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equivalent (rate), since that controlled area is not likely to be contaminated, e.g. a storage facility to store solid waste enclosed in drums.

  1. Confirmation of Radiation Environment

In controlled areas, the radiation levels, such as dose equivalent rate, concentration of airborne radioactive material, surface contamination density, and concentration of radioactive material in water are monitored, and the frequencies and measuring methods are appropriately selected according to the monitoring objectives.

As ways to continuously monitor the conditions in controlled areas, fixed radiation monitoring devices, such as area radiation monitors, process monitors, and dust monitors, are provided, and they are continuous monitored in the main control room. The surface contamination density, which cannot be measured by fixed radiation monitoring devices, is confirmed to be normal and satisfy the standards of control through periodic sampling.

Table 6.5.2 shows example measurement items and frequencies of measurements of radioactive materials etc.

Many power plants use a computer for measurement and monitoring, making it possible to confirm a minute change in trend control by graphically recording the data, even if the data are within the criteria. When an anomaly is found by monitoring, steps are taken, as necessary, such as decontaminating, flashing, removing and/or moving

items acting as radiation sources or installing shields to maintain a good radiation environment

  1. Access to and Exit from Controlled Areas

The entrance to and exit from the controlled area is usually set at one place, and guards are stationed there to confirm that persons intending to enter the area are authorized to do so and that they wear personal dosimeters, and that persons intending to exit the area perform dose measurements and contamination checks of items to be taken out to see if there is any anomaly.

The entrances and exits of the contamination controlled areas are provided with changing facilities, where anti-contamination clothing is put on or taken off, and where persons can wash up and showering. There is also contamination monitoring of persons and of items to be taken from the areas. Guards are usually stationed also here to confirm compliance with procedures for access to and exit from the contamination controlled areas and to give guidance about the procedures

At a place with some potential for contamination in the controlled area, eating, drinking and smoking are prohibited by law from the viewpoint of preventing intake of radioactive materials. In addition, some power plants currently provide drinking fountains to ensure a better working environment by setting up an area with no contamination risk within an area with contamination risk.

NSRA, Japan

6- 12

Chapter 6 Radiation Control

Table 6.5.2 Example radioactive material measurement items and their frequencies of measurement

Area

Items to be measured

Contents of measurement

Frequency

Measuring points

BWR

PWR

Within the controlled area

Dose equivalent rate due to external radiation

Gamma rays

Once per day

13*1

16*2

Concentration of air-born particulates of radioactive materials

“Co, 137Cs, etc.

Once per week

7

5

Surface contamination density

Beta rays

Once per week

26

24

Drinking water

“Co, 137Cs, etc.

Once per month

1

1

Dose due to external radiation

Gamma rays

Every week

22

10

At the boundary of the controlled area

Dose due to external radiation

Gamma rays

Every week

10*1

13*2

Inside the peripheral monitoring area

Concentration of air-born particulates of radioactive materials

“Co, 137Cs, etc.

Once per month

3

Surface contamination density

Beta rays

Once per month

10

13

Drinking water

“Co, 137Cs, etc.

Once per month

1

Discharged water at general drainage canal

“Co, 137Cs, etc.

Once per month

5

Near the boundary of the peripheral monitoring area

Air absorbed dose

Gamma rays

Every three months

3

Air absorbed dose rate

Gamma ray

Contunuosly

3

Concentration of air-born particulates of radioactive materials

“Co, 137Cs, etc.

Once per month

1

Outside the peripheral monitoring area

Sea water

“Co, 137Cs, etc.

Once per three months

2

Soil of sea floor

“Co, 137Cs, etc.

Once per six months

3

Marine organisms (seaweed)

“Co, 137Cs, 13II, etc.

Once per three months

3

Soil

“Co, 137Cs, etc.

Once per six months

1

Land organisms

“Co, 137Cs, 131I, etc.

Once per six months

1

Air absorbed dose

Gamma rays

Every three months

11

Concentration of air-born particulates of radioactive materials

“Co, 137Cs, etc.

Once per three months

3

Drinking water

“Co, 137Cs, etc.

Once per three months

1

Seafood (top shell, yellowtail, brown seaweed)

“Co, 137Cs, etc.

Fishing season

3 kinds