engleski

Verification of the dispersion model by airborne carbon 14C

Lagrangean model is used at Krško Nuclear Power Plant (NPP) for calculation of dispersion coefficients and dose in the environment. To show compliance to the authorized dose limits it is required to present a realistic calculation of the dose to the public. Five years ago the numerical model was installed to calculate hypothetical air pollution dispersion in the area of 25km x 25km. The model uses on-line local meteorological measurements. The wind field is reconstructed using a three-dimensional mass-consistent wind-field model. The same model was already verified for another location around a coal- fired power plant based on emission and environmental measurements of SO2. But each of the location is specific. Krško NPP is placed near the Sava River in a semi-opened basin surrounded with several hills. The region is characterized by low winds and often thermal inversions. This paper presents first practical verification of the short range dispersion model based on the fact that the airborne carbon 14C concentration can be slightly increased close to the nuclear power plant. The other radioactive effluents are not detectable in the environment and carbon 14C measurements are accurate enough to detect small deviations from the natural 14C levels and to be used for comparison with the calculated concentration based on 14C effluents. The most of airborne 14C is released during refueling outage from the opened reactor. Within the pre-selected period of ten days increased effluents of 14C in the form of CO2 were sampled from the plant ventilation. The average atmospheric dispersion parameters were calculated for two locations in the environment where CO2 sampling plates were installed. Increased 14C activities were detected at the both locations close to the plant for this short time period of ten days. The model has been thus verified for the two points within 500 m distance from the reactor using average dispersion coefficients. There is also described a method how to estimate the emission rates to minimize the uncertainties.

air pollution dispersion model; airborne 14C; nuclear power plant; environmental monitoring; airborne 14C dose assessment

Cjeloviti rad objavljen u zborniku (IRPA 12 - Proceedings) na CD ROM, broj 0582, Topic II.2.2., a sažetak objavljen u knjizi IRPA 12 - Abstracts, str. 184