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Transport / Storage > ... > Effects of targeted air crashes
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Effects of targeted air crashes on interim storage facilities for nuclear fuel
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Legal foundationsThe Federal Office for Radiation Protection (BfS) is responsible for licensing the storage of nuclear fuel in interim storage facilities pursuant to § 6 of the Atomic Energy Act (AtG). It has to examine whether the legal requirements for granting a nuclear licence pursuant to § 6 AtG are fulfilled. In connection with this, it has also to examine pursuant to § 6 para. 2 no. 4 AtG whether the necessary protection from disruptive action or other interference by third parties (SEWD) is ensured. This examination must include acts of terror and sabotage.
The evaluation of the probability of occurrence of such a scenario is of particular importance to the examination. The evaluation cannot be based on the methods applied in the field of damage precaution pursuant to § 6 para. 2 no. 2 AtG, as with SEWD events it is not a matter of probability of failure or error but a matter of probability of realisation of events that are controlled by will.
As a consequence of the events of 11 September 2001, in the USA, it can no more be ruled out that also an interim storage facility in Germany may be the aim of a targeted attack with a wide-bodied aircraft. According to the Federal Ministry of the Interior’s assessment, a deliberately caused air crash on a nuclear facility is not probable but cannot be basically ruled out.
Therefore, BfS meanwhile also examines the consequences of a targeted air crash of a wide-bodied air craft on interim storage facilities. In order to fulfil the protection goals for interference by third parties, such an event must not lead to a considerable release of radioactive substances into the environment. Prior to 11 September 2001, only the accidental crash of military aircrafts with significantly less amounts of fuel had been considered.
Test procedureFor each currently existing interim storage facility, the possible landing and impact scenarios were determined, taking into consideration all established types of commercial aircrafts. Starting points of the investigations were the maximum weights and maximum tank capacities of the respective aircraft types.
For all on-site interim storage facilities and all three interim storage facility concepts, a duration of approximately 15 minutes for the kerosene fire was determined with peak temperatures of up to 1,100 °C. The other fire loads (such as seats, trims, luggage) would lead to a subsequent mixed fire with temperatures below 700 °C which would decay within 25 minutes.
In the case of this fire, the thermal impacts on the casks containing radioactive waste may lead to an increase in the amount of gas that could flow through a cask leakage (standard helium leakage rate ≤ 10-8 Pascal (Pa) cubic metre per second (m3/s) to maximum 10-4 Pa·m3/s). That means that there will be no serious loss of density in the transport and storage casks.
Depending on the wall thickness and resistivity of the interim storage facility hall and of the entrance building in the case of the tunnel concept, the extent of the damage to the walls in case of an impact would vary.
Results The final specific results are available for all three technical basic concepts of the interim storage facility constructed in Germany:
Hall construction STEAG concept Characteristic: thick concrete structures, wall thickness approx. 1.2 metres, roof thickness approx. 1.3 metres, single-nave building.
In the case of halls constructed according to this concept on the sites of Lingen, Grohnde, Brokdorf, Unterweser, Krümmel, and Brunsbüttel, the structural stability of the building would be preserved in case of an attack with a large airliner. Only aircraft parts and little kerosene would locally enter the building. In case of fire, the standard helium leakage rate could be increased by thermal impacts on the casks. However, this means no serious loss of density in the transport and storage casks.
Hall construction WTI concept Characteristic: Wall thickness approx. 70 cm or 85 cm, respectively, roof thickness approx. 55 cm, two-nave building consisting of two halls separated by an internal partitioning.
With the halls constructed according to this concept on the sites of Grafenrheinbeld, Biblis, Gundremmingen, Isar, and Philippsburg, a targeted aircraft attack can lead to larger damage including collapsing of walls and roof. Thus, it would be possible that larger amounts of kerosene entered the halls. However, in these interim storage facilities, kerosene or other liquids can flow out via discharge outlets. Thus, the development of a long-lasting kerosene fire is counteracted. With halls constructed according to the WTI-concept, the lid system of single transport and storage casks can be directly hit in case of an unfavourable impact of quickly flying, hard fragments or accelerated construction parts of the hall’s roof truss. This can lead to an increase in the leakage rate for a few casks. The cask integrity will remain stable in these cases, too.
Tunnel concept On account of site-specific conditions the tunnel concept is a special underground solution. The casks are emplaced in two tunnel tubes coated with jetcrete.
With the hall in Neckarwestheim constructed according to the tunnel concept, both the stability of the above ground entrance building and of the underground tunnel sections would be kept in case of a targeted crash of a wide-bodies 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. The possible effects due to flying fragments are so little that they do not involve any decrease in specific density (standard-helium leakage rate of ≤ 10-8 Pa m3/s).
Summary The considered aircrash events do not lead to life and health risks as a result of direct radiation or of the release of a significant amount of radioactive substances (SEWD directive). BfS examinations have shown that the intervention limits for emergency management ( 44 kB, in German only) of 100 millisievert (mSv) of effective dose for an evacuation would not be reached. The protection goal of the SEWD directive is, thus, complied with.
The incident planning values are also below the values set out in the provisions § 49 of the Radiation Protection Ordinance. Thus, the necessary safety of the storage of nuclear fuel for the examined on-site interim storage facilities on the nuclear power plant sites is given, even in case of a terrorist attack with a large fully-fuelled commercial airliner. BfS carries out an individual case study for possible new interim storage facilities applied for.
The Reactor Safety Commission, an independent advisory body to the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety, concluded in its statement of July 11, 2002 ( 129 kB, in German only), on the “Safety of German Interim Storage Facilities for Spent Fuel Elements in Storage Ponds in Case of a Targeted Crash of Wide-Bodied Aircrafts”, that the transport and storage casks guarantee the essential protective function of safe enclosure of the radioactive substances, even in case of a targeted crash of a wide-bodied aircraft.
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