다수기 원자력발전소 사고 시 소외 방사성물질 농도 계산 방법

A Method to Calculate Off-site Radionuclide Concentration for Multi-unit Nuclear Power Plant Accident

Abstract

Level 3 Probabilistic Safety Assessment (PSA) is performed for the risk assessment that calculates radioactive material dispersion to the environment. This risk assessment is performed with a tool of MELCOR Accident Consequence Code System (MACCS2 or WinMACCS). For the off-site consequence analysis of multi-unit nuclear power plant (NPP) accident, the single location (Center Of Mass, COM) method has been usually adopted with the assumption that all the NPPs in the nuclear site are located at the same COM point. It was well known that this COM calculation can lead to underestimated or overestimated radionuclide concentration. In order to overcome this underestimation or overestimation of radionuclide concentrations in the COM method, Multiple Location (ML) method was developed in this study. The radionuclide concentrations for the individual NPPs are separately calculated, and they are summed at every location in the nuclear site by the post-processing of radionuclide concentrations that is based on two-dimensional Gaussian Plume equations. In order to demonstrate the efficiency of the ML method, radionuclide concentrations were calculated for the six-unit NPP site, radionuclide concentrations of the ML method were compared with those by COM method. This comparison was performed for conditions of constant weather, yearly weather in Korea, and four seasons, and the results were discussed. This new ML method (1) improves accuracy of radionuclide concentrations when multi-unit NPP accident occurs, (2) calculates realistic atmospheric dispersion of radionuclides under various weather conditions, and finally (3) supports off-site emergency plan optimization. It is recommended that this new method be applied to the risk assessment of multi-unit NPP accident. This new method drastically improves the accuracy of radionuclide concentrations at the locations adjacent to or very close to NPPs. This ML method has a great strength over the COM method when people live near nuclear site, since it provides accurate radionuclide concentrations or radiation doses.

Fig. 1. Radionuclide concentration calculation⁹⁾.

Fig. 2. Radionuclide concentration calculation using ML method.

Fig. 3. Radionuclide concentration calculation at (X, Y).

Fig. 4. Calculation of radionuclide concentration.

Fig. 5. Global and local coordinate systems.

Fig. 6. Calculation procedure of radionuclide concentrations for multi-unit NPP accident.

Fig. 7. Site layout

Fig. 8. Yearly weather windrose.

Fig. 9. Seasonal windrose.

Fig. 10. Air concentration of Cs-137 on constant weather (COM method)

Fig. 11. Air concentration of Cs-137 on constant weather (ML method)

Fig. 12. Ground concentration of Cs-137 on constant weather (COM method).

Fig. 13. Ground concentration of Cs-137 on constant weather (ML method).

Fig. 14. Air concentration of Cs-137 on yearly weather (COM method).

Fig. 15. Air concentration of Cs-137 on yearly weather (ML method).

Fig. 16. Ground concentration of Cs-137 on yearly weather (COM method).

Fig. 17. Ground concentration of Cs-137 on yearly weather (ML method).

Fig. 18. Air concentration of Cs-137 in spring (COM method).

Fig. 19. Air concentration of Cs-137 in spring (ML method).

Fig. 20. Ground concentration of Cs-137 in spring (COM method).

Fig. 21. Ground concentration of Cs-137 in spring (ML method).

Fig. 22. Air concentration of Cs-137 in summer (COM method)

Fig. 23. Air concentration of Cs-137 in summer (ML method).

Fig. 24. Ground concentration of Cs-137 in summer (COM method).

Fig. 25. Ground concentration of Cs-137 in summer (ML method).

Fig. 26. Air concentration of Cs-137 in autumn (COM method).

Fig. 27. Air concentration of Cs-137 in autumn (ML method).

Fig. 28. Ground concentration of Cs-137 in autumn (COM method).

Fig. 29. Ground concentration of Cs-137 in autumn (ML method).

Fig. 30. Air concentration of Cs-137 in winter (COM method).

Fig. 31. Air concentration of Cs-137 in winter (ML method).

Fig. 32. Ground concentration of Cs-137 in winter (COM method).

Fig. 33. Ground concentration of Cs-137 in winter (ML method).

Table 1. Locations and power levels

Table 2. Constant weather data

Table 3. Maximum values of Cs-137 concentration in whole cases