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15. Accident Analyses

AP1000 Design Control Document


Atmospheric Dispersion Factors

Subsection 2.3.4 lists the off-site short-term atmospheric dispersion factors (χ/Q) for the reference site. Table 15A-5 (Sheet 1 of 2) reiterates these χ/Q values.


The atmospheric dispersion factors (χ/Q) to be applied to air entering the main control room following a design basis accident are specified at the HVAC intake and at the annex building entrance (which would be the air pathway to the main control room due to ingress/egress). A set of χ/Q values is identified for each potential activity release location that has been identified and the two control room receptor locations. The χ/Q values have been selected in concert with the design basis accident radiological consequences analyses to obtain limiting values. In this manner, the maximum acceptable χ/Q values consistent with meeting dose acceptance criteria have been obtained. These χ/Q values are listed in Table 15A-6 and are provided in Table 2-1 (Sheet 3 of 3).

Combined License applicants referencing the AP1000 certified design will confirm that the site-specific χ/Q values are bounded by the values in Table 15A-6. For a site selected that has χ/Q values that exceed the values in Table 15A-6, the Combined License applicant will address how the radiological consequences associated with the controlling design basis accident continue to meet the control room operator dose limits given in General Design Criteria 19 using site-specific χ/Q values. The Combined License Applicant should consider topographical characteristics in the vicinity of the site for restrictions of horizontal and/or vertical plume spread, channeling or other changes in airflow trajectories, and other unusual conditions affecting atmospheric transport and diffusion between the source and the receptors. No further action is required for sites within the bounds of the site parameters for atmospheric dispersion.

Table 15A-7 identifies the AP1000 source and receptor data that the Combined License applicant can use when determining the site-specific control room χ/Q values using the ARCON96 code (References 4 and 5).

The main control room χ/Q values do not incorporate occupancy factors.

The locations of the potential release points and their relationship to the main control room air intake and the annex building access door are shown in Figure 15A-1.


  • 1.

    Murphy, K. G., Campe, K. M., "Nuclear Power Plant Control Room Ventilation System Design for Meeting General Criterion 19," paper presented at the 13th AEC Air Cleaning Conference.

  • 2.

    EPA Federal Guidance Report No. 11, "Limiting Values of Radionuclide Intake and Air Concentration and Dose Conversion Factors for Inhalation, Submersion, and Ingestion," EPA-520/1-88-020, September 1988.


EPA Federal Guidance Report No. 12, "External Exposure to Radionuclides in Air, Water, and Soil," EPA 402-R-93-081, September 1993.

Tier 2 Material


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