Real emergencies and exercises – quick start and intervention

Real emergencies and exercises – quick start and intervention

Since Casus is versatile and very fast, it is perfect for the evaluation of the dose to the public during real accidents and exercises. Note that the dose assessment for real emergencies should be realistic – in contrast to the dose assessment for design basis accidents, which typically is very conservative.

In principle, the basic procedure, which consists of input of source term, adaptation of parameters, dispersion calculation, and dose assessment, can be used for real accidents as well. However, it is in the nature of things that reliable detailed source term data are unavailable during the early phase of a real emergency. Therefore, Casus offers various tools that can help the user to find a suitable source term for a reasonable estimate of the radiological consequences. The most simple tool is the Quick Start form.

Using the Quick Start form, the user can enter some basic data that is typically available as long as the release of radioactive substances occurs through a designed pathway (e.g. the stack) and the corresponding radiological and meteorological instrumentation systems of the affected nuclear facility are operational. Such data are usually included in the first reports from the affected nuclear facility to the emergency crisis team.

The data include

• the time of (or the duration between) reactor shutdown, start of release, and end of release,
• the wind speed in any given reference height (preferably but not necessarily equal to the release height),
• the precipitation rate,
• the release height,
• the atmospheric stability class, and
• the activity of the released radioactive substances, in terms of nuclide groups (noble gases, iodine, and aerosols) or reference nuclides (Xe-133, I-131, and Cs-137) or any combination of such values.

Based on these data, the Quick Start form estimates a detailed source term including all relevant nuclides and automatically generates the corresponding input for the Source Term form. Furthermore, the Quick Start form automatically sets several parameters in the Parameters form in accordance with the requirements for the doses assessment during real accidents.

Now, the user can follow the basic procedure as usual, check the source term and the selected parameter values, change further parameters, investigate the dispersion calculation, and finally view the results of the dose assessment. During the early phase of a real emergency, however, the user may want to skip all the intermediate steps and view the results of the dose assessment at once. Of course, this is possible with Casus – just click Dose at Downwind Location on the Results menu or press F9.

In fact, the user might even not be interested in dose results (in mSv), the emergency crisis team might actually want to know whether intervention for protection of the public is necessary. For this purpose, Casus includes another special tool: the Intervention form.

The Intervention form automatically checks the dose criteria for intervention for protection of the public. The default criteria are in accordance with the German Radiological Fundamentals for Decisions on Measures for the Protection of the Population against Accidental Releases of Radionulides of 27 October 2008. However, the user may specify different criteria.

The considered measures include

• iodine prophylaxis,
• sheltering,
• evacuation,
• short-term relocation,
• long-term relocation, and
• permanent relocation.

If a measure is justified, the Intervention form indicates the maximum downwind distance of the affected area. (Note that in the example image above, the seven green text boxes indicate that no intervention is justified.)

Therefore, the user only needs two forms (the Quick Start form and the Intervention form) in order to make a first complete estimation of the radiological emergency within only a few minutes. After that, the user may relax and use all the other forms and tools that are available in Casus in order to improve the analysis and examine the detailed results.