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Licensing of interim storage facilities: Checkpoint targeted air crash

  • A deliberately caused air crash on a nuclear facility is not probable but cannot be entirely ruled out.
  • In addition to the crime scenarios contained in the SEWD Guidelines of the Federal Environment Ministry (SEWD = Protection against Disruptive Acts or Other Intervention of Third Parties), the BfE thus also examines in licensing procedures pursuant to § 6 AtG the consequences of a targeted crash of a wide-bodied aircraft on the interim storage facilities.

According to the Federal Ministry of the Interior, a deliberately caused air crash on a nuclear facility is not probable but cannot be entirely ruled out after the events in the USA on 11 September 2001. In the aftermath of 11 September 2001, the BfS - being previously competent licensing authority - brought attention to this changed security situation when it licensed interim storage facilities. Since 30 July 2016, the Federal Office for the Safety of Nuclear Waste Management (BfE) is the licensing authority for interim storage facilities for nuclear fuels. In addition to the crime scenarios contained in the SEWD Guidelines of the Federal Environment Ministry (SEWD = Protection against Disruptive Acts or Other Intervention of Third Parties), the BfE therefore tests the effects of a targeted air-crash. This had been done previously by the BfS as an enhancement to the test scenarios set out in the SEWD Guidelines, which are to be carried out by the BfE as part of the interim storage procedures.

For this purpose, corresponding examinations started immediately after 11 September 2001 in the scope of the licensing procedures for on-site interim storage facilities. Furthermore, subsequent examinations were initiated with procedures pursuant to § 17 AtG for the already existing central interim storage facilities. Since then, the protection against the crime scenario "Targeted air crash" is part of the BfS - respectively since 30 July 2016 BfE - examination criteria in procedures pursuant to § 6 AtG, although up until now, it is not among the pre-defined scenarios to be considered in the guidelines.

Basic approach

As no experience was available for the examination of targeted air crashes, examinations and tests were carried out in co-operation with expert organisations and engineering consultants (TÜV Nord, GRS, BAM, SPI) and a calculation model was developed which simulates a targeted air crash. The model is designed in such a manner that it does not at all underestimate the radiological consequences of all realistic air crash scenarios.

If the model values for a concrete interim storage facility fall below the intervention reference level for the evacuation in the field of emergency response, the BfE assumes that the necessary protection in case of all realistic air crash scenarios is guaranteed.

Key model assumptions

The calculation model contains a multitude of different influencing factors (parameters) that are relevant inside the chain of events, from the flying aircraft via the crash up to the radiation exposure to the neighbouring residents. The model assumptions were determined in such a way that the overall model provides reliable results. Some examples are:

  • When choosing representative aircraft types, all aircraft types from a variety of manufacturers that are common in European airspace with their critical geometrical dimensions and weights were compiled and the aircraft models relevant for the crime scenario (such as Airbus A 340 and Boeing 747-400) were selected. After the Airbus A 380 had been commissioned, this aircraft type was also included in the examination.
  • To determine the mechanical load assumptions the maximum take-off weight of the aircraft type was assumed.
  • From the theoretically possible locations of impact the representative loadcases were selected that lead to the least unfavourable mechanical and/or thermal influences.
  • It is assumed that the aircraft is fully fuelled for the starting operation.
  • For the different approach scenarios, the scenario is selected that provides the highest fuel load (amount of kerosene), so that all possible approach scenarios to the interim storage facility are covered in terms of thermal influences.
  • The thermal and mechanical loads depend on the design of the respective interim storage facility. One differentiates between interim storage facilities according to the STEAG concept (Brokdorf, Brunsbüttel, Grohnde, Krümmel, Lingen, Unterweser), WTI concept (Biblis, Grafenrheinfeld, Gundremmingen, Isar, Philipsburg), tunnel (Neckarwestheim) and the central interim storage facilities (Ahaus, Gorleben, Lubmin).
  • On the basis of the highest possible mechanical and thermal influences, the cask behaviour is analysed. One assumes that the storage facility is completely filled; all casks being stressed thermally and a pre-determined number of casks being additionally stressed mechanically.
  • To examine the release, the maximum nuclide inventory per cask is assumed for all casks, irrespective of the actually existing loading variant.
  • Since there is currently no basis available for the calculation of SEWD events particularly, the dispersion of radioactive material with the air is calculated with the help of the accident calculation bases (in German only).

Examination results

The result of these considerations is that a targeted air crash does not lead to a considerable release according to the framework recommendations in the field of emergency response, since the intervention reference level in the field of emergency response for evacuation amounting to 100 mSv will not be exceeded. In detail, the results vary according to type of interim storage facility:

STEAG

The mechanical stresses do not lead to construction faults. Local damage may occur and aircraft parts and relatively small amounts of kerosene may enter the building. The thermal and mechanical loads do not lead to a relevant loss of density of the emplaced casks.

WTI

The building does not withstand. The walls and the roof may collapse. As a result of this, larger amounts of kerosene enter the building, which can flow out via drainage apertures. Examinations of the thermal and mechanical loads and consequences show that the cask integrity will remain intact, even in storage facilities according to the WTI concept.

Tunnel

The tunnel interim storage facility Neckarwestheim is an exceptional case. In the case of the tunnel concept applied in Neckarwestheim, both the stability of the above ground entrance building and of the underground tunnel sections will be kept in case of a targeted crash of a wide-bodied aircraft. The entrance building has wall and roof thicknesses of 1.5 m and will resist the impact of a commercial airliner. Only to a limited extent can kerosene enter via existing openings (e. g. ventilation). In the case of the tunnel concept no direct mechanical load to the casks would result from the aircraft impact.

Central interim storage facilities

The central interim storage facilities’ behaviour is similar to that of the storage facilities constructed according to the WTI concept. In view of planned constructional changes and further use, the GNS Gesellschaft für Nuklear-Service mbH intends to integrate kerosine drainage openings into the storage areas at the Ahaus and Gorleben interim storage sites.

State of 2016.09.20

© Federal Office for the Safety of Nuclear Waste Management