1.1 General
"Safety Requirements for Selection of Nuclear Power Plant Site" (HAF 101, hereinafter referred to as the "Requirements") defines the minimum safety requirements for nuclear power plant siting of land-based thermal reactor. This guideline is a supplement and instruction to relevant provisions of the "Requirements". In practice, methods and schemes different from those specified in this guideline may be adopted, but it must be proved to the National Nuclear Safety Administration that the adopted methods and schemes have equivalent safety level to those in this guideline and won't increase risk against the nuclear power plant personnel and the public.
Atmosphere is an important way to transport radioactive substance released from the nuclear power plant to the environment and carry it into human body.
Therefore, in order to estimate dispersion of the radioactive substance released from the nuclear power plant to the residential district in this area and hereby evaluate radiation effect on human beings, relevant atmosphere data must be sufficiently mastered. This guideline describes meteorological phenomena and mechanism regarding dispersion of the released substance in the atmosphere, discusses concentration of pollutants in this area and calculation method for sediment as well as some relevant subjects, determines parameters required for calculation patterns and indicates necessary measuring instrument and characteristics of data analysis system. Moreover, for types of radiative releases, it proposes some methods for estimating short-term and long-term concentration.
Methods recommended in this guideline, according to topographical complexity, are applicable to a distance within about 10km. For farther distance, they shall be adopted with caution and consent from the National Nuclear Safety Administration shall be obtained.
Extreme meteorological phenomena with possible influence on the nuclear power plant will be discussed in another safety guideline "Extreme Meteorological Events in Nuclear Power Plant Siting" (HAD 101/10).
1.2 Meteorological Survey in Different Stages
In different stages of safety analysis on nuclear power plant, there are different emphases and precision requirements for dispersion estimation. The above stages are: (a) site survey, (b) site evaluation, (c) operation of nuclear power plant and coping with accidents.
1.2.1 Site survey
In the stage of site survey, meteorological condition is one of necessary factors. In many cases, meteorological characteristic of one site, when considered together with other factors such as population density in this area and land use, is an important factor to determine whether the site is suitable.
In the stages of site survey, multi-site comparison and site determination, generally special meteorological observation may be omitted; instead, existing meteorological data is mainly adopted. Moreover, the estimation is carried out by conventional weather classification method.
If local meteorological data is available, further evaluation [see "Site Selection and Evaluation for Nuclear Power Plants with Respect to Population Distribution" (HAD 101/03)] may be carried out. If local meteorological data is unavailable, data of representative meteorological station nearby may be used.
For area with relatively complex topography, besides collection of local meteorological data, further observation also shall be carried out and it shall be supplemented by data from other sources so that appropriate evaluation is made. Extremely meteorological conditions in the site, such as channeling and adverse prevailing wind direction or long-term adverse stability condition, shall be studied in combination with population distribution.
1.2.2 Site evaluation
After the site is determined, concentration of the effluent possibly released from the nuclear power plant under operation conditions and accident condition must be calculated. Hourly meteorological observation shall be carried out on the site, including determination or selection suitable diffusion parameter, for the convenience of dispersion calculation and statistical analysis; moreover, such data shall be taken advantage of to calculate probability distribution regarding concentration of radioactive substance released from the nuclear power plant.
1.2.3 Meteorological data under normal operation and accident conditions
Meteorological data required during normal operation of the nuclear power plant is less extensive and detailed than that required in the stage of site evaluation. When a nuclear power plant comes into the stage of normal operation, by virtue of previous measurement and study results, meteorological characteristics of the site has been well understood. Therefore, the meteorological observation tasks in the operation stage of the nuclear power plant are as follows:
(1) Provide necessary meteorological data to determine actual effect of short-term or long-term conventional radiative release on the environment.
(2) Provide actual meteorological parameter in case of any accident so that staff can take the most suitable protective measures.
(3) Provide meteorological data (see Chapter 5) to establish and implement emergency measures.
1.3 Inherent Limitation of Meteorological Observation and Evaluation
The majority of meteorological data is characterized by Eulerian, which is at once one or several fixed positions and often measured at a tower, while the actual dispersion is characterized by Lagrangian, i.e. each part of air flow may encounter various conditions greatly different from those at source point during its floating. If topography, physical and chemical states of effluent, height and meteorological conditions vary with time and distance, it will be very important to analyze limitation of Eulerian data, especially the estimated error. Such analysis may correctly estimate whether it is effective to randomly expand the dispersion pattern beyond the applicable distance, which will be discussed in Chapter 3.
In area with topographic relief, air flow and temperature distribution has some locality. Therefore, it is very vital to understand effectiveness of site observation data, for example, data of meteorological tower near hills is only applicable to its vicinity. In addition, attention shall be paid to factory buildings, especially cooling tower may affect atmospheric dispersion. During collection of meteorological data, attention must be paid that local effect won't excessively affect the measured parameter value.
During development of meteorological observation plan, meteorological data required for other environmental impacts beyond the discussion scope of this guideline must be taken into consideration.
1 Introduction
2 On-site and Off-site Meteorological Survey Outline
3 Atmospheric Dispersion Pattern
4 Short-term Average Concentration Estimation
5 Weather Problems in the Emergency Plan of Nuclear Power Plant
6 Training
Appendix I Turbulence and Atmospheric Dispersion
Appendix II Atmospheric Stability
Appendix III Effective Height of the Plume Rise △h (Without Buoyant Plume)
Appendix IV Examples of Simplified Patterns
Appendix V Method for Directly Determining Stability (Pasquill Method and Its Improvement)
Appendix VI Relation between Concentration and Sampling Time
Appendix VII The Improved Macro-Richardson Number Method for Calculating σy and σz
Appendix VIII Attached Figures for Calculating σy and σz
