8. Environmental Radiation Monitoring

As objectives of environmental radiation monitoring, the following items are described in the ''Guideline for Environmental Radiation Monitoring":

1. To estimate and evaluate radiation doses to residents etc. in the vicinity;

2. To understand accumulation of radioactive materials in the environment;

3. To use the monitored data for evaluation of the effects of an unexpected release of radioactive material or radiation from a nuclear facility on the surrounding environment; and

4. To reinforce normal monitoring and consolidate it with a system for emergency monitoring on receiving a report of emergency.

Environmental radiation monitoring is performed by electric power companies as their responsibility as establishers of NPPs and it is done by local governments from the standpoint of third-party monitoring. Since the objectives and contents of monitoring by both parties are the same, it is important to ensure consistency for the entire region. Therefore, in establishing an environmental monitoring program, role-sharing arrangements (safety agreements etc.) are made between local governments and reactor licensees.

In establishing the program, the following matters are taken into consideration: type and quantity of radioactive materials to be discharged; form and mode of the discharges (gas or liquid, continuous or intermittent discharges); meteorological and oceanic conditions (flow diffusion); behaviors of radioactive materials in the environment (possibility of deposition and biological concentration); and type, cultivation status, harvest time of agricultural and marine products, etc.

Items to be measured or monitored are spatial radiation to be continuously measured at monitoring posts (M/P) or monitoring stations (M/S), the cumulative dosage to be measured with thermoluminescence dosimeters (TLDs) etc., and various items for environmental samples (water, soil, plants, marine organisms, and radioactive materials in air, etc.)

Example items currently monitored by the NPPs are shown in Table 6.5.2.

There are other items to be monitored according

to arrangements with local governments.

In order to confirm that the dose limit 1 mSv/year for residents outside of the peripheral monitoring area or the dose target value 0.05 mSv/year provided in the "Guide for Dose Objectives around Light Water Nuclear Power Reactor Facilities" are satisfied, it is renecessary to measure very low level radiation. Since direct measurements of samples do not satisfy the sensitivity requirements, water and vegetable samples are concentrated and/or chemically separated. The methods for the concentration and separation are evaporation to dryness, co-precipitation, ion exchange, incineration, solvent extraction, separation by ion solubility difference, etc., and the target nuclide is preferentially extracted and measured for its radioactivity.

The measurement results are collected each three months, for example, and officially announced to residents after evaluation and confirmation. In evaluating the data, the past variation range must be established beforehand, and each new measurement result is compared with the range to see if there is any significant change.

Items (c) and (d) of the objectives of environmental radiation monitoring are closely related to emergency measures, and the evaluation of measured data in an emergency is possible when locations of the measuring points and the environmental levels at the locations are fully known during normal times.

As for the emergency measures, the following guidelines issued by the Nuclear Safety Commission show how the monitoring should be performed.

• Emergency Measures in the Vicinities of Nuclear Power Plants etc., partially revised in May 2007

• Guides for Environmental Radiation Monitoring in an Emergency; partially revised in March 2001

• Guides for Environmental Radiation Monitoring; March 1989

The Ministry of Education, Culture, Sports, Science and Technology (MEXT) has established a system to expeditiously predict the environmental impacts, such as airborne concentrations of radioactive materials and exposure doses, etc. in the surrounding environment based on the information

6-.^

NSRA, Japan

⁽*⁴⁾ Source: HP of the Nuclear Safety Technology Center

(httpy7www.nustcc.or.jp/)

NSRA, Japan

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