Aircraft crash impact

The incidence of aircraft impacts may be significantly higher in certain areas (e g., in the vicinity or airports). The aircraft crash hazard is site specific and tlie failure is strongly dependent on the kinetic energy of tlie aircraft. Two types of data are needed to analyze for aircraft impact the aircraft crash rate in tlie site vicinity (per unit area per year) and tlie effective target area of tlie vulnerable item. Crash rates for different categories of aircraft can be obtained from state and national autliorities (e.g., FAA). The proximity of the site to airfields must be taken into account because crashes are much more frequent witliin a radius of approximately 3 miles. 

Furthennore the impact of external events such as earthquakes, aircraft crash, tornado, flooding or pressure waves (possibly resulting from events in neighbouring plants or transportation routes) have to be accounted for as initiating events or events triggering initiating events. 

Because of the large restricted area around the facilities and the remote location of the site, no industrial facility accidents are credible. The hazards associated vrith military accidents (i.e., expiosions, aircraft crash) are considered separately in the discussions of Aircraft Impacts, Chemical/Toxic Releases, External Explosions, and Missiles. Accidents in adjacent facilities in TA-V, such as the adjacent reactor fadlities, could have limited impact on the HCF as those faciiities are in separate buildings or physically separated from the HCF in an adjoining building. The nuciear faciiities have been designed to prevent accidents with the hazardous material in one faciiity from affecting the material in another facility. Thus, the impact of those adjacent faciiities on the HCF would likely be the same or less than External Fires. 

As the German nuclear power plants are designed to withstand the impact of external explosions and aircraft crashes, loads due to high winds are not expected to he important risk contributors. Nevertheless, outdoor switchyards and transformers are susceptible to wind driven missiles. If such equipment fads, loss of offsite power event sequences (transients typically analyzed as part of the plant internal events) might result. Similar simations can also arise fiwm an increased rainwater, sea salt spray, sand, or dust loading. 

This Safety Report addresses only the internal events that originate in the reactor or in its associated process systems. Some initiating events that affect a broad spectrum of activities at a nuclear power plant (often referred to as internal or external risks), such as fires (internal and external), flooding (internal and external), earthquakes and local external impacts, such as aircraft crashes, are not discussed in detail. Nevertheless, the guidance provided may be used for analysing the consequences of such events from the viewpoint of neutronics and thermohydraulics. 

The reactor building is in the center of the plant. In addition to two HTR modules, it contains some auxiliary and ancillary systems. Components of the start-up and cool-down systems, the steam generator fast discharge systems, and the intermediate cooling systems are installed in the annex to the reactor building. The two modular units are separated from each other by a central service area. An outer protective shell encloses the inner building structure. It fulfills the requirements for protecting the reactor plant from external impacts (e.g. aircraft crash). 

External Events Analysis. This component of frequency analysis considers the impact of external events (sueh as earthquakes, tornadoes, floods, aircraft crashes, terrorism, and vandalism) as initiating events to undesirable event scenarios. Quantitative frequency information is then used in fault and event trees. 

The upper hemisphere of the steel shell is surrounded by a shielding made of reinforced concrete with a wall thickness of about 2 m. This shielding protects the nuclear part of the plant against any external impact (e. g. gas explosion, military aircraft crash) it also significantly reduces the likelihood that radionuclides will escape to the environment. The interspace between the steel shell and the secondary containment is held at sub-atmospheric pressure, so that any radionuclides penetrating the steel shell via leaks in the event of a loss-of-coolant accident would be transported by the annulus air extraction system to the standby filters and retained here, thus preventing release to the environment. 

The reactor compartment accommodating the VBER-150 reactor installation is shielded from outside by a protective guard consisting of the multi-layer ceilings of a superstructure roof, walls of the stern and bow machine rooms and board compartments of the floating NPP superstructure. Altogether, these structures constitute the external reactor compartment protection, which can withstand external impacts including aircraft crash. 

Earthquakes, wind loads, low and high temperatures, aircraft crashes, shock waves and other impacts referred to as natural and human-induced external events impacts are carefully taken into consideration starting from the original safety design concept. 

These structures constitute the external protection circuit of a reactor compartment capable of withstanding external physical impacts including aircraft crash. 

The reactor installation has its own steel leak-tight protective shell. The reactor compartment is closed by a protective guard consisting of multi-layered ceilings of the superstmcture roof, walls of the stern and bow machine rooms and the superstmcture premises. Altogether, these stmctures constitute the external protection of a reactor compartment capable of withstanding external physical impacts including an aircraft crash. 

As it was already mentioned, placing not only the reactor but other equipment of the heat and power plant under an earth-berm and concrete shelter (Fig. XVni-1 and XVIII-3) provides a reliable protection against aircraft crash, external explosions and impacts of cumulative weapons. 

The probability of an accidental aircraft impact can be said to be acceptably low because of the regulatory and administrative arrangements that prohibit aircraft access close to UK nuclear power station sites. An aircraft crashing into the APIOOO will need a site-specific assessment to determine if this event is beyond design basis. 

