2. Specific Applications of Legislation

As a special feature in application of radiation protection legislation to NPPs, it is required that two laws, the “Reactor Regulation Law'¹ and the "Industrial Safety and Health Law" be simultaneously observed as mentioned above. As things are now, many activities of daily facility checks, maintenance tasks, and periodical inspection tasks particularly at NPPs are carried out by workers of contractors, and the responsibility of reactor establishers for radiation protection of the persons engaged in work in controlled areas (radiation workers) in accordance with the "Reactor Regulation Law" and the management responsibility of contractors employing the workers provided in the "Industrial Safety and Health Law" overlap (Figure 6.2.1).

According to these two laws, both an establisher and a contractor are responsible for the same worker in the same facility, but it is irrational for both to redundantly perform monitoring and surveillance of the work environment and dose control of workers for the same work activity in the same area of a NPP

Therefore, for practical control of contracted works, the establisher fulfills its responsibility to comply with the provisions of the "Reactor Regulation Law" by confirming the radiation protection measures to be carried out by contractors in accordance with the "Industrial Safety and Health Law", and in drawing up the contract agreements. The establisher is also responsible for the specifications for the radiation control which specify that the contents of radiation control are prepared and shown to the contractors beforehand to clarify sharing of responsibility, and that the contracted work activities are performed according to these specifications.

For those work activities, the establisher confirms as appropriate that the contractors are performing the radiation control according to the specifications and gives advice and guidance as necessary. Additionally, it is specified that the contractors record the results of their radiation control and submit them to the establisher after completion of their work. Ulis procedure ensures contractors clearly recognize the legislative policy to perform radiation control for their own work is their own

responsibility, and it also clearly positions radiation protection within the integrated labor safety management (prevention of electric shock, falls, etc.).

Utility Company A Contractor H Utility Company B Nuclear Power Station Manufacturer Nuclear Power Station

Industrial Safety and Health Law

Figure 6.2.1 Regulatory framework according to the “Reactor Regulation Law” and the “Industrial Safety and Health Law”

3. Radiation Sources at npPs

1. Actual Conditions concerning Radiation Sources

The fundamentals of radiation protection are to eliminate any concern about radiation protection by providing satisfactorily functioning radiation safety facilities at plants. However, from a practical standpoint and taking into consideration economical and socially rational aspects,, a part of radiation protection is left to human activities in addition to the facilities. In order to work safely in the environment that requires radiation control, first of all, it is important to have full knowledge on radiation fields (radiation sources) in the facilities.

At a NPP, radiation sources are fission products produced mainly in fuel during nuclear reactor operation and corrosion products produced by activation of metals in the reactor structural materials, etc., but their quantities or behavior are not uniform and therefore, radiation levels due to the sources at any part of the nuclear reactor system are different and depend on each nuclear reactor.

For reduction of personnel doses, prevention of contamination, and reduction of radioactive materials discharged to the environment, the following measures are taken into consideration:

1. To contain generated fission products in fuel

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control situations and measures taken for the water chemistry control (Figure 6.3.1).

Dose reduction measures are important for NPPs together with safety and reliability improvements; therefore, multilateral dose reduction measures have been adopted particularly at Japanese NPPs. Whenever new-generation plants have started their operations, excellent dose reduction results have been achieved.

Trends in collective doses at the first periodic inspection of BWR and PWR plants are shown in Figure 6.3.2. Some of the latest plants have their annual total dose below 0.2 man-Sv.

Also for the preceding reactors, measures have been taken including improvements of corrosion resistance and composition of steel materials as originating sources, control of corrosion products to be introduced into a reactor that become radiation sources, removal and decontamination of radiation sources, shielding of radiation sources, and improvement of work practices, all of which have resulted in a significant dose reduction.

Moreover, efforts to reduce piping dose equivalent rate by zinc injection into the feedwater and condensate system have been made. This approach suppresses deposition of ionic state “Co by having the oxide film on the piping surface take in zinc from DZO (Depleted Zinc Oxide) in which the abundance ratio of ^&'Zn is reduced in order to avoid an increase in dose equivalent rate due to “Zn. The effect of reduction of piping dose equivalent rate by application of this technology to BWR plants in and outside Japan has been confirmed, but, as a secondary effect, there have been some cases showing performance degradation of the primary loop recirculation system (increase in flow path resistance due to precipitation of zinc compound (ZnCr₂OJ on jet pumps), which means that the application should be studied on a case-by-case basis depending on the water chemistry control of each plant.

Major measures for dose reduction at old and new plants are shown in Table 6.3.4.

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