**8. Concluding remarks**

148 Nuclear Power – Practical Aspects

without damage.

plant according to [30]

conservative.

relevant structures of the nuclear power plants.

arrives at the plant under consideration.

decisions about the kinds and number of design changes needed to effectively protect the

This is, in particular, required for the designs of nuclear power plants which are currently under construction or even in the planning phase. Such a hazard assessment has been recently performed [29-30] and for this case a detonation at the highway close to the nuclear power plant has been postulated. For the scenario, the maximum overpressure caused by the explosion has been determined to check if the plant could survive the detonation

Figure 15 shows the particle velocity field in the pressure wave just before the wave front

**Figure 15.** Velocity field at the pressure wave front just before shock wave arrival at the nuclear power

In case of a plant already operating since several years, the implementation of effective

On the one hand, comprehensive calculations can be performed to show that existing assumptions in the calculation provided for the licensing of the plant have been very

On the other hand, organizational and technical provisions can be taken to reduce the

countermeasures is much more difficult or even not possible.

occurrence of an external explosion pressure wave at the plant.

The evaluation of external hazards in relation to nuclear power plant design is traditionally considered as a two-step process. The detailed evaluation is preceded by a screening phase where potential scenarios are identified. Many scenarios are screened out on the basis of different criteria, such as distance from the site, probability of occurrence, expected consequence on the plant, or because their effects on the plant are expected to be enveloped by some others. Typically, explosion pressure waves are part of the probabilistic safety assessment as in case of comprehensive periodic safety reviews.

In the German safety guidance document on methods [3] the screening process for the explosion events is explicitly described. The classes of buildings with respect to their protection are the same as for the aircraft crash assessments. Since the updated PSA guideline has been issued in 2005 also requiring the assessment of external events, first practical experience in performing and reviewing the external probabilistic safety assessments are available. One topic is the assessment of the conditional probability of the occurrence of external explosion pressure wave and the discussion of appropriate methods according to the state of the art.

The presented case study and its results (provided in Figures 10, 12, 14 and Tables 4, 5, 6) in the second part of this paper indicate that the conditional probability of occurrence of external explosion pressure waves in consideration of realistic conditions (accident frequency depending on environmental conditions, wind direction and wind speed) can be successfully assessed by means of the Monte Carlo simulation.

As a next step the assessment of explosion events should be extended to include much more realistic boundary conditions regarding


Different ignition models are discussed in [32]. The applied model should be more realistic like the applied exponentially-distributed ignition model; moreover the applicability to integrate the new ignition model into the Monte Carlo algorithm should be given.
