ventilation systems, and paper or clothing used in controlled areas; and

6. highly radioactive solid wastes of materials used in the reactor, such as spent control rods and spent fuel channel boxes.

The amounts of solid wastes generated in a 1,350 MWe class power plant which adopts demineralized filters in the condensate system can be estimated as follows:

• concentrates: about 5 m³/y;

• filter sludge and spent resins: about 20 m³/y;

• miscellaneous solid wastes (before volume reduction): about 40 m³/y; and

• highly radioactive solid wastes (control rods): about 10 rods/y;

These wastes have their own characteristics and

different levels of radioactivity according to their sources and they are therefore properly processed separately according to their characteristics.

Category (a) wastes are stored in interim storage tanks for a certain period to allow radioactivity to decay, and then solidified in drums with solidification materials before storing the filled drums in solid waste storage facilities. As a solidification method, in addition to the cement solidification method which mixes concentrates with cement, an asphalt solidification method has been adopted as an improved method which reduces the number of drums. New solidification methods with further volume reduction efficiency have been adopted. In these newest methods, concentrates are dried into powder by a dryer, and the powder is solidified with plastics or is pelletized followed by solidification using cement glass which is poured into the gaps between pellets. One other option is to crush pellets, which are under interim storage, into powder followed by cement solidification. Recently simple cement solidification has been re-introduced by new plants, since the amount of concentrated liquid wastes is much less than in old plants.

Category (b) wastes have relatively low radioactivity and therefore at some plants they are solidified and stored in drums by the same methods as category (a) wastes after decaying in storage tanks. However, recently, an incineration method has been adopted to improve the volume reduction efficiency.

Category (c) wastes are so highly radioactive .that several years of decay are too short for the radioactivity to reach a suitable level for solidification. The storage tanks for those wastes are designed with a capacity for 30 to 40 years of storage to provide sufficient decay time before processing.

Category (d) wastes are between wastes of categories (b) and (c) in terms of their radioactivity level. Therefore they are processed like (b) or (c).

Most of the miscellaneous wastes in category

5. generally have a very low radioactivity. They are segregated into combustible wastes and noncombustible wastes that are compactable or non- compactable. The volume reduction of compactable wastes is achieved by a compactor and the volume of combustible wastes is reduced by burning in an incinerator. Noncombustible wastes are also treated

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The solid wastes packed in drums are stored in solid wastes storage facilities in the plant site. Hie storage facilities are controlled areas and are under strict control which includes radiation surveys of surrounding areas. With respect to final disposal of solidified wastes, the Low-Level Radioactive Waste Disposal Center at Rokkasho in Aomori Prefecture started its operations in December 1992, and it accepts homogeneously solidified drums. Since October 2000, the Center has been accepting heterogeneously solidified drums, in which the solid wastes are solidified in the container by cement. Inspection systems were installed in the power plants to inspect solidified wastes before shipping them to the Center. The inspection includes surface dose rate and radionuclide concentration measurements. The disposal facility for relatively high radioactive wastes is in the planning stage and a site survey is being made.

A flow sheet of the latest radioactive waste treatment systems described briefly in this section is shown in Figure 2.9.3.

spent fuel storage pool

main condensed :

■ ^J

I 1 a 0 S 1 mtad bed (femneraizer non-pcecoaled

filter demlnerallzer filter dernJneraJizer, {remEgererafFreopa^cn) filter

—H ~ ~ noble gas holdup

Turbine ^{AIrGJ0Ctor recomb,ner} _system

stack

evaporator

(charcoal bed)

' Incombustible

’condensate I storage lank ™

reuse

collection nan-pteocated non-regenerative

^uidwasj^^ mixed bed sampingtank

0 a

charcoal treainier^ sampingtank

(Boor drain regenerated waste Equid) shower drain

(equipment drain)

.. . , . collection

high conductivity 1.-1.

Squid waste ™

forced circulation

evaporaier rarH^afemnattei _safnpingtar*

coHedbn tank

OJdry laundry

• evaporator

■ reverse osmosis system ete.

non-regenerative

concentrator^mixed bed

laundry wain'

washer

stormdrain

'mtermedate level . sludge storage tank

low level sludge storage tarft

concentrated waste liquid storage tank

volume reduction laoTrties

incinerator

combustible miscellaneous solid waste

■ tri-axial high pressure drumming

compactor

■meta etc.

drumming

dryer

mixer

„ _e cement glass

pelletizer “

drumming

drumming

outlet

mixer ^cerner>t etc.

Figure 2.9.3 A typical flow sheet of the latest radioactive waste treatment systems

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