The potential for aircraft crashes shall be evaluated, including impacts, fire and explosions on the site, with account taken of present and future characteristics for air traffic, the locations and types of airports, and aircraft characteristics, including aircraft with special permission to fly over or close to the facility such as fire fighting aircraft and helicopters. 

If the affected area is limited but is not confined to a specific location, the designer should analyse which functions could be impaired, on the assumption that the impact area may be anywhere on the site (Box 6). As a case in point, it is not possible to predict the location of the impact area for an aircraft crash or a missile, but it may be possible to identify areas where aircraft crashes are not probable. For example, when a building is near other buildings these may serve to shield against the effects of an aircraft crash. 

In general, full 3-D finite element analysis of the fluid domain (impulse, in the case of wind or explosions) or full impact analysis (impact, in the case of aircraft crash or tornado missiles) are not used in the design process for the derivation of a suitable load function. Very detailed research programmes have been carried out in the engineering community and in some cases simplified engineering approaches are now available for a reliable design process, on the basis of the interpretation of test data or data from numerical analysis. 

Reference [2] gives recommendations and guidance for a site specific review of the potential risk of an aircraft crash on the site and the nuclear power plant itself. The result of this analysis, which is based on a screening procedure to identify the potential hazard associated with an aircraft crash, is expressed in terms of either specific parameters for the aircraft (mass, velocity and stiffness) or load-time functions (with associated impact areas). 

All SSCs classified as EE-Cl, EE-C2 and EE-C3 should be designed or evaluated for the aircraft crash event. In some cases and for some phenomena, such as overall aircraft impact, selected structures may be shielded by other structures designed to resist the aircraft crash. For these cases, the shielded structure may not need to be assessed with respect to direct impact. 

The BN-800 power unit was designed to take account of such external impacts as earthquakes and other external natural phenomena (eg tornados), aircraft crashes and shock waves. 

Enhanced immunity of the power unit to external impact (aircraft crash, shock wave) is provided by location of the reactor and the related safety systems in protected rooms below ground level (Fig. 9.68). Enhanced seismic stability of the unit is provided by the use of shock... 

The GTHTR300 units are installed in an underground level of the reactor building as shown in Fig. XVI-14. This arrangement is effective in protecting the system from the crash impact of an aircraft. 

The choice of means of separation will depend on the PIEs considered in the design basis, such as effects of fire, chemical explosion, aircraft crash, missile impact, flooding, extreme temperature or humidity, as applicable. 

As an application of the theory discussed earlier, the crash responses of aircraft occupant/stnicture will be presented. To improve aircraft crash safety, conditions critical to occupants survival during a crash must be known. In view of the importance of this problem, studies of post-crash dynamic behavior of victims are necessary in order to reduce severe injuries. In this study, crash dynamics program SOM-LA/TA (Seat Occupant Model - Light Aircraft / Transport Aircraft) was used (13,14]. Modifications were performed in the program for reconstruction of an occupant s head impact with the interior walls or bulkhead. A viscoelastic-type contact force model of exponential form was used to represent the compliance characteristics of the bulkhead. Correlated studies of analytical simulations with impact sled test results were accomplished. A parametric study of the coefficients in the contact force model was then performed in order to obtain the correlations between the coefficients and the Head Injury Criteria. A measure of optimal values for the bulkhead compliance and displacement requirements was thus achieved in order to keep the possibility of a head injury as little as possible. This information could in turn be usm in the selection of suitable materials for the bulkhead, instrument panel, or interior walls of an aircraft. Before introducing the contact force model representing the occupant head impacting the interior walls, descriptions of impact sled test facilities, multibody dynamics and finite element models of the occupant/seat/restraint system, duplication of experiments, and measure of head injury are provided. 

Fortunately, for a couple of reasons, the likelihood of a terrorist attack on a nuclear reactor is quite low. Nuclear reactors operate under tight security and incorporate safety systems. In addition, the extensive shielding around reactors would require large amounts of explosives to create a breach. Even if terrorists could transport large amounts of explosives, they would have to breach a security cordon to reach the reactor. Alternatively, they could commandeer a jumbo jet plane to crash into a reactor or a nuclear pond of used cores, but they would have to breach security measures to do so. Computer modeling indicates that the constraction of most reactors would sustain a 300 mph impact from a commercial aircraft, but not aU scientists agree with these findings (1). 

Accidents with submarines and their possible impact on the marine environment are seldom noticed in the open literature and there is therefore little common knowledge available. An accident, however, that is well known is the crash of a US B-52 aircraft, carrying four nuclear bombs, on the ice off Thule air base on the northwest coast of Greenland in January 1968. Approximately 0.4 kg plutonium ended up on the sea floor at a depth of 100-300 m. The marine environment became contaminated by about 1 TBq 239,240p which led to enhanced levels of plutonium in benthic animals, such as bivalves, sea-stars and shrimps after the accident. This contamination has decreased rapidly to the present level of one order of magnitude below the initial levels. 

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