accidents shall meet the criteria set forth in 10CFR 50.34(a) (1)

(The requirements in 10CFR 50.34(a)(1) on Radiological Dose Consequences of Postulated Accidents are excerpted below:}

The safety features that are to be engineered into the facility and those barriers that must be breached as a result of an accident before a release of radioactive material to the environment can occur. Special attention must be directed to plant design features intended to mitigate the radiological consequences of accidents. In performing this assessment, an applicant shall assume a fission product release (this release is a hypothetical accident for the site assessment, so, core melt down and succeeding significant release to the primary containment vessel (PCV) are postulated in general) from the core into the containment assuming that the facility is operated at the ultimate power level contemplated. The applicant shall perform an evaluation and analysis of the postulated fission product release, using the expected demonstrable containment leak rate and any fission product cleanup systems intended to mitigate the consequences of the accidents, together with applicable site characteristics, including site meteorology, to evaluate the offsite radiological consequences. The evaluation must determine that:

-An individual located at any point on the boundary of the exclusion area for any 2 hour period following the onset of the postulated fission product release, would not receive a radiation dose in excess of 25 rem (0.25 Sv) total effective dose equivalent (TEDE).

-An individual located at any point on the outer boundary of the low population zone, who is exposed to the radioactive cloud resulting from the postulated fission product release (during the entire period of its passage) would not receive a radiation dose in excess of 25 rem (0.25 Sv) total effective dose equivalent (TEDE).

3. Siting Philosophy

   1. Site Assessment

In summary, the conditions in the “Regulatory Guide for Reviewing Nuclear Reactor Siting Evaluation and Application Criteria” as described in

Section 9.2.1 require that a nuclear installation must be located at an specified distance away from the nearby population. This specified distance is defined as “Distance”. The appropriateness of the Distance may be confirmed by the evaluation of distance to the nearby population as in the Site Assessment.

In the Site Assessment, focus is on those accidents, which are postulated in the safety design assessment as “Accident” and through which propagation of radioactive material release is foreseeable; they are serious accidents which are deemed to have a possibility of occurrence under the worst scenario from a technological viewpoint (defined as “Major Accident*) and accidents which exceed the Major Accident level of radioactive material release and are not expected to occur from a technological viewpoint (defined as 'Hypothetical Accident”). The purpose of these two types of accidents is to evaluate the Distance between the nuclear installation in question and the public which must be secured appropriately in relation to the engineered safety features of the nuclear installation. With respect to the classification of accidents, consequences assumed for the objectives and the evaluation method of accidents, “Accident” in safety design assessment and “Major Accident” and “Hypothetical Accident” in site assessment, details are given in Chapter 7 and Chapter 8.

As evident in the above, the scale of a Major Accident and a Hypothetical Accident and the evaluation criteria of each, are of major importance in the evaluation of the appropriate Distance between the nuclear installation and the public, which is most important item in siting. In assuming the Major Accident and Hypothetical Accident, the following basic conditions are important

The minimum Distance necessary between a reactor and the public should vary and depends on the basic structure, thermal output and other performance characteristics, engineered safety features and other safety measures of the reactor in question. Accordingly, in selecting the Major Accident and Hypothetical Accident, the philosophy mentioned above should be considered within reason. In the selection of the Hypothetical Accident, for example, the necessary Distance will be dictated factually by the thermal output of the reactor alone if all of the multiple barriers against

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NSRA, Japan