VII. Means to deal with an emergency situation
From Intamap
VII. Means to deal with an emergency situation
In the event of a nuclear accident, the criteria for implementing countermeasures to protect population will depend upon the phase of the accident. At the early phase, decisions are based on a compariso粑 of the estimated radiation doses and intervention levels of doses. In this phase, short before the release is expected to take place, protective counterÂmeasures are based on release data which are crude estimates taken over a short period of time. Nevertheless it is inevitable to have so called decision support systems available (like PARK and RODOS) which provide the only means to calculate dose estimations depending on only 2 parameters: the so called source term and the meteorological situation.
In an emergency situation in Germany the responsibility of BMU is to provide fast decision on countermeasures, whereas the BfS is responsible to evaluate the radiological situation - which must be done in due time. To continuously evaluate the radiological situation under routine or emergency conditions, the BfS runs the Integrated Measurement- and Informationsystem (IMIS). Part of IMIS are different decision support systems for assessing the contamination of the environment and for calculating the dose to man.
RODOS (http://www.rodos.fzk.de)
In case of a nuclear accident in Europe, the Real-time On-line Decision Support system for off-site emergency management in Europe (RODOS) provides consistent and comprehensive information on the present and future radiological situation, the extent and the benefits and drawbacks of emergency actions and countermeasures, and methodological support for taking decisions on emergency response strategies. The system is designed for
- local/regional/national/European scales.
- early and later phases of an accident.
- all types of emergency actions and countermeasures.
- Full and consistent information every 30 minutes about the actual and future radiological situation in the vicinity (here up to 80 km) and in greater distances.
To that purpose, models and data bases can be customised to different site and plant characteristics and to the geographical, climatic and environmental variations in Europe. Its operational application requires on-line coupling to radiological and meteorological real-time measurements and meteorological forecasts from national weather services.
The PARK (programme system for assessing radiological consequences) system is designed for
- Processing of measured and prognosticated data from IMIS in cases of large-scale contamination.
- Determination of the actual radiological situation.
- Radioecological modelling of the long-term consequences of contamination and the expected dose.
- Estimation of the effects of protection and countermeasures (ban of contaminated food, sheltering).
- The generation of new results every 2 hours.
In addition, the DWD' (German Weather Service) provides f'orward trajectories and prognosis calculations of precipitation and I-131 contamination in air.
The prognosis of PARK, RODOS and the DWD have a high degree of uncertainty particularly in the early phase, where source-term and dispersion have to be estimated. Therefore measurements have to initiated as soon as possible. Measurement results are used as input parameters into the decision support systems to improve the results of the dose calculations.
The design of the automatically operated radioactivity networks in IMIS have been based of the question: which measurements will be done:
- when,
- where and
- in which frequency?
The answers to these questions are given in the accident exposure timetable below.
First of all the ambient gamma dose rate must be measured with high spatial resolution in all phases after a nuclear accident. This is done using the GDR network which measures the dose rate automatically every 10 minutes at 2150 stations.
Additionally during the passage of a radioactive cloud, radionuclide concentration and composition in air are measured at 52 stations every 2-hours by DWD and BfS. These stations are cover ing Germany almost homogenuously. At 40 stations the DWD also operates stationary In situ system which every hour give detailed information about the radionuclide concentration and composition on the groun:
After the passage of a radioactive cloud the nuclides deposited to the ground must be know with high precision. Therefore radionuclide concentration and composition on the ground are measured every hour by:
- the DWD at 40 stations using stationary In situ detectors
- 6/16 mobile In situ vehicles of the BfS/the federal states
For Phase IIb, long time after the reactor accident, the concentration of all nuclides deposited to the ground must be known to PARK at all stations of the Gamma dose rate network. It is planned that the 6 vehicles of the BfS together with the 16 vehicles of the federal states will cooperate to provide this information with a delay of about 2 weeks.
| Phase I During passage of a radioactive cloud | Phase IIa and Phase IIb After the passage of a radioactive cloud | |||
| Relevant exposure-pathways | * Direct radiation * Inhalation | * Direct radiation * Ingestion | ||
| Characterization of the radiological situation | * Radioactivity concentration in air is high * Wet and dry Deposition of radionuclides to the ground depending on the local weather | * Radioactivity concentration in air is low * Deposition of radionuclides on the ground has ended | ||
| Informations relevant for decision makers | * Which areas are affected * The actual level of the external dose rate * The composition of radionuclides | |||
| Types of measurements relevant to get these information | * Ambient gamma dose rate, measured at 2150 stations automatically every 10 minutes by the BfS * Radionuclide concentration and composition on the ground measured every hour by: * Radionuclide concentration and composition in air measured at 52 stations every 2-hours by DWD and BfS | * Ambient gamma dose rate, measured at 2150 stations automatically every 10 minutes by the BfS * Radionuclide concentration and composition on the ground measured every hour by: * the DWD at 40 stations using stationary In situ detectors 66/16 mobile In situ vehicles of the BfS/the federal states |
Table 3 The accident exposure timetable
Countermeasures as protective actions
In any nuclear accident, there are two fundamental protective action options: evacuation or sheltering. Persons living in the vicinity of any nuclear facility during a major nuclear accident have only one viable option: evacuation to an unimpacted area. This is easier said than done because, in most accident situations, including Chernobyl, the authorities or any other governmental authority, had or will have minimal information about the amount of contamination (source term) in and direction of the plume passage. The Chernobyl accident illustrates the possibility that population groups could be evacuated from the immediate area of the accident (+/- 10 km) and moved to distant areas (+/- 200 km) and actually be entering areas with greater amounts of ground contamination than occurred in the immediate vicinity of the accident. Governmental agencies responsible for nuclear accidents can almost always be relied upon to provide inaccurate or insufficient information with respect to plume pathways and deposition activity. Unless you are sure you are close to and downwind from a major nuclear accident, immediate sheltering to avoid the most intense short-lived activity in the passing plume is usually your safest option. (http://www.davistownmuseum.org/cbm/Rad3.html).
A list of the three most important countermeasures together with the intervention level is shown table 4. The intervention level is based on the dose considerations taking into account integration times and exposure paths.
